Playing Around with Mouthfeel

Whenever we prepare food, we put our own distinct stamp on it so that it has a particular texture and, with it, mouthfeel. This holds true both in home kitchens and in industrial plants. Our most obvious way of doing this is by using heat, which, after all, is the basis of the culinary arts.

Transforming the properties of raw ingredients to achieve the desired texture and preserving it until the food is about to be eaten can be challenging. If prepared commercially, the food might need to be transported and may be kept on supermarket shelves for a long time. It is also necessary to take into account the changes that occur in the final stages of preparation. And in all cases, it is important to make allowances for what happens when the food goes into the mouth and mouthfeel comes into play. Here the texture is affected by temperature, saliva, enzymes, and the way in which we chew.

This is also where knowledge of rheology—that is, the study of the flow properties of liquids and soft solids—becomes important. We can feel how the food flows in our oral cavity on its own or after we have worked on it with our tongue, palate, and teeth. We notice whether it is sticky (like syrup), slimy (like a thin jelly), or fatty (like oil). Liquid foods such as drinks flow into the mouth more or less quickly and fill it up. Semisolids, such as emulsions, flow more slowly and behave in a viscoelastic manner. Solids do not flow at all, but sometimes they can be dissolved in saliva or melt, or can be reduced to very small bits by the action of tongue and teeth.

Preparing food, the culinary arts, and gastronomy are centered on working with raw materials to produce food that is tasty, interesting, and nutritious. All of this necessarily involves finding ways to work with mouthfeel in the course of a long series of transformations, first in the kitchen and then in the mouth.

Many of the processes carried out in the kitchen are irreversible. Once a potato has been boiled, it is not possible to cool it and return it to its raw state. Similarly, a cooked egg that has set will not become liquid again. In addition, subjecting a raw ingredient to a combination of processes will not necessarily lead to the same result if the processes are carried out in a different sequence. An example is the addition of an acidic substance to a sauce that contains milk or cream.

The simple preparation of food rises to a whole other level when the cook has grasped that the individual operations that are performed in the kitchen cannot be changed around arbitrarily and that the outcome depends on the way he or she has chosen to proceed. This, basically, is what we call following a recipe.

Transforming Raw Ingredients

We need to take into consideration the initial material properties of the raw ingredients themselves and acknowledge that they will usually change over time. After all, they are derived from living organisms and can be broken down or altered by the action of enzymes, microorganisms, and a number of chemical reactions, or the evaporation of some of their water content or volatile components. Catching or harvesting, storing, and curing the raw ingredients before transforming them into food in the kitchen becomes either a race against time to preserve freshness or a matter of judging how long to keep them to allow their taste substances to develop fully.

Many of us like to prepare food based on what is seasonally available. Fresh raw ingredients can be tasty and contain a multitude of vitamins and nutrients. Nevertheless, much of what we eat is fresh only in the sense that it is derived from fresh raw ingredients that have been treated in a number of ways: to decrease perishability and increase texture and nutritional value, to make them easier to chew and digest, or to bring out particular taste impressions. Many of the foodstuffs we associate most closely with savoriness and an interesting mouthfeel are, therefore, not fresh in the true meaning of the word, but have been processed extensively. Examples include the fermenting of ripe cheeses; souring of milk products; brining, pickling, or drying of fruits and vegetables; and smoking of meat and fish.

Second, the physical processes involved in the preparation of food and the relationships between the raw ingredients and their component parts have an important influence on mouthfeel and the release of taste and aroma substances. The raw ingredients themselves contain a certain quantity of water and oils, which may behave in a hydrophilic, hydrophobic, or amphiphilic manner, and more of these are often added. Conversely, water may be removed by reduction or various forms of dehydration. Changes in thermodynamic conditions, such as temperature and pressure, may also have an effect.

Last, but not least, it is very important to note that the structure and texture of prepared foods are rarely in equilibrium—they will change over time. Warm food may get cold, cold food may take on the ambient temperature. The food may grow stale or simply undergo changes due to its constituent parts’ either separating or mixing together. Oil and vinegar dressings usually separate out after a little while, ice melts once it is taken out of the freezer or put in the mouth, bread dries out, and the whey separates from the curds in fresh cheeses. Thus, time is an important factor in food preparation. And it is not a given that one can reverse these time-driven processes and arrive at the same structure and texture that the food had originally.

Texture covers not only the static or molecular structure of the food, but also dynamic conditions, such as whether the food undergoes change when subjected to other forces, whether it is deformed, fractured into small particles, or flows. Texture is also altered in the mouth where several factors are at work—its original structure, how the food and its breakdown products are softened by saliva, and how long the food stays in the mouth before it is swallowed.

In connection with mouthfeel, the food is also described and judged in relation to other influences to which it is exposed. When we say that something is sticky, fatty, grainy, wet, or dry, it is just as much a description of how we perceive the food’s interaction with our fingers, lips, and mouth as it is of the food per se. Wine feels wet because it can moisten our tongue and salivary glands, but if our mouth were made of Teflon, the wine would feel dry. Nori used to make sushi feels dry because the seaweed sheet draws moisture out of our salivary glands. Fats feel fatty because they do not mix easily with our saliva, but spread out like lumps or a coating in the mouth. Milk ice feels grainy because the water crystals in it are so large that they can be perceived by the tongue and the teeth. Water and oil feel like lubricants because they cause the food to move easily in the mouth and because they can help dissolve and soften the various components of the food.

Heat and Temperature

The place where the food is cooked has always been, and will always be, the most important installation in the kitchen, regardless of whether it is a hearth, an oven, a grill, a stove, or a state-of-the-art sous vide cooker. Using heat to turn raw ingredients into food that is ready to eat is the basis for the culinary arts and a healthy, sufficiently nutritious diet. Heating ingredients while controlling the temperature is the one kitchen operation that has the most potential to change texture. Think of cooking eggs, steaming vegetables, or grilling a steak. The opposite process, taking away heat by cooling or freezing, also has a marked effect on mouthfeel—for example, allowing a jelly to set or turning a liquid mixture into ice cream.

Food	Texture change	Cause
Bread crumbs	Firmness increases, springiness decreases	Starch retrogradation, moisture transfer from starch to gluten
Bread crust	Crispness decreases, toughness increases	Moisture migrates from crumb to crust
Butter and margarine	Firmness and graininess increase, spreadability decreases	Growth of fat crystals, change in crystal form, strengthening of network bonds
Cheese, ripe	Firmness and fracturability increase, elasticity decreases	Enzymatic changes
Chocolate	Graininess develops	Change of the crystal structure of the cocoa butter
	Surface “bloom” (white spots)	Sugars and fats crystallize on surface
Crackers	Loss of crispness	Moisture absorption from air
Fruit, fresh	Softening, wilting, loss of crispness, loss of juiciness	Pectin degradation, respiration, bruising, loss of moisture and turgor, weakening of middle lamella
Ice cream	Coarseness increases	Ice crystals enlarge
	Butteriness	Clumping of fat globules
	Sandiness	Crystallization of lactose
	Crumbliness	Poor protein hydration
Mayonnaise	Emulsion breaks	Fat crystallization
Meat, fresh	Toughness increases at first	Rigor mortis
	Toughness decreases later	Autolysis
Meat, frozen	Freezer burn, drip	Surface desiccation, reduced water-holding capacity
Mustard, prepared	Leakage of water (syneresis)	Aggregation of particles
Pickles	Softening	Breakdown caused by enzymes and microorganisms
Pies	Crust loses crispness, filling becomes dry	Moisture migrates from filling to crust
	Filling seeps out	Leakage of water from the gelling agent (syneresis)
Shellfish	Softening and mushiness	Enzymatic breakdown
Sugar confections	Crystallinity, stickiness	Sugars change from amorphous to crystalline state
Vegetables, fresh	Toughening	Deposition of lignin in the cell walls (e.g., asparagus, green beans). Conversion of sugar to starch (e.g., green beans, sweet corn)
	Softening	Pectin degradation, loss of water (e.g., tomatoes)
	Pitting	Chilling injury (e.g., bell peppers, green beans)
	Loss of crispness	Moisture loss and turgor loss (e.g., lettuce, celery)

Source: M. Bourne, Food Texture and Viscosity: Concept and Measurement, 2nd ed. (San Diego, Calif.: Academic Press, 2002).

Three different techniques are used in the kitchen to increase the temperature of foodstuffs: heat transfer by conduction, convection, and radiation. When an egg is boiled in water, conduction transfers the heat directly from the ambient hot water. Similarly, ingredients placed in a tightly sealed plastic pouch can be cooked sous vide in a warm water bath. Heat transfer in ovens equipped with fans relies on convection currents to circulate warm air and distribute it evenly around the food. In a regular oven, radiation is involved in baking, roasting, and grilling.

On a grill, radiation is the most important process. Radiated heat is absorbed first, very quickly, on the surface of a steak, leading to browning and the formation of a crisp crust, which is the main source of the meat’s taste and aroma. From the surface, heat is transmitted to the interior of the steak as the result of a slower conduction process. The balance between these two processes determines the outcome. In the course of grilling, a large number of chemical processes take place. For example, pyrolysis of amino acids can lead to the formation of aromatic aldehydes, Maillard reactions give rise to a series of tasty compounds, and caramelizing browns the meat adding visual appeal and creates organic compounds called furans that contribute both taste and aroma.

Pyrolysis

The word “pyrolysis” is derived from the Greek pyro, referring to fire, and lysis, “to separate.” This process breaks down organic material by using high heat in the absence of oxygen. It causes changes to the physical and chemical properties of the food and is irreversible.

Temperature Control

Even though thermometers have been in the culinary tool kit for centuries, cooks generally rely on their knowledge of how water behaves at the freezing and boiling points to effect fairly accurate temperature control. Most raw ingredients have a very high water content, which determines their response to warming and cooling. For this reason, it is often sufficient for a recipe to state that whatever is being prepared must be brought to the boiling point, because this is easily seen when bubbles start to appear. In fact, this is not a particularly precise instruction, as the actual boiling point is raised or lowered depending on the makeup of the liquid—for instance, a clear broth and a creamy soup will start to boil at a different temperature.

The way fats behave has also served as an indicator of temperature. Hot oil has been used to maintain a reasonably well-controlled temperature for searing, deep-frying, and so on. Different fats have different melting points, smoke points, and boiling points, which are especially dependent on whether the fats are saturated or unsaturated and how pure they are.

Sous Vide Techniques

The science of chemistry, with its strong focus on the importance of temperature and how processes unfold, has a long historical association with the culinary arts. But the emergence of molecular gastronomy in the past few decades has given impetus to the development of techniques for measuring and controlling temperature much more accurately.

Sous vide methods are based on heating raw ingredients in a vacuum-sealed plastic bag that is placed in a temperature-controlled warm water bath for a longer period of time than would normally be required to cook them. The technique, which had been used for industrial food preservation since the 1960s, was first introduced into a high-end kitchen in France in 1974 to poach foie gras so that it retained its texture and color, and lost only 5 percent of its total weight rather than 50 percent. Since its first appearance in avant-garde restaurants, sous vide cooking has slowly made inroads into the home kitchen, thanks to the availability of a range of appliances for domestic use.

Molecular gastronomy

In a way, it is paradoxical that the two methods that are most closely identified with molecular gastronomy in the popular imagination—the use of liquid nitrogen to flash freeze and precise temperature control in sous vide water baths—actually have very little to do with a description or understanding on the molecular level.

In principle, sous vide cooking is very simple. The raw ingredients are put into a plastic pouch and vacuum-sealed. The pouch is placed in a warm water bath in a container that circulates the water at a precisely controlled, constant temperature. The heat is transferred by conduction, as opposed to the radiation that takes place in a traditional oven.

Sous vide techniques have been adopted for the slow-cooking of meats at low temperatures, first and foremost because they optimize the texture of the final products so that they are both juicy and tender.

Another benefit of sous vide cooking is that the vacuum-sealed plastic pouches prevent the raw ingredients from losing any of their natural juices. It is also possible to enhance the taste of the prepared food by adding spices and taste substances to a marinade in the pouch, allowing them to permeate completely throughout the food in the course of the long cooking time.

Sous vide cooking typically takes place at temperatures in the range of 131°–140°F (55°–60°C) for meat, with fish being cooked at a slightly lower temperature and vegetables at a slightly higher one. These low temperatures are not without problems with respect to bacteria. Vacuum-packing excludes air, preventing those bacteria that need oxygen to grow from spoiling the food, but the unintended consequence is that the long immersion in warm water provides an ideal environment for those bacteria that thrive without it. Some possible ways of averting this are to sear the surface of the meat with a gas kitchen torch or to brown it quickly over high heat before sealing it in the pouch.

Marinating meat in a sous vide pouch.

The cooking times in the water bath depend to a great extent on the raw ingredients and the desired outcome. Preparation of tender cuts of beef, lamb, and pork usually requires four to eight hours, whereas very tough pieces may need to cook for several days. Fish is usually done in about thirty minutes; vegetables take two to four hours.

One has to be aware that a great deal of moisture, which has no way of escape, can accumulate inside the plastic pouch. This is why it is not possible to prepare meat with skin on it—for example, a duck leg or breast—in this way. The temperature is too low to tenderize the skin and it turns out disagreeably moist and sticky.

Naturally occurring enzymes in the meat can also help make it more tender in the course of slow cooking, provided the temperature does not rise above 122°–131°F (50°–55°C).

A central problem with sous vide preparation of meat is that it does not brown and lacks a crisp, tasty crust. Those Maillard reactions that create this effect usually take place extremely slowly at 122°–140°F (50°–60°C), but they happen quickly in the temperature range of 230°–338°F (110°–170°C). For this reason, it is necessary to brown the meat for a short period of time once the sous vide cooking is complete—for example, on a grill or with a gas kitchen torch.

Tender, Juicy Meat

When we chew on a piece of meat, the first bite will release tasty meat juices. A more lasting juiciness, described as succulence, is provided by the fats and gelatin that are drawn out as we continue to chew on the meat. They coast the mouth and elicit a juicy mouthfeel.

Entrecôte de Boeuf

There is not a great deal of cooking involved in preparing a tender piece of meat by either fast-frying it or placing it in a sous vide pouch. But tender cuts lose some of their taste in the pouch. Here is a recipe for making perfect steaks from premium-quality, tender beef, while still using slow-roasting at a low temperature. It happens without having to resort to sous vide methods.

•  Season the meat well with salt and pepper and place the steaks on a roasting rack together with the herbs. It is important that the air can circulate freely around the meat.

•  Preheat the oven to 200°F (90°C) and roast the steaks in the oven for 30–45 minutes. Take them out when they have reached an internal temperature of 129°F (54°C) and cover them with foil.

•  Just before serving, quickly sear the steaks in a skillet over high heat in duck fat, beef tallow, or virgin olive oil.

8 ounces (220 g) steak per person (tenderloin, strip loin, or similar quality)

Salt and pepper

Fresh herbs, such as savory, sage, rosemary, and thyme

Duck fat, beef tallow, or virgin olive oil

Sous vide methods have become fashionable for cooking all kinds of meats, even when it makes no sense or does not even improve the taste or mouthfeel. Using them to prepare tender cuts is done primarily for aesthetic reasons because it is possible to turn out a piece of meat that is perfectly juicy and a rare pink color to its very edge. It is then quickly browned to give it a very thin, but tasty crust.

How tender and juicy a cut of meat will be once it is heated is determined by a delicate balance between the amount of muscle and of connective tissue. This balance depends on the structure of the meat, the temperature at which it is cooked, and for how long it is heated. In turn, the structure is determined by the age of the animal; the part of the animal from which the meat is cut; and whether it has been aged, for how long, and by which method.

At high temperatures, the collagen in the connective tissue contracts quickly and expels the juice, making the cut firmer and drier. Collagen is broken down into gelatin so that the meat becomes more tender and softer only by slow heating over a long period of time at a high temperature, generally over 158°F (70°C). The proteins in the muscle denature when the meat is heated, which helps leave it firmer and more tender, but some of the juice runs out, and therefore, the result is less juicy.

In summary, we can say that slow-cooking meat at low temperatures using sous vide methods is especially valuable for tough cuts. It is all a question of finding the right combination of temperature and time.

Slow-Cooked Sous Vide Beef Brisket

•  Trim the meat and score the fat, if any, with a sharp knife.

•  Pour all the oil into a small pot, crush the garlic cloves with your hands, and add to the oil. Allow to simmer for a little while, then remove and discard the garlic when the oil has taken on a little of its taste. Allow the oil to cool.

•  Rub salt into the meat on both sides and rub it with the flavored oil, reserving a little of the oil for browning later.

•  Seal the meat in a vacuum pouch with the sage, bay leaf, and peppercorns.

•  Set the sous vide water bath at 135°F (57°C), immerse the pouch, and set the timer for 5–7 hours.

•  Remove the meat and brown it in the remaining flavored oil.

•  Cut the meat into 2-inch (5 cm) squares and serve with appropriate accompaniments.

4½ pounds (2 kg) beef brisket

¾ cup + 1½ tablespoons (200 ml) good olive oil

2 garlic cloves

Salt

10–12 fresh sage leaves

1 bay leaf

15 black peppercorns

Slow-Cooked Sous Vide Beef Brisket.

Texture in a Bottle or a Can

In contrast to taste and aroma, which can be adjusted by adding seasoning substances, it is not easy to change the texture and mouthfeel of a foodstuff simply the adding some sort of “texture concentrate.” Ideally, raw ingredients should have the desired texture built in as part of their structure or it should be created by the way in which they are prepared. The group of additives most often used to change texture are thickeners, stabilizers, gelling agents, and emulsifiers. Probably the best known of these are ordinary potato starch and cornstarch, used to thicken sauces and fruit juices.

Of the many thousands of different additives used in processed foods, about 10 percent are substances that alter the consistency and texture of liquid or semisolid foods, such as yogurt. In comparison with deriving texture from the raw ingredients, creating it by using an additive that comes in a bottle or a can is relatively simple. The distinctive characteristic of these additives is that only a very small quantity is required to achieve the desired effect. Texture is big business. Many of the large multinational enterprises are huge food companies that manufacture additives to control texture and make use of the food science technology to incorporate them into products with specific textures.

Starch: A Very Particular Kind of Thickener

Starch is a kitchen classic, one of the most commonly used types of thickener. It serves as stored energy in the form of carbohydrates in plants, especially in their seeds and edible roots—for example, rice, wheat, corn, and potatoes. On a global scale, starch makes up around 50 percent of the calories consumed by humans. It consists of two types of polysaccharides, amylose and amylopectin, which are tightly and neatly packed together in small starch granules in the plant tissue. In different plants, these granules vary in size and shape. Those in rice are typically small (about 5 micrometers), those in wheat are somewhat bigger (20 micrometers), and those in potatoes are much larger (30–50 micrometers).

Starch granules are covered by a variety of proteins, the characteristics of which totally determine the capacity of the starch granules to absorb water and their resistance to enzymatic action. These proteins can bind water. At low temperatures, starch with a high protein content has a greater tendency to absorb water than does one that has fewer proteins. When the proteins have bound water, they can cause the starch granules to stick to one another, thereby preventing the starch from absorbing more water. This is why starch with many proteins tends to form lumps.

The relationship between amylose and amylopectin varies somewhat from one plant to another. Amylose generally makes up 20–25 percent of a starch, but the proportion can be as high as 85 percent. For example, starch from peas contain about 60 percent amylose. Conversely, there are also starches, known as waxy starches, composed almost entirely of amylopectin. This type of starch is found in sticky rice, corn, barley, and mung beans, among other foods.

These two types of polysaccharides in starch play different roles in the ability of the starch to act as a thickener. Both are made up of a large number of glucose units that are bound together. In amylose, they form long chains; in amylopectin, they take the shape of large, branched networks. A single amylopectin molecule can contain up to 1 million glucose units. When they form gels, the amylose molecules bind water and form intertwined structures, whereas the very large amylopectin molecules stay away from one another and create more compact structures. This can be seen in the case of tapioca, a starch derived from the cassava root, which contains 83 percent amylopectin and can be used to form an incredibly thick, viscous gel.

The two polysaccharides in starch: (left) amylose and (right) amylopectin.

Whole starch granules are not soluble in cold water but can absorb it, increasing their water content to as much as 30 percent. The situation changes markedly at higher temperatures. This is why potatoes can be cooked to make mash and cereals to make gruel. In the temperature range of 131°–158°F (55°–70°C), the starch granules begin to melt and absorb water in increasing quantities. The ordered structure of the granules is fully broken down only at about 212°F (100°C).

Starch with a large amylose content is better at absorbing water. Potato starch, which is rich in amylose, has an incredible capacity for binding water. It is, therefore, a better thickener than cornstarch, which has a greater proportion of amylopectin. The starch granules can swell up to a size that is one hundred times that of their original one in the raw potato. Mashed potatoes can easily bind with water weighing three times as much as the potatoes and still hold their shape.

As the starch granules absorb water, some of the amylose molecules will start to seep out into the liquid and stiffen it. These long molecules will gradually intertwine and partially capture the starch granules, making them less mobile. Both of these effects cause the solution to become more viscous.

If the concentration of amylose molecules is sufficiently high, and if the temperature is sufficiently low, the resulting network of amylose molecules will become stiff and begin to resemble a solid. A gel has been formed. This process, in which the starch granules melt and absorb water, is called gelatinization. If this gel is stirred, the network of amylose molecules will be broken into pieces, the starch granules will start to break, and the viscosity will decrease. On cooling, however, the gel will be partly reconstituted, because the network of amylose molecules forms again, but the starch granules themselves remain broken up. This effect is familiar to us from thickening gravy with flour and from cooking, stirring, and allowing porridge to cool.

(Top) Electronmicrographs of starch in a raw potato (left) and a cooked one (right). The starch granules in the raw potato are typically between 30 and 50 micrometers in size. When cooked, they are broken down by water absorption and the starch has been gelatinized. (Bottom) How starch granules absorb water when heated to form a gel.

Gelatinization of starch is also affected by conditions other than temperature and water content. As described earlier, how well the starch granules stay in one piece depends on the proteins that coat them; fats also play a role in controlling gelatinization. This is an important factor when making a roux, where equal proportions of flour and butter limit the absorption of water by the starch granules.

POTATO STARCH IS SOMETHING SPECIAL

Starch derived from raw potatoes makes an especially good thickener because the amylose molecules are longer and the starch granules larger than those in other starches. It is very useful for thickening savory and sweet sauces, but because the starch granules are large, the result is often lumpier than when cornstarch or rice flour are used. Luckily, an easy remedy is literally at hand, because vigorous stirring breaks up the potato starch granules. Starch can also be derived from cooked potatoes in the form of potato flour. Potato flour has different thickening properties than potato starch because it also contains some proteins and fibers.

WHEN A THICKENED FOOD STARTS TO BECOME LIQUID AGAIN

Starch is often used to thicken gravy and gruel or to stiffen pasta. When the starch has bound as much water as it is able to, water may start to seep out again and the food becomes more liquid. This frequently happens when the food is warmed up to the boiling point, while being stirred vigorously, causing the swelled up starch granules to break up into smaller pieces. Even though this has drawn a greater proportion of amylose molecules out of the starch granules, creating a more extensive network of these molecules, the gel can become thinner and less viscous, especially if there was a large concentration of starch granules in the first place, such as in a thick puree.

If a starch gel is allowed to cool off and stand for a period of time, the gel becomes firmer and rubbery and water seeps out. This causes the amylose molecules, which are not soluble in cold water, to start to reconstitute themselves into a crystal-like structure, which is different in nature from that of the original compact structure of the starch granules. This process is called retrogradation. Incidentally, this is why one should not keep bread in a refrigerator. Even though we tend to say that bread kept this way becomes stale and dry, we are not identifying the problem correctly. The bread is less palatable not because it has lost water, but because the starch has undergone retrogradation. Seepage of liquid, in this case referred to as syneresis, can take place when the amylose molecules crystallize and squeeze out the water. This can also happen to a gravy that has been thickened with starch. When the gravy cools and becomes stiff after it has been standing for a period of time, water may seep out and accumulate on the surface.

Retrogradation also takes place in frozen foods that contain starch. This results in the release of liquid when the food is thawed—for example, the leakage of pie filling. To a certain extent, it is possible to prevent retrogradation by using starches with a greater amylopectin content. And if retrogradation of amylopectin occurs, it can be reversed by heating, which is not the case for amylose. Also, cakes and bread products that contain a certain fat content or emulsifiers might not undergo retrogradation because the fat molecules prevent the crystallization of the starch.

Baking and drying of starch-filled gels—for example, bread dough—can cause the starch to form glasses, which are responsible for the characteristic crisp texture of a freshly baked bread crust, cookie, or potato chip.

Emulsions and Emulsifiers

An emulsion is a particular type of mixture of two liquids that, in principle, are not miscible. It is formed mechanically by shaking the two liquids so thoroughly that tiny droplets of one of the liquids become suspended in the other. These droplets can remain in suspension for a shorter or a longer period of time, but eventually they will merge and the two liquids will separate again. The emulsions most often found in the kitchen are mixtures of a watery liquid (water, vinegar, or lemon juice) and an oily liquid (oil or fat).

In everyday cooking, the two emulsions that are used most frequently are butter and margarine, which have a very similar composition of about 80 percent oil or fat and about 20 percent water. Technically speaking, both are water-in-oil emulsions; in this case, the fats constitute the continuous phase with the water droplets dispersed in it. Butter is made from animal fats with a preponderance of saturated fatty acids, which are held in suspension with water with the help of the naturally occurring emulsifiers, such as lipids and lipoproteins, found in the milk. In contrast, the margarines now being produced are made primarily from unsaturated vegetable fats to which are added a small quantity of emulsifiers from either natural proteins—for example, milk proteins and lecithin—or commercial emulsifiers. Other common culinary emulsions include vinaigrettes, mayonnaise, and a variety of sauces and dressings. Among the emulsifiers readily available in a home kitchen are eggs, honey, and mustard.

Many pure emulsifiers are produced industrially for food production; these are often designed to optimize their use in a specific end product. This is particularly true in commercial baking, where emulsifiers for cakes can increase and stabilize volume while retaining the soft and often juicy nature of the crumbs. Other types are used to produce fluffy, stable cake creams and still others are required in the margarine used to make flaky pastries that have a crisp structure but no obvious surface fats.

Ingredients That Contain Natural Emulsifiers

Ingredients	Emulsifier
Egg white	Protein
Egg yolk	Phospholipid (lecithin)
Flaxseeds	Flax gel (polysaccharides)
Milk powder	Casein and whey protein
Mustard seeds	Mustard mucilage (and polysaccharides)
Soy beans	Phospholipid and protein
Whey powder	Whey protein

Source: P. Barham et al., Molecular gastronomy: A new emerging scientific discipline, Chemical Reviews 110 (2010): 2313–2365.

Gels and Gelation

Many substances can thicken liquids and, in the appropriate amounts and under the right conditions, form gels. Most of these substances occur naturally in a variety of foodstuffs—for example, fruits, seaweeds, meat, and fish, are used in that form or extracted from them as pure substances. Other gelling agents are artificially produced with the help of chemical and biotechnological techniques, including the use of enzymes and bacteria. What they all have in common is their superior ability to bind great quantities of water. They add texture to a food and help maintain its shape; they also help bind aroma and taste substances for later release in the mouth.

MARGARINE: A COMPLEX EMULSION WITH A LONG HISTORY

Margarine is not just any old spread. It the course of its history it has gone through many transformations—from its origins a century and a half ago as a safe and inexpensive substitute for butter, to a food that was championed by those who followed a low-cholesterol diet or who eschewed animal products, to one that caused health concerns—before finally taking on its present form: a complex emulsion that is widely used both in home cooking and in industrially prepared food. Along the way, perfecting it was the spark that launched a major, modern emulsifier industry.

The story of margarine is an illustration of the way in which a competition can have a major economic and historical impact. The increase in industrialization in Europe from the middle of the nineteenth century had led to skyrocketing food prices. There was a need for a less costly alternative to butter, partly to meet the needs of the military and of those with a lower income. So, in 1866, the French emperor, Napoleon III, announced the creation of a prize to be awarded to whoever could produce a cheap substitute.

Perhaps the emperor was inspired by the example of his late uncle, Napoleon Bonaparte, who had offered a prize for whoever could discover a safe way of preserving foods so that the army could bring provisions with them when on campaign. That competition was won in 1809 by Nicolas François Appert, who hit on the idea of conserving food by cooking it and putting it into sealed glass jars, a technique that was soon adapted for use with cans. A half-century passed before Louis Pasteur found out that this worked because heat kills the microorganisms in the food.

The competition for the butter substitute was won by French chemist Hippolyte Mège-Mouriès, who took out a patent in 1869 for a product made from beef tallow mixed with a little milk and water. He called it oleomargarine, a name that was later shortened to “margarine.” The origin of the word can be traced to the work of another French chemist, Michel Eugène Chevreul. In 1813, Chevreul discovered a saturated fatty acid, margaric acid, later found to be simply a mixture of palmitic acid and stearic acid. The invention of margarine did not catch on and it was only after a Dutch company had bought the patent in 1871 that the large-scale manufacture of margarine became a reality. The production of margarine rapidly gained a foothold in agricultural countries, such as Holland, Germany, and Denmark, which had a large surplus of skim milk left over from butter making.

Technically speaking, margarine is a water-in-oil emulsion, made by heating a mixture of animal fats or vegetable oils together with skim milk or skim milk powder and water, as well as salt to add taste and to act as a preservative. The milk proteins function as emulsifiers, stiffening the margarine and contributing a slightly acidic taste similar to that of butter. Next, the mixture is made to crystallize very rapidly and then subjected to mechanical mixing and kneading until it has the desired consistency. The original product was not nearly as stable and homogeneous as today’s version, which incorporates a revolutionary emulsifier invented in Denmark in 1919. That fascinating story is recounted in the box below “Mouthfeel and Margarine.”

The change from animal fats to vegetable fats was not long in coming, as it reduced the cost of production. A major drawback with using vegetable oils, however, is that they are made up primarily of unsaturated fats, which means that they are not solid at room temperature. This problem was solved by the discovery of a process called hydrogenation, which is carried out using hydrogen and the metal nickel as a catalyst. It involves breaking, either entirely or partly, the double bonds in the unsaturated fats, elevating their melting points, and making the oils stiffer. But hydrogenation does not break down all the double bonds, and in the course of the process the fatty acid chain can wrap itself around a double bond (changing from what is known as a cis- to a trans-formation). Fatty acids with these trans-bonds are called trans-fatty acids. They help stiffen the fats even though they are unsaturated. A classical hard margarine manufactured in this way could contain 20–50 percent trans-fatty acids, which made the margarine more stable and reduced the likelihood that it would become rancid. As we will see later, this had unfortunate side effects, which were identified only about twenty years ago.

Because margarine is made from a combination of raw ingredients that have little color, the result is a pale white product that does not resemble butter. But consumers had grown used to spreading their bread or frying their food in something that had a yellowish appearance, and to that end, the manufacturers of margarine had a marketing problem. Their preferred solution was to add yellow food color, but this move sparked a great deal of controversy, especially in North America, where dairy farmers waged a veritable war against margarine up until the 1970s. It was an issue that was tailor-made for exploitation by the defenders of butter and dairy products, who lobbied persistently against this measure. Their cause was successful and in many countries it was illegal to add food color to what some referred to as artificial butter. In Canada, the sale of margarine was actually banned completely between 1886 and 1948, apart from a brief period toward the end of, and just after, World War I. In the American dairy strongholds of Minnesota and Wisconsin, the sale of yellow margarine was prohibited right up until the mid-1960s; and it was not until 1995 and 2008, respectively, that the Canadian provinces of Ontario and Quebec removed this restriction.

Apart from its early association with times of scarcity and the campaigns against it, the reputation and popularity of margarine has had its ups and downs in the course of its evolution over the past 150 years. Two health-related issues have had an especially notable impact. First, as a consequence of the publicity about the harmful effects of fatty foods to which consumers were exposed in the 1960s, many switched from butter to margarine. Being made from vegetable oils, margarine can be a healthier choice than butter in some cases, as it contains more unsaturated fats and is completely cholesterol-free. There was, however, a proverbial fly in the ointment. As described earlier, hydrogenation had been adopted to increase the melting point of the margarine, making it hard and more stable. This was desirable, but the residual trans-fatty acids became the second source of concern.

In the mid-1990s, questions were raised in Denmark about the potentially harmful effects of trans-fatty acids. They are found most commonly in deep-fried food and a variety of fast foods, but also occur naturally in smaller quantities (1–5 percent) in other foods—for example, butter, cheeses, and other dairy products, as well as the meat from sheep, where the trans-fatty acids are formed by bacterial action in the stomach of ruminants. In 2003, two Danish doctors, Jørn Dyerberg and Steen Stender, demonstrated that the presence of trans-fatty acids in foods can increase the risk of hardening of the arteries and blood clots in the heart. As a consequence, one year later, Denmark was the first country in the world to prohibit the sale of foods containing ingredients with more than 2 percent industrially produced trans-fatty acids. Many other countries have since implemented similar controls, or are in the process of doing so, and the margarines currently being produced no longer contain any trans-fatty acids.

We might be curious to know what the margarine manufacturers and makers of fast-food products and a vast number of other items have substituted for the trans-fatty acids to produce the right consistency and stability. It turns out that in many places they have resisted the temptation simply to add more saturated fats and have turned instead to a using a mixture of saturated fats and a variety of unsaturated fatty acids.

Margarine is now finally and firmly established as a dependable and versatile culinary ingredient. The ordinary consumer can generally choose from a range of widely available margarine products, most of them based on vegetable oils. Those commonly used for frying and baking are solid and contain about 80 percent fats, of which 30 percent are saturated fats. In addition, there are spreadable margarines and liquid margarine, which contain more unsaturated fats, especially polyunsaturated fats in the case of the softer varieties. Those with the least fat have less than 10 percent and it is possible to manufacture them only with the help of specific emulsifiers.

Even though it is a manufactured product, margarine, in many ways, is just as “natural” as butter. And we should not forget why it was invented in the first place—to give access to a cheap, calorie-rich food to a great number of people who could not get or afford butter, particularly in times of shortage and war. Sadly, the way in which it was processed at one time resulted in the formation of harmful trans-fatty acids, a problem that has been recognized and rectified. Margarine has, however, proven its worth as a butter substitute for those on cholesterol-reduced diets and for those who avoid animal products for ethical reasons.

Gums are another class of substances that are good at binding water and on rare occasion form gels. But their particular strength is the ability to make liquids extremely viscous and very tough, thereby stabilizing them. Gums differ widely as to their nature and sources. Examples include locust bean gum, guar gum, and gum arabic, extracted from plants; xanthan gum and gellan gum, produced by bacterial fermentation; and methyl cellulose, manufactured from plant materials via a chemical process. These gums, which will be described in more detail, are sometimes partnered with specifically designed gelling agents.

MOUTHFEEL AND MARGARINE: A DANISH INDUSTRIAL SUCCESS STORY

This is the story of how the vision, technical expertise, and entrepreneurial drive of one individual was instrumental in establishing a family firm that grew into a large multinational enterprise producing an extensive line of sophisticated emulsifiers, ranging from food additives to antistatic agents.

Since the invention of margarine in 1869 as a substitute for butter, this water-in-oil emulsion has been an important food staple throughout the Western world. The prototype was made from beef tallow, skim milk, and water, but this first attempt was soon followed by experiments that used vegetable oils, although the quality of these early products remained very poor and variable. It was not until appropriate emulsification systems were invented that margarine acquired a texture that had a good mouthfeel and that could be used for cooking. This was due in no small way to the work of Danish inventor and industrialist Einar Viggo Schou (1866–1925).

Einar Viggo Schou, inventor of the first emulsifier for the production of margarine.

Those who have delved into the subject may associate the large-scale commercial production of margarine with grocery wholesaler and manufacturer Otto Mønsted (1838–1916), who built the first margarine factory in Denmark in 1883 and later set up the biggest margarine factory in the world in England in 1894. But there is more to it and his story intertwines with that of Schou, with whom he was associated for many years.

Early in this career Schou worked for Mønsted’s company as an assistant bookkeeper. In 1886, after he had been there for two years, he requested a raise from 1,000 to 1,200 Danish crowns per annum, only to receive the reply that he was not worth that much. Schou promptly quit. This was not to be the last time that these two strong personalities would end up on a collision course.

The two men crossed paths again in 1888, this time quite by accident on the street in London, where Schou was working at a financial institution. Mønsted offered him a position as the head bookkeeper at his newly established margarine factory near Manchester. Schou accepted the offer, and within a year, was in charge of the operation. It worked out so well that, five years later, Mønsted decided to set up yet another factory, to be the biggest in the world, just outside London. He turned to Schou to oversee the construction and bring this ambitious project to fruition. The factory opened in 1894, with Schou in charge.

Much of the credit belonged to Schou. He had been running the operation extremely successfully for almost twenty years, when he abruptly resigned. The reason was a long-simmering dispute over licenses for Schou’s groundbreaking invention of a machine for which he and his brother had obtained a patent in 1907. This machine, called the double cooling drum, had revolutionized the manufacture of margarine because its design made it possible to produce an emulsion in a continuous process without the use of water for cooling. The resulting spread was tastier, had a better consistency, and was less costly.

Some years earlier, in 1908, Schou had acquired the beautiful manor house Palsgaard in Juelsminde on Jutland, but he was still working in England. When he broke with Mønsted in 1912, he retired with his family to Palsgaard. The ordinary life of a landowner and gentleman farmer was hardly enough to fill his days, though. Just as Mønsted had a head for business, Schou’s talents were directed toward inventiveness and entrepreneurship. To meet this need, he set up shop in the estate’s farm buildings and began to experiment once again with different ways to produce better margarine. Six years later, there was a breakthrough when Schou invented the world’s first industrial emulsifier.

By heating a mixture of two different fatty acids (linoleic acid and linolenic acid) in oil he succeeded in making a product that could get oil and water to unite into a homogeneous, stable emulsion with a good mouthfeel. This invention was used to manufacture an improved type of margarine that did not splatter when heated for frying, but foamed instead, much like butter. In addition, it was possible to increase the water content and reduce costs by using less oil.

Schou described this type of emulsion as having an outer oil phase and an inner water phase. The tiny, stable droplets of water are coated with the almost magical emulsion oil and contained within the vegetable oil. On the basis of this invention, Schou founded a company, Emulsion A/S, in 1919. It was the first company in the world dedicated to the manufacture of emulsifiers for the food industry.

The invention of this emulsifier and the associated patents paved the way not only for an improved method for producing margarine, but also for a whole family of emulsifiers that are now used in baked goods, chocolates, dairy products, margarine, mayonnaise, and dressings. In all of these, the emulsifiers create the mouthfeel and are a major factor in the product’s taste, functionality, and keeping qualities.

When Schou died in 1925, his son, Herbert Schou, who shared this father’s strong interest in promoting the development of emulsifiers, became head of the company and turned it into a major international enterprise. In 1949 he founded Nexus A/S, a research and development company that would collaborate with Palsgaard. As he had no children, he established the Schou Foundation in 1957. It eventually became the owner of the companies and continues to run them and maintain the estate.

The legacy of Schou’s outstandingly successful career is the work that continues today at Palsgaard, the site of a state-of-the-art, internationally recognized emulsifier factory located on the historic estate in a beautiful parklike setting by the sea. The company has come a long way from the family firm that grew out of a single patent—it now has subsidiaries on five continents and is considered to be a world leader in the production of specialized emulsifiers.

The capacity of different gelling agents to bind water and form pleasing, homogeneous gels can depend on the way in which the liquid is added and its temperature at the time. It is usually best to dissolve the gelling agent in a little water until it is completely dissolved before adding the rest of the liquid. Once the bulk of the water is added the agent swells up and a gel starts to form.

Some gelling agents—for example, alginate—can form a gel only in the presence of calcium ions. Certain types of pectin also form stiff gels when calcium ions are present. As a number of raw ingredients—for example, a dairy product, such as yogurt—have naturally occurring calcium ions, a degree of gelation can occur even before calcium ions are added in the form of calcium chloride or calcium lactate. Hard water also contains calcium and potassium ions that can have an effect on gelation. Other gels, such as those made with agar and pectin, are formed only when the substances are heated; others, such as those made with alginate and gelatin, set at room temperature. Yet another type of gels, including those made with agar and gellan gum, create what are known as liquid gels when stirred. As they flow, they readily mix with saliva and consequently facilitate the release of taste substances.

Gelling agent or gum	Properties	Uses	Mouthfeel
Agar	Sets on cooling. Thermoreversible gel formation. Cloudy and very fragile gels.	Thickener, stabilizer, and gelling agent.	Clean
Alginate (sodium alginate)	Sets in the presence of calcium ions. Soluble in cold water. Thermoreversible gel formation.	Thickener, stabilizer (e.g., in ice cream and frozen desserts), and gelling agent (e.g., in marmalade). Used for spherification.	Clean, lingering
Carrageenan	Forms somewhat clear and fragile gels containing proteins. ɩ-carrageenan forms elastic gels in the presence of calcium ions.	Thickener, stabilizer, and gelling agent (e.g., in dairy products, such as yogurt and chocolate milk).	Creamy, clean, lingering
Gelatin	When cooled, forms very clear, pliable, and elastic gels. Thermoreversible.	Gelling agent used in a wide range of food products.	Clean to lingering and sticky
Gellan gum	Gelation properties resemble those of agar, carrageenan, and alginate. Stable at temperatures up to 248°F (120°C).	Thickener and stabilizer.	Clean, creamy
Guar gum	Easily soluble in cold water. Forms opaque liquids that flow slowly.	Thickener (e.g., in ketchup, dressings) and stabilizer (e.g., in ice cream, dough).	Lingering, smooth
Gum arabic	Easily soluble in water. At high concentrations in an acidic environment forms opaque, viscous liquids. Inhibits sugar from crystallizing in candies.	Thickener (e.g., in wine gums, soft candies, syrups), emulsifier, and stabilizer. Binding agent in glazes. Medium for aroma additives and food dyes.	Lingering, sticky
Locust bean gum	Forms cloudy, elastic gels, especially when combined with xanthan gum.	Thickener and stabilizer. Improves freezing and thawing (e.g., in ice cream). Adds softness and elasticity to bread dough.	Lingering, sticky
Methyl cellulose	Swells and thickens when heated. Clear.	Stabilizer, emulsifier, and thickener (e.g., in ice cream).	Clean to lingering and sticky
Pectin	Forms clear gels in sour foods with a high sugar content. Some types of pectin form strong gels in the presence of calcium ions.	Thickener (e.g., in ice cream, desserts, ketchup) and gelling agent (e.g., in marmalade, jams, candies). Stabilizer in emulsions and certain drinks.	Clean, lingering
Starch	Swells up and dissolves in warm water. Opaque.	Thickener used in a wide range of food products.	Sticky and lingering
Xanthan gum	Soluble in both cold and warm water. Forms clear gels (together with locust bean gum) and slowly flowing, complex liquids that exhibit shear thinning. Thermoreversible.	Versatile thickener (e.g., in sauces, salad dressings) and stabilizer.	Lingering, smooth to sticky

Sources: P. Barham et al., Molecular gastronomy: A new emerging scientific discipline, Chemical Reviews 110 (2010): 2313–2365; N. Myhrvold, Modernist Cuisine: The Art and Science of Cooking, vol. 4 (Bellevue, Wash.: Cooking Lab, 2010).

The different gelling agents and gums normally used in home cooking can be divided into two groups: those that can be used cold or in liquid form and others that tolerate high temperatures. Cold gels are typically based on pectin, gelatin, carrageenan, locust bean gum, guar gum, and xanthan gum. Those that can be heated are made with agar, gellan gum, and methyl cellulose. Alginate can be used in both cold and warm dishes.

The mouthfeel and taste of certain gels is sometimes described as being clean. This expression is not particularly well defined and it is hard to separate it from the visual impact of the product. In this instance, “clean” can probably be understood as a taste and mouthfeel that are simple and uncomplicated.

Pectin

Pectin is a complex, water-soluble polysaccharide that is found in almost all terrestrial plants, but mostly in fruits, especially the rind of cooking apples and citrus fruits. In a sense, pectin is part of the glue that holds the cells of the plant together and provides structure. The pectin content reaches its peak when the fruit is fully ripe. In unripe fruits, the pectin, called propectin, is not water soluble; and in overripe ones, it is broken down by enzymes.

The pectin content varies considerably from one type of plant to another. It is found in large quantities in apples (especially those growing wild), black currants (especially unripe ones), cranberries, quince, and prune plums, whereas there are only small amounts in other types of fruit, such as cherries, strawberries, and grapes.

When pectin molecules are dissolved in water, they take on a negative charge so that they repel one another. To form a gel it is necessary to counteract this repulsion. This can be done by adding sugar, which binds with water, with the result that the pectin molecules are held together more tightly. Another possibility is to add an acid, which decreases the electrical repulsion. Still another option is to add calcium ions, which have a positive charge that allows them to bind the negatively charged pectin molecules together.

As pectin is found in different forms with a variety of gelling properties, the choice of which of the above three possibilities should be used depends on the type of pectin in question. Those with a high methoxyl content require an acidic environment and a certain sugar content to from stiff, elastic gels. Apples and citrus peel are examples of fruits that contain 60–80 percent methoxyl. Others with a low methoxyl content, such as strawberries, can gel without sugar and acid, but only in the presence of calcium ions, which allow them to form stiff gels that can be quite brittle. These gels melt at higher temperatures and form gels at temperatures that are lower than do those that have a high methoxyl content, but they set more slowly. The melting point increases as more calcium is added. The ability of calcium ions to stiffen foodstuffs containing pectin can be harnessed to help preserve the firmness of cooked or pickled vegetables. It is simply a matter of adding sea salt or calcium citrate.

A gel formed with pectin or alginate in water. The bonds between the individual polysaccharide molecules are represented by the jagged “egg carton” structure. The red dots indicate that in some cases the gels can be stabilized by the addition of calcium ions.

Commercially, pectin is extracted, using acid and alcohol, primarily from lemon and lime peels, as well as the solid leftovers from apples that have been pressed to make juice. It is usually sold in powder or liquid form.

Pectin can be used to set jams and marmalades and to solidify fruit juices for use in gels and candies. It can also help to stabilize low-fat yogurt and baked goods and give them a creamy mouthfeel. Adding it to sorbets can prevent the formation of large ice crystals.

Most types of fruit jellies, marmalades, and jams are thickened with sugar, acid, and pectin. Pectin sourced from apples results in elastic gels, whereas that from lemon peel leads to gels that are more fragile and brittle. To form a gel, a mixture must have 0.5–1 percent pectin, 60–65 percent sugar, and an acidity reading lower than pH 3.5. In addition, the mixture must be boiled for the sucrose to break down into glucose and fructose, enabling them to bind a sufficient proportion of the water.

In contrast to other gelation processes, the formation of a pectin-based gel—for example, one with fruit juice—takes place by cooking the mixture until a sufficient amount of water has evaporated and the correct concentration of pectin and sugar has been reached. This must be done carefully so that the concentration of pectin is not so great that the resulting gel becomes sticky. As it cools, the gel forms at between 104°F (40°C) and 176°F (80°C), depending on the type of pectin used. Pectins with a low methoxyl content set at the lowest temperature.

Gels made with pectin have a clean and agreeably lingering mouthfeel and they break apart easily in the mouth, which has an effect on the release of taste and aroma substances. In contrast to gels formed with gelatin, gels set with pectin do not melt in the mouth, but only at temperatures of 158°–185°F (70°–85°C).

Gelatin

Gelatin is a protein found in collagen, which is the main component of the connective tissue that gives structure to all animal tissue. In mammals, it makes up 25–35 percent of the total protein mass. Most of the collagen in an animal is found in the skin and bones, rather than in the muscles. The word “collagen” is derived from the Greek word kólla, meaning “glue,” which in this case is gelatin. Unlike collagen, gelatin is soluble in water.

The strength of the collagen that forms connective tissue depends on the degree to which its protein molecules are chemically connected, a process known as cross-linking of tropocollagen molecules. When an animal exercises its muscles, the collagen becomes stronger, making the muscles tougher with age. Similarly, those muscles that are required to perform heavy work are also tougher. Newborn animals contain loosely bound collagen, which easily breaks down into gelatin. Meat from younger animals is more tender, not because it has a lower collagen content, but because the collagen has fewer cross-linkages.

Commercially produced gelatin is sourced primarily from pigskin and, to a lesser extent, from beef skin and bones. The connective tissue is heated over a long period of time to a temperature of at least 158°F (70°C), breaking down the cross-links between the tropocollagen so that the three fibrils that make up the individual molecules unwind and form the gelatin that seeps out into the water. This process is irreversible and the tropocollagen cannot be reconstituted. Once cooled to below around 59°F (15°C), the gelatin molecules instead aggregate into a more open structure that contains a great deal of water, up to 99 percent of the total. This structure is a gel and exhibits some of the properties of a solid. If this gel is made from cooling the juices extracted from animal meat, fowl, or fish, it is known as aspic. Heating the gel to a temperature over around 86°F (30°C) will melt it again and release the water.

The properties of gelatin completely determine how it can be used in food products. It is very easy to use in the form of a powder or sheets, as the gelatin can readily be dissolved in cold water. But it starts to melt only in warm liquid and the gel is not formed until the mixture is cooled again. In contrast to a gel made with agar, gelatin gels melt and congeal at the same temperature. The gelatin must make up at least 1 percent of the total to set a liquid; to make a really stiff gel, about 3 percent is required.

Gels made with only gelatin are clear and elastic. Sheets of gelatin trap fewer air bubbles than gelatin powder does, and therefore, they are used to make gels that are especially transparent. The visual appearance of the gel will of course depend on whether the other ingredients are also transparent.

Salt weakens the bonds between the gelatin molecules, resulting in a weaker gel, whereas sugar draws the water away from the gelatin, allowing it to form a firmer gel. Milk protein and alcohol also tend to help form a stronger gel, although more than 30 percent alcohol causes the gelatin to draw together into hard lumps and the gel falls apart. Gelatin has good resistance to the effect of acid, but gels made with it cannot be frozen. They start to melt when stirred, in which case they must be heated to over 99°F (37°C) and cooled again so as to reset.

Gelatin is used to stiffen a range of products, including fruit desserts, mousses, wine gums, and a number of low-fat foodstuffs. As some plant juices—for example, those from papaya, pineapple, and ginger—contain enzymes that break down gelatin, these juices can be set with gelatin only if they are first warmed to denature the enzymes.

A gel made with gelatin.

One great advantage of preparing gels with gelatin is that they melt at around 99°F (37°C), which is the normal human body temperature, and they literally melt in the mouth. As a result, they have a pleasing mouthfeel that is both elastic and long-lasting.

Very Special Hydrogels Made with Seaweeds

The gelling agents agar, carrageenan, and alginate, which are made up of complex polysaccharides, are used extensively in the food industry, and in recent years have found their way into gourmet kitchens in Europe and North America. In Asian cooking, these gelling agents, especially agar, which is extracted from red algae, have been a staple for centuries. In Europe, carrageenan sourced, as indicated by its name, from the red alga carrageen (Chondrus crispus), has traditionally been used to thicken puddings.

AGAR

Agar is a complex combination of two different polysaccharides, agarose and agaropectin, which are extracted by cooking red algae and then freeze-drying the filtered, warm liquid. Commercially, it is sold in the form of a powder, granules, or thin filaments and often serves as a vegetarian substitute for gelatin. Agar is insoluble in cold water, but dissolves readily in boiling water and can be used to form thermoreversible gels. To form gels, the agar is first softened in cold water, which is then brought to the boiling point and subsequently cooled to below about 100°F (38°C). Once set, however, the gel will not melt again before it is heated to at least 185°F (85°C). Stirring can change solid gels made with agar into liquid ones, but they do not withstand freezing. In contrast to gels made with gelatin, those made with agar are less sticky; have a clean, crisp mouthfeel; and do not melt in the mouth but keep their shape and stay firm. This latter property can be exploited to make pieces of gel that can be incorporated into a warm dish to add structural interest and release additional taste substances. Agar also forms gels at much lower concentrations than gelatin does, having the formidable capacity to set mixtures of up to 99.5 percent water. But one drawback with using agar, as compared with pectin and gelatin, is that the gels are less clear, have a coarser texture, and crumble easily. Unlike alginate, agar is not affected to any great extent by the presence of ions and it tolerates an acidic environment.

CARRAGEENAN

Carrageenan is an umbrella term applied to a number of complex polysaccharides that are extracted from red algae. Their gelation properties differ widely from one variety to another and their behavior is affected by surrounding conditions of temperature, pH, and the presence of ions, especially those from potassium and calcium. Some can curl into helical structures that are able to link loosely together to make up networks. There are three important types of carrageenans, two of which are used as gelling agents: κ-carrageenan, which forms strong, stiff gels; and ι-carrageenan, which forms softer gels that can reassemble themselves after being broken up. The third, λ-carrageenan, is the only one that can be dissolved in cold water; it cannot form gels but is well suited for emulsifying proteins, in particular in dairy products. Gels made from κ- and ι-carrageenan are formed by heating the liquid to the boiling point and then cooling it. Both types are thermoreversible, melting at about 158°F (70°C) and setting again at about 140°F (60°C). They are formed in mixtures containing a carrageenan concentration of 0.8–1 percent in water and 0.3–0.5 percent in milk. In contrast to gels made with ι-carrageenan, those set with κ-carrageenan do not hold up well to being frozen and then thawed. Only 0.02 percent carrageenan is required to slow down the rate at which ice cream melts. In addition, the carrageenan brings out a mouthfeel similar to that of an oil-in-water emulsion, even in a mixture with a low fat content, and it inhibits the formation of ice and sugar crystals in the ice cream so that it does not feel gritty like sand between the teeth. The ability of carrageenan to hold proteins and liquids together has recently found applications in what are called designer fats for meat products, where it helps retain the juices in low-fat meat. Carrageenan also has uses in dairy products and bread, giving structure and preserving moisture. Finally, it has a well-known effect in chocolate milk, holding cocoa particles in suspension so that they do not fall to the bottom. Carrageenan imparts a clean, creamy mouthfeel.

Two types of hydrogel (I and II) made with agar or carrageenan.

BUBBLES AND SPHERES: A WHOLE NEW WORLD OF TEXTURES

Agar has been used as a thickener and gelling agent in Asian dishes for many centuries. It was, in a sense, rediscovered in 1998 by chef Ferran Adrià, renowned for his creative modern cuisine and his promotion of molecular gastronomy at the now-closed elBulli restaurant in Spain. Agar gels have a less fatty and less greasy feel than do those made with gelatin and are also less fragile. These properties, together with their higher melting points, were exploited to the fullest to create imaginative, novel dishes such as Parmesan spaghetti, potato jelly, and wine vinegar snack chips.

Starting in 2003, Adrià turned his attention to alginates, for which he found new applications, especially in a technique called spherification. This process has become something of a trademark of the new molecular gastronomy and avant-garde cuisine. Adrià found out that it is relatively easy to make small bubbles (spheres) from sodium alginate by dipping an alginate solution in a fluid that contains calcium ions. In some cases, it is possible to trap liquids inside the bubbles for a limited period of time. This quickly inspired him to experiment with larger spheres, leading to the creation of the first artificial egg yolk and spherical ravioli. Artificial caviar, spherical balloons, noodles, and bubbles containing fruit juice were soon added to the repertoire.

A major breakthrough took place in 2005, with the invention of what is called the reverse spherification method. This technique makes it possible to control precisely the formation of spheres, as well as to use liquids that are otherwise too acidic (a pH less than 5), have too high a concentration of alcohol, or already contain calcium ions (e.g., milk products and olives). The difficulty associated with the direct spherification method is to stop the gelation before the contents of the bubbles also gel. To a certain extent, this can be done by quickly removing the newly formed spheres from the liquid containing calcium ions and washing them thoroughly in pure water. In the reverse spherification process, a liquid containing calcium ions is dripped into an alginate solution, which causes a shell to form around the droplet. As alginate cannot penetrate this gelatinous layer, the contents of the sphere remain fluid.

From a culinary standpoint, spheres offer some exceptional opportunities for introducing unusual, and often surprising, textures into a meal. With their firm exterior and liquid interior, spheres can add interesting fullness to a drink, impart a crunchy mouthfeel similar to that from fish roe but with completely different tastes, or create spectacularly novel effects, such as an “egg yolk” that tastes like papaya.

Ferran Adrià and his brother, Albert, saw the commercial potential in these culinary discoveries and together founded the company Texturas, which is now bringing a whole series of thickening and gelation products to the market. In addition to alginate and agar, the product line includes carrageenans, gelatins, methyl cellulose, gellan gum, xanthan gum, and a number of emulsifiers and composite products that have a variety of applications in molecular gastronomy.

It is easy to see that their enterprise is a good business. Selling the alginate in an attractive jar bearing the label of Texturas and enveloped in the magic aura of elBulli, markedly increases the price of ordinary food-grade alginate.

ALGINATE

Alginates are a group of complex polysaccharides extracted from brown algae. Because of their solubility, alginates have many practical, industrial, and culinary applications and are used extensively in the preparation of commercial food products and gastronomic specialties. The melting point of alginate gels lies just above the boiling point of water. Because alginate gels bind a great quantity of water, alginates are good thickeners and stabilizers. On the one hand, they are not readily broken down by acids, which gives them an advantage over other stabilizers, but on the other, their mouthfeel can be a little sticky.

Sodium alginate is the most versatile and has the most culinary applications as it can be used to create an interesting texture in food products and gastronomic specialties. In water, sodium alginate splits into sodium ions and alginate ions. The latter can form gels in the presence of calcium ions or magnesium ions and the gelation takes place at much lower temperatures than is the case for gels made with pectin. It serves as a thickener, gelling agent, binding agent, emulsifier, and stabilizer in a wide range of products, including conserved fish and meat, salad dressings, fruit and dessert jellies, and puddings. It can also help in two ways to preserve the shape of various foods, such as pasta, while they cook. It binds a great deal of the cooking water and the gel that it forms is very stable mechanically so that the food does not break apart or dissolve. In addition, it can compensate for a lower gluten content in some pasta products. A particular application of aliginate is as a stabilizer in ice cream, where it counteracts the formation of crystals and prevents the fats from separating from the water. It is also used to stabilize the foam in beer.

In recent years, new uses have been found for alginates in molecular gastronomy creations, where they are used in spherification. This involves making very small tubes or spheres that are filled with liquid. These can have a very interesting effect on the interplay between mouthfeel and taste.

From a nutritional standpoint, agar, carrageenan, and alginates are classified as soluble dietary fibers, which cannot be broken down in the stomach and intestines. Consequently, although they contribute virtually no calories to the diet, their ability to bind water has a very positive effect on the digestive process.

Gums

It is possible to extract gums directly from a variety of raw ingredients, such as grains and vegetables. For thickening foods, however, the most important gums are a number of specific substances extracted from plant cells (e.g., locust bean gum, guar gum, and gum arabic), others produced by bacterial fermentation (e.g., xanthan gum and gellan gum), and still others manufactured using a chemical process (e.g., methyl cellulose). All these substances bind water very effectively and can be used as thickeners and stabilizers. As they are made up of very complex molecules that are highly branched, with the exception of gellan gum, they cannot be used for gelation unless actual gelling substances are also present. But even in minute concentrations, these gums can form very viscous liquids and stabilize emulsions, creating a soft texture in foods such as ice cream. They are stable across a range of temperatures and can tolerate freezing. When present in a greater concentration, gums retain their plasticity, a property that is useful in certain types of candy.

Locust Bean Gum

Locust bean gum, which is actually derived as a powder from the pods of the carob tree, contains water-soluble, branched polysaccharides. The powder is dissolved in water, causing it to swell and form a sticky mass. It can be used to stabilize emulsions and thicken a range of foodstuffs—for example, cheeses, salad dressings, and sauces—often in combination with carrageenan. Unlike ordinary gelling agents, locust bean gum powder is effective at low temperatures, therefore, it helps increase ice cream’s tolerance for melting and freezing without developing an unwanted slimy mouthfeel. When used in bread dough, it contributes to making it soft and elastic. By itself, locust bean gum powder cannot form gels. When paired with xanthan gum, however, the result is a gel that is stable over a range of temperatures and in an acidic environment. The mouthfeel of products thickened with locust bean gum powder is somewhat sticky and lingering.

Guar Gum

Guar gum is derived from the seeds found in the pods of the leguminous guar plant. The gum is a branched polysaccharide that dissolves readily in cold water. Guar gum can form liquids that have some of the highest levels of viscosity—typically, eight times as much cornstarch would be required to produce the same effect. Liquids stiffened with guar gum exhibit shear thinning; that is, they flow more readily when subjected to a shear force that is parallel to their surface. Like locust bean gum, guar gum cannot form gels. It is used as a thickener and stabilizer in such emulsions as ice cream and salad dressings. The mouthfeel of products thickened with guar gum is smooth and lingering.

Guar gum (left) and locust bean gum (right).

Gum Arabic

Gum arabic, a complex mixture of polysaccharides and glycoproteins, is derived from the hardened sap of acacia trees. It is very soluble in water and used as an emulsifier and stabilizer, for thickening syrups and drinks; for glazes; and in soft candies, such as marshmallows and wine gums. In hard, sweet candies, it ensures that the sugar does not crystallize. The mouthfeel of products that contain gum arabic is a little sticky and lingering.

Xanthan Gum

Xanthan gum, made up of complex, branched polysaccharides, is produced by the action of a bacteria (Xanthomonas campestris). It is soluble in both cold and warm water, where it serves as a thickener in concentrations as small as 0.1–0.3 percent. Liquids stiffened with xanthan gum exhibit shear thinning, an effect well known from ketchup and dressings, which are usually made with it. This imparts a tough, stable consistency during storage, but these products flow easily, without dripping, when they are poured out of the bottle or when they are put in the mouth. The viscosity of a product thickened with xanthan gum changes very little in a temperature range between 32°F (0°C) and 212°F (100°C). Xanthan gum can also stabilize emulsions, such as ice cream, and it is not affected by acidity. The mouthfeel of products incorporating xanthan gum is lingering and somewhere between sticky and smooth. Either xanthan gum or guar gum is typically added to gluten-free baked goods to keep the alternative flours and starches from crumbling and to add chewiness.

Gellan Gum

Gellan gum contains sour polysaccharides, isolated from cultures of the bacteria Pseudomonas elodea. It comes in forms that have both short and long polysaccharides, which have different gelling and melting properties. As these polysaccharides are not branched, but can form cross-linked networks in water, gellan gum can be used to gel food products. For this reason it is often used as a substitute for more costly hydrogels, such as agar, carrageenan, and alginate. Only half as much gellan gum as agar is required to form a gel, which it can do in concentrations as small as 0.1 percent. Opinions differ as to whether it is best first to dissolve the gellan gum in cold or in warm water. But the gelling process does require heating and the presence of acid and positive ions—for example, calcium ions. Gels made with it can become very stiff and some are stable to temperatures of up to 248°F (120°C). As they are quite fragile, they break apart easily in the mouth, giving the impression that the gel is melting and releasing aroma and taste substances. When they are stirred, liquid gels can be created. The mouthfeel of foods thickened with gellan gum is clean and creamy.

Methyl Cellulose

The term “methyl cellulose” covers a group of related products that are derived synthetically from cellulose, using a chemical process. Although not a gum in the traditional sense, methyl cellulose is used as both a thickener and a stabilizer, such as in pie fillings. It can be dissolved in cold water, but not in warm, and it tolerates an acidic environment. Like carrageenan, it can be used to limit the formation of crystals in ice cream; it also prevents sugar in candy from crystallizing. Methyl cellulose has the peculiar property that it becomes stiff when heated and melts when cooled. The mouthfeel of foods made with methyl cellulose varies from clean to sticky and lingering.

The Effect of Enzymes on Texture

Enzymes, which are found in great number and many varieties in the raw ingredients we use in cooking, are particular proteins that can break down and rework molecules. Each of them has its natural function in living organisms—for example, in aiding digestion or defending against bacteria. They also help break down dead biological matter in the foods we eat. Some enzymes act on proteins; others, on carbohydrates and fats. Most enzymes are highly specific and target only certain types of molecules and are sensitive to ambient conditions, such as temperature, salinity, and acidity. Temperature is particularly important; at high temperatures they are denatured, meaning that they are ruined and their functionality cannot be reestablished. This is one of the reasons for using heat as a way to preserve food. Enzymes in pure form can be extracted from biological materials and a growing number of them are now being produced by using biotechnological principles.

The use of enzymes is one of the most effective ways of changing the structure of foods and, with it, their mouthfeel. Sometimes, naturally present enzymes carry out their work quite spontaneously—for example, when meat or fish is aged or fruit is left to ripen. Other times, they are introduced for a specific purpose, an instance being the use of rennet in cheese production. In addition, enzymes are central to fermentation processes and the effect of surface molds on meat and dairy products is often due to enzymes.

The enzyme chymosin in rennet helps coagulate milk and form cheese curds. Chymosin cleaves away the electric charges from the small particles (micelles) of the protein casein, allowing them to bind together to form a network throughout the milk and create a liquid gel in which the milk fat is trapped.

Cheese made with rennet derived from plants

A traditional way of making cheese in Portugal uses enzymes extracted from the pistils in the flower buds of the artichoke thistle (Cynara cardunculus). These enzymes work in the same way as those sourced from calf stomachs. They cause the micelles in the milk to bind to one another in a network that keeps the fat particles together.

The enzyme transglutaminase is a more recent discovery that has many applications in both commercial food processing and molecular gastronomy. It is used to thicken and introduce consistency into foods containing proteins, such as meat and dairy products. It acts as a sort of binding agent that causes the proteins to bond with one another and form a gel. As transglutaminase can cause proteins from different pieces of meat to stick together—for example, in surimi and ham—the enzyme has also, rather unattractively, been dubbed “the meat glue.”

How transglutaminase works

The enzyme catalyzes the formation of a bond between a free amine group on one protein and an acyl group on the amino acid glutamine on another protein. This causes them to bind together in such a way that they cannot be broken down by proteases, the enzymes that usually degrade proteins. This enzymatic bonding of the proteins is carried out according to the same mechanism that is related to the formation of blood clots.

There are also enzymes that break down gels or inhibit their formation. Many a cook is familiar with the failure that results from trying to use gelatin to set fruit gels containing papaya or pineapple juice. It is simply not possible, because the enzymes in these fruits—papain from papaya and bromelian from pineapple—break down proteins and, with them, the gelatin. To make gels from these fruits, it is necessary to use agar and pectin instead, as these are carbohydrates and are not affected by these enzymes. The only other recourse is to warm the juices to denature the enzymes, but this might also spoil their fresh fruit taste.

Electronmicrograph of a cheese mass formed when the casein micelles in milk coagulate into a network in the presence of rennet (left), and illustration of this network (right). There is room for milk fat spheres in the spaces in the network, which are typically 2–5 micrometers in size.

SURIMI

Surimi is a firm solid consisting almost entirely of proteins, typically those from the flesh of fish with light-colored muscles, that are bound together with starch, emulsifiers, or transglutaminase. Its production has its origins in centuries-old techniques developed in the Far East, where it has been used to make fish balls, fish sausage, and the Japanese fish cakes kamaboko, among other foods. Gefilte fish, a classic staple of Jewish cuisine, is closely related to kamaboko. Outside Asia, surimi is commonly sold as imitation crab or shrimp, mimicking their shape, texture, and color, and is often used in sushi rolls.

The production of fish surimi is now a large-scale commercial operation with a global reach, which utilizes fish that otherwise has low economic value. The flesh is first minced and rinsed to remove fats, soluble proteins, blood, and connective tissue, as well as unwanted odor and taste substances, resulting in a paste that is almost tasteless. It is then mixed with numerous ingredients, such as starch, oil, egg white, salt, sorbitol, aromatic substances, food coloring, and possibly transglutaminase. The paste is pressed together and cooked or steamed.

In addition to fish, various types of surimi are made from pork, beef, beef tendons, and turkey meat. These types are very similar to meatballs and usually contain no transglutaminase. Unlike the meats that go into these products, which display the characteristic and differentiated tissue structure of the muscles, the resulting surimi has a uniform, firm, and slightly elastic texture.

Sugars in Food

Carbohydrates—simple sugars (such as sucrose, fructose, and glucose) as well as the more complex ones, which we have met in the form of hydrogels—are essential ingredients for sweetening, preserving, and adding texture. Their special properties are due to their ability to bind water and make it less chemically active. In the case of long-chained polysaccharides, this extends to forming cross-linkages with one another. Sugars round out and balance the mouthfeel in a dish.

Dissolving simple sugars, such as ordinary household sugar (sucrose), in water increases its viscosity, but the solutions remain liquid and do not form gels even at high concentrations of sugar. Sugar dissolved in water also depresses the freezing point, an effect that reduces the formation of ice crystals in ice cream and sorbet.

Very viscous, sticky liquids (e.g., syrup), soft solids (e.g., caramels), or hard, crunchy solids (e.g., candies that technically are glasses), can be made by melting sugars that have different melting points and by boiling down sugar solutions. All have in common their being prepared in such a way that the sugar is prevented from crystallizing. The different types of sugar are incorporated into all kinds of sweets, which can have many different types of mouthfeel, from creamy and soft, gummy, tough, sticky, sandy, and grainy to crisp and hard. The texture can be controlled by the addition of a variety of other substances—for example, cream.

Syrup

Syrup is a solution with a high concentration of sugar in water. The sugar does not precipitate into crystals because sugar and water have bound to each other, making the liquid very viscous. Syrup is produced either by dissolving sugar in water or by reducing juices that have a certain sugar content, such as the juice from sugar cane, birch sap, or maple sap. When the liquid is heated and its volume reduced, the sugar molecules have a number of ways to form compounds, some of which take on a brown color and constitute a variety of aromatic substances. In general, the mouthfeel is sticky and the extent to which it flows freely depends on the juice from which it is made. Many of the commercial syrups now on the market are produced largely from starches—for example, from corn—and many of them have a large fructose component.

Inverted Sugar

Inverted sugar is a particular form of the disaccharide sucrose, in which its two component sugars, glucose and fructose, have been split apart. This produces two effects: inverted sugar tastes sweeter than ordinary sugar because fructose is sweeter than sucrose, and the glucose prevents the sugar from crystallizing—for example, when used to make ice cream and sweets.

Maltodextrin

Maltodextrin is a type of polysaccharide that can be produced by the hydrolysis of starch, such as that derived from cassava. It is usually sold as a powder that weighs little and that pours easily. It is only slightly sweet, has practically no taste, and can serve as a thickener and prevent the formation of crystals in ice cream and sorbet. Maltodextrin has found its way into modernist cuisine because it can turn fats and oils into powders that release taste substances in the mouth when they are mixed with saliva. To do so, liquid fats or oils, in liquid form, are mixed with maltodextrin to make a paste that is then put through a sieve and dried. A more elaborate procedure utilizes a spray-drying technique to produce a powder that melts on the tongue, almost like snow.

Fats in Food

Fats, whether in the form of solid fats or liquid oils, can affect the mouthfeel of a food in a number of ways. These depend on the melting properties of the fats, as well as how they can form emulsions with watery liquids. Of all culinary ingredients, fats are possibly the ones that can be used most flexibly to influence texture. The most common ones are derived from either plants (margarine and plant oils) or animals (butter, margarine, lard, suet, and fowl).

Large pieces of pure fat are rarely incorporated into prepared foods, even though very fatty animal products, such as lard and suet, play a greater or lesser role in some dishes. Nevertheless, fats are often present in raw ingredients sourced from both plants and animals, either in the form of discrete fat deposits or trapped in their tissues. So, as a matter of course, they contribute to the mouthfeel these ingredients impart to prepared food as well as help release taste and odor substances. How a low-fat content affects mouthfeel is well known from the uninspiring taste of a beef patty made with very lean meat.

Culinary Fats from Plants

Margarine was originally produced from animal fats, but over time, the source was switched to more unsaturated oils from plants, which were hardened to increase the melting point. In many countries, the margarine now produced has none of these undesirable trans-fatty acids, which have a high melting point. Instead they are made from a combination of plant oils to adjust their melting point in accordance with their end use—for example, firm for sautéing or soft for baking. Firm margarines from plant oils contain about 80 percent fats, a proportion similar to that in butter. Therefore, they can be used as butter substitutes in terms of texture, even though opinion varies as to whether they make a positive contribution to taste. Other margarines contain only 40 percent fats, with the remainder of the weight made up of water. As a result, their volume reduces considerably when they are heated, making them unsuitable for frying. However, they are an excellent choice for use in baked goods that are to be airy and crisp.

Two types of fats with high and low melting points: butter and olive oil, respectively.

Oils extracted from seeds and nuts are less saturated than animal fats. For example, the proportion of unsaturated fats in olive oil and rapeseed oil is 82 and 84 percent, respectively. Plant oils can be used for baking, and because of their low melting points, they are eminently suitable for making cold sauces, dressings, and emulsions that need to flow at room temperature. Olive oil is well known for its ability to impart a coating mouthfeel to an oil and vinegar dressing.

Culinary Fats from Animals

An important source of animal fats is cow’s milk, which has a 3.5 percent fat content. When churned into butter, the fat content rises to 82 percent, of which about 65 percent is saturated fat, depending on what the cows have been fed. On account of both melting properties and taste, butter is widely used in food preparation to provide texture, especially in sauces and baked goods. Clarified butter and ghee are almost pure fat.

As Julia Child famously said: “If you’re afraid of butter, use cream.”

Lard is 100 percent fat, of which 61 percent is unsaturated, and is made by rendering pork fat. Lard can be used like butter and it was once a common ingredient in baked goods, to which it contributed a noticeably meaty taste.

Adipose tissue from fowl, usually ducks or geese, is made up of about 98 percent fat, of which 70 percent is unsaturated. One of its main uses is to make confit, a way of preserving meat in lard. The best known of these is confit de canard, salt-cured duck meat cooked in its own fat that then sets and solidifies.

Suet is made up of about 99 percent fat, of which 48 percent is unsaturated. Its high melting point makes it very suitable for frying.

Fats derived from fish are highly unsaturated. They have very low melting points and oxidize readily, leaving them with a rancid taste. This is why fish oils are rarely used directly to affect the mouthfeel of food, although, of course, they are largely responsible for the soft texture of an oily fish.

Fats and Mouthfeel

The ability of fats to influence the texture of food is due to two things. First, they can form crystals that eventually can melt in the mouth, as is the case with cocoa butter in chocolate. Second, they can form complex phases with water in the form of emulsions. Fats are often added to foodstuffs in the form of oil.

The degree to which a fat is unsaturated, which dictates its melting point, often determines how it can be used in cooking. Hard, pliable fats—for example, butter, firm margarine, and lard—which all have high melting points, are well suited for baking. Cakes and pastries made with them are generally airy and exhibit the delicious flaky, tender, and crisp structure that we know from piecrusts, cookies, and Danish pastries. The fatty dough helps trap small droplets of water in the dough. The droplets evaporate during baking, leaving behind the air pockets that are responsible for the flaky structure. To achieve the best results it is necessary to pulse or rub together thoroughly flour, fat, and sugar (if used) to make a crumbly mixture. How fine it is determines the size of the flakes in the baked pastry.

When used in baking, liquid oils have a different effect from solid fats. Because they flow freely, they are easy to mix in and combine almost completely with flour, as well as with sugar. The resulting baked goods have a less flaky structure, as is seen in pound cakes and muffins, which have a somewhat crumbly mouthfeel. Soft margarines and shortening mixtures are not suitable for a making soft dough, such as shortbread, that is rolled out.

Fats will generally impart an agreeable mouthfeel, which is often attributable to their ability to spread out in the mouth as they melt. But if they are very viscous, they may instead feel unpleasantly sticky. Liquid fats will spread out in the mouth like a membrane and impart a coating mouthfeel. This is why oils and fats are used to round out or thicken sauces, an effect often achieved by using cream.

Fats, especially when combined with emulsifiers, enhance creaminess and can prevent the formation of lumps—for example, in chocolate. When present in large quantities, fats can modify and decrease the intensity of other tastes such as acidity, which can be either an advantage or a drawback.

The Surprisingly Diverse Textures of Milk

Milk and dairy products are good examples of a group of foods that exhibit a whole range of textures, from that of milk in its natural state to those of buttermilk, yogurt, butter, cheese, and so on. This diversity is a core illustration of how processing can transform texture. Milk is also able to function as an emulsifier and stabilizer of foam and can be used to thicken sauces. Last, but not least, it is the central ingredient in a treat that almost everyone loves—ice cream.

CHOCOLATE: WHY IT MELTS IN YOUR MOUTH

Chocolate is made from the seeds found in the pods of the cacao fruit tree. These beans are first partially fermented; then dried, roasted, and crushed; and finally pressed to extract their fats in the form of cacao butter. The remaining solid particles can be milled to make cacao powder or cocoa powder, which is very similar but is processed at a higher temperature.

Dark chocolate, which is solid at room temperature, is a complex mixture of cacao powder, cacao butter, and sugar. In most types of chocolate, the individual cacao particles are ground up so finely that they are not distinguishable on the tongue. Technically speaking, chocolate is a sol, or a solid colloidal system—that is, a suspension of solid particles of sugar and cacao powder in a solid matrix of cacao butter. The very special mouthfeel of chocolate is due to the specific melting properties of the cacao butter.

Fats from plants and animals are usually made up of a number of components that have different melting points. Consequently, a given fat melts over a wide range of temperatures. This is true, for example, for butter and lard. In exceptional cases, some mixtures of fats melt over a narrow temperature interval, almost at a well-defined temperature. Cacao butter is one of these very special cases. It is primarily made up of three different types of triglycerides, which contain both saturated and unsaturated fatty acids. But due to its large proportion of saturated fatty acids, the mixture has a relatively high melting point of 90°–97°F (32°–36°C), just below the normal temperature in the mouth. This is the crucial factor that contributes a mouthfeel that is so agreeable that most people love—even crave—chocolate. And the actual process of melting the cacao butter requires a certain amount of heat, which is drawn from the body, so the overall effect can be a sensation of coolness.

The inner structure of chocolate depends on how it is processed. Even though two different pieces of chocolate have an identical chemical composition, they may not have the same mouthfeel. For instance, if a piece of chocolate is melted and then solidifies again, it will not taste the same, because its mouthfeel has been altered. This happens because the fats in the cacao butter can form six different types of crystals with discrete structures and only one of these types will result in a glossy surface and the right degree of brittleness.

Chocolate intended for use in baking and candy making is produced using a method known as tempering. This is a way to ensure that it crystallizes into precisely those structures that will result in what is considered a good mouthfeel. Untempered chocolate is soft and does not snap, whereas tempered chocolate has a glossy surface, is brittle, and does not melt when you hold it between your fingers. The desired structure can be obtained by seeding the melted chocolate mass with small pieces of chocolate before allowing it to cool. Another way of doing this is to pour the melted chocolate out onto a marble slab and repeatedly fold it over on itself with a spatula while it cools slowly. This mechanical action encourages the growth of the right crystals. In both cases, it is vital that neither water nor steam is incorporated into the chocolate, as this would result in the wrong crystals, known as seizing, producing an undesirable graininess or lumpiness. Tempered chocolate can be made more stable by the addition of a number of emulsifiers—for example, lecithin.

Incorrect crystal formation can also result in what is called a bloom, the white or grayish spots that are seen on the surface of chocolate that has been stored at too high a temperature or in too moist an environment, has been kept too long, or that has been exposed to the sun. It is best to store chocolate in a dark, dry place with a constant temperature of around 61°F (16°C), so as to prevent recrystallization of the cacao butter. The bloom is made up of either sugar or fat that has migrated to the surface and formed a crystal with a high melting point. These spots can also be attributed to fats from nuts that have been added to the chocolate. Formation of bloom can to a certain extent be prevented by adding emulsifiers or other fats that can combine with the fats in the cacao butter—for example, milk fat, which is used in baked goods.

Unlike dark chocolate, white chocolate contains only cacao butter, milk fat, and sugar. Its color is due to the absence of cacao particles. Milk chocolate also contains milk fat, making it lighter than dark chocolate. Ganache, used as a filling in chocolates and cakes, is a mixture of chocolate with cream or butter—the more cream or butter, the softer the ganache. Because it is an even more complex mixture than chocolate, it can be tricky to work with ganache.

Different cultures tend to have preferences with regard to the mouthfeel of chocolate. For example, Mexican chocolate has a coarser-grained texture than the creamy, even texture of Swiss or Belgian chocolate, which typically has particles that are only 20 micrometers in size. For Mexican chocolate, the beans are not ground as finely; the cacao is often mixed with spices and contains sugar that has bigger crystals. The result is a more complex sandy and gritty texture. Particle size also has a major influence on how the chocolate flows, which in turn has an impact on the mouthfeel of the melted chocolate. The finer the particle size, the lower the viscosity and the greater the creaminess of the melted chocolate. Swiss chocolate is renowned for its especially soft texture, which is due to a discovery made by Rodolphe Lindt in 1897. Lindt observed that by conching (which resembles kneading) the cacao particles with cacao butter, the resulting chocolate became very smooth and flavorful. Lindt then invented a machine to mechanize this process.

It is not possible to use tempered chocolate to coat ice cream and frozen desserts because the temperature in the oral cavity, thanks to the cold food, seldom rises above 86°F (30°C). At such a relatively low temperature, tempered chocolate remains solid and firm. In contrast, untempered chocolate is captured in the correct crystalline form by flash freezing it to 0°F (−18°C), causing the cacao butter to crystallize into a series of different structures with low melting points, typically around 77°F (25°C). As a result, the untempered chocolate coating melts in the mouth along with the ice cream. As long as the product is stored in a freezer kept at 0°F (−18°C) or less, the crystal structure remains intact. Another method for achieving a low melting point is to mix in other fats—for example, coconut oil.

Grainy Mexican chocolate (left) and smooth Swiss chocolate (right).

Really Crisp Old-Fashioned Crullers

Traditionally, crullers in northern Europe were deep-fried in pork fat, which contributed the particular meaty umami tastes that are absent when they are fried in oil. Nevertheless, most people prefer the less fatty taste of doughnuts fried in coconut oil. The crucial point is to heat the fat to a very high temperature to obtain a truly crisp result. This recipe, based on an old Swedish one, makes small crullers that are crisp and delicate, rather than the large, soft ones that have come to be associated with the name. The mouthfeel of the two types of crullers is completely different.

•  Beat the eggs and sugar together thoroughly, then knead in the flour, margarine, cream, and lemon zest.

•  Refrigerate the dough for about 2 hours.

•  Roll out the dough evenly to a thickness of about ⅛ inch (2–3 mm). Using a pastry wheel, divide the dough into rhomboid-shaped pieces of around 1½ × 2¾ inches (4 × 7 cm).

•  Make a slit in the middle of each piece and pull one end through the hole, forming a twisted shape.

•  Cover the bottom of a heavy pot with about 2¾ inches (7 cm) of coconut oil and heat it until the oil sizzles when a cruller is dropped into it. If the oil is not hot enough, the cruller will sink to the bottom.

•  Deep-fry the crullers, a few at a time, until they are light brown. Remove them from the pot with a slotted spoon and place on paper toweling to absorb the excess fat.

Makes 30 to 40 crullers

2 large eggs

¾ cup (165 g) granulated sugar

1¾ cups (400 g) all-purpose flour

¾ cup (165 g) margarine

3–4 tablespoons (45–60 ml) 9% light cream

Finely grated lemon zest from 1 lemon

Coconut oil

Really Crisp Old-Fashioned Crullers.

Fresh cow’s milk is a suspension of particles and dissolved molecules in water, which makes up 88 percent of the total. The structure of the suspension, and with it, the mouthfeel can be altered dramatically if the particles clump together. There are three main ways of making this happen: changing the nature of the particles, such as by modifying their surfaces as when cream is churned into butter; introducing enzymes, as in cheese making; or altering the electric charge on the particles. Another possibility is to change the properties of the continuous phase—for example, by modifying the acid and salt content—which increases the effective attraction among the particles. This is what happens when milk is soured or as a result of certain gelation processes. A third option is to create a gel with a suitable gelling agent.

Amy’s Apple Pie

This recipe, contributed by Amy Rowat, makes one double-crust pie.

•  Cut the butter into cubes about ¾ inch (2 cm) in size, and freeze until frozen.

•  Add an ice cube to 1 cup (250 ml) of water and place in the freezer.

•  In a large bowl, thoroughly mix the flour, salt, and sugar. Add the butter cubes to the mixture and crumble it all together with your fingers or pulse in a food processor. Be sure to leave some pieces that are the size of a pea; and others, the size of an almond.

•  Sprinkle 2 tablespoons (30 ml) of the ice water on the mixture and work in with a fork or a pastry cutter until it forms small lumps that can stick together when pressed between your fingers. Add more ice water, if necessary, but do not overwork the dough or it will be too hard.

•  Place the dough on a surface dusted with a little flour and press it into two circles that are about ¾ inch (2 cm) thick. Wrap the dough in plastic wrap and freeze until it is firm, about 1 hour. If placed in a freezer bag, the dough can be kept in the freezer for up to 3 months before use.

•  Place the circles of dough on a piece of parchment paper and roll them out. The bottom crust should have a diameter of 14 inches (35 cm) and the top crust should be a little smaller.

•  Grease a pie pan. Place the bottom crust in the pan. Core the apples; peel them or leave unpeeled. Cut the apples into slices about ⅛ inch (3 mm) thick, and distribute them evenly over the crust.

•  Place the top crust on the pie, allowing the edge to extend over the rim. Press the two edges of the crust together with a fork to make a decorative pattern.

•  Make a few decorative vents in the top crust to allow steam to escape.

•  Bake at 375°F (190°C) for about 1 hour, or until the top crust is lightly browned.

½ pound (230 g) cold unsalted butter, plus more for pan

2½ cups (660 g) all-purpose flour, plus more for dusting

1 teaspoon (6 g) salt

1 teaspoon (5 g) granulated sugar

4–8 tablespoons (60–120 ml) ice water

3 pounds (about 1.5 kg) apples, preferably a mixture of sweet and tart

Amy’s Apple Pie.

AMY’S CRISP APPLE PIE: A PHYSICIST’S APPROACH TO MOUTHFEEL

Canadian biophysicist Amy Rowat undertook her graduate studies in Denmark, where she delved deeply into the relationship between food and science. She next spent several years at Harvard University, where she helped launch a completely new general education course, Science and Cooking, said at the time to have become the most popular course on campus. Amy has moved on to a professorship at the University of California, Los Angeles, where she initiated the program Science&Food, which seeks to increase both scientific literacy through the study of food and culinary expertise through the knowledge of science. Students and members of the public turn out in large numbers to hear lectures and see demonstrations presented by famous chefs and researchers who share their passion for food and how it tastes.

In one of Amy’s many Science&Food projects, she and her students set to work to use physics to come up with a better pie, in other words, to construct the perfect American apple pie. The result was so amazing that it made it to the pages of the New York Times.

Making the perfect pie is largely a matter of getting the mouthfeel right. A successful, tasty pie must have a crisp crust with a flaky structure and a soft, slightly runny, spongy filling.

A crisp crust is due to a network of gluten proteins that are formed when the flour is mixed with water. If the network is too dense, the crust may turn out too hard. This problem can be solved by replacing some of the water with another liquid—for example, alcohol (vodka or rum work well)—so that is unable to form a network with gluten. It is also possible to use beer or carbonated mineral water, but these are less effective than alcohol.

Using a large quantity of fat (butter) and only a little water ensures that the pastry will be truly flaky. The water forms small droplets in the fatty dough. As the crust bakes, these droplets create small pockets of steam that are trapped in the dough, leaving the finished pie with an appropriately flaky structure.

The structure of the pie filling is equally important in terms of mouthfeel. If the filling is made up of apples, which contain great quantities of water, the water will evaporate under baking and the piecrust will bubble up, while the apple slices collapse on one another. To make sure that the apples actually fill up the entire inside of the baked pie, it is necessary to do two things. First, the apples can be cut up into thin slices that can be packed closely, so that there is less scope for them to fall together as their water content evaporates. Second, some of the water in the apples can be bound with flour or cornstarch, so that the liquid around the filling becomes more viscous.

Finally, Amy and her students discovered how the mouthfeel of the crust could be made even better. Generally, a piecrust is made by rubbing butter, flour, and sugar together thoroughly to make a crumbly mixture. The butter prevents all the water from binding to the gluten in the flour, resulting in a crisp, but not too hard, crust. But if the butter is first cut up into pieces of different sizes, resembling peas and almonds, two things happen. The butter lumps that are the size of almonds help create large air pockets and those that are the size of peas ensure that, nevertheless, the butter is distributed fairly evenly throughout the dough.

This, of course, is not the whole story. The pie also has to have an agreeable lightly toasted color, due to the browning that takes place as it bakes. This is a result of Maillard reactions between amino acids (e.g., from the proteins in the egg whites with which the top crust is brushed) and carbohydrates (e.g., from the lactose in the cream that is also brushed on top). The pie must not be too deep, otherwise the bottom crust will bake for too long and become hard before the filling is cooked through. It is also necessary to make vents in the top crust to allow the steam from the filling to escape, to prevent the top crust from rising.

Milk, Cream, and Homogenized Milk

Cow’s milk contains 3.5 percent total fat, primarily in the form of small globules that are on the order of 5 micrometers in size, but that can be as small as 0.1 micrometer and as big as 10 micrometers. The fat globules are less dense than water, and after the milk has been cooled for twelve to twenty-four hours, they will float to the top as cream. This process is rapid because it is enhanced by the tendency of the fat globules to bind to whey protein. It would take much longer for small globules to rise to the surface. Cream forms on milk from goats and sheep much more slowly because the fat globules are smaller and it is harder for them to bind together.

Heating denatures some of the whey protein, which slows down the rate at which the cream separates from the water. This is why pasteurized milk forms a smaller layer of cream than does milk that has not been heated.

To avoid completely any separation of milk and cream, it is necessary to homogenize the milk. In this process, the milk is forced through small nozzles at high temperature, so that the fat globules are broken up into particles that, on average, are no larger than 1 micrometer. At the same time, the high temperature destroys the enzymes that would otherwise attack the damaged globules. The original globules in raw milk are covered by a lipid membrane. After they have been broken up into many small ones, the lipid content is insufficient to cover all of their surface areas. As a consequence, casein micelles bind to the fat globules, increasing their specific gravity. These smaller, somewhat heavier fat globules have lost the ability to bind together and they remain suspended in the homogenized milk.

Three milk products with very different textures: milk, Icelandic skyr, and cheese.

In whipped cream, the fat globules are partially broken to pieces and clumped together in a network that contributes stability and a certain amount of stiffness.

If the casein micelles are removed from skim milk—for example, in the form of cheese curds—what remains is whey, which has very little fat and contains whey proteins only.

Butter and Its Very Particular Mouthfeel

The very particular mouthfeel of butter comes from the melting properties of milk fat. Butter gradually softens at temperatures above 59°F (15°C), but does not start to melt before it is at 86°F (30°C). In the mouth, this means that the fat runs out, coats the mucous membranes, and mixes with the food on which the butter is spread. This is why a thick layer of butter on a piece of bread is so satisfying.

Softened butter above 59°F (15°C) is easy to work into other food—for example, baked goods and pastry creams—also, savory ingredients—for example, herbs, spices, or garlic—can be mixed into it.

Typically, butter is made up of 81 percent fat, broken down as follows: 51 percent saturated, 26 percent monounsaturated, and 4 percent polyunsaturated. The exact composition is a reflection of what the cows have been eating; increasing the amount of grass in their diet results in a greater proportion of polyunsaturated fats. Hence, milk from cows that are put out to pasture in the spring and summer produces a butter that is softer and easier to spread. The natural yellow color of butter is due to carotene, an antioxidant that is familiar from the orange color of carrots. As grazing also increases carotene content, the resulting butter is yellower.

Microscopy image (left) and illustration (right) showing the structure of butter. The yellow regions are fats, and the blue droplets are water. The fats are partially crystalline and partially semisolid. The water droplets are between 0.1 micrometer and 10 micrometers in size.

The small fat globules in milk and cream are held together by a membrane composed of lipids and proteins, which prevents the globules from merging. The mechanical action of churning the milk to make butter breaks up these membranes into pieces in such a way that the globules are collected into a solid fat phase in which water droplets are trapped. So, to a large extent, the process of making butter consists of turning the milk inside out, in the sense that we start with an oil-in-water emulsion (milk and cream) and end up with a water-in-oil emulsion (butter). In the latter, the milk fat is found in three forms: as free, semisolid milk fat that makes up the aggregated phase, as crystallized milk fat, and as fat globules in their original state. Water droplets of different sizes are incorporated into this complex mixture. The crystallized milk fat ensures that the butter remains solid at room temperature and the aggregated phase of semisolid fat makes it easy to spread.

Traditional buttermilk is the liquid that is left over from churning cream to make butter. It has only a little fat, about 0.5 percent, and about the same amount of protein, 3–4 percent, as in whole milk. There are now other types of buttermilk, some of which are cultured, and that have a fat content of 1 percent, 2 percent, or 3.25 percent.

Cultured Butter

This recipe calls for a special type of fermentation culture that is not readily available in the average household. In addition, it has to be scaled down to a quantity that can be prepared in an ordinary kitchen. Nevertheless, the recipe is included as an example of how a small artisanal producer of fine dairy products or a restaurant that prides itself in serving food that is made “in house” might make cultured butter.

•  Pour the cream into a bowl and allow it to come to a temperature of 68°F (20°C).

•  Add 1–5 units FD-RS Flora Danica Culture (or another similar culture) per 10½ quarts (10 L) of cream.

•  Allow the mixture to stand at room temperature for 8–10 hours.

•  Chill to 50°F (10°C).

•  Beat at high speed with a mixer until the whey separates out.

•  Add salt or other seasonings according to taste.

•  Place the butter in a clean cloth, tie up like a bag, hang the bag over a bowl, and allow the moisture to drain at room temperature for at least 6 hours.

•  Using waxed paper, roll the butter into cylinders in the desired sizes. Store, wrapped, in the refrigerator.

Makes about 10 pounds (5 kg)

Organic 38% cream

FD-RS Flora Danica culture

Moisture draining from cultured butter.

Instant Churned Butter

•  Mix together the cream and crème fraîche and leave them at room temperature for 1–1½ hours.

•  Chill the mixture to 50°F (10°C), then whip at the highest speed until it starts to clot. Sieve the mixture. Season with salt.

•  Finely chop the seaweed, herbs, or other additives and mix into the butter thoroughly.

•  Pipe the butter into a dish or shape it into a cylinder and roll in waxed paper. Refrigerate.

Makes about 8 ounces (225 g)

2 cups (500 ml) organic 38% cream

1 cup (250 ml) organic 38% crème fraîche

Salt

Dried seaweed—for example, dulse—or other taste additives, such as herbs

Instant Churned Butter.

There are a number of ways to make butter. Some start with fresh cream, whereas others first allow the cream to ferment slightly with the help of lactic acid bacteria, which add both acidity and aromatic substances. In Europe, the latter approach is traditional. A little buttermilk from the previous churning is added to the cream to start the bacterial culture. While the culture is doing its work, the cream is kept cool at 41°F (5°C), which causes some of the milk fat to crystallize. These crystals help break up the fat globules as the milk is being churned. Commercially produced butter is now usually made from pasteurized fresh cream and the culture is added only after it has been churned. Normally 1.2 percent salt is added to enhance taste and improve keeping qualities.

Clarified butter is butter from which the water has been removed, made up almost entirely of pure milk fat (99.8 percent). It is very firm and especially suitable for sautéing and deep-frying at high temperatures. The traditional Indian form of clarified butter, ghee, has a grainy structure due to fat crystals. It is often a shade of brown, which is caused by the caramelizing of the lactose in the milk that is added to the butter as it is being heated.

A large number of commercial butter substitutes are various mixtures of butter and plant oils. These are softer and easier to spread.

Fermented Dairy Products

The large selection of fermented dairy products found in most supermarkets is a testament to the broad spectrum of textures that can be produced in processed milk. Most are creamy, some are grainy; others feel a bit dry; and still others fall apart easily and are semifirm and jellylike.

There are three principal ways to make sour dairy products. One consists of warming or souring milk or cream, resulting in such products as crème fraîche, cream cheese, and cottage cheese. The second way is to add rennet to the milk to make fresh cheese, which can serve as the starting point for fermentation and aging of myriad other cheeses. The third method makes use of a variety of microorganisms, especially lactic acid bacteria and certain fungi, to ferment milk and convert the lactose to lactic acid and other substances. Products made this way include yogurt, kefir, Icelandic skyr, and the Middle Eastern labneh and doogh.

All three methods produce foods that are more acidic than the raw ingredients and change the texture so that they are more viscous and even semisolid. But the fat and protein content of these products varies greatly and this, in turn, has a marked effect on their textures.

Fat content and its effect on texture are primarily responsible for the creaminess of dairy products, especially liquids (e.g., milk and drinks made from it); semisoft products (e.g., cream cheese); and firmer, jellylike solids (e.g., yogurt). In soft gels such as stirred yogurt, however, aromatic substances and a sweet taste influence the experience of creaminess. And there can be major variations in the perception of creaminess from one individual to another.

The demand for low-fat dairy products, especially fermented ones, can have a negative effect on creaminess. A secondary problem is that it is more difficult to incorporate, and subsequently release in the oral cavity, those aromatic substances that are fat soluble. It is estimated that 75–90 percent of all new low-fat dairy products are not commercially viable and many of these fail because consumers prefer the mouthfeel of those with a greater fat content.

Cheese

Of all products made from milk, cheeses, in all their varied forms, are probably the source of the most outstanding textures. Cheeses can be hard and firm, moist, soft, creamy, crumbly, grainy, crunchy, sticky, or chewy. Their texture depends on a whole range of factors, especially the type of milk from which they are made, their fat content, and how they are produced. In addition, as a cheese undergoes change as it ripens, one that has been aged will be quite different from its newly made counterpart.

Water content determines whether a cheese will be soft or hard, with the softer one having more water. Soft cheeses, such as cottage cheese, are about 80 percent water; mozzarella is about 60 percent. Roquefort and Gorgonzola, which are semisoft, have 42–45 percent water; firmer cheeses—for example, Emmentaler, Cheddar, and Gruyère—contain 39–41 percent. Finally, Parmigiano-Reggiano and other really hard cheeses contain only about 32 percent water. The fat content of the different types of melted cheeses also varies widely, affecting their creaminess.

In some cheeses, such as Parmigiano-Reggiano and various types of Gouda, that have been aged for a long time there are small crystals of calcium lactate and the bitter-tasting amino acid tyrosine. These add a pleasant crunchy feeling when one chews on the cheeses.

Amazing Eggs

Eggs are not only among the most widely used foods, but just about the most versatile ingredients to be found in the kitchen. If eggs are not contaminated with salmonella, they can be eaten raw. Eggs may be cooked in their shell, or cracked open and poached or fried, as cooking destroys salmonella. In addition, they can be used to thicken, emulsify, or make foam. They are used in many sauces and are vital ingredients in all types of baked goods, soufflés, and meringues. But an egg is not just an egg. The yolk and the white have a very different composition and their own distinct properties; they can be used together or separately.

Cooking an Egg: It Is All About Texture

There is probably no culinary process that is more widely discussed than how to prepare the perfect soft-boiled egg. Should the egg be placed in cold water before the heat is turned on or only when the water is boiling? Should a little vinegar be added to the water? For how long should it be cooked? Should it instead be simmered at a lower temperature just below the boiling point? And so on. All these questions are implicitly related to each individual’s expectations about the mouthfeel of the cooked egg. It all comes down to texture.

MELTED CHEESE: RUNNY, STRINGY, OR FIRM?

Have you ever wondered why some grilled cheese sandwiches are so stringy that they are almost like chewing gum? Dig into the chemistry a bit and you will find that the culprit is the melting point of the cheese that went into it. Some cheeses, particularly mild, soft ones, melt to form a homogeneous, viscous liquid, where the fats are trapped in it. Others that are firmer or older melt in lumps, releasing some of their fat content.

The considerable differences in texture have a lot to do with the forces that bind the casein proteins within the cheese solids. These proteins provide structure and keep the fats and the water content from going their separate ways. How well the proteins are bound to one another is a function of the calcium content and the associated calcium ions. In turn, the ability of these ions to do the job depends on other factors, especially the acidity of the cheese. The more acidic, or sour, the cheese—that is, the lower its pH—the harder it is for the calcium ions to bind the proteins together. When the proteins are more loosely bound, they can wander around and have an easier time keeping the fats in place, but this works only up to a certain point. As a cheese ages, its lactose is gradually converted to lactic acid. But if it becomes too acidic, the proteins become soluble and clump together, and the cheese begins to release its fats. Its acidity may even reach the point where the protein molecules bind so tightly that the cheese will not flow when it is heated and instead it melts in lumps. Cheeses that melt most satisfactorily have a pH of about 5.3–5.5.

Some cheeses, such as mild Cheddar and mozzarella, become stringy when they melt. This might also happen on a pizza made with “Parmesan-style” cheese rather than genuine aged Parmigiano-Reggiano, which tends to clump together and can be cut apart more easily. Stringiness can be fun, but not always, and there are several ways to minimize it. Finely grating the cheese helps, as does the addition of a bit of acid, such as lemon juice or tartaric acid. If you are making cheese sauce, you can get the same effect by putting a little cornstarch into it, or use Parmigiano-Reggiano, which will act as a thickener, and as a bonus, is a source of an abundance of delicious umami taste.

The stage is now set for a little experiment. It is more fun if you recruit a friend or two so that you can compare notes, and incidentally, get to test your hand at slicing the melted cheese. To start, lightly toast four slices of bread. On the first, put slices of mild Cheddar; on the second, some of the same mild Cheddar grated finely and mixed with a few drops of lemon juice; on the third, slices of a medium cheese, such as Tilsit or Emmentaler; on the fourth, genuine Parmigiano-Reggiano shavings. Use approximately the same amount of cheese on all of them. Put them all under a hot grill until they are just melted and starting to brown. Then sit back, taste, and evaluate the results—runny, stringy, or firm?

Parmesan-Flavored Smoked Cheese with Dried Radishes

A special type of smoked cheese, called rygeost, is considered to be the only type of cheese that is native to Denmark or, more precisely, to the island of Funen. Originally this was a very simple fresh cheese that was a staple of traditional peasant cuisine. In recent years it has evolved, taking on more elaborate gourmet incarnations. Here is a recipe for a modern variation that incorporates Parmesan cheese, which adds umami taste substances.

•  Grate the cheese coarsely, place it in a vacuum bag with the milk and seal the bag.

•  Place the bag in a water bath at 140°F (60°C) for 5 hours, sieve the milk, and discard the Parmigiano-Reggiano cheese.

•  Chill the sieved milk to 68°F (20°C), add the cream, buttermilk, and rennet, and allow to stand at room temperature for 24 hours after which it has formed a cheese curd.

•  Remove the cheese curd with a slotted spoon and place it in a clean cloth. Season with the salt and suspend the cheese mass for 12 hours so that the liquid will drip away. Set aside a scant 6½ tablespoons (100 ml) of the resulting whey for the radishes.

•  Place the cheese curd in a mold or sieve so that it has a shape that can be handled during the smoking process.

SMOKING

•  Make a smoking tube, using a piece of tin that has a hole at the bottom of one side, or use a very large pot, metal pail, or something similar.

•  Place the straw in the container, at first a little loosely, and then more closely packed—a little like the way that tobacco is tamped into a pipe. Lightly spray the straw with a bit of water and place the nettles and leaves on top.

•  Light the straw at the bottom. When the smoke is quite intense place the covered cheese on top of the straw, cover the smoking tube or pot, and allow to stand for 1–2 minutes.

•  Turn out the cheese onto a plate and keep it cool until served, or refrigerate if it is to be kept.

RADISHES

•  Dehydrate the radishes in a dehydrator for 5–8 hours at 85°F (40°C), or until they have shriveled up completely.

•  Using the remaining whey make an 8% w/w brine by adding an appropriate amount of salt to the whey and place the dried radishes in it. Refrigerate them, preferably for about 2 days. The radishes can keep a long time in the refrigerator. It is also possible to use a brine made with water or to place a piece of konbu seaweed in the brine.

Makes about 2 pounds (1 kg)

7 ounces (200 g) Parmigiano-Reggiano cheese

8½ cups (2 L) unhomogenized milk

1 cup (250 ml) unhomogenized 38% cream

1 cup (250 ml) fresh buttermilk

6 or 7 drops rennet

2–3 teaspoons (12–18 g) fine salt

10 long radishes

Oat straw

Stinging nettles, beech leaves, or dandelion leaves

Parmesan-Flavored Smoked Cheese with Dried Radishes.

WHAT IS A SOFT-BOILED EGG? THE 6X°C EGG

The questions about the true nature of a soft-boiled egg and what actually allows it to take on so many different textures have been investigated scientifically by a renowned food chemist, César Vega. His focus is the texture of the yolk, as this is, first and foremost, the distinctive feature of a soft-boiled egg.

Together with his colleague Rube Mercadé-Prieto, Vega came up with the designation “the 6X°C egg,” where X stands for a number between 0 and 7, which means that different chefs prepare a soft-boiled egg by slow cooking it for at least one hour, allowing it to simmer in a water bath at a temperature that is far below the boiling point (212°F [100°C]).

Vega starts by demonstrating that cooking an egg is a complicated process, the success of which depends to a large extent on temperature heat transfer and time. There are two reasons for this. One is chemical and has to do with the gelling properties of the molecules that make up the white and the yolk. The other is physical and has to do with how quickly the heat from the surrounding water is conducted to the various parts of the egg.

Vega has shown that he can produce the whole gamut of desired textures by using an appropriate combination of temperature and cooking time. In all, he tested sixty-six different combinations, and for each he evaluated the texture of the cooked egg. It turned out that altering the temperature by as little as 2°F (1°C) could have a major influence on the outcome. The problem was to figure out how to characterize the resulting texture. So, Vega suggested that the best indicator was to measure the viscosity and then compare the result with the viscosity of other well-known products—for example, runny like syrup or firm like toothpaste. Based on their many experiments, Vega and Mercadé-Prieto were able to construct a table that lists which combination of temperature and cooking time should be chosen so as to achieve the desired consistency in the yolk, but only the yolk. What remains to be done is to carry out a similarly meticulous study of the egg white.

Despite all the scientific data that he has collected, Vega admits that he prefers to cook an egg using the same approach as most of us: Bring the water to a boil. Take the eggs from the refrigerator and place them right away in the boiling water, but not too many because that would decrease the water temperature too much. Let them cook for six minutes. Remove the eggs from the water and cool them with running cold water.

The difficulty in trying to assess the texture of the egg as it boils is that it is encased in a shell and there is no way to know how it will turn out without breaking it open. This is not the case with poaching or frying, where we can look at the egg to judge whether it has the right consistency or even lightly touch the egg.

But what is a soft-boiled egg? This is more than a trivial topic for discussion at the breakfast table because an egg is made up of two distinct parts. The raw egg white and the raw yolk are both complex fluids made up of large macromolecules, such as proteins and amphiphilic fats. Their properties depend on temperature and on what type of force is applied to the liquid—for example, in the mouth.

Cooking an egg is an example of a gelling process, in which the proteins in the white and the yolk are denatured and become firm like a gel. This process is irreversible: once gelation has taken place, the egg remains firm, even when cooled. As the proteins in the egg white denature at a lower temperature (126°F [52°C]) than do those in the yolks (at least 136°F [58°C]), it is possible to prepare the perfect soft-boiled egg with a firm white and a runny yolk, but it requires either very precise temperature control or careful monitoring of the cooking time and quick cooling to stop the cooking.

Eggs as Thickeners and Emulsifiers: Sauces, Cream Puddings, and Foam

Eggs can be used in a variety of ways to contribute to texture in food. They can thicken, emulsify, and create foams. In many cases, the eggs fulfill several of these functions at the same time.

In principle, a raw egg yolk is an emulsion of fat in a large quantity of water, and the proteins and phospholipids (lecithin) function as emulsifiers in such foods as hollandaise sauce and mayonnaise.

About half of the egg yolk is made up of water and its fantastic ability to bind water is exploited in crème anglaise. To prepare it, scalded milk and cream are allowed to cool and then mixed with egg yolks and sugar. The mixture is then heated gently until the desired consistency has been achieved.

Crème anglaise can be regarded as the basis for other dishes, often desserts, where the egg yolk elicits a different mouthfeel. If crème anglaise is frozen, it becomes ice cream. If starch is added to it, it can be made into cake cream or pudding. If it is baked in a water bath, it turns into crème brûlée, which is usually topped with a layer of caramel.

Eggs are also used to thicken soups. In a classic Chinese dish, hot and sour soup, a lightly beaten raw egg is added just before serving. It coagulates in the hot liquid to form fine, pale yellow threads that thicken the soup but do not bind it together firmly. They introduce a soft textural element that contrasts with the more solid pieces of mushroom and meat.

Glassy, Glossy Foods

There is a special category of solid materials known as glasses, which lack the crystal structure that characterizes a true solid. Instead, their molecules, like those in liquid, are not ordered, but either are fixed into position or move only very slowly past one another. A large proportion of the foods that have crisp and crunchy textures owe these properties to their being in a glassy state and to the special effect this has on their mouthfeel. Unlike crystals, glasses can feel fragile or brittle in the mouth, which results in a crunchy mouthfeel rather than the sensation of crushing a hard crystal. An example is the contrast between eating a caramel and a crystalline sugar.

The glass state is often preferable to the crystal state, but it may not be the more stable of the two. It might, therefore, be necessary to prepare the food in such a way that it is trapped in the glass state—for example, by cooling the food so quickly that the molecules do not have the time to organize themselves with respect to one another. The glass state occurs below a temperature known as the glass-transition temperature. As glasses are actually very viscous liquids, their viscosity can be altered by increasing the temperature. This is known from caramel, which becomes softer when heated.

The transition to the glass state can be changed by making appropriate mixtures. For example, fructose, which has a low glass-transition temperature, can decrease the glass-transition temperature of a sugar mixture that is used to make hard candy or caramel. This process, known as plasticization, makes the mixture more malleable and deformable, but it also has more difficulty in retaining its shape under pressure—for example, when it is chewed.

Water is the most important component in making food more plastic. This is easily demonstrated by the way a crisp bread crust or cracker becomes soft if it absorbs liquid. The transition from the glass to the plastic phase is reversible and takes place over a certain temperature range. This process can be seen when a cracker that is a bit soggy is made crisp again by toasting or heating it slightly.

Caramel

Caramel is a mixture of different compounds that form when sugar molecules are heated and fragment. The easiest way to make caramel is to dissolve sugar in water and then cook the mixture. The temperature at which it turns into caramel depends on the type of sugar used—for example, 221°F (105°C), 302°F (150°C), and 338°F (170°C), respectively, for fructose, glucose, and sucrose. A light, viscous fluid, which is a syrup, is formed first.

Eggs, twelve ways: (top) hard-boiled egg, egg cooked with onion peels and brined, and fried egg; (middle above) egg in mayonnaise, egg in soufflé, and egg pickled in vinegar; (middle below) scrambled egg, omelet, poached yolk; (bottom) frittata, poached egg, and raw egg.

Peppery, Chewy, Chocolaty Caramel

Forget the salted caramel—try a peppery one instead!

•  Heat the cream with the whole peppercorns, sugar, and glucose until boiling.

•  Chop the chocolate into small pieces and place them in a heavy pot. Passing it through a sieve to remove the peppercorns, pour the hot cream mixture into the pot with the chocolate pieces. Heat to 257°F (125°C). Pour the caramel mixture into a small silicone mold or one lined with parchment paper and allow it to cool to room temperature.

•  Cut the caramel into serving-size pieces.

Makes about 18 ounces (500 g)

⅔ cup (150 ml) organic 38% cream

10 black peppercorns

⅔ cup (130 g) granulated sugar

5 tablespoons (110 g) glucose

7 ounces (200 g) good, dark chocolate

Peppery, Chewy, Chocolaty Caramel.

The brown color of caramel is attributable to polymerization of the sugar. This occurs when the mixture is heated for a long period of time and more of the water evaporates. The longer it is heated, the darker the color and the less sweet and more bitter the taste of the caramel. When cooled, the mixture becomes a solid caramel, which is a glass.

A caramel can be soft, chewy, mealy, hard, or crisp, depending on the exact way it is made, with regard both to heating and cooling and to the other substances that are added to the sugar and water mixture. Egg whites, cream, milk, butter, and gelatin can be used to prevent the sugar from crystallizing and to achieve the desired texture. If cream is used, the fats in it help make the caramel soft and possibly a little mealy. This type of caramel is used in desserts, ice cream, and candy—for example, chocolate-covered caramels.

Caramelized Potatoes

No traditional Danish Christmas dinner is complete without a dish of small caramelized potatoes.

The potatoes must be boiled until well done but still firm and then peeled carefully rather than scraped so as to preserve the fine membrane that is found just under the peel. This membrane helps ensure that the potato starch does not seep out when they are browned, as this would result in a fuzzy and less smooth surface.

For the browning process to be successful, high heat is required to prevent the layer of caramel from becoming lumpy. The best results are achieved by sprinkling a layer of sugar over the bottom of a very hot pan and leaving it to melt without stirring it. It is also possible to achieve a more even melting of the sugar if a little water is mixed in with it.

When the sugar has melted and the water, if any, has evaporated, and before it becomes too brown, butter is melted into the sugar. The next step is the critical one: when the butter has started to froth, the peeled potatoes are placed in the melted sugar. Preferably the potatoes should be cold and have been rinsed with water. To prevent the sugar from solidifying and forming hard lumps of caramel when the ice-cold potatoes are added, it is necessary to have very high heat to keep the sugar liquid.

The browning process now proceeds by simmering the potatoes in the liquid caramel for a good period of time, all the while turning them carefully from time to time so that they do not burn at the bottom. The butter helps create a beautiful, shiny surface on the caramelized potatoes.

•  Rinse the potatoes, then place in a pot and add just enough water to cover them.

•  Add salt, cook the potatoes for about 15 minutes, peel them, and put them in the refrigerator.

•  Sprinkle the sugar in the bottom of a pan and allow it to caramelize without stirring it.

•  Add the butter and allow it to froth, then mix together the sugar and the butter.

•  Rinse the peeled, cooked potatoes in cold water and let them drain a bit so that they are still moist. Place them in the caramel and turn them carefully until their surfaces are covered with caramel and they are warmed through.

•  The potatoes are done when they are completely reheated, golden and dark, and have a fine, bitter-tasting, caramelized surface.

Caramelized Potatoes.

Serves 6

2¼ pounds (1 kg) firm, very small potatoes

1 tablespoon (18 g) salt per quart (L) of cooking water for the potatoes

½ cup (100 g) sugar

2 tablespoons (30 g) butter

Heating the sugar for the syrup or caramel together with other ingredients that contain proteins and amino acids can result in the formation of some brown, tasty substances caused by Maillard reactions. These chemical reactions work their magic in the recipe for caramelized potatoes.

The natural sugars found in vegetables are another source of caramel. Browning onions and leeks slowly allows Maillard reactions and caramelization to take place, creating substances that can greatly enhance their taste. Some of these compounds and their associated tastes are furanes (nutty), ethyl acetates (fruity), maltol (toasty), and acetic acid (sour).

Hard Candies

Hard candies are made the same way as caramel by boiling sugar mixtures. Normally taste substances—for example, fruit extracts, nuts, or licorice—are added to the mixture, but not cream. The boiling point for the mixture depends on the water content; it rises as the water evaporates.

The cold-water test for hard candies

Cooks often use a candy thermometer to determine when the cooked sugar mixture is ready to be made into candy. But there is also a very old technique that is quite useful for making these and other types of sweets. Simply put some of the mixture onto a spoon and let it drip into a small bowl of cold water. If it forms thin, soft filaments, it is not suited for making firm candies. If it forms little spheres that can be compressed, it can be made into soft caramels or fudge. And if it forms hard threads that snap with a crackle, it is just right for hard candies.

Hard candies are formed when a sugar mixture that has lost 99 percent of its water content is cooled suddenly so that it is trapped in a glass state. The hardness and fragility of the candies depends on the glass-transition temperature of the sugars being used. These can be quite different: 41°F (5°C) for fructose, 88°F (31°C) for glucose (grape sugar), and 144°F (62°C) for sucrose (ordinary sugar). The glass-transition temperature can be determined reasonably accurately by using a weighted average of the glass-transition temperatures of the sugars in the mixture. Below this temperature, the melted sugar will harden and become a glass. Consequently, mixtures containing a sugar with a very low glass-transition temperature will turn to glass at a lower temperature, resulting in a more plastic substance.

A dessert with a glass lid

The well-known dessert crème brûlée is simply a creamy custard with a layer of caramelized sugar, or a glass lid, on top. To avoid heating the custard part, it is necessary to use very fine sugar crystals that will melt more quickly when heated with a kitchen torch.

Candy floss is produced by swirling a sugar mixture around while the mixture is cooling, turning it into a glass made up of long, thin threads that intertwine and form a loose bundle that is composed mostly of air. This structure has a very special light mouthfeel, followed by a sticky one as the floss collapses into a solid mass of sugar in the mouth.

Candied Seaweed

The simple recipe was elaborated by chefs Daniel Burns and Florent Ladeyn at a workshop in Illulissat that centered on discovering new uses for the natural ingredients that could be harvested in Greenland.

•  Blanch the kelp two times.

•  Mix together the water and sugar and heat the mixture. Place the kelp in the mixture.

•  Reduce the liquid over low heat for 30 minutes.

•  Remove the kelp fronds and spread them out on a dehydrator sheet.

•  Dehydrate the kelp for 15 hours at room temperature.

•  The candied kelp can be eaten as a sweet snack, used as an accompaniment for a frozen dessert, or crushed into granules for toppings on desserts and cakes.

14 ounces (400 g) cleaned, wet winged kelp (Alaria esculenta)

1 cup (230 ml) water

1¼ cups (300 g) table sugar

Candied Seaweed.

Glazes and Fondants

A glaze is a topping made from icing sugar and water, to which an egg white may be added. As the name implies, a glaze is sometimes a glass, and it is almost always the sugar content that stabilizes it in that state when the water has been evaporated by heating.

A glaze serves both to decorate and to prevent the food that it covers from drying out. In addition, a glaze can impart a delicate and crisp mouthfeel that might provide a contrast with a soft cake or a pastry under it.

A cold cake glaze is made from a mixture of icing sugar, a little water, and possibly an egg white or syrup. Adding a little fat (butter or cream) helps prevent the sugar from crystallizing, and as a bonus, results in a shiny surface on the glaze. As icing sugar is a very fine powder, there are no crunchy crystals in the glaze. Depending on the ingredients, the glaze can harden or remain a little soft and shiny.

Glazes that can tolerate being heated, such as those used on meat that is to be roasted or barbecued, are made from sugar (or possibly honey) and fat (butter), mixed with mustard or other spices. A little glucose can be mixed in to ensure that the glaze takes on the glass state rather than crystallizing. As the meat is heated, Maillard reactions involving the sugar and the meat proteins produce delicious brown taste substances. Because the sugar melts when heated, it is not necessary to use it in powdered form in these types of glazes.

A fondant is a special type of glaze that is related to a soft, solid caramel, such as fudge. Fondants are used both as icings for cakes and as filling in confections. A fondant is made by cooking sugar or syrup, which is then worked mechanically, possibly with the addition of glucose, until it has a texture that resembles that of clay. The texture of a fondant is critically dependent on its water content—it can be either dry and lumpy with small sugar crystals or slightly runny.

Fudge is more complex because it contains milk, fats, and sometimes cocoa or chocolate. Consequently, fudge also incorporates fat droplets.

Baked Goods with a Crispy Crust

We usually expect the crust on baked goods, other than some cakes, to have a mouthfeel that can be characterized as crispy, crunchy, or crackly. These different expressions tell us that the way we experience eating a crust is linked to, and intermingled with, tactile, visual, and auditory sensory impressions.

Crispness is related to the high-frequency sound that is generated when the front teeth break through the crust, before it has been deformed by chewing—this is the sign of a good crust. The crunchy sound is tied to the merciless way in which the molars finish the job started by the incisors, reducing the pieces in ever smaller bits.

A problem that sometimes crops up with all baked goods that have a crisp crust and a softer interior, whether they are savory or sweet, is that over time the crust becomes soft or chewy because liquid seeps from the moister interior to the dry exterior. When the water becomes more active, it changes the state of the crust from a glass to something more gummy and plastic. As this change is reversible, a bread crust that has gone soft can be made crisp again by heating it in the oven, thereby evaporating some of the water.

Old-Fashioned Crispy Spice Cookies

This recipe has been used by Ole’s mother for almost six decades. Seemingly, it was published in a newspaper column by Lise Nørgaard and Mogens Brandt in the 1950s. They wrote that the recipe must be followed to the letter to bake the world’s best crispy spice cookies.

•  Mix the butter, 2¼ cups (500 g) of the sugar, and the syrup in a pot and heat the mixture until has melted together and is about to boil.

•  Stir the almonds, cloves, cinnamon, and potash into the mixture and allow it to cool to lukewarm.

•  Chop the orange rind into coarse pieces and bring it to a boil together with the remaining ¼ cup (50 g) of sugar and a little water. Allow it to cool to lukewarm.

•  While the butter mixture, almond mixture, and zest mixture are still lukewarm, mix all of them into the flour to make a firm dough.

•  Knead the dough thoroughly, then shape it into a thick roll 2–2¼ inches (5–6 cm) in diameter.

•  Place the dough in a cold place for a couple of hours. It can also be frozen for use later.

•  Cut the roll into thin slices; the thinner they are, the more delicate and crisp the cookies.

•  Place the slices on a cookie sheet covered with parchment paper. Bake them at 400°–425°F (200°–220°C) for 10–12 minutes, depending on the thickness of the slices.

1 pound + 4 tablespoons (500 g) butter

2½ cups (550 g) granulated sugar

½ cup + 2 tablespoons (250 g) dark corn syrup

¼ pound (125 g) almonds, coarsely chopped

1 tablespoon (7 g) ground cloves

3½ tablespoons (25 g) ground cinnamon

1 tablespoon (15 g) potash dissolved in a little water

Rind of 1 organic orange

6⅓ cups (800 g) all-purpose flour

Old-Fashioned Crispy Spice Cookies.

Biscuits and cookies of different types are the embodiment of crispness. If they become the least bit soft, they are unappetizing, because their true worth is judged by their mouthfeel. Nevertheless, there is little unanimity about the degree of crispness that is desirable in certain traditional types of cookies. Crullers are a good example of the way in which this question divides people into camps. Some individuals like them to be very small and crisp right through, whereas others prefer them large and quite soft.

Crisp Coatings

The surfaces of vegetables, meat, and fish are often made crisp by coating them with a layer of a starchy product, such as flour or bread crumbs. This layer can be made crisp by deep-frying in oil or panfrying in fats. Milk or beaten eggs are often used to get the coating to stick.

In principle there are two types of coating, one that attaches itself directly onto the piece of food to be cooked; the other, best known from tempura, forms a coagulated shell around it.

The type of coating that clings directly to the food makes use of a substance that will help it stick—for example, by dredging the food in flour before rolling it in bread crumbs. It is best if this substance does not affect the mouthfeel. When fried, the bread crumbs cover the surface of foods, such as cutlets or fish fillets, with a crisp, golden crust.

The other way of coating the surface is with a batter that contains a leavening agent, such as beer, that forms small bubbles of carbon dioxide in a mixture of beaten egg yolk and bread crumbs. The bubbles are stabilized by the lecithin in the egg yolk; when fried, the bubbles are trapped in a crisp, slightly spongy shell. The open structure of this shell allows moisture in the food that is being cooked to evaporate. A classic example of this batter is the one used to make vegetable tempura.

The flaky, very dry Japanese bread crumbs, called panko, are particularly suitable for use in these very crisp coatings. Panko is made from a special bread that is baked by passing an electric current through a bread dough that has been allowed to rise several times. The finished product is light and fluffy and has no crust. After it has dried thoroughly, it is shaved into flakes. Because of its particular airy structure, a batter or coating made with panko absorbs less oil when deep-fried, and consequently, the result is a lighter, crisper crust.

It is well known that a crisp mouthfeel is the key to making some types of offal—for example liver, heart, and brain—into a real taste treat and a culinary adventure. The reproductive organs of an animal are also eminently edible, but many people consider this idea so repulsive that they will not even consider it. In some cultures, though, dishes that incorporate organs, such as the uterus and testicles, are common and are associated with legends that forge a symbolic relationship between the persons eating the organs and enhancement of fertility in a female or virility in a male.

Crisp-Fried Bull Testicle with Sprouts and Parsnip Emulsion

In this recipe, bull testicles are the turned into a savory delicacy.

PREPARE THE SPROUTS

•  The sprouts must be prepared several days ahead of time.

•  Soak the wheat grains in water with a little vinegar for 8 hours.

•  Rinse the wheat grains and place them on trays to sprout.

•  Place the trays in a cool place with ample light and rinse the wheat berries carefully twice daily for 3–5 days (depending on the surrounding temperature), or until they have sprouted to a desired size.

POACH THE TESTICLE

•  Peel the carrot and cut into slices.

•  Peel the onion and cut into large chunks.

•  Pour the white wine, vinegar, and water (or stock) into a pot; add the thyme, herbs, peppercorns, salt, yeast flakes, and the cut-up vegetables.

•  Allow the mixture to simmer for 10 minutes.

•  Wrap the testicle in a clean cloth, place in the pot, and allow to simmer for 10–15 minutes, depending on the size.

•  Turn off the heat and let the pot stand for about 30 minutes. Remove the testicle and refrigerate it, placing a plate with a little weight on top to press it down.

PARSNIP EMULSION

•  Peel the parsnips, cut them into large pieces, and boil them in the water and milk with 2 teaspoons (10 g) of salt until they are soft.

•  Drain the parsnips in a sieve and then dry them in a pot for about 10 minutes at low heat. Do not allow them to brown.

•  Weigh the parsnips, place them in a blender with the xanthan gum, and blend for 5 minutes.

•  Add the equivalent quantity of oil in a thin stream while the blender is running.

•  Season with salt and a little freshly ground pepper.

FRY THE TESTICLE

•  Slice the testicle into slices about ¾ inch (2 cm) thick, and season with salt and pepper. Dredge them first in the flour, then the egg white, and finally the panko crumbs.

•  Fry the pieces in a neutral-tasting oil at 338°F (170°C) until they are golden. Place them on a piece of paper to absorb any excess oil and sprinkle with Maldon salt.

TO SERVE

•  Place some warm parsnip emulsion on the middle of each plate. Place the warm, crisp testicle pieces on top and surround with small bunches of sprouts. Serve immediately.

Serves 6

SPROUTS

3½ ounces (100 g) organic wheat grains of sprouting quality

1 tablespoon (15 ml) malt vinegar

Water

TESTICLE

1 carrot

1 large onion

1 cup (250 ml) dry white wine

6½ tablespoons (100 ml) good white wine vinegar

1 cup (250 ml) water or chicken stock

Sprigs of thyme

1 bundle of soup herbs (e.g., leek tops, parsley sprigs)

1 sprig of lovage

Salt and peppercorns

1 tablespoon (12 g) yeast flakes

1 large bull testicle (about 21 ounces [600 g])

PARSNIP EMULSION

½ pound (250 g) parsnips

6½ tablespoons (100 ml) water

6½ tablespoons (100 ml) milk

Pinch (0.25 g) of xanthan gum

⅕ cup (50 ml) neutral-tasting oil

Salt and freshly ground pepper

FOR FRYING

A little all-purpose flour

Egg white

Panko bread crumbs

Maldon sea salt

Neutral-tasting oil

Particles in Food

The mouthfeel of a food is very much influenced by particles that are distributed more or less evenly throughout it. It is possible for the mouth to detect particles as small as 7–10 micrometers. If the particles are bigger than that, the mouthfeel will be perceived as sandy or mealy, an example being small ice crystals in ice cream. The particles can also be so big that they are visible to the naked eye—bits of meat in a meat sauce, tapioca grains in a pudding, or julienned vegetables. The mouthfeel of the particles will depend on their size, shape, and hardness. Particles in the form of liquid droplets or fats in a solid, but still plastic, phase will feel creamy, and ice crystals as hard and gritty, even crunchy.

Much of the work that takes place in a kitchen centers on cutting raw ingredients into the desired shapes and sizes or changing their structure. We slice, tear, grind, blend, puree, crush, chop, mince, press, sieve, shake, and so on, all with the aim of changing the particle size. Modern blenders, electric grinders, and food processors have taken the drudgery out of most of these operations.

Pureeing

Making a puree with a smooth mouthfeel from plant materials is a question of reducing the ingredients to particles that are so small that their mouthfeel is fundamentally altered. This is most easily done with a blender or an electric grinder. Adding a little oil or other fat will enhance the softness of the puree.

Because some plants have very hard parts, it can be difficult to reduce them to a fine puree. But a granular texture, similar to that of hummus, can be quite appealing. To facilitate the process, the raw ingredients should be cooked first to loosen their cell structure. Pureeing too vigorously foods that have a significant starch content can smash the grains of starch to bits, resulting in an elastic, gummy consistency. This is all too familiar from the texture of potatoes that have been mashed too aggressively. Fruits have a variety of cell structures that react differently to being mashed or pureed after cooking. The resulting textures are also affected by the pectin content of the fruit.

Hummus.

The mouthfeel of two different purees made from exactly the same raw ingredients—for example, ketchup—can diverge so much that we perceive the two types to taste different. Think also of the example of peanut butter—our impression of the taste of the smooth version is very dissimilar from that of the crunchy one.

A puree can help thicken and stabilize a sauce if the particles are not too big. Small particles can bind more water if they contain a starch or pectin, and furthermore, they have less of a tendency to sediment out. If the puree still separates, it can be reduced by evaporating some of the water. In this way, a fine puree can serve as a stiffening and gelling agent.

Ketchup, which is a source of both umami tastes and smooth texture, is now an almost universal condiment. Originally, ketchup was an Asian fish sauce that was brought to Europe by British sailors. It underwent a transformation, with the addition of mushrooms, walnuts, wine vinegar, and a long list of spices. So, from 1750 to 1850, the word “ketchup” was used in England as a general term for a variety of thick brown sauces that contained mushrooms. Tomatoes were not added until the beginning of the nineteenth century, presumably by the English. By about 1850, all traces of fish had more or less disappeared as an ingredient, and in the United States it was modified to have a sweeter and sourer taste and a thicker consistency.

An Experiment: Two Types of Ketchup

Make two versions—one with a coarse consistency and the other finely pureed. Taste the difference.

•  Peel and core the apples and chop them into small cubes (about ½ inch [1 cm]).

•  Blanch and remove the skin from the fresh tomatoes. Canned tomatoes are ready for use.

•  Remove the seeds and stalk from the peppers and cut them into small pieces.

•  Chop the shallots.

•  Remove the seeds and stalk from the chile peppers and mince them.

•  Sprinkle the sugar in a pot, heat it until it caramelizes, and add the warm apple cider vinegar.

•  Add the apples, tomatoes, peppers, shallots, chile peppers, and cloves and bring it to a boil. Meanwhile, peel the garlic, put it through a garlic press, and add it to the pot. Allow everything to simmer without a lid for 1 hour.

•  Remove the cloves and add the olive oil. Blend half the mixture with an immersion blender until it has a coarse consistency. Blend the other half until it is a very smooth puree.

•  Season each mixture with equal amounts of additional vinegar and sugar, if desired, and add salt to taste; reduce over low heat if a thicker consistency is desired.

Taste both ketchups and evaluate whether the mouthfeel influences the taste impression.

Makes up to 3 pounds (1.5 kg)

½ pound (225 g) apples, peeled and cored

4½ pounds (2 kg) ripe tomatoes (could be canned organic tomatoes)

1 pound (500 g) red bell peppers

10½ ounces (300 g) shallots

4 ordinary chile peppers, or 2 cayenne peppers

1¼ cups (250 g) light cane sugar

2 cups (500 ml) apple cider vinegar, warmed up almost to the boiling point

2 whole cloves

6 garlic cloves

5 ounces (150 g) tomato puree (unspiced)

3½ tablespoons (50 ml) olive oil

Salt

Two types of ketchup: (left) puréed and (right) coarsely blended.

Pesto

Pesto is a puree or sauce that is also an oil emulsion. The name comes from the Italian pestare, meaning “to crush.” The classic version is made by pounding together fresh basil, garlic, and pine nuts; stirring the mixture into olive oil; and optionally adding grated Parmesan cheese. The plant pieces are particles that are big enough to be chewed but small enough to give the pesto an integrated and soft mouthfeel. Pesto can be spread on bread or used as a sauce on pasta.

•  Boil the seaweed in water for 10 minutes.

•  Set aside a few of the pumpkin seeds.

•  Blend the seaweeds together with all the other ingredients to make a smooth puree.

•  Just before serving, stir in the remaining pumpkin seeds to add a little crunch.

Pesto.

Makes 7 ounces (300 g)

This recipe for seaweed pesto comes from Anita Dietz, a Danish chef who is a passionate advocate of cooking with marine algae.

7 ounces (20 g) dried seaweed (e.g., a combination of sugar kelp, serrated wrack, winged kelp, and sea tangle)

1¾–3½ ounces (50–100 g) pumpkin seeds

1 avocado

1 red onion

1 garlic clove

1½ tablespoons (20 g) capers

¼ tablespoon (about 1 g) grated Parmesan cheese

A little fresh parsley or fresh spinach

2 tablespoons (30 ml) olive oil

Salt and pepper

Frozen Desserts with a Crunch

While there are numerous ways to make frozen desserts, they are all complex mixtures of ice crystals, air bubbles, and a sugar solution that is not frozen. In addition, they may contain small solid particles of fruit or other ingredients that are there to enhance their taste.

A traditional ice cream is made from milk, cream, possibly eggs, and a range of taste substances. Ideally, the ice cream itself should have a creamy texture and be free of any particles that might crunch between the teeth. But many also incorporate chocolate chips, dried fruit, caramel, nougat, or nuts to add a textural element. It is said that a famous brand of ice cream, Ben & Jerry’s, contains crunchy particles in each and every bite because one of the founders, Ben Cohen, suffered from anosmia, a lack of the sense of smell. To compensate, he oversaw the development of recipes for ice cream that had abundant texture and an interesting mouthfeel.

Sago Soup with Raisins

•  Soak the raisins in the Madeira the day before they are to be used.

•  Cut the lemon zest into large slices.

•  Bring the water to a boil with the lemon zest, sprinkle the sago pearls into the pot, and stir vigorously.

•  Cover the pot and allow the sago pearls to cook for 15–20 minutes. Remove the pieces of lemon peel.

•  Thoroughly beat the egg yolks with two-thirds of the sugar until they are a very pale yellow. Stir a little of the hot liquid into the egg mixture, then whisk it a little at a time into the liquid to thicken it. Season with remaining sugar, lemon juice, and the Madeira in which the raisins were softened. Keep warm, but do not allow the soup to boil.

•  Stir in the raisins and serve immediately while the soup is still warm.

Serves 4−6

⅔ cup (100 g) raisins

3–5 tablespoons (45–75 ml) Madeira wine

Zest and juice of 1 organic lemon

6 cups (1.5 L) water

2¾ ounces (80 g) sago or small tapioca pearls

3 or 4 egg yolks

½ cup (100 g) sugar

Sago Soup with Raisins.

A GOURMET FEAST IN NORTHERN GREENLAND: TEXTURE FAR NORTH OF THE ARCTIC CIRCLE

A visit to Ilulissat is unique in many ways—the place and the experience are best described in superlatives. Ilulissat is the main town in the world’s largest and most northerly municipality, Qaasuitsup, which covers 255,000 square miles (660,000 sq km) in northern Greenland, making it larger than all of France. The town is located 220 miles (350 km) north of the Arctic Circle at the mouth of the Ilulissat Icefjord, an awe-inspiring natural setting that was designated as a UNESCO world heritage site in 2004. At the head of the inlet, Sermeq Kujalleq, one of the most active glaciers in the world, calves giant icebergs, up to 3,280 feet (1,000 m) in height, that sail majestically past the town out to the open sea.

The water and natural surroundings of Ilulissat are among the least polluted in the world. The foods harvested from the ocean and the rocky fields bring unique arctic flavors to the table. Among them are halibut, shrimp, whales, and seaweeds, as well as musk oxen, reindeer, angelica, lichen, crowberry, and wild arctic herbs.

The head chef at the town’s Hotel Arctic, considered the best hotel in Greenland, is Jeppe Ejvind Nielsen. He also presides over the kitchen at Ulo, the top-rated restaurant located on the premises, which has been described as being closer to nature than any other restaurant in the world. It is, in fact, a locavore’s dream. Jeppe has won many championships for this culinary skills, which reflect his approach to food. For him, the purity of the air, fjord, and rocky fields, as well as the evolution of fresh local, Greenlandic produce, are the focal point of his kitchen. This purity is expressed in dishes that are a study in simplicity with a maximum of four to five different tastes in each serving, to mirror the natural sparseness of the land. It should be possible both to see nature in the food and to acknowledge it in its taste. This is where mouthfeel takes on a central importance.

In January 2015, one of us (Ole) was invited to Ilulissat to participate in a workshop together with local chefs from Hotel Arctic and two chefs from other countries, among others. The goal of the workshop was to encourage new economic activity in that region and create employment opportunities by finding new ways of using Greenlandic raw ingredients to produce foodstuffs. We quickly turned our attention to the local growths of different seaweed species, which are largely underutilized and used only sparingly in Greenlandic cuisine. At the end of three days, we had devised twelve new recipes for seaweed products that met all the requirements of being made locally employing simple methods, but being of a sufficiently high standard with the potential to penetrate the global market.

Some of these products found their way onto the menu for the gourmet dinner at the conclusion of the workshop where the chefs could demonstrate Jeppe’s approach to Greenlandic cuisine, especially the combination of purity and simplicity. This meal illustrated how Jeppe juggles with the mouthfeel of a variety of dishes made with local ingredients.

The menu consisted of seven courses. Along the way, it was accompanied by a white bread with a wonderfully crisp crust and an unusually fine-tuned salt seasoning, which was due to the use of fresh seawater in the bread dough. It was simplicity itself.

The first dish highlighted the clean natural taste of the sea—cured halibut prepared by the Greenlandic cookbook author Anne Sofie Hardenberg. The halibut is aged for two days with salt and native herbs so that its texture becomes soft and slightly jellylike, but is still a little firm. Like other flatfish, the texture of raw halibut is best after being cured for a couple of days, which allows its natural enzymes to tenderize the muscles of the flesh. This is similar to the classical Japanese ikijime technique.

Glimpse of the midwinter sun in Ilulissat and an array of the dishes served at the gourmet dinner.

The second course was presented in spectacular fashion. The chefs, each with two lit cooking torches, charred fresh halibut for a dish with apples, celery, and aioli seasoned with Greenlandic angelica. The dish has a clean, delicate appearance with nuances of white and light green, broken only by the slightly burned edges of the small pieces of fish and apples. It almost resembles the iceberg fragments floating in the fjord. The soft halibut is a good match for the crisp apple and celery pieces.

At this point, we came to what was styled “Chef’s Surprise” on the menu. The two international chefs, Daniel Burns (Restaurant Luksus in Brooklyn, New York) and Florent Ladeyn (L’Auberge du Vert Mont in northern France), who both run restaurants that have earned a Michelin star, had used their imagination to create a Greenlandic beef tartare with tenderloin, potatoes, dried halibut, and one of the seaweed granulates that had been developed in the workshop. Dried halibut is a local specialty called ræklinger, made from strips of fresh halibut that are dried outside in the cold, extremely dry arctic air. Even at −13°F (−25°C), ræklinger taken straight from the drying shed is soft, elastic, and juicy, because the halibut flesh contains many polyunsaturated fats.

The fourth dish was fin whale tataki, pieces of fresh, red fin whale, lightly seared. It was accompanied by fronds of sea tangle marinated in soy sauce, pickled shallots, and smoked bladder wrack. A Greenlandic dashi made from grilled halibut heads, charred onions, dried cod, soy sauce, and seaweeds was drizzled over it. The whale meat was tender, but still firm. The marinated sea tangle was soft and jellylike, whereas the smoked bladder wrack had retained some of its toughness, which enhanced the smoked taste.

Next, we were served salted lamb’s hearts with room-temperature egg yolks, deep-fried black salsify root, puree of charred celery, and seaweed salt. This dish appealed to many different types of mouthfeel. The hearts were elastic, but very easy to chew. The black salsify root was slightly tough on the outside, but was crisp on the inside. The egg yolk had its own mouthfeel; when the membrane was pierced, the fluid interior flowed out onto the other ingredients with a burst of umami.

After this parade of preliminaries, we came to the main course, which featured meat from Dexter cattle, a very hardy miniature breed that is raised in southern Greenland. Only twenty-five cows are slaughtered each year. The cut of beef was larded with bacon, sautéed, and served with beets and sunchokes. Even though we were beginning to feel sated, we fully enjoyed the perfectly tender meat. And Jeppe had added a final casual, but elegant, touch—placing a pair of toasted, crisp ribs from winged kelp on top of dish.

The dessert presented a new cascade of texture impressions—a honey-flavored soft ice cream with frozen pearled spelt and candied winged kelp and a granita containing leaves of Greenlandic mountain juniper. The contrast between firm, frozen grain kernels and the soft ice cream created an amusing sensory impression, which was enhanced by the candied winged kelp. The winged kelp consisted of a very thin, very crisp front of candied seaweed. The granita reminded us of the small pieces of ice floating in the fjord. In this dish Jeppe had captured a quintessential aspect of the winter landscape in northern Greenland—an ice fjord served in a bowl.

Arctic Textures

Jeppe Ejvind Nielsen, the head chef at the Ulo Restaurant in Hotel Arctic in Ilulissat, northern Greenland, has created a frozen dessert that delivers a veritable cascade of texture sensations. It is combines a honey-flavored soft ice cream with frozen pearled spelt and candied winged kelp and a granita containing leaves of Greenlandic mountain juniper. It is topped with a sprinkling of crüsli toasted with Greenland beer and honey. The juxtaposition of firm grains and crunchy candied seaweed, granita, and crüsli with the soft ice cream is a study in textural contrasts.

The honey used in Jeppe’s dessert comes from Ole Guldager’s hives in Narsaq in southern Greenland. This honey has a very strong, characteristic flowery taste that, together with that of the juniper, suffuses the dessert and gives it a distinctive character.

It is important to churn the ice cream part just before it is to be served so that it takes on the consistency of soft ice cream, but that the pearled spelt and the crüsli remain firmly frozen, as it is this combination that is responsible for the unique mouthfeel of the dish.

GRANITA WITH JUNIPER NEEDLES

2 teaspoons (10 g) dried juniper needles (black tea leaves can be substituted for the juniper)

2 cups (500 g) water

⅓ cup (75 g) granulated sugar

2 teaspoons (10 g) lemon juice

CANDIED WINGED KELP

2 large fronds of fresh or frozen winged kelp

6½ tablespoons (100 ml) water

2 tablespoons (30 g) sugar

PREPARE THE ICE CREAM

•  Bring the milk, cream, and honey to a boil, then remove from the heat. Place the egg yolks in a separate pan.

•  Slowly whisk the milk mixture into the egg yolks. Pour the mixture into the beaker of a Pacojet and freeze. Alternatively, allow it to thicken over low heat, remove from the heat and allow to cool, then freeze in an ice-cream maker according to the manufacturer’s instructions. Keep frozen until ready to serve.

PREPARE THE CRÜSLI

•  Heat the beer, honey, and butter in a pot until the butter has melted.

•  Mix in the dry ingredients first and then the beaten egg whites.

•  Spread out the crüsli in a thin layer on a baking sheet covered with parchment paper. Bake at 250°F (130°C) for 2–3 hours, or until it is dry. Break up into small pieces and store them in an airtight container until used.

PREPARE THE SPELT

•  Cover the pearled spelt with water and cook it until tender.

•  Allow it to cool and refrigerate it.

PREPARE THE GRANITA

•  Allow the juniper needles to soak overnight in cold water.

•  Drain the juniper needles and cook them with the water, sugar, and lemon juice.

•  Freeze the mixture and work it over with a fork so that it breaks up into small crystals.

PREPARE THE KELP

•  Cut away the central rib of the kelp and immerse the fronds in boiling water for 2–3 minutes until they become soft. Drain.

•  Cook the fronds in the water with the sugar until the water has evaporated completely.

•  Spread the fronds out on a silicone sheet and dry them in a dehydrator at 105°F (40°C) for 8–10 hours, or until they are dry.

•  Crush the candied kelp coarsely and store the granules in an airtight container.

PRESENTING THE DISH

•  Freeze a bowl. Set aside a little of the crüsli and the candied kelp. Set a bowl in ice water and place the remaining crüsli, candied winged kelp, and pearled spelt in the bottom. Top it with the ice cream.

•  Transfer the dessert to the frozen bowl, decorate with the broken-up granita, and sprinkle the reserved crüsli mixture on top.

Serves 8–10

HONEY SOFT ICE CREAM

1 cup (250 ml) milk

1 cup (250 ml) 38% cream

¼ cup + 1 tablespoon (100 g) honey

⅓ cup (100 g) egg yolks

CRÜSLI

4 teaspoons (20 g) dark, strong beer

1 tablespoon (20 g) honey

1 tablespoon (15 g) butter

¼ cup (20 g) rolled oats

2 teaspoons (10 g) spelt flakes

2 teaspoons (10 g) wheat flakes

2 teaspoons (10 g) flaked hazelnuts

2 teaspoons (10 g) sunflower seeds

Scant 1 ounce (25 g) egg whites, beaten

PEARLED SPELT

5 teaspoons (25 g) pearled spelt

Arctic Textures.

Many other types of frozen desserts, especially sorbets and granitas, are characterized by a granular structure. A sorbet is typically made with fruit juice and fruit puree, water, and sugar or syrup. A granita is similar to a sorbet but usually has larger ice crystals and incorporates some form of alcohol. The large water content in both provides a fertile environment for the formation of many small ice crystals, while the sugar content together with mechanical churning of the mixture helps limit their size. A sorbet will have fewer air bubbles than ice cream, and therefore, gives a less creamy impression. Because they bind water, a gelling agent such as fruit pectin or gelatin can help soften the mouthfeel of a sorbet, even though they have only a minor effect on the freezing properties of the mixture.

While a sample of sorbet and one of ice cream may be at an identical temperature, the sorbet will feel colder because it contains no fat, exhibiting a well-known effect called insulation. However, if the temperature at which the ice cream is made is conducive to the formation of very small ice crystals, the sorbet may feel warmer. This is because the ice crystals are so small that they melt more quickly in the mouth, which draws more heat from the tongue and the palate, and thus the ice cream feels colder.

Bubbles in Food

The raw ingredients used in food may incorporate air in the form of small pockets between or inside the cells. We are often not aware of them, and in addition, many foods are very compact. So, it would probably come as a surprise to most people that crisp apples contain about 25 percent air; and pears, 5–10 percent.

We love to whisk or beat air into a variety of foods because it results in an exciting and pleasant mouthfeel. Foams, whipped cream, soufflés, fluffy desserts, and meringues are just a few among many examples. In some cases, air in the form of bubbles can make fluid foods, such as cream or egg whites, much stiffer. The stiffness disappears when the food meets the tongue and the palate, as the bubbles burst and run together, allowing the food to flow and lending it a very creamy mouthfeel. The air-filled bubbles in foam can catch and trap aroma substances that are released when the foam collapses in the mouth. In the avant-garde kitchen there are practically no ingredients that escape the chefs’ efforts to make them into foams.

Stabilizing Foam

Technically speaking, a foam is a dispersion of bubbles of some type of gas in a liquid. In principle, it is possible to create a foam from just about any liquid, but in most cases the newly formed bubbles burst very rapidly. Generally speaking, it is therefore necessary to stabilize the surfaces of the bubbles in the same way as soap bubbles are stabilized: by reducing the surface tension between the water and the air. The bubbles in a foam are usually large, about 1 millimeter in size, whereas the walls between the bubbles are extremely thin, on the order of micrometers.

Of course, soap would not be used to stabilize bubbles in food. Other substances—edible amphiphilic molecules—are introduced to reduce the surface tension. There are many to choose from, just as is the case with emulsifiers. In a way, a foam is an emulsion where an emulsifier makes it possible to mix gas and liquid. It is possible to use both warm and cold milk, where the milk proteins act as emulsifiers, or egg whites or egg yolks, which contain lecithin and amphiphilic proteins, respectively. Another possibility is to add pure emulsifiers, such as soy lecithin, or chemically produced emulsifiers that have been optimized for specific end-uses.

In some cases, adding an emulsifier on its own is not sufficient to form a stable foam. A foam can collapse simply because the liquid separates out on account of its own weight. This is precisely the same effect as the one that causes soap bubbles to burst. The water drains off or evaporates, causing the walls of the bubbles to become so thin that they finally burst. To prevent the water from separating out, the food can be stabilized with an appropriate gelling agent. This is where the familiar gelling agents, such as agar, starch, pectin, gums, and gelatin, again have a role. For each of these thickeners it is important to pay attention to the temperatures to which they will be subjected.

When foams become unstable, fats are often the culprits. The fats can position themselves as small drops lying between the walls of the foam, forming something like hydrophobic bridges between the air pockets in neighboring bubbles. This can cause the bubbles to run together into larger bubbles and eventually the foam collapses. Emulsifiers can help mitigate this problem.

Drinks that contain dissolved carbon dioxide in the form of carbonic acid—for example, mineral water, beer, and sparkling wines—can also form a foam when the bubbles of the gas rise up through the liquid. If the substances that stabilize the boundary surface are present in sufficient quantities either in the liquid or on its surface—for example, in the form of proteins or lipids—a foam made up of bubbles containing carbon dioxide will be formed. These bubbles also contain airborne aromatics, which are released when the bubbles burst. This is why the foam can be an important aspect of the drinking experience, especially the head on a glass of beer. The foam from champagne or mineral water collapses very quickly, however.

FOAM IN A BOTTLE

It is the mechanical action of whipping that introduces gas into the liquid. Nowadays, electric beaters are generally chosen for this task. A blender does not work because it does not incorporate a sufficient quantity of air, unless one allows an immersion blender to work just on the surface of the liquid. Alternatively, one can use a siphon, which is a closed bottle filled with pressurized gas—for example, carbon dioxide (CO₂) or nitrous oxide (N₂O), both of which are tasteless, harmless gases. An advantage of using a siphon is that in contrast to normal atmospheric pressure, the gas in it does not have any free oxygen, which can otherwise help oxidize fats and make them rancid. Carbon dioxide has the drawback that it introduces carbonic acid into the liquid and the taste of the burst bubbles will be a little acidic. In addition, carbon dioxide is much easier to dissolve in water than nitrous oxide, so it takes longer for it to produce bubbles. A particular advantage of nitrous oxide is that it is more soluble in fats than carbon dioxide.

The liquid from which the foam is to be made is poured into the siphon and the gas is introduced in a capsule that produces such a high pressure inside the siphon that the gas is dissolved in the liquid. When the liquid is then squirted from the siphon under pressure, the gas will spontaneously form bubbles throughout the liquid and the foam is created.

Strawberry foam and fresh strawberries coated with fresh honey and verbena.

Foam with Thick Walls: Ice Cream, Whipped Cream, Mousse, and Soufflé

Some foods that are very rich in fats can form a type of foam without help—for example, cream, cheese with a high fat content, and even foie gras. In this type of foam, the fats stabilize the air bubbles, which lie far apart from one another, the opposite of what happens in a real foam. This is the case in whipped cream, ice cream, and whipped butter and margarine, all of which can contain up to 50 percent air.

Whipped cream is more complex than many other types of cream because it is actually a solidly packed network of air bubbles, held together by small spheres of fat that attach themselves to the surface of the air bubbles. Whipped cream can turn out to be just as stiff as a solid. As the fats are what hold the cream together, it is possible to make a stable foam only if the percentage of fat particles in the cream is sufficiently large, at least 30 percent and preferably greater. In addition, the larger fat particles in the cream must be broken up into pieces that are sufficiently small to be captured by the air bubbles. This process also releases the milk proteins from their original fat spheres, which makes them more unstable and increases their tendency to form larger fat particles. That is why the cream needs to be beaten, in fact, whipped to the stage where the fat particles are so small that they do not run together again before the stiff network of air bubbles is in place. This is also why temperature is important—when the cream is cold, it is much harder for the fat particles to coalesce. Whipped cream can also be made with the help of a siphon bottle using nitrous oxide (N₂O). In the siphon, the gas is dissolved in the fat spheres of the cream, and when the pressure falls, a creamy foam with a very large number of air bubbles is formed.

Microscopy image of whipped cream (left) and illustration of its internal structure (right). The large bubbles are air, and the walls between them are made up primarily of fats interspersed with water. The bubbles are generally 10–100 micrometers in size.

Other types of foam consisting of air bubbles separated by thick walls are bread, mousse, soufflé, and meringue. In bread, the carbon dioxide bubbles are formed by the addition of a leavening agent or by the action of the yeast. Small pockets of water in a dough will also form bubbles when the water evaporates on being heated. These bubbles do not collapse when cooled once the baked goods have become firm.

In a mousse that contains an ingredient such as chocolate, the beaten egg whites and sugar together with the cocoa particles from the melted chocolate form thick walls between the air bubbles. As the mousse cools these walls become stronger, making the mousse stiffer and more stable. When the mousse is put in the mouth, the cocoa butter in the chocolate melts at the same time as the air bubbles burst, giving this dessert its special, unique mouthfeel.

A soufflé is probably the type of foam that is most shrouded in mystery and that causes endless worries about whether it will collapse—which it always does, sooner or later. There are many different soufflé recipes encompassing a broad array of ingredients, resulting in a range of taste impressions. Soufflés can take their place among the desserts just as easily as among the savory dishes. What they have in common is that they consist of a mixture of egg yolks and a variety of other ingredients into which stiff-beaten egg whites are folded, and that they are baked in the oven. Heating creates steam in the soufflé, forming a foam that rises right up above the rim of the bowl in which it is being baked. The characteristics of the finished soufflé depend on the baking temperature. When baked at a higher temperature, it will turn out to be quite solid with a crisp top crust and a moist interior; at a lower temperature, the soufflé is firm right through. If the temperature drops partway through the baking process, such as by the baker’s opening the oven door, the soufflé can collapse.

Elastic Foam

Marshmallows are filled with air bubbles that have been whipped into a viscous gelatin solution together with sugar or syrup and, optionally, egg whites. The gelatin helps stabilize the air bubbles and create the characteristic elastic texture of marshmallows.

Meringue

There are several types of meringue, which are foams that are usually made by whipping egg whites with sugar. In one particular type, known as French meringue, the foam is initially stabilized by the proteins in the egg whites and it is then baked until it is completely or partially dry. As it bakes, water evaporates and the sugar is concentrated in the walls of the foam, eventually forming a firm glass phase that makes the foam very stiff and stable. If all the water is not evaporated away, the outside of the meringue will still be stiff and crisp, but the inside will remain somewhat moist with an interesting soft and possibly slightly chewy mouthfeel.

For a meringue to dry out completely, it must be baked for a very long time at a low temperature, under 221°F (105°C), which ensures that the meringue turns into a glass when the water is removed. As the melting point of sucrose is much higher, 365°F (185°C), the sugar dehydrates at the lower temperature. It can be advantageous to use icing sugar in the meringue so as to avoid ending up with a crunchy texture from sugar crystals that did not melt before the glass was formed.

French nougat is an air-filled meringue with nuts, which is made solid and chewy by whipping very warm syrup into it.

Carbonated sugars that prickle on the tongue

It is possible to bind carbon dioxide to sugar so that it is released when the sugar is dissolved in saliva. This carbonated sugar, also called popping sugar, leaves a prickly and crackly sensation in the mouth. As popping sugar does not dissolve in fats, it can be incorporated into treats such as chocolate and different types of frozen desserts. It is released when these are eaten. Popping sugar is made by pumping carbon dioxide, under pressure, into a flowing syrup, which is then cooled rapidly and pulverized. Some of the carbon dioxide remains trapped in the powder.

Sour and Prickly Bubbles

Carbon dioxide bubbles in drinks and culinary foams deliver both a particular physical mouthfeel and a somewhat sour taste when they burst. In addition, the actual mini-explosion of the bubbles causes a tactile impression that reinforces the prickly sensation in the mouth, on the palate, and up into the nostrils. These prickly bubbles are so important for taste and mouthfeel that many drinks quickly become completely uninteresting when the carbon dioxide has escaped. Who wants to drink sodas, beer, or champagne that have gone flat?

Carbon dioxide bubbles actually work in two distinct ways. They have an effect on the trigeminal nerves. They are also detected by a particular receptor, known as Car₄, found on taste buds that are sensitive to sourness.

Carbon dioxide is more soluble in water at lower temperatures than at higher ones. In fact, about twice as much of the gas can be dissolved at 41°F (5°C) as at 68°F (20°C). When using a soda siphon to carbonate water, it is more effective to do so if the water has already been cooled in the refrigerator, rather than left at room temperature.

When carbonated liquids, such as sodas, beer, and champagne, are kept in a sealed bottle under pressure, the carbon dioxide is dissolved in the liquid, partially in the form of molecules and partially as carbonic acid. When the bottle is opened, the carbon dioxide molecules spontaneously assemble themselves into bubbles. The speed with which they are formed and how large they become before they rise and burst at the surface depends to a large extent on the particles that are dissolved in the liquid, on defects in the glass into which they are poured, and on how clean it is. It is easy to demonstrate this effect by sprinkling a little salt or sugar in sparkling mineral water. In a pub, the bartender will usually rinse out the inside of the glass with water before pouring the beer, to smooth out any scratches in, or smudges on, the glass and that may prevent too many bubbles and a head of foam from forming. In a clean glass, the bubbles will form mainly in the middle of the glass and not along the sides. The opposite is true with a plastic glass, as it has hydrophobic sides. Here the bubbles are instead found along the sides. This is why drinking champagne from a plastic glass results in a mouthfeel that is very different from the one we experience when drinking it from a clean glass flute, where we might even be lucky enough to see the bubbles rising neatly up the middle.

DELVING INTO THE MYSTERIES OF THE BUBBLES IN CHAMPAGNE AND GUINNESS

The very special and vastly different ways that bubbles behave in champagne and in Guinness are no doubt the reason that the mouthfeel of these drinks is so appealing. The bubbles and the foam carry aromatic substances—when they are the right size, we experience both drinks as soft and almost creamy. Small bubbles impart the most pleasant, softest mouthfeel, whereas the large bubbles in many mineral waters feel too hard.

There have been many discussions about what determines the size of the bubbles in champagne and other sparkling wines. For a long time it was thought that the operative factor was the amount of carbon dioxide and its diffusion throughout the wine. Recently, researchers have found that it is actually the dissolved salts, carbon dioxide molecules, and minerals that govern the size of the bubbles.

In the case of Guinness, the quest was to determine what is responsible for the distinctive creamy foam head that is made up of a mass of small bubbles. And even more mysteriously, why the bubbles along the edges of the glass move downward, whereas the bubbles in the middle move upward. The latter is to be expected, as the bubbles are lighter than the stout. But what about the counterintuitive downward motion? It turns out that the answer has nothing to do with the liquid and everything to do with the special shape of the glass in which Guinness is traditionally served—wide in the middle and narrower at both the bottom and the top. Consequently, more bubbles form in the middle of the glass. These bubbles rise as if in a fountain, pushing the bubbles that form along the edges downward.

Champagne with a decorative piece of seaweed floating on the bubbles.

Another determining factor is the extent to which the liquid contains amphiphilic substances—for example, in the form of fats and proteins. The more of these substances there are in the liquid, the fewer the bubbles and the longer they last before bursting. This is because the amphiphilic substances collect on the surfaces of the bubbles, depressing their surface tension. The result is an audible fizzing sound of small bubbles. To dampen the effect, guar gum is sometimes added to carbonated drinks. The small bubbles then impart a softer and creamier mouthfeel, familiar from the texture of Guinness stout.

Airy, Flaky Pastry

There is a whole assortment of pastries that are characterized by their airy, flaky texture. This creates a very special mouthfeel, due to the combination of individual flakes that are very thin, crisp, and hard and the interspersed layers of air that introduce a soft and supple feel. They are made from a type of dough, sometimes referred to as feuilleté, or puff pastry, which has a high fat content, typically about 35 percent.

Croissants, Danish pastries, and the French mille-feuille, the name of which means “a thousand leaves,” are classic examples of this family of flaky and laminated baked goods. In contrast to mille-feuille, whose flakiness is derived from butter, the dough for croissants and Danish pastries also includes eggs, sugar, and leavening agents, with the result that they are softer and the flakes are less crisp.

The secret of getting the mouthfeel of mille-feuille absolutely perfect is to layer butter into the dough by folding it over on itself and rolling it thin again, time and time again. The number of individual layers increases and they become thinner and thinner, often less than one-hundredth of a millimeter thick, or about the size of a grain of starch in the flour. There can easily be several hundred layers, with one sample known to have had 1,458 layers! It is a time-consuming process.

To achieve the best texture in pastry, it is important for the fat to be plastic and have the right consistency. It must be quite firm and not sticky, so that it can be rolled into the dough easily, but not so hard that it will pierce the dough when it is folded over and rolled out again. If the fat is too soft, it has a tendency to melt into the dough, making the finished product harder and less crisp. If butter is used, the butter needs to be cold, not more than 68°F (20°C), and the rolling and folding process must done when the dough is chilled.

Illustration of how the flaky structure is formed, when the water vapor pushes the layers of dough and margarine or butter apart as the pastry bakes (top), and mille-feuille (bottom).

To preserve maximum plasticity, the fat must not be able to crystallize. This can be prevented with the help of an appropriate emulsifier. It is especially important to address the problem if using such a fat as a margarine with a reduced fat content.

As the dough bakes, the water in the layers form steam, which pushes the layers apart, leaving the pastry airy and flaky. The steam will also shift around the fat between the layers, breaking it up without causing the pastry to fall apart. In the course of this process, the thickness of the pastry increases to several times its original size.

From Soft to Hard and Back Again

Many foodstuffs are processed in such a way that their texture is changed quite dramatically—for example, when they are preserved, dried, or fermented. Sometimes, soft raw ingredients become firm, and in some cases, turn out so hard that they must be processed again to make them soft enough to be edible. All of this usually has an distinct effect on the nutritional value and taste of these raw ingredients.

In traditional Japanese cuisine, there are many examples of products made in this way, using ingredients harvested from the sea, especially fish and seaweeds. The two most fascinating examples are made from bonito, a fish related to mackerel and tuna, and from the popular macrokelp konbu. The former becomes hard as stone, whereas the latter ends up softer than a feather—they could justifiably be said to win the prize as the hardest and the softest foods in the world.

Katsuobushi is the end product of an involved five-step process: Fillets of bonito are cooked, salted, dried, smoked, and fermented. In the course of its careful, lengthy transformation from fresh fish with a water content of 70 percent to a compact, dry fillet it has become rock hard and its water content has been reduced to less than 20 percent. To be able to eat these pieces of fish or use them to make soup stock, they must be planed into incredibly thin, light shavings that are only about 20 micrometers in diameter, less than that of a human hair. The texture of these shavings is so soft and airy that they more or less melt in the mouth.

Freshly harvested konbu has a water content of 90 percent. This falls to 20–30 percent as the seaweed is dried in the sun and then aged in special cellars with low humidity. The dried and very hard konbu cannot be eaten as is and must first be soaked in water to soften it and release its umami taste substances. Like katsuobushi, the dried blades of konbu can also be cut into similarly thin, virtually sheer shavings, using special ultrasharp knives. These fine layers, called oboru konbu or tororo konbu, have a soft, delicate mouthfeel. They almost melt on the tongue and are traditionally eaten in soups or together with rice or noodles.

The processing of these raw ingredients, from the time when they are caught or harvested to their packaging for culinary applications, is a wonderful example of optimization of their gastronomic value, which plays up their unique mouthfeel.

THE HARDEST FOOD IN THE WORLD

Throughout the centuries, the age-old Japanese food culture has availed itself of everything edible from the ocean—fish, shellfish, and seaweeds. The ways in which they are harvested, processed, and prepared have been refined to optimize their tastes and textures. One such product is katsuobushi, thought of as the world’s hardest food.

Katsuobushi is an unusual fish product that has evolved over a long period of time. In principle, it is simply a dried fillet of bonito (katsuo), a fish related to mackerel and tuna. In the eighth century, the term was used for a fish that had only been dried. In 1675, Youchi Tosa discovered that its taste could be improved by smoking it and then allowing a fungus to grow on the fillet. Today, katsuobushi is made in a number of Japanese port cities, foremost among them Yaizu, Tosa, and Makurazaki.

The desire to find out, firsthand, how katsuobushi is made took one of us (Ole) on a trip to one of these cities, Yaizu, which calls itself “Japan’s fishing city.” It is located in the Shizuoka Prefecture, only about an hour from Tokyo on the wonderful bullet train, Shinkansen. My guide was Dr. Kumiko Ninomiya, one of Japan’s most prominent umami researchers. She has contacts among those people in Yaizu who can make it possible for a foreigner like myself to gain admission to the harbor area. Tooru Tomimatsu, president of the organization Katsuo Gijutsu Kenkyujo, took us to Yanagiya Honten, a katsuobushi factory.

We were lucky to arrive on a day when the frozen raw ingredients, katsuo, were being unloaded from the large fishing vessels, which had been at sea for a month. They had sailed as far as the southern Pacific Ocean and the seas around Micronesia so as to catch this highly desirable fish.

The rock-hard fish, which are frozen to −22°F (−30ºC), each weighs 4–10 pounds (1.8–4.5 kg). They are sorted right on the quay, at first automatically and then by an army of workers who take over and sort them again carefully by hand. The fish are then transported to the factory for processing.

Step one is to defrost the fish in water with air bubbles circulating through it. The temperature must not rise above 40°F (4.4ºC), so as to prevent the important taste substance inosinate from breaking down. Inosinate is absolutely central to the umami taste of the finished katsuobushi. Once they have thawed, the heads of the fish are cut off and the entrails removed mechanically. These castoffs are ground into a mush and used to make fish sauce. The fish is now simmered at 208°F (98ºC) for almost two hours in a brine that is used over and over. Many of the substances that impart the desired taste to the finished product accumulate in this brine. The cooked fish are next cut into fillets, trimmed, deboned, and skinned by hand.

Now comes the most important part of the process: dehydrating the fish and reducing the water content from 65 to 20 percent, first by drying and smoking, and then, in some cases, by fermentation.

The real secret lies in how the fillets are smoked. Here our timing was also lucky. Just as we arrived at the area where the four-story-high smoking ovens are located, the smoke master was ready to start fires in the special places called hidoku that lie at the bottom of each oven. We eased ourselves through the little trapdoor in the floor and climbed down a steep ladder just in time to see him light the fires in an rectangular array of large smoke basins where the firewood had been piled up. By crouching down on the floor of the oven, we were able to escape the worst of the smoke and for a brief moment experience the tension in the air as the wood burst into flames and the process began. Then, it was a question of scrambling quickly up the ladder and out of the oven before the large trapdoor shut.

Only two types of hard oak wood (konara and kunugi, a type of chestnut oak) are used, as they impart the exact smoky taste that the Japanese prefer in their katsuobushi. The firewood is replenished and the fires relit up to four times a day. The company guards its trade secrets very well, and the inside of the oven was the only place where I was not allowed to take photographs.

The fish are arranged on wire trays stacked at the bottom of the smoke oven to dry out for about a day, reducing their water content to 40 percent. Then, the trays are moved up to the topmost stories of the oven and smoked for ten days, thus reducing their water content even further, to 20 percent. The finished fillets are arabushi, one of the several varieties of katsuobushi. This is the product that is referred to as the hardest foodstuff in the world. A piece of arabushi is as hard as a wooden chair leg, and one has to wonder how it can possibly be used as food. We will return to that question shortly.

Arabushi can undergo yet more processing and be dehydrated further by fermenting it, resulting in a stronger taste. This is a time-consuming process and consequently the product, called karebushi, is more expensive and more sought after. Unfortunately, we were not able to see how karebushi is made in the course of our visit to Yaizu, but this is a description of the process.

First, the tar-covered outer layer of the arabushi, a result of prolonged exposure to smoke, is planed or scraped off and the fillets are sprayed with a mold culture (Aspergillus glaucus) at a temperature of 82°F (28ºC). Over the course of the following weeks, the mold spores sprout on the fillet and the fungal mycelia bore into the fillet. Once it is covered with mold, the fillet is brought out into the sun to dry, and all the mold is scraped off. This alternation between returning the fillet to the mold chamber and bringing it outside to dry in the sun continues for one to two months. The quality of the fish is thought to improve with each successive cycle.

There are actually two types of karebushi. One type uses the whole fillet and has a more bitter taste. The other type has a milder, more refined taste because the dark red bloodline of the fillet, which lies against the lateral side of the fish, is cut away.

Before we left the factory to have lunch at one of Yaizu’s best fish restaurants, a humble establishment right at the harbor frequented by the fishers themselves, we took a quick peek into its enormous walk-in freezers. The frozen katsuo are kept at −22°F (−30°C) if they are to be made into katsuobushi and at −76°F (−60°C), a temperature at which all breakdown processes are arrested, if they are to be eaten raw as sashimi. In another room we saw some of the most expensive fish in the world, top-quality frozen tuna, in a sense hibernating until the price on the global market was just right.

Arabushi is normally ground to a powder and much of it is used in the production of hon-dashi, which is an important ingredient in many Japanese soup powders, prepared foods, and a variety of taste additives. Hon-dashi is produced by Ajinomoto, a major industrial food conglomerate, which was founded on the basis of a patent taken out by the researcher Kikunae Ikeda. He coined the term “umami” to describe a basic taste after he had isolated glutamate from konbu extracts.

The longer and more meticulous process used to make karebushi leads to a dried product that has fewer cracks. As a result, it is possible to make shavings that stay together instead of crumbling.

When it is to be used, the hard fillet is placed on top of special box, which is like an inverted plane, so that ultrathin shavings can be cut from it. The karebushi yields the best taste when it is freshly shaved. Because the shavings are so thin, it is technically possible to extract 98 percent of the taste substance inosinate from them. These shavings are combined with dried konbu to prepare dashi, the unbelievably tasty soup stock that is an essential element in Japanese cuisine. One can buy several varieties of ready-cut shavings of different thicknesses in airtight packages containing nitrogen to prevent oxidation. Naturally, the desirable umami taste substances seep out much more quickly from the thinner shavings.

Katsuobushi flakes are also sprinkled on soups, vegetables, and rice. When the dried flakes encounter the steam from the hot food, they contract and move as if dancing. That is why the Japanese call them “dancing” fish flakes.

How does katsuobushi taste? First and foremost, there is a mild smoky taste, then a little saltiness, and then umami. Bitterness from an amino acid, histidine, is quite prominent. The umami taste really comes to the forefront when katsuobushi is combined with other ingredients that contain glutamate, such as konbu.

THE SOFTEST FOOD IN THE WORLD

In a quest to seek out the softest food in the world, one of us (Ole) traveled to Sakai, an important old port town adjacent to Osaka, one of Japan’s major metropolitan areas. Sakai is probably best known for the knife smiths who forged the swords of the samurai. It remains the center for the manufacture of Japan’s famous kitchen and chef’s knives. But is also a center for the specialist processing of the large brown alga, konbu.

For centuries, right back to the fourteenth century, Kyoto was the end-station of a 745-mile (1,200-kilometer) route, known as the Konbu Road. Konbu was harvested and dried in Hokkaido in northern Japan and then shipped by sea to the coastal town of Tsuruga, where it was often aged for a year or two. It was next carried overland to Lake Biwa and sent on by boat, ending up in Kyoto. From the seventeenth century, the maritime route was expanded and the final destination moved to Sakai, which came to be regarded as the preeminent center for konbu products.

By a stroke of luck, I had the good fortune to be granted access to one of the places where the seaweeds are processed, a privilege that is granted to few outsiders. Japanese businesswoman Saori Sawano, who owns a wonderful tableware and knife shop called Korin in New York City, had put me in contact with Hiroki Yamanaka of the Sakai City Industrial Promotion Center. He kindly made the arrangements for my colleague, Dr. Koji Kinoshita, and me to visit Matsumoto, a company that turns out more than one hundred different seaweed products.

Mr. Yamanaka took us first to the large warehouse, where we were shown around by the company’s director, Tsutomu Matsumoto, who explained everything to us with a great deal of enthusiasm. Here the konbu is aged, a process that is an absolutely vital factor in the texture and taste of the finished products. It is stored at 59°F (15°C) in a humidity-controlled environment and fills the warehouse with the most fantastic smell of the ocean.

Next, we were able to look into the factory to observe how the sharp blades in specialized machines slice superthin layers across the ends of large bundles of konbu that have been marinated in rice vinegar and then compressed firmly. The result is a wide, almost sheer, pale-green tissuelike product called tororo konbu. It is featherlight and ultrasoft.

Originally tororo konbu was prepared by hand by scraping layers lengthwise from the seaweed blades by using a sharp blade, making shavings that were light and looked like crepe paper. When made according to this old-fashioned technique, the product is called oboro konbu. I had always wanted to see how this was done, but had been told beforehand that this would not be possible.

Nevertheless, other doors were opened for us. A telephone call from Mr. Matsumoto arranged for us to visit a small factory, Goda Shoten, where the craft of making the world’s softest food is still practiced in the traditional way. Even my host, Hiroki Yamanaka, had never seen this before.

This was a true adventure and the high-water mark of my visit to Sakai. Goda Shoten is located in one of the small characteristic houses in the old part of the city. We went up a narrow staircase to the second story, into a tiny room in which five people worked, two men and three women. Seated on the floor on crushed cardboard boxes, they were busy making oboro konbu as it has been done for about five centuries.

The type of konbu used to make oboro konbu is ma-konbu, which has relatively narrow blades that are 3¼–5 feet (1–1.5 m) long. The dried blades are bundled and immersed in a marinade of rice vinegar for a very short time, only about ten minutes. The marinade is used over and over again and gradually develops a powerful umami taste from the glutamate that is released by the seaweeds. The marinade is the secret behind the sweet and sour umami taste that is acquired by the finished oboro konbu. The presoaked and marinated seaweed is then allowed to rest for twenty-four hours so that its texture becomes sufficiently soft to allow a skilled worker to shave off thin layers from the blades. These are about 50 micrometers in thickness, about twice as thick as the machine-made tororo konbu. When the outermost layer of the seaweed has been scraped away, a pale-green core of the blade remains. This is the very sought-after product shiraita konbu, which is flexible and strong, but soft as silk. Among other dishes, shiraita konbu is used to make a type of sushi with marinated mackerel (battera) that is a specialty in the area around Osaka. Hanging on the wall of the workshop are many rectangular pieces of wood of slightly different sizes. They are used to slice the shiraita konbu so that it will fit precisely the measurements specified by client restaurants for their version of battera.

In former times, there were about a hundred Sakai craftsmen who could make oboro konbu or tororo konbu by hand. Now only eight are left!

In contrast to tororo konbu, the production of oboro konbu cannot be mechanized. Whereas a machine in Matsumoto’s factory can turn out nearly 200 pounds (90 kg) of tororo konbu every day, the workers at Goda Shoten can produce only 22 pounds (10 kg) of oboro konbu daily. And even that much smaller quantity must take an enormous physical effort.

But how is the special tool—the unique knife that makes it possible to shave the konbu—made? It requires a very special blade, so it is obvious why it is forged in Sakai, the city that is famous for its knife smiths. My host, Hiroki Yamanaka, had asked in the oboro konbu workshop for the name of someone who made these special knives. A few telephone calls later, it was arranged that we should visit an old knife smith, Izumi Riki, an acknowledged master of this craft, who would be able to enlighten us. Riki-san is a colorful character who is very interested in gastronomy and who told me that he once played saxophone with the band Santana.

We met Riki-san in his store, which was bursting with knife blades. The workers were seated on the floor, attaching them to handles and packing the orders. Above the shop there is a large area filled with traditional Japanese kitchenware, as well as a big, well-appointed kitchen where Riki-san works with chefs and demonstrates the correct use of his knives.

The time finally arrived for us to see the actual knife blades that are used to cut oboro konbu. Riki-san took his time and explained that they are made from a specific type of carbon-tempered steel, which must be neither too hard nor too soft. In addition, the cutting edge has to curve slightly so that the blade shaves off a layer of the seaweed rather than slicing into it. To do this requires both know-how and skilled manual labor.

I had asked my host, who was acting as interpreter, to ask very tactfully whether it might be possible to buy one of the knife blades. The request was turned down very politely. The knives were not for sale and may be used by only true oboro konbu artisans. I sensed that there was a great deal of professional pride behind this refusal and I felt a bit of regret that I had even entertained the idea that such knives could be sold to a foreigner.

As tororo konbu is soft, fine, and a little stringy it is at its best when used to enhance a soup or a tofu dish. Oboro konbu is just as soft, but because the shavings are cut along the fibers of the seaweed it has a firmer texture and can be wrapped around balls of cooked rice or combined with udon noodles.

How does it taste? The immediate taste sensation is a subtle combination of salt with a slightly acidic undertone from the rice vinegar. And, of course, umami comes into play. The most interesting aspect, and the most surprising, is that the softest foodstuff in the world imparts a completely unusual mouthfeel. It almost melts on the tongue, just like cotton candy.