Some readers may ask why a glossary is needed that defines terms such as butter, egg white, milk, caramel, and chocolate. Let me respond to this perfectly reasonable question with an anecdote. The Hungarian physicist Leo Szilard used to edit a journal. One day he ran into his friend Hans Bethe, who asked him why he edited a journal. “Because,” Szilard replied, “I want God to know the facts.” “But don’t you believe He already knows the facts?” “Yes, but I want Him to be informed of my version of the facts.”
In what follows I want to give you my idea of foods, molecules, and the reactions that take place in cooking. But rather than give a comprehensive set of strict definitions—omnia definitio pericolosa!—let me share instead my thoughts about a few specific terms.
ACETIC ACID: One of a number of acids present in vinegar. Vinegar also owes its taste to malic acid, formic acid, and tartaric acid, among others. The essential step in the transformation of wine into vinegar involves the oxidation (caused by microorganisms of the species Mycoderma acetii) of the wine’s ethyl alcohol (or ethanol) into acetic acid.
ACIDITY: A food may be said to be acid, or sour, in the mouth when it causes a sensation analogous to that produced by vinegar or lemon juice. Adding sugar changes this sensation by altering the real acidity of the food (as measured by its ability to dissolve metals, for example). Acidity therefore is better characterized in units of pH, with the aid of small strips of paper and electrodes connected to a measuring device (two items that deserve a place in modern cooking, by the way). Because lentils cook better in a basic than an acid medium, you can adjust the pH of the cooking water with the aid of bicarbonate soda and, once the cooking is done, add vinegar to neutralize the unsavory taste of the bicarbonate.
ACTIN: An important protein in cooking because it is abundant in meats and fish. It acts in concert with myosin in the elongated cells of muscle fibers as an essential agent of muscle contraction.
ALBUMEN: The white of an egg—but if you look at it you will see that it’s yellow. Why did our ancestors choose such an ill-suited word? In the Viandier, a fourteenth-century French cookbook, the egg white was called “albun,” from the Latin alba, meaning “white.” An egg can have different colors, of course, depending on what the hen eats. In a cookbook from the eighteenth century one reads that in spring, when the hen eats beetles, the egg white is bitter and green.
ALBUMIN: An old word, formerly used in cookbooks to denote what today are called proteins. The term is now reserved for globular proteins such as ovalbumin, the principal protein of albumen. See also Egg white.
AMINO ACIDS: The building blocks of proteins. Some twenty kinds are found in cooking.
AMYLOPECTIN: Along with amylose, one of the two molecules that are the principal constituents of starch. Instead of being a mere linear chain of glucose subunits, it has a branching structure, also made of glucose subunits.
AMYLOSE: A glucose polymer. Amylose molecules are composed of long chains of identical subunits of glucose molecules.
AROMA: There us no consensus among specialists concerning the meaning of this term. In the view of some authorities it is the name of the sensation created by volatile molecules released during mastication that rise up through the retronasal fossae into the nose. But others, a majority, take it to describe a part of the overall sensation of flavor. When you drink wine, for example, and perceive a flavor of green pepper, you say that it has a green pepper aroma. This effect is caused by both odorant and taste molecules that stimulate the trigeminal nerve (producing a sensation of freshness, for example). Here I use the term to refer to a distinctive sensation that is a component of the overall flavor of a food or wine.
ASCORBIC ACID: Also known as vitamin C. It is responsible for the antioxidant properties of lemon juice, in which it is present in large quantities (37 milligrams per 100 grams). Instead of using lemon juice to prevent pears, bananas, and apples from browning, why not use ascorbic acid? It’s cheaper and much more efficient.
ASPARTAME: A sweetener made by the conjunction of two amino acids, L-asparrtic acid and L-phenylalanine methylene. This molecule in itself furnishes proof that there is not just one sweet taste but many. Taste it and see for yourself!
ASTRINGENCY: Characteristic of a molecule that binds with salivary proteins and suppresses their lubricating action, producing the sensation of a dry, tightened mouth. Many polyphenols are astringents because their hydroxyl (–OH) groups bind with such proteins. If you take a sip of a very astringent wine, swirl it around in your mouth for a few seconds, and then spit it out into a glass, you will see precipitates—proteins bound to tannins.
AUTOXIDATION: An essential chemical reaction that causes fats to turn rancid. Because it is self-catalyzing, the reaction takes place quickly. To retard it, protect foods against exposure to oxygen, light (whose ultraviolet rays promote autoxidation), and certain metals.
BASES: Purists are alarmed when these are said to be the opposite of acids, yet it is easier and more helpful to describe them in this way. Pedantry is not always a sign of clarity: Who will understand me, apart from those who already know, if I say that acids release protons whereas bases capture them?
BITTER: This annoyingly vague word is used to denote one of the sensations given by the gustatory papillae. Why annoyingly vague? Because each of us has a very particular impression of tastes and because we do not know which tastes go to make up the flavor of a given dish. In the mouth foods release volatile molecules that travel up to the nose through the retronasal fossae along with molecules that give a sensation of spiciness, while mechanical and thermal sensors in the mouth detect texture and temperature. We therefore have an overall sensation that is customarily called flavor, but no one has ever succeeded in identifying its component tastes in the course of everyday eating and drinking. The problem is compounded by the fact that we now know there is not just one bitter taste but several; electrophysiologists recently demonstrated that the papillary cells that detect quinine (a “bitter” molecule), for example, differ from those that detect denatonium benzoate (another “bitter” molecule).
BOILING: Not the same thing as evaporation. For example, a bowl of water left to sit out for a long time is emptied through the evaporation of the water at room temperature. By contrast, evaporation accompanies boiling when a pan of water is placed over high heat. At what temperature does water simmer? Knowing the answer is important because meat is more tender when it is simmered.
BROWNING: Meats heated at high temperatures brown, as do apples that are cut up and left uncovered, as does sugar that is heated. Browning has various causes, including oxidation, enzymatic reactions caused by polyphenoloxidases, Maillard reactions, and thermal degradation.
BUTTER: A substance that was long considered to be emulsion in which water is dispersed in fatty matter in the form of casein-coated droplets. (Water molecules account for roughly 15–20% of its mass and triglyceride [fat] molecules roughly 80%.) But this view is wrong because at room temperature some of the fat is solid. Butter is better thought of as an emulsion trapped in a solid network, that is, an emulsion contained by a gel.
CALCIUM: This chemical element is found in ionized rather than neutral form in foods, for it has lost two electrons. This divalence makes it an interesting ion, in part because it can bond simultaneously with two pectin molecules, which means that it hardens not only vegetables but also jams. Calcium therefore is neither good nor bad. It is up to the cook either to use it or to seek to eliminate it, keeping in mind that it is readily trapped with citrate ions, for example.
CARAMEL: A delicious brown product that is classically obtained by the thermodegradation of ordinary sugar (sucrose). Different caramels can be obtained depending on the acidity or alkalinity of the medium in which a sugar is heated. Sugars such as glucose and fructose yield distinct flavors from those of sucrose. I love the fructose flavor!
CARAM ELIZATION: A term that cooks use indifferently to denote the browning of meats and the thermal degradation of sugars. Yet the chemical reactions are quite different in the two cases. If progress is to be made in the domain of cooking, its terminology must be made more exact: A cat is not a dog, and it would be a poor biologist who confused the two.
CASEINS: Proteins present in milk, where they are assembled into calcium phosphate–cemented aggregates known as micelles.
CELL: Roughly speaking, a small sac filled with water. The wall of the cell is essentially a double layer of phospholipid molecules. A closer look reveals that cells contain a host of interesting molecules, including proteins, sugars, lipids, and desoxyribonucleic acid (DNA), which makes these sacs living entities.
CHEMISTRY: A science of central importance to us as human beings, for it is what allows us to live. In fact, it allows us to live for two reasons: On one hand, our organism functions only by virtue of a coordinated set of chemical reactions; on the other hand, cooking is a form of chemistry that creates the foods that we consume. Chemistry sometimes is defined as the science of the transformations of matter, but this is an exaggeration: Many biological phenomena (the act of chewing, for example) and many of the phenomena of particle physics (the annihilation of a particle and its antiparticle) are transformations of matter (in the first case food is divided up, in the second matter is converted into energy) that do not involve chemistry. It is nonetheless accurate to say that chemistry creates its own subject matter and that it is concerned with the structure of atoms and molecules.
CHLOROPHYLL: A platelet-like molecule, with a tail and a magnesium atom at the center, that contributes to the color of green vegetables. The magnesium atom can be dislodged by a hydrogen ion during cooking in an acidic medium. This replacement of magnesium by hydrogen is accompanied by a change of color: The food turns from green to brown.
CHOCOLATE: Let’s not kid ourselves: It’s almost impossible for chocolate lovers to stay slim. Chocolate is composed mainly of fat (which accounts for roughly 30 grams of every 100 grams of dark chocolate) and sugar (60 grams). This bare description neglects the fact that chocolate has remarkable organoleptic properties and physical properties that are no less wonderful. For example, its fats melt in the mouth (at 37°C [99°F]) but not in the hand (at 34°C [93°F]). Mineral fats are sometimes added, but very few artisanal or industrial producers show their customers the courtesy of honestly and clearly admitting on their labels the difference between true chocolate and chocolate enriched with fats other than cocoa butter, a situation that seems to bother only me.
CLARIFICATION: A medieval culinary procedure that consists of adding egg white to a stock (wines are also clarified, but here we are concerned chiefly with cooking) and then heating it. The egg white traps the particles that cloud the stock, making it possible to obtain a fairly clear result by means of a final filtering. Rather than waste perfectly good eggs, we can use good laboratory filters instead.
COAGULATION: A transformation whose culinary prototype is the transformation of the egg white, a transparent yellow liquid, into a cooked egg white, an opaque white solid.
COLLAGEN: In meats, a fibrous tissue that sheathes muscle fiber cells. It is composed of proteins that are braided in triple strands, which combine in a way vaguely similar to cellulose fibers in paper. When meat is cooked, the thermal agitation breaks the bonds between collagen proteins, and they pass into solution (the bouillon subsequently gelatinizes as it cools because the proteins recombine with one another).
CONCENTRATION: A term that refers to both a physical phenomenon and a form of measurement. The phenomenon is the grouping together of entities in space or time. Thus, for example, there is a concentration of spectators in a stadium for a sporting event. Obviously molecules can also be concentrated, particularly in herbs; for example, anethol molecules are numerous in fennel. Concentration measures this effect. In cooking, the term often is used in connection with the cooking of a piece of meat. This is an odd way of talking: Juices come out from a roast rather than becoming concentrated inside, odorant and taste molecules are formed as a result of chemical reactions only on the surface, and the temperature inside the roast is lower than that of the oven. What, then, is being concentrated here?
CONDUCTION: In cooking, this phenomenon occurs principally by means of heating: The thermal agitation of molecules on the surface of a food is communicated to neighboring molecules inside. These molecules in their turn disturb molecules still further inside, and so on. This is why the internal temperature of foods progressively rises as they are cooked.
CONVECTION: A phenomenon that accelerates exchanges of heat in a liquid by virtue of differences in density between hot and cold parts. A broth cools rapidly because the liquid at the surface cools from contact with the air, so that its density increases; it then falls to the bottom of the bowl, while the hot liquid rises, then cools, and falls to the bottom. By contrast, a thick soup cools thoroughly only at the surface because its viscosity prevents convection. You can create a remarkable gastronomic sensation with a fragrant liquid (wine or hot chocolate, for example) if you put some of the liquid in a glass at room temperature and then, having heated the rest, gently pour it in the glass. Because of differences in density, stratification occurs between the two liquids. Although it is not visible, you will be able to perceive the effect as you drink.
COOKING: A marvelous activity because it is infinitely variable. The cooking of an egg white is not the same as the preparation of a fish with acids in the Tahitian manner or the same as subjecting a fish to the pressure of several hundreds of thousands of atmospheres. Even if one limits oneself to cooking by heating, cooking is a vast phenomenon. For example, a roast of beef is considered cooked even when it is raw in the center (although in this case the temperature of the meat in the center is actually a little lower than if you were to put the meat out in the sun during the summer). At what point can a food be said to be cooked? Rainwater is the product of prior evaporation. Should we therefore considered it cooked?
CUSTARD: An example of the sort of complex physicochemical systems whose study draws extensively on the work of two Nobel Prize winners, the physicist Pierre-Gilles de Gennes (custard is an example of a suspension–emulsion) and the chemist Jean-Marie Lehn (its proteins combine into supramolecular aggregates).
DECANTING: One of the operations that chemists have learned to master and that cooks could perform more expertly if only they were willing to depart from tradition. But who is prepared to assume responsibility for breaking with the ancients?
DECOCTION: Both very ancient chemistry and cooking—even modern cooking—distinguish between maceration, which involves placing a substance in cold water; decoction, which puts it in boiling water; and infusion, which puts it in boiling water and then quickly removes it. This distinction no longer holds when the solvent is oil, which decomposes before the boiling point is reached.
DEHYDRATION: Water may be drawn out from the tissues of vegetables, meats, and fish with sugar or salt, often in order to make the surface dry and to protect foods against deterioration.
DENATURATION: Proteins are said to be denatured when their form changes, for example by unfolding.
DIFFUSION: An important phenomenon in the kitchen. It is because of the diffusion of light that milk is perceived to be white and because of the diffusion of water molecules that fluids are drawn out from the tissues of salted vegetables and meat.
DOUGH: From the physicochemical point of view, doughs are wonderfully complex systems: solid suspensions in which a solid (starch) is dispersed into another solid (a gluten network formed by kneading).
EGG: A food that consists of a shell (accounting for about 10% of the mass of the egg), white (57%), and yolk (33%).
EGG WHITE: A transparent yellow—not white—liquid containing areas of differing viscosity. If one looks closely one also sees slender white strands and a few bubbles. When heated it solidifies, becoming opaque and white. A first microscopic approximation indicates that it is composed of 90% water and 10% proteins. On closer inspection, it can be seen to contain different proteins, including ovalbumin (58% of the total), ovotransferrin (3%), ovomucoid (1%), ovoglobulin (8%), and lysozyme (3.5%). Coagulation begins at 62°C (144°F); at this temperature the ovotransferrin is denatured, forming a delicate, white, almost transparent network that barely retains the liquid trapped inside it.
EGG YOLK: A remarkable substance composed of approximately 50% water and 15% proteins, with a great many lipids. It has a powerful taste and an unusual texture that changes at temperatures above 68°C (154°F).
EMULSION: A dispersion of droplets of one liquid in another liquid that does not mix with it. Mayonnaise is an emulsion of oil in water.
ENHANCERS: Certain preparations are said to be flavor enhancers, but physiological analysis does not yet justify use of this term.
ENZYMES: Proteins that are responsible for the reactions of other molecules.
ETHANOL: An important molecule because it is found in concentrations exceeding 10% in wines and contributes significantly to their gastronomic interest. The discovery of distillation, which allowed higher concentrations of ethanol to be achieved in the form of eaux-de-vie or brandies, was a major event in human history. Certain animals apart from human beings have a sort of language, and some have a form of laughter, but none of them knows how to distill.
EVAPORATION: Not the same thing as boiling, as I remarked earlier.
EXPANSION: There is an old idea that boiled meat cooks by expansion. But boiled meat does not expand. On the contrary, it contracts, and it is this contraction that causes its juices to be expelled into the surrounding liquid.
EXTRACTION: Cooking extracts aromatic and taste molecules from various foods. Nonetheless the flavor of dishes sometimes is wrongly attributed to extraction. For example, a stock owes its flavor to chemical reactions between the molecules extracted from the meat; contrary to what is often said, however, it is not an example of cooking by extraction.
FLAVOR: A term that describes the synthetic sensation produced by eating and drinking (including odor, taste, texture, heat, mechanical properties, and so on) that corresponds to the French goût. It is a pity that the English word has been imported into French (flaveur) and that goût usually is translated in English as “taste”! But let us persevere in our campaign against error: The world of tomorrow will be the one that we create today. See also Gustation, Sapiction.
FOAM: A dispersion of air bubbles in a liquid or a solid. A stiffly whipped egg white is a foam. A soufflé is also a foam, but the liquid phase is a suspension–emulsion. The sweetened dessert known as a mousse is an example of an uncooked foam.
FRUCTOSE: A sugar found in certain fruits and in the aisles of your local supermarket. It has a remarkable taste.
GEL: A liquid immobilized by molecules that are linked together to form a network. A cooked egg white, for example, is a chemical gel, for the network formed by the proteins is permanent. By contrast, jams and preserves form a physical—that is, reversible—gel.
GELATIN: Proteins extracted from meat that are reassembled in the form of sheets or powder. In hot water these molecules are dispersed; when the liquid cools, their extremities are linked in threes as segments of a triple helical strand, forming a network known as a gel in physics and, in cooking, as a gelatinous stock or jelly.
GLUCIDES: Molecules formerly considered carbohydrates because the first ones to be discovered had the general structure cn(H2o)n, containing as much water as carbon. Nonetheless, it is a mistake to believe that these molecules are composed of water molecules attached to carbon atoms. The various atoms of glucides are arranged in a different manner, with the result that the molecules they compose have numerous hydroxyl (-OH) chemical groups that determine their capacities for combination. It would not be imprecise to call these molecules sugars.
GLUCOSE: A very simple sugar that is found particularly in our bloodstream. The blood carries it to the body’s cells, which use it as fuel.
GUSTATION: Flavor (goût) is the sensation experienced when one eats and drinks—a synthetic, global sensation produced not only by taste and olfactory and visual perception but also by the perception of textures and various trigeminal stimuli. Nor should the papillae be called gustatory, because they communicate only the small part of the overall sensation known as taste. I propose instead to call the papillae sapictive because they detect tastes (saveurs). See also Sapiction.
HEAT: A form of energy that is characterized in terms of temperature. Strictly speaking, expressions such as “Heat propagates toward the center of a roast” are mistaken. It is more accurate to say that, in each part of a roasted piece of meat, the temperature increases during the course of cooking or that the rate of molecular agitation of the molecules increases in the meat during roasting, with greater average agitation on the periphery.
INFRARED RAYS: Invisible radiation that is abundantly emitted by hot bodies. Infrared rays are detectable with the aid of a thermometer in the spectrum of sunlight dispersed by a prism, where they come after red. You can perceive them by putting your hand next to your cheek without touching it: The warm sensation you feel is created by infrared rays emitted by your hand.
INFUSION: Tea is an infusion. See also Decoction.
IODINE: In alcohol solution a very useful substance for detecting the presence of starch: After a few seconds starch granules turn blue (rather than brown).
KURTI: The Oxford physicist Nicholas Kurti (1908–1998), known for his discovery of nuclear adiabatic demagnetization. In 1988 Kurti and I gave the name “molecular and physical gastronomy” to the scientific discipline that studies the chemical, physical, and biological transformations produced by cooking and eating foods. After his death I shortened it to “molecular gastronomy” and gave Nicholas’s own name to the workshops devoted to this subject that are held every two or three years in Sicily.
LACTIC ACID: Produced by lactic bacteria from the lactose found in milk. The characteristic sourness of foods such as sauerkraut is caused by lactic acid.
LACTOSE: A milk sugar. Milk sometimes is said to be sweet on account of its presence, but if you pay close attention you will find it has a salty taste.
LIPIDS: Dictionaries of biochemistry make a point of defining them because several types of related molecules are grouped under this term. Many alimentary lipids are triglycerides or phospholipids.
LUMP: A disagreeable structure, the prototype of which is obtained by putting flour in hot water. The starched periphery of the resulting agglomerations prevents the diffusion of water toward the center, which remains dry.
MACERATION: See Decoction.
MAGNETIC RESONANCE IMAGING (MRI): Common name for an imaging process that exploits the phenomenon of nuclear magnetic resonance. In hospitals, the term is a euphemism: In deference to public fears of imagined radioactive dangers associated with nuclear magnetic resonance, one speaks instead of magnetic resonance imaging.
MAILLARD: French biochemist Louis-Camille Maillard (1878–1936). Maillard studied medicine and chemistry at Nancy, writing his medical thesis on urinary indoxyl; his thesis in chemistry, on the action of glycerine and sugars on alpha-amino acids, earned him an international reputation. After volunteering for service in World War I, Maillard joined the medical faculty of the University of Algiers as professor of biological chemistry and toxicology, teaching there until his sudden death in Paris. The reaction that bears his name was announced in a three-page paper published by the French Academy of Sciences in 1912.
MAILLARD REACTION: A transformation that begins with the reaction of a sugar and an amino acid. What follows is very complicated, however, and a complete description would fill several volumes. It suffices for our purposes here simply to say that once an Amadori or a Heyns rearrangement has taken place (depending on the nature of the reactive sugar), several parallel paths lead to the formation of brown compounds, notably the ones found on the surface of meats that are cooked at high temperatures.
MEAT: Roughly speaking, a packet of elongated sacs, or muscle fibers. These sacs contain water and proteins, as in the case of egg whites. The muscle fibers are supported by a tissue, collagen, that is made of elongated (rather than globular) proteins and that dissolves when heated in water.
MEMBRANE: The lining of living cells, consisting of a double layer of phospholipids in which various molecules are dispersed, notably proteins and sugars.
MICROWAVES: Electromagnetic waves that were first harnessed by radar. Engineers observed that pigeons that flew in front of the antenna were cooked, which led to the development of microwave ovens. These utensils are the only ones used in cooking today whose principles were not understood in the Middle Ages.
MILK: Mainly water, but it also contains fats dispersed in the form of droplets that are too small to be seen individually by the naked eye, and proteins, also microscopic in size, that are aggregated in micelles.
MONOSODIUM GLUTAMATE: A compound used by Asian cooks because it produces a remarkable taste called umami.
MUSCLE FIBERS: The slender elongated cells (up to 20 centimeters long) found in meats.
MYOFIBRILS: Cellular complexes of actin and myosin that are responsible for muscle contraction.
MYOGLOBIN: A muscle protein that contains an iron atom, just as chlorophyll contains a magnesium atom.
MYOSIN: Along with actin, an essential protein for muscle contraction.
NEURONS: The brain contains nerve cells, or neurons, that transmit and receive signals in the form of neurotransmitter molecules. Once a certain excitation threshold is exceeded, an electrical impulse is propagated through a prolongation of the cell, known as an axon, triggering the release of neurotransmitters, which traverse a synaptic cleft and activate other neurons.
NUCLEAR MAGNETIC RESONANCE (NMR): A nondestructive method for determining molecular composition that exploits the magnetic properties of certain atomic nuclei along with radio waves. No radioactivity is involved. See also Magnetic resonance imaging.
ODOR: A sensation that occurs in cooking when one puts one’s nose above a pan on the stove: The heated foods release volatile molecules that attach themselves to the receptors of olfactory cells in the nose—hence the invention of the cover, which retains heat and traps the odorant molecules inside.
ODORANT COMPOUNDS: Molecules that are sufficiently volatile to reach receptor proteins, located on the surface of olfactory cells in the nose. Volatility by itself is not sufficient: A molecule is aromatic only if it binds to one of these receptors, thus triggering the excitation of the olfactory cell, which signals to the brain that an aroma (or an odor) has been detected.
OIL: In cooking, a liquid whose molecules are almost exclusively triglycerides.
OLFACTION: The faculty that permits us to detect the presence of molecules in the air above a dish that have evaporated from it and that contribute to the flavor of the food.
OSMAZOME: A mistaken notion that arose toward the end of the eighteenth century. Alcohol was believed to extract a well-defined principle peculiar to meats—the osmazome—that was responsible for their flavor. Why was this idea mistaken? Because the alcoholic extract in question is composed of many sorts of molecules and because the principle changes depending on the meat.
OSMOSIS: A remarkable physicochemical phenomenon that used to be demonstrated with the aid of a pig’s bladder immersed in a volume of water. A bladder partly filled with sweetened water was observed to swell up: The sugar is unable to escape the bladder, and more water seeps in from outside. The underlying reason for this phenomenon is the tendency of concentrations of various molecules on either side of a permeable barrier to be equalized.
OXIDATION: An important reaction that has been insufficiently explored in cooking. In recent years it has often been said that the browning of the surface of meats is caused by a chemical transformation known as the Maillard reaction. It is more accurate to say that the Maillard reaction contributes to browning together with other reactions, among them the Strecker degradation and various oxidizing reactions.
PAPILLAE: Drink a glass of milk, stick out your tongue in front of a mirror, and you will be able to make out small round projections on the tongue. These papillae (usually called gustatory, although I prefer to say sapictive because they detect tastes rather than flavor) are composed of cells whose surface supports proteins known as receptors. When a taste molecule interacts with these receptors, the cells are electrically activated and send a signal to the brain indicating that they have detected this particular molecule. The papillae tell us when we ought to stop eating.
PECTIN: Chemists consider it a D-galacturonic acid polymer, a complex definition that can be simplified by observing, first of all, that it is a sugar. The properties of this molecule result from a long chain of atoms consisting of hydroxyl (–OH) groups, a methyl (–CH3) group, carboxylic acid (–COOH) groups, and methyl ester (–COOCH3) groups. The carboxylic acid groups are important in cooking because they electrically repel one another in a basic medium, with the result that pectins are unable to combine with one another. Therefore in making preserves (which is to say gels created by the association of pectins) the acid groups must be neutralized by H+ ions. In other words, the cooking medium must be sufficiently acidic.
PECTINASES: Enzymes that degrade pectin. If you want to make apple juice without wearing yourself out, simply add pectinases to an apple and let them act for a while at room temperature.
PEPTIDES: Molecules formed by the bonding of certain amino acids.
PH: A measure of the acidity or alkalinity of a given environment. The scale runs from 0 to 14. Values between 0 and 7 correspond to acid environments and values between 7 and 14 to alkaline (basic) environments. It is inexcusable that pH paper is not commonly found in kitchens today. How else can one determine a solution’s relative acidity?
PHENOLICS. See Polyphenols.
PHOSPHOLIPIDS: We could not live without these molecules because, along with glycerolipids, they constitute the double molecular layers that form the membranes of living cells. They have a lipid part and a phosphate part (a phosphorus atom surrounded by oxygen atoms), but most owe their distinctive properties to the presence of an electrically charged part and a hydrocarbon part (composed solely of carbon and hydrogen atoms).
PHYSICS: One of the pillars of gastronomy, involving not particle physics or astrophysics but the physics of “soft” or “condensed” matter. Emulsions, foams, and gels are best studied collaboratively by physicists and chemists.
POLYPHENOL OXIDASES: Enzymes that oxidize molecules of the polyphenol class, forming quinones that react to produce brown compounds. These enzymes are responsible for the discoloration one sees in apples that have been cut up and left out, exposed to the air.
POLYPHENOLS: Molecules containing at least one benzene ring (a hexagonal ring with six carbon atoms attached to hydrogen atoms) and hydroxyl (–OH) groups. Tannins are polyphenols, as are many of the molecules that give foods their color.
POLYSACCHARIDES: Another name for complex sugars.
POTATO: A vegetable whose cells have the peculiar property of containing small granules of starch, which absorb water and swell during cooking.
PRECIPITATION: The French humorist Alphonse Allais used to say that water is a dangerous liquid because a single drop is enough to cloud the purest absinthe. This cloudiness is caused by the precipitation of anethol, a component of absinthe. Precipitation is a phenomenon that has been studied by chemists for centuries and that could be put to better use by cooks.
PRESERVES: Pectin molecules in fruits are joined together by cooking, forming a network—or gel—that traps water, sugar, and the various molecules that give fruits their good taste.
PROTEASES (including proteinases): Enzymes that degrade proteins. Fresh pineapple, for example, contains the protease bromelin; papaya, papain; figs, ficin. These enzymes are our enemies when we try to make pineapple, papaya, and fig jellies.
PROTEINS: Chains of amino acids that are longer than peptides.
RANCIDITY: The result of leaving fat exposed to air. See Autoxidation.
RECEPTORS: Proteins on the surface of cells that react by means of weak forces with compounds in the cellular environment and trigger various physiological reactions: detection of an odor, a taste, and so on.
RENNET: An extract from the abomasum of calves that permits the formation of certain cheeses made from milk: Casein micelles, once chemically modified by rennet, cease to repel one another and combine to form a gel that traps fats.
RETRO-OLFACTION: As food is chewed in the mouth it is very slightly heated and releases volatile molecules that rise up through the retronasal fossae at the rear of the mouth and reach the nose, where they are detected by olfactory receptors.
SALT: The kind you find in the kitchen is sodium chloride. As one would expect, its taste is usually salty, but in its unrefined state it may contain other salts that give it a bitter taste.
SALTY: The sensation produced by salt and certain other compounds.
SAPICTION: Both French and English ought to adopt this word, which is much more precise than gustation. If the physiology of flavor (not taste) is to make further progress we must take into account what we have learned so far. Just as we have abandoned erroneous notions such as phlogiston and caloric, should we not adopt other more useful ones in their place? See also Taste molecules.
SAUCES: Remarkable physicochemical systems that accompany a great variety of dishes. Traditionally they are softer than the meats and vegetables they accompany, but their viscosity must be greater than that of water. Mastery of the rheological behavior of sauces is one of the great challenges of cooking.
SODIUM BICARBONATE: Also known as bicarbonate of soda, or baking soda, it is a valuable base in cooking, used to soften lentils and to accelerate the cooking of vegetables.
SOUFFLÉ: A foam that expands not because its air bubbles are dilated by the heat of the oven but because a portion of its water evaporates.
SOUR. See Acidity.
STARCH : Dough is made by mixing flour with water. If the dough is then kneaded under a thin stream of water, a white powder composed of minute granules appears. This material, starch, is also found in the cells of potatoes and other vegetables.
STARCHES: Foods that contain starch. They can be identified by a test familiar to children: Pour a little tincture of iodine on them and see whether a purple stain appears that then turns blue.
STARCHING: A process by which starch granules heated in water lose some of their amylose molecules and swell up, forming a starch paste.
STRECKER REACTION: Amino acids react when carbonyl compounds (which have a –C=O group) are present, producing a degradation named after the German chemist Adolph Strecker (1822–1871). This reaction often occurs in cooking because Maillard reactions are sources of carbonyl compounds.
SUCROSE: Ordinary sugar, composed of a glucose molecule joined together with a fructose molecule (both molecules lose their identity during bonding, however). Sucrose is the prototype sugar molecule, but there are many others.
SUGARS: Some are made up of small molecules, such as glucose, fructose, and lactose. Others are made up of large molecules, such as cellulose and pectin.
SUSPENSION: A physicochemical system obtained by the dispersion of solid particles in a liquid. India ink is an example of a suspension. Custard, in which aggregates of egg proteins are suspended in the water contained in the milk, is another.
SWEET: The taste produced by sucrose and other sugars. The sensation varies, depending on the sugar.
TANNINS: Extracted from various kinds of vegetable matter, including wood, they have the property of combining with proteins and iron. For example, a sheet of (protein) gelatin soaked in strong tea (a solution containing tannins) causes the tea to become cloudy.
TASTE MOLECULES: Certain food molecules dissolve in water and then become attached to receptors on the surface of the papillary cells in the mouth. It is sometimes said that excitation of these cells causes a signal to be sent to the brain that a flavor has been detected. But this terminology is confused, for taste receptors register the sensation of specific tastes. The perception of a food’s flavor is the product of a whole set of sensations in addition to the sensation of tastes: perceptions of smell, texture, temperature, and so on. It would be more helpful if the term sapiction were used to refer to the detection of a particular taste by sapictive receptors that are carried by sapictive cells in the papillae.
TASTES: It was long thought that only four existed (salt, sweet, sour, bitter), but recent advances in neurophysiology have shown that monosodium glutamate, for example, has a distinctive taste (called umami) and that various bitter molecules stimulate different papillary cells. But consider licorice. Is it salty? No. Is it sweet? No. Sour? No. Bitter? No. Umami? No. Well, then, what is it?
TENSIOACTIVE MOLECULES: Laundry detergents contain molecules that adhere to the surface of greasy stains, enveloping and detaching them from soiled fabrics. The droplets of water-insoluble matter coated with these tensioactive molecules are dispersed in water and then carried off during the rinse cycle. In cooking, molecules of the same type coat droplets of oil introduced into water to form emulsions. See for yourself and try making an emulsion with a drop of liquid detergent, but don’t eat it.
TRIGLYCERIDE: An ester of glycerol, attached to three fatty acids. These molecules, which have the shape of a comb with three teeth, make up dietary fats. The teeth—the fatty acids—come in different lengths, and some have carbon atoms that are joined together by double bonds. These unsaturated compounds determine the fusion properties and nutritive properties of foods.
VANILLIN: A surprising molecule that is abundantly present in vanilla. It is also formed when alcohols are left to age in oak casks: The ethyl alcohol reacts with the lignin of the wood, eventually producing vanillin—hence the vanilla flavor of certain old alcohols.
VEGETABLES: Plants whose cells differ from those of animals in that they contain hard walls, softened by cooking. These walls are remarkable structures made up of several layers. It is important for culinary purposes to know that they contain pectin, a complex sugar that causes preserves to set, for example.
YEASTS: Very useful unicellular organisms that help us make bread, wine, beer, and many other dishes.