Chapter 20

Cooking Nutritious Food

IN THIS CHAPTER

Naming the various cooking methods

Changing the look, aroma, and flavor of food

Picking the perfect pot

Preserving nutrients in cooked food

Explaining how cooking makes food safe

You can bet that the first cooked dinner was an accident involving some poor wandering animal and a bolt of lightning that charred the beast into medium rare sirloin. Then a caveman attracted by the aroma tore off a sizzled hunk and forthwith offered up the first restaurant rating: “Yum.”

After that, it was but a hop, a skip, and a jump, anthropologically speaking, to gas ranges, electric broilers, and microwave ovens. This chapter explains how these technologies affect the safety, nutritional value, appearance, flavor, and aroma of the foods that you heat.

For more pragmatic details on what and how to cook, check out Cooking Basics For Dummies, 4th Edition, by Brian Miller, Marie Rama, and Eve Adamson (Wiley), and then fire up the stove.

Exploring Different Methods of Cooking

The dictionary defines cooking as preparing food by heating it. In your kitchen, that means exposing food to the energy created either by a gas fire, an electric heating plate, or the radio waves in your microwave.

Cooking with fire

Ever since man discovered fire and how to control cooking — rather than having to wait for that passing lightning flash — the human race has generally relied on three simple ways of heating food:

  • An open flame: You hold the food directly over — or under — the flame or put the food on a griddle on top of the flame. (The electric heating coil is a 20th-century variation on the open flame.)
  • Hot air: You put the food in a closed box (an oven) and heat the air in the oven to create high-temperature dry heat.
  • Hot liquid: You submerge the food in hot liquid or suspend the food over the liquid so it cooks in the steam escaping from the surface.

Sophisticated cooks may combine two or more of these methods. For example, cooking food in a wrapper, such as aluminum foil or a papaya leaf (see Chapter 31), combines two methods: open fire (the grill) or hot air (the oven) plus the steam from the food’s own juices (hot liquid).

The basic methods for cooking with heat generated by fire or an electric coil are

Open Flame

Hot Air

Hot Liquid

Broiling

Baking

Boiling

Grilling

Roasting

Deep-frying

Toasting

Poaching

Simmering

Steaming

Stewing

Cooking with electromagnetic waves

A microwave oven generates electromagnetic energy (microwaves) produced by a device called a magnetron.

The energy transmitted from the magnetron excites water molecules in food. The water molecules leap about like hyperactive 3-year-olds, producing friction, which produces the heat that cooks the food.

warning Because the dish on which food sits in a microwave oven has very few water molecules, it generally stays cool. But some dishes or containers do heat up. To be safe, use a potholder when taking a dish out of the microwave.

Understanding How Cooking Alters Food

Cooking changes the way food looks, smells, feels, and tastes with appetizing texture, rich color, intense flavor, and fragrant aroma all due to exposure to heat.

Changing food’s texture

Exposure to heat alters the structures of proteins, fats, and carbohydrates, changing their texture (the way food particles are linked to make the food feel hard or soft). In other words, cooking can turn crisp carrots soft and tough meat tender.

Protein

Proteins are made of very long molecules that sometimes fold over into accordion-like structures (see Chapter 6 for details about proteins). Although heating food doesn’t lower its protein value, it does

  • Break protein molecules into smaller fragments
  • Cause protein molecules to unfold and form new bonds to other protein molecules

Need an example? Consider the egg. When you cook one, the long protein molecules in the white unfold, form new connections to other protein molecules, and link up in a network that tightens to squeeze out moisture so the egg white hardens and turns opaque. The same unfold-link-squeeze reaction turns translucent poultry firm and makes gelatin set. The longer you heat proteins, the stronger the network becomes, and the tougher, or more solid, the food will be. The inevitable exception to this rule is that connective tissue — the tissue that connects, supports, and holds other tissues and organ — softens when exposed to heat, which is why meat becomes more tender when cooked even though it contains proteins in the form of cartilage.

To see this work, scramble two eggs — one beaten and cooked plain and one beaten with milk and then cooked. Adding liquid (milk) makes it more difficult for the protein network to squeeze out all the moisture, so the egg with the added milk cooks up softer than the plain egg.

Fat

Heat melts fat, allowing it to run off, which lowers the calorie count. In addition, heat breaks down connective tissue — the supporting framework of the body, which includes some adipose (fatty) tissue — thus, making the food softer and more pliable. You can see this most clearly when cooking fish, which flakes when it’s done because its connective tissue has been destroyed.

When meat and poultry are stored after cooking, their fats continue to change, picking up oxygen from the air. Oxidized fats have a slightly rancid taste, more politely known as warmed-over flavor. You can slow — but not entirely prevent — this reaction by cooking and storing meat, fish, and poultry under a blanket of food rich in natural antioxidants, chemicals that prevent other chemicals from reacting with oxygen. Vitamin C is a natural antioxidant, so gravies and marinades made with tomatoes, citrus fruits, or tart cherries slow the natural oxidation of fats in cooked or stored foods.

Carbohydrates

Cooking has different effects on simple carbohydrates and complex ones (more about them in Chapter 8). When heated

  • Simple sugars — such as sucrose or the sugars on the surface of meat and poultry — caramelize, or melt and turn brown. (Think of the top of a crème caramel.)
  • Starch, a complex carbohydrate, becomes more absorbent, which is why pasta expands and softens in boiling water (see the sidebar “Grains: Split personality performers”).
  • Some dietary fibers (gums, pectins, hemicellulose) dissolve, which is why vegetables and fruits soften when cooked.

The last two reactions have the added benefit of making nutrients inside previously fiber-stiffened cells more available to your body.

A less beneficial effect of heat on carbs surfaced early in 2002 when Swedish researchers announced that exposing starchy carbohydrate foods — such as potatoes and bread — to the high heat of baking or frying produces acrylamides, a family of chemicals known to cause cancer in rats. Then things got worse when scientists at the City of Hope Cancer Research Center (Los Angeles) said that acrylamides could trigger cell changes leading to cancer in human beings.

A 2003 analysis of data from a study of 987 cancer patients and 538 healthy “controls” conducted by researchers at Harvard School of Public Health and the Departments of Oncology–Pathology and Medical Epidemiology at Karolinska Institutet in Stockholm showed no evidence of an increased risk of bowel, bladder, or kidney cancer among fans of fries and toast.

By 2010, the official FDA position on acrylamides was, essentially, no big deal. In 2013, the FDA’s best advice was that consumers should “adopt a healthy eating plan, consistent with the Dietary Guidelines for Americans, that emphasizes fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products; includes lean meats, poultry, fish, beans, eggs, and nuts; and is low in saturated fats, trans fats, cholesterol, salt (sodium), and added sugars.”

Enhancing flavor and aroma

Heat degrades (breaks apart) flavor and aroma chemicals, allowing the molecules to float off into space, like your nose. As a result, most cooked food has a more intense flavor and aroma than raw food.

A good example is what happens when you cook cruciferous vegetables, such as cabbage and cauliflower. These vegetables get their distinctive flavor and aroma from mustard oils, whose sensory signals grow more intense the longer the vegetables are cooked. But every rule has an exception: Heat destroys diallyl disulfide, the chemical that gives raw garlic its bite and bark; cooked garlic tastes and smells milder than raw.

By the way, if you, like President George Herbert Walker Bush, absolutely hate the taste of cruciferous veggies, you are a person who is sensitive to phenylthiocarbamide (PTC), a bitter chemical in these plants. The theory is that disliking bitter tastes helped protect early man (and woman) from poisonous plants. Today, nutritionists know that in some cases — like broccoli, Brussels sprouts, and their relatives — bitter is better.

Shading the color palette

Carotenoids — the natural red and yellow pigments that make carrots and sweet potatoes orange and tomatoes red — are practically impervious to heat and the acidity or alkalinity of cooking liquids. No matter how you cook them or how long, these particular pigments stay bright and sunny.

That’s not the case for the other pigments that make other foods naturally red, green, or white. These pigments react — usually for the worse — to heat, acids (such as wine, vinegar, or tomato juice), and basic (alkaline) chemicals (such as mineral water or baking soda and water). Here’s a brief rundown on the color changes that you can expect when you cook food:

  • Red beets and red cabbage get their colors from pigments called anthocyanins. Acids make these pigments redder. Alkaline solutions fade anthocyanins from red to bluish purple.
  • Potatoes, cauliflower, rice, and white onions are whitened by pigments called anthoxanthins. When anthoxanthins are exposed to alkaline chemicals (mineralized water or baking soda), they turn yellow or brownish. Acids prevent this reaction. Boil cauliflower florets in water, and they darken slightly. Boil them in tomato juice, rinse off the juice, and you’ll see — white cauliflower.
  • Green veggies are colored by chlorophyll, a pigment that reacts with acids in cooking water (or in the vegetable itself) to form pheophytin, a brown pigment. The only way to short-circuit this reaction is to protect the vegetables from acids. Old-time cooks added alkaline baking soda, but that increases the loss of certain vitamins (see the section “Protecting the Nutrients in Cooked Foods,” later in this chapter) and softens the vegetables. Fast cooking at high heat or cooking in lots of water (which dilutes acids) lessens these color changes.
  • The natural red color of fresh meat comes from myoglobin in the muscle tissue and hemoglobin in blood. When meat is heated, the pigment molecules are denatured, or broken into fragments. They lose oxygen and turn brown or — after long cooking — turn the really unappetizing gray characteristic of steam-table meats. This inevitable change is more noticeable in beef than in pork or veal because beef, which contains more myoglobin, starts out naturally redder.

Picking the Right Cooking Materials

The pot you choose may affect the nutritional value of food by

In addition, some pots make the food’s natural flavors and aromas more intense, which, in turn, can make the food more — or less — appetizing. The following sections describe the effects different pots and materials have on your food.

Aluminum

Aluminum is lightweight and conducts heat well. That’s good. But the metal makes some aroma chemicals, such as those in the cruciferous veggies, much smellier and releases microscopic flakes that can turn white foods, such as cauliflower or potatoes, yellow or brownish.

technicalstuff Yes, that old chestnut about aluminum being hazardous to your health is f-a-l-s-e. True, cooking salty or acidic foods (wine, tomatoes) in aluminum pots increases the flaking, but even then, the amount of aluminum you get from the pot is less than you get naturally every day from plain food and water.

Copper

Copper pots heat steadily and evenly. To take advantage of this property, many aluminum or stainless steel pots are made with a layer of copper sandwiched into the bottom. But naked copper is a potentially poisonous metal, so copper pots are lined with tin or stainless steel. To be safe, check the lining of your copper pots from time to time. If it’s damaged — meaning that you can see the orange copper through the silvery surface — have the pot relined or throw it out.

Ceramics

The chief virtue of plain terra cotta (the orange clay that looks like red bricks) is its porosity, the fact that it contains millions of tiny pores that allow excess steam to escape while holding in just enough moisture to make food tender.

Decorated ceramic vessels are another matter. For one thing, the glaze makes the pot much less porous so meat or poultry cooked in a covered painted ceramic pan steams instead of roasts, producing a soggy surface rather than a crisp one.

More importantly, some pigments used to paint or glaze the pots may contain lead. To seal the decoration and prevent lead from leaching into food, the painted pots are fired (baked in an oven). If the pots are fired in an oven that isn’t hot enough or if they aren’t fired for a long enough period of time, lead will leach from ceramics when in contact with acidic foods, such as fruit juices or foods marinated in wine or vinegar.

Ceramics made in the United States, Japan, and Great Britain generally are considered safe, but for maximum protection, hedge your bets. Unless the pot comes with a tag or brochure that specifically says it’s acid-safe, don’t use it for cooking or storing foods. And always wash decorated ceramics by hand; repeated passes through the dishwasher can wear down the surface.

Enamelware

Enameled pots are made of metal covered with porcelain, a fine translucent china. Enamelware heats more slowly and less evenly than plain metal. A good-quality enameled surface resists discoloration and doesn’t react with food, but it can chip, and it’s easily marked or scratched by cooking utensils other than wood or hard plastic. If the surface chips and you can see the metal underneath, discard the pot lest metals flake into your food.

Glass

Glass is a neutral material that doesn’t react with food. However, two cautions apply:

  • Don’t use a glass-and-metal pot in the microwave oven. The metal blocks microwaves. More importantly, it can cause arcing — a sudden electrical flare that may damage the oven and scare you out of your wits.
  • Glass breaks, sometimes all over the floor. Are you a person who often drops things? Pass on the glass.

Iron

Iron conducts heat well and stays hot significantly longer than other pots. It’s easy to clean. It lasts forever, and it releases iron ions into food, which may improve the nutritional value of dinner.

In 1985, nutrition researchers at Texas Tech University (Lubbock) conducted a classic experiment to measure the iron content of foods cooked in iron pots. Among their conclusions: Beef stew (0.7 milligrams of iron per 100 grams/3.5 ounces, raw) can end up with as much as 3.4 milligrams of iron per 100 grams after cooking slightly longer than an hour in an iron pot.

The downside? “Pumping iron” isn’t a bad way to describe the experience of cooking with iron pots. They’re really, really heavy.

Nonstick

Nonstick surfaces are made of plastic (polytetrafluoroethylene — PTFE for short) plus hardeners — chemicals that harden and seal the surface. As long as the surface is unscratched and intact, it won’t react with food.

To avoid surface scratches, stick to wooden or plastic spoons when using these pots. Otherwise, your pot may end up looking like chickens have been stomping on the surface. Scratched nonstick pots and pans are not a health hazard. If you swallow tiny pieces of the nonstick coating, they pass through your body undigested.

However, when nonstick surfaces get very hot, they may

  • Separate from the metal to which they’re bound (the sides and bottom of the pot).
  • Emit odorless fumes. If the cooking area isn’t properly ventilated, you may experience polymer fume fever — flulike symptoms with no known long-term effect. To prevent this, keep the stove flame moderate. And you may as well open a window.

Stainless steel

Stainless steel is an alloy, a substance composed of two or more metals. Its virtues are hardness and durability; its drawback is poor heat conduction. In addition, stainless steel isn’t really stainless. When exposed to high heat, stainless steel develops a characteristic multi-hued “rainbow” discoloration. Starchy foods, such as pasta and potatoes, may darken the pot, and undissolved salt can pit the surface. If your stainless steel pot is scratched deeply enough to expose the inner layer under the shiny surface, the metals in the alloy may flake into your food. Toss the pot.

Plastic and paper

Plastic melts and paper burns, so you obviously can’t use plastic or paper containers in a stove with an open flame (gas) or heat source (electric). But you can use them in the microwave so long as you pick a proper plastic.

When plastic dishes or plastic wrap are heated in a microwave oven, they may emit potentially carcinogenic compounds that can migrate into your food. Because the Food and Drug Administration (FDA) requires microwave-safe plastics to meet strict safety standards, repeated studies show no ill effects from their minimal leakage.

The U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS) offer these rules for safe microwave cooking with plastics:

  • Only use cookware that is specially manufactured for use in the microwave oven. Glass, ceramic containers, and all plastics should be labeled for microwave oven use.
  • Plastic storage containers such as margarine tubs, take-out containers, whipped topping bowls, and other one-time use containers should not be used in microwave ovens. These containers can warp or melt, possibly causing harmful chemicals to migrate into the food.
  • Microwave plastic wraps, wax paper, cooking bags, parchment paper, and white microwave-safe paper towels should be safe to use. Do not let plastic wrap touch foods during microwaving.
  • Never use thin plastic storage bags, brown paper or plastic grocery bags, newspapers, or aluminum foil in the microwave oven.

Protecting the Nutrients in Cooked Foods

Myth: All raw foods are more nutritious than cooked ones.

Fact #1: Some foods (such as meat, poultry, and eggs) are positively dangerous when consumed raw (or undercooked). Other foods are less nutritious raw because they contain substances that destroy or disarm other nutrients. For example, raw dried beans contain enzyme inhibitors that interfere with your body’s ability to digest protein. Heating disarms the enzyme inhibitor.

Fact #2: That said, there’s no denying that some nutrients are lost when foods are cooked. Simple strategies such as steaming vegetables quickly rather than boiling, or broiling rather than frying, can significantly reduce the loss of nutrients.

Maintaining minerals

Virtually all minerals are unaffected by heat. Cooked or raw, food has the same amount of calcium, phosphorus, magnesium, iron, zinc, iodine, selenium, copper, manganese, chromium, and sodium. However, potassium, like the B vitamins (see Table 20-1), does leech from foods into the cooking liquid.

Table 20-1 What Takes Vitamins Out of Food?

Vitamin

Heat

Air

Water

Fat

Vitamin A

X

X

Vitamin D

X

Vitamin E

X

X

X

Vitamin C

X

X

X

Thiamin

X

X

Riboflavin

X

Vitamin B6

X

X

X

Folate

X

X

Vitamin B12

X

X

Biotin

X

Pantothenic acid

X

Potassium

X

Keeping those volatile vitamins

Many vitamins are sensitive to and easily destroyed by heat, air, water, or fats (cooking oils). Table 20-1 shows which vitamins are sensitive to these influences.

tip To avoid specific types of vitamin loss, keep in mind the following tips for the different vitamins:

  • Vitamins A, E, and D: To reduce the loss of fat-soluble vitamins, cook with very little oil. For example, bake or broil liver, which is rich in vitamin A, with very little oil. Ditto for fatty fish (salmon, tuna, and mackerel), one of the few natural food sources of vitamin D.

  • B vitamins: Conserve the B vitamins that leak out of meat and poultry into cooking liquid or drippings by using the liquid in soup or sauce. Caution: Don’t shorten cooking times or use lower temperatures to lessen the loss of heat-sensitive vitamin B12 from meat, fish, or poultry. These foods and their drippings must be thoroughly cooked to ensure that they’re safe to eat.

    To preserve the B vitamins in grains, don’t rinse the grains before cooking unless the package advises you to do so. Some rice, such as basmati, does need to be rinsed and/or soaked to release its nutrients when cooked, but rinsing other rices even once may wash away as much as 25 percent of their thiamin (vitamin B1).

  • Vitamin C: To reduce the loss of water-soluble, oxygen-sensitive vitamin C, cook fruits and vegetables in the least possible amount of water. A series of experiments at Cornell University demonstrated that when you cook 1 cup of cabbage in 4 cups of water, the leaves lose as much as 90 percent of their vitamin C. Reverse the ratio — 1 cup water to 4 cups cabbage — and you hold on to more than 50 percent of the vitamin C.

    Another vitamin C–saver is to bake or boil root vegetables (carrots, potatoes, and sweet potatoes) whole, in their well-washed skins. This trick retains about 65 percent of the vitamin C.

    Serve cooked vegetables quickly: After 24 hours in the fridge, most vegetables lose one-fourth of their vitamin C; after two days, nearly half.

Keeping Food Safe by Cooking

In 2013, the Food and Drug Administration estimated that each year one in six Americans falls ill after eating contaminated food, about 130,000 end up in the hospital, and 3,000 die from foodborne illness caused primarily by pathogens (disease-causing organisms).

If you’re good at math, you’ll see right away that based on the Census’s July 4, 2014, estimates of 318,881,992 people in the country, these numbers equal

The good news is that these numbers appear to be down from several years ago. The bad news is that these numbers exist. Should they worry you? Yes. Although pathogens in food are most dangerous for the very young, the very old, and those whose immune systems have been weakened by illness or medication, the truth is that these microorganisms are equal-opportunity troublemakers — anyone who eats food carrying them may get sick.

Naming the bad guys

Many microbes living naturally in food are harmless or even beneficial. For example:

Some organisms, however, are decidedly unfriendly. For example:

  • Clostridium botulinum (C. botulinum) thrives in the absence of air and acidity to churn out a potentially fatal neurotoxin, which is why it is important to be careful about such low-acid canned foods as string beans. A bulging can means air has gotten in. Don’t taste. Don’t test. As the saying goes, “When in doubt, throw it out.” (Note: Yes, this is the same microbe used in a purified, nontoxic injection to relax facial muscles and reduce wrinkles.)
  • Campylobacter jejuni (C. jejuni), which flourishes in raw meat and poultry and unpasteurized milk, has been linked to Guillain-Barré syndrome, a paralytic illness that sometimes follows flu infection.

Table 20-2 lists the most common food pathogens and the foods in which they’re most likely to be found.

Table 20-2 Disease-Causing Organisms in Food

The Bug

Where You Find It

Campylobacter jejuni

Raw meat and poultry, unpasteurized milk

Clostridium botulinum

Underprocessed low-acid canned foods, vacuum-packed smoked fish, herb-infused oils

Clostridium perfringens

Foods made from poultry or meat

E. coli

Raw beef, precut bagged salads, raw sprouts

Listeria monocytogenes

Raw meat and seafood, raw milk, some raw cheeses, ready-to-eat deli meats and hot dogs, refrigerated smoked fish, raw vegetables

Salmonella

Poultry, meat, eggs, dried foods, dairy products, raw sprouts, nuts

Shigella

Salads, raw vegetables, milk and other dairy products, poultry

Staphylococcus aureus

Custards, salads (that is, egg, chicken, and tuna salads)

USDA Meat and Poultry Hotline, Centers for Disease Control

Heating to the appropriate temperature

Cleanliness along the line from field to processing to marketing to dinner table is essential for controlling foodborne illness. Proper cooking is equally important.

Simply heating food to the temperatures shown in Table 20-3 isn’t a guaranteed protection against foodborne illness, but cooking food thoroughly and keeping it hot (or chilling it quickly) after it has been cooked will incapacitate many dangerous microbes or slow the rate at which they reproduce, thus reducing the risk.

Table 20-3 How Hot Is Safe?

Category

Food

Temperature (°F)

Ground meat and meat mixtures

Beef, pork, veal, lamb

160

Turkey, chicken

165

Fresh beef, veal, lamb

Steaks, roasts, chops

145

Poultry

Chicken and turkey, whole (all cuts)

165

Pork and ham

Fresh pork

145

Fresh ham (raw)

145

Precooked ham (to reheat)

140

Eggs and egg dishes

Eggs

Cook until yolk and white are firm.

Egg dishes

160

Leftovers and casseroles

Leftovers

165

Casseroles

165

Seafood

Fin fish

145 or cook until flesh is opaque and separates easily with a fork.

Shrimp, lobster, and crabs

Cook until flesh is pearly and opaque.

Clams, oysters, and mussels

Cook until shells open during cooking.

Scallops

Cook until flesh is milky white or opaque and firm.

www.foodsafety.gov/keep/charts/mintemp.html

tip Don’t rely on instinct to tell you whether a food has reached safe temperature during cooking. Use a food thermometer. And because some things are more complicated than they seem, read the directions that come with the thermometer to be sure you’re doing it right.

tip When cooking a stuffed chicken or turkey, it’s smart to heat up the stuffing before stuffing it into the bird. After the chicken or turkey is done, make sure the temperature inside the stuffing as well as in the body of the bird (the wide part of the leg is a good place to test) is safely high, and then remove the stuffing and refrigerate it separately. To be absolutely safe, many experts recommend cooking the stuffing separate from the bird, particularly if the stuffing is not heated prior to putting it in the bird.