Cooking changes the appearance and flavor of beef, alters nutritional value, makes it safer, and extends its shelf life.

Browning meat after you cook it does not "seal in the juices," but it does change the flavor by caramelizing sugars on the surface. Because beef's only sugars are the small amounts of glycogen in the muscles, we add sugars in marinades or basting liquids that may also contain acids (vinegar, lemon juice, wine) to break down muscle fibers and tenderize the meat. (Browning has one minor nutritional drawback. It breaks amino acids on the surface of the meat into smaller compounds that are no longer useful proteins.)

When beef is cooked, it loses water and shrinks. Its pigments, which combine with oxygen, are denatured (broken into fragments) by the heat and turn brown, the natural color of well-done meat.

At the same time, the fats in the beef are oxidized. Oxidized fats, whether formed in cooking or when the cooked meat is stored in the refrigerator, give cooked meat a characteristic warmed-over flavor. Cooking and storing meat under a blanket of antioxidants—catsup or a gravy made of tomatoes, peppers, and other vitamin C–rich vegetables—reduces the oxidation of fats and the intensity of warmed-over flavor. Meat reheated in a microwave oven also has less warmed-over flavor.

An obvious nutritional benefit of cooking is the fact that heat lowers the fat content of beef by liquifying the fat so it can run off the meat. One concrete example of how well this works comes from a comparison of the fat content in regular and extra-lean ground beef. According to research at the University of Missouri in 1985, both kinds of beef lose mass when cooked, but the lean beef loses water and the regular beef loses fat and cholesterol. Thus, while regular raw ground beef has about three times as much fat (by weight) as raw ground extra-lean beef, their fat varies by only 5 percent after broiling.

To reduce the amount of fat in ground beef, heat the beef in a pan until it browns. Then put the beef in a colander, and pour one cup of warm water over the beef. Repeat with a second cup of warm water to rinse away fat melted by heating the beef. Use the ground beef in sauce and other dishes that do not require it to hold together.

Finally, cooking makes beef safer by killing Salmonella and other organisms in the meat. As a result, cooking also serves as a natural preservative. According to the USDA, large pieces of fresh beef can be refrigerated for two or three days, then cooked and held safely for another day or two because the heat of cooking has reduced the number of bacteria on the surface of the meat and temporarily interrupted the natural cycle of deterioration.

How Other Kinds of Processing Affect Beef

Aging. Hanging fresh meat exposed to the air, in a refrigerated room, reduces the moisture content and shrinks the meat slightly. As the meat ages enzymes break down muscle proteins, "tenderizing" the beef.

Canning. Canned beef does not develop a warmed-over flavor because the high temperatures in canning food and the long cooking process alter proteins in the meat so that they act as antioxidants. Once the can is open, however, the meat should be protected from oxygen that will change the flavor of the beef.

Curing. Salt-curing preserves meat through osmosis, the physical reaction in which liquids flow across a membrane, such as the wall of a cell, from a less dense to a more dense solution. The salt or sugar used in curing dissolves in the liquid on the surface of the meat to make a solution that is more dense than the liquid inside the cells of the meat. Water flows out of the meat and out of the cells of any microorganisms living on the meat, killing the microorganisms and protecting the meat from bacterial damage. Salt-cured meat is much higher in sodium than fresh meat.

Freezing. When you freeze beef, the water inside its cells freezes into sharp ice crystals that can puncture cell membranes. When the beef thaws, moisture (and some of the B vitamins) will leak out through these torn cell walls. The loss of moisture is irreversible, but some of the vitamins can be saved by using the drippings when the meat is cooked. Freezing may also cause freezer bum—dry spots left when moisture evaporates from the surface of the meat. Waxed freezer paper is designed specifically to hold the moisture in meat; plastic wrap and aluminum foil are less effective. NOTE: Commercially prepared beef, which is frozen very quickly at very low temperatures, is less likely to show changes in texture.

Irradiation. Irradiation makes meat safer by exposing it to gamma rays, the kind of high-energy ionizing radiation that kills living cells, including bacteria. Irradiation does not change the way meat looks, feels or tastes, or make the food radioactive, but it does alter the structure of some naturally occurring chemicals in beef, breaking molecules apart to form new compounds called radiolytic products (RP). About 90 percent of RPs are also found in nonirradiated foods. The rest, called unique radiolytic products (URP), are found only in irradiated foods. There is currently no evidence to suggest that URPs are harmful; irradiation is an approved technique in more than 37 countries around the world, including the United States.

Smoking. Hanging cured or salted meat over an open fire slowly dries the meat, kills microorganisms on its surface, and gives the meat a rich, "smoky" flavor that varies with the wood used in the fire. Meats smoked over an open fire are exposed to carcinogenic chemicals in the smoke, including a-benzopyrene. Meats treated with "artificial smoke flavoring" are not, since the flavoring is commercially treated to remove tar and a-benzopyrene.