One of the VARIETY MEATS, the kidney is a glandular organ. The most popular kidneys for cooking are beef, veal, lamb and pork. They're easily distinguishable because beef and veal kidneys are multi-lobed while lamb and pork are single-lobed. In general, the texture is more tender and the flavor more delicate in younger animals. The kidneys from younger animals are pale while those from older animals become deep reddish-brown; they're also tougher and stronger-flavored. Look for kidneys that are firm, with a rich, even color. Avoid those with dry spots or a dull surface. Kidneys should be used the day they're purchased, or store loosely wrapped in the refrigerator for up to 1 day. Before cooking, remove skin and any excess fat. Soaking helps reduce the strong odor in kidneys from more mature animals. See a general cookbook for details pertaining to the particular type of kidney you wish to cook. Kidneys may be braised, broiled, simmered or cooked in casseroles, stews and dishes like the famous STEAK AND KIDNEY PIE. All kidneys are a good source of protein, iron, phosphorus, vitamin A, thiamine and riboflavin.