Kidney (food)
The kidneys of animals are a commonly consumed offal. Kidneys can be grilled, sautéed, roasted or braised. They can be used in cooking meat casseroles, stews or pies. Typically used in cooking are beef, veal, lamb and pork kidneys. Chicken kidneys are used in cooking, too, but fowl kidneys are very small and generally not collected to be used in food separately. Veal kidneys are preferred among cooks. The kidneys of small animals are grilled or fried, and the kidneys of larger ones are usually stewed. Kidneys are intended to be stored in the refrigerator for no longer than one day, but they also can be frozen. Defrosted kidneys are meant to be used as soon as possible. During grilling or frying kidneys can be overcooked, because they easily dry out. There are different recipes for cooking kidneys including recipes with such ingredients as potatoes, onions, tomatoes, shallot, mushrooms or with other meat. Kidneys are a good source of proteins, vitamin A, riboflavin (vitamin B2 vitamer), niacin (vitamin B3 vitamer), vitamin B12, iron, phosphorus and zink. Lamb and beef kidneys contain folate (vitamin B9 vitamer). Kidneys also contain small amounts of vitamin C. They are low-fat food, but they contain high amounts of cholesterol. History 
The kidneys had been used in cooking from ancient times. There is an evidence of cooked kidneys in ancient Egypt. Egyptians supplied tombs of the dead with everything that dead people would need afterlife. The food was found in tombs, too, including cooked kidneys. The poor people usually ate bread and boiled vegetables, while the wealthy people might eat food of animal origin two or three times a day. Cooked kidneys were found in the Saqqara tomb of female noble among other dishes. See also 

 Steak and kidney pie
 Mixed grill
 Skirts and kidneys
 Devilled kidneys

References 

Offal