FAT

any substance of plant or animal origin that is nonvolatile, insoluble in water, and oily or greasy to the touch. Fats are usually solid at ordinary temperatures, such as 25 C (77 F), but they begin to liquefy at somewhat higher temperatures. Chemically, fats are identical to animal and vegetable oils, consisting primarily of glycerides, which are esters formed by the reaction of three molecules of fatty acids with one molecule of glycerol (see oil). Together with oils, fats comprise one of the three principal classes of foodstuffs, the others being proteins and carbohydrates. Nearly all cells contain these basic substances. Fat is sometimes called nature's storehouse of energy because on a weight basis it contains more than twice as much energy as does carbohydrate or protein. It is probably as storehouses or depots of concentrated energy that fats appear in plant reproductive organs, such as pollen grains and seeds. It is this fat that humans recover from plants for use as food or in industry. The fat content of the nonreproductive tissue of plants is usually so low that recovery is impracticable. Yet much dietary fat comes from natural foodstuffs without being separated from the other plant materials with which it occurs. The proportion of fat in these foodstuffs varies from 0.1 percent in white potatoes to 70 percent in some nut kernels. More than 90 percent of the fat recovered in the world is obtained from about 20 species of plants and animals. Most of this separated fat is used eventually as human food. Consequently, fat technology deals largely with the separation and processing of fats into forms acceptable to the various dietary customs in the countries in which they are to be used. (For further information on the subject, see Food Processing.)