Definition

Fats are food-stuffs having the same ultimate chemical composition as carbohydrates; i. e., consisting of carbon, hydrogen and oxygen, but the latter element is present in less proportion than in carbohydrates. Fats were formerly spoken of as hydrocarbons, but this term is now reserved for substances which contain no oxygen at all, such as benzine.

Description

True fats, whether solid or oily, are chemically compounds of fatty acids with glycerine, and differ among themselves according to the particular fatty acids they contain. These commonly comprise stearic, palmitic and oleic acids. The stearates or combinations of stearic acid with glycerine (also generally spoken of as stearins) are solid fats as are also palmitates or palmitins. The oleates or oleins on the other hand are fluid at ordinary temperatures. It is therefore evident that solid fats contain much more stearin or palmitin than olein, while fat oils consist chiefly of olein. Stearin is found only in fat of animal origin. Animal fats are therefore a mixture of all three classes, while vegetable fats consist of mixtures of palmitins and oleins. Suet and tallow owe their firmness largely to the amount of stearin present, while lard owes its softness to the amount of olein present. Butter consists largely of palmitin. The most prominent of the animal fats are butter, cream, lard, suet, tallow, butterine, oleomargarine and cod-liver oil. The vegetable oils are obtained from fruits and nuts (olive, cottonseed, peanut, cocoanut, cocoa bean and almond). Vegetable oils and the liver oil of fish are composed chiefly of olein. Certain dietetic substances not usually thought of as fatty, contain much oil. Some of these are yolks of eggs, Indian corn and nearly all nuts except chestnuts. Artificial products like butterine are described elsewhere. They are often preferred to butter because their melting point is lowered by the addition of suet or tallow (beef-drippings) so that they keep better in warm weather.

Lecithin is a substance usually classed with fats and oils. Besides fatty acids it contains phosphorus. It is a necessary constituent of every living cell and is especially plentiful in the nervous tissues. At present it is used to a considerable extent in medicine in the belief that it is of value as a food-drug and reconstituent. It is prepared from the yolk of egg and from brain substance. Feeding yolks of eggs is usually as advantageous and cheaper.

Volatile Oils

These, as already stated, have little in common with true oils. They stain paper only temporarily, while a fat stain is permanent. They vary much among themselves in composition and agree chiefly in their tendency to disappear by evaporation; and their odor, taste and pungency. A few of them are used in diet for flavoring. The oil of bergamot is obtained from orange peel, oil of lemon from lemon peel, etc. The act of cooking tends to volatilize them, so that such flavoring should be added at the last moment.