CHAPTER XI ANIMAL AND VEGETABLE FATS AND OILS When we speak of Animal and Vegetable Fats or Oils, the so-called fixed oils are usually meant. These should not be confused with the essential oils, which are entirely different in their composition and properties. The latter are the volatile constituents of plants (rarely of animals), and can usually be distilled from the parent substance by steam or under a vacuum. As they are important constituents of Spices, a more complete discussion will be found under that head. (See p. 440.) Fixed oils and fats are from two sources, Viz.; animals and vegetables. Many of these substances are important constituents of foods, while others are utilized in various industries, such as in soap and paint manufacture. Many of the animal oils, such as whale oil and fish oil, are not agreeable to the taste of the people of the United States, but even these when properly "deoderized” or "hydrogenated," are used in increasing quantities as food. In fact the edibility of a fat depends more often on custom than on chemical composition. Linseed and sunflower oils are staple foods in Russia, and whale-blubber in the far North. Most vegetable oils, if properly refined, make good food products, but occasionally one, like croton oil, contains poisons. Vegetable oils are usually found in the seeds of plants, and are obtained by pressing the ground seed, or by extracting with some solvent like gasoline. Animal fats are obtained from animal tissues by "rendering," or heating until the fat is melted so that it can be separated from the surrounding membranes. Composition Considered chemically, fats are glycerol esters of fatty acids, or they may be looked upon as salts of the higher saturated or unsaturated fatty acids in which the glycerol acts as the base. Just as nitric acid when treated with caustic soda forms water and sodium nitrate (Chili salt peter), so stearic acid will theoretically combine with glycerol to give glycerol stearate (ordinary stearin). Some of the fatty acids contain a relatively higher proportion of hydrogen than others; those to which more hydrogen can be added we term unsaturated, while those that are fully supplied with hydrogen we speak of as saturated. To the former class belong oleic and linoleic acids, and to the latter stearic, palmitic, arachedic acid, etc. Ordinary tallow is composed largely of stearic, palmitic and oleic acids combined with glycerol to form glycerides. The physical condition of the fat or oil, i.e., whether it is a solid or a liquid at ordinary temperatures, depends largely on the relative proportion of the saturated and unsaturated glycerides present. Hardening of Oils About 15 years ago a practical commercial method was discovered' for saturating the unsaturated glycerides by merely heating them with hydrogen in the presence of some catalytic agent such as nickel, so that now we have, instead of the liquid cotton-seed oil which is high in glyceryl oleate and low in the stearate, a white solid similar to tallow in which a considerable quantity of the oleate is changed to stearate. This process is also known as "hydrogenating." The change may be represented by the equation: The work of Sabatier and Senderens has greatly advanced the processes used in the hardening of fats. The catalyzers used are of the two classes of metals, those of the nickel group, the only ones used commercially in the United States, and those of the platinum group. These when in a finely divided form are very 1 J. Soc. Ch. Ind., Vol. 31, p. 1115. active in hydrogenating fats. In the process a small amount of the metal is introduced into the fat, which is at the same time heated in a current of hydrogen to a temperature of from 100° C. to 225° C. often under pressure. The metal used is, after the completion of the hydrogenation, removed by filtration.1 Saponification When fats or oils are "saponified" by treatment with caustic soda or potash the corresponding soap is formed, and commercial glycerine remains in the mother liquor, from which it may be separated and afterward purified by vacuum distillation. VEGETABLE AND ANIMAL FATS Vegetable oils usually contain more of the unsaturated, and animal fats more of the saturated glycerides. On this account the animal fats are more frequently solid and the vegetable fats more often liquid, in which case they are known as oils. The liquid condition of the vegetable oils is rather an advantage than otherwise, as far as ease of digestion is concerned. In the extraction of the fat or oil from the animal or vegetable tissue, it is difficult to avoid obtaining other substances which are not oils. These impurities are mechanically mixed, and therefore most oils must be purified and refined before they are fit for use as food. ANIMAL FATS The common animal fats used as food are lard, beef fat (suet), mutton fat, butter, and small quantities of the fat of the hen, duck, goose, etc. By the process of "rendering," the fat is separated from the connecting tissue, which settles to the lower part of the kettle as "scrap" or "cracklings." 1 Chem. Abs., Vol. 6, pp. 2550-2551. LARD There are several grades of hog fat, sold under the name of lard, as made at the large packing houses. The highest grade which is known as "Leaf Lard" or occasionally as Neutral Lard No. 1, is made from the fat surrounding the kidneys. This fat, after being well washed and chopped, is heated at as low a temperature as possible, in steam-jacketed kettles, as there is less charring of the residual matter and consequently the product is of a lighter color than when the fat is heated in an open kettle. The fat thus obtained is sometimes washed with water containing a little salt and sodium bicarbonate. "Refined Lard" is a product that is sometimes made from "prime steam lard" by heating it in a tank to 170° F. and at the same time blowing air through it to remove the moisture. It is then agitated at a temperature of 160° F. with Fuller's Earth, to bleach it, and finally filtered in a large mechanical filter press. In order to "bring it to grain," it is cooled rapidly, either by agitating in a tank surrounded by cold water, or more often by running it on to a large revolving roll which is filled with ice-cold brine. (Fig. 65.) The lard is scraped from the roll as the drum revolves, and is then ready to be packed for market. "Steam rendered Lard," or "prime steam lard," is the lowest grade of the packing house. It is extracted from the "stock,” under a pressure of about 50. pounds, by admitting steam to the tank which contains the hog fat from various parts of the animal. When the material is completely "rendered," the fat is run off from the scraps, and quickly cooled. "Kettle rendered" lard should be of a high quality, and the process should be similar to domestic practice in which the kettle is heated externally, and the temperature used is not excessive. Lard is frequently stiffened by the addition of lard stearin, but the use of beef stearin for this purpose would be considered an adulteration. Lards thus stiffened "stand up" better in a warm climate, and are therefore more satisfactory in the tropics. Lard oil is obtained by subjecting the lard contained in woolen bags, to hydraulic pressure. The oil which is expressed is chiefly olein, and is of a pale yellow color and has a peculiar bland taste. It was formerly used as a burning oil for lamps, and at the present time finds some use as an edible oil and for lubricating purposes. In France it has been used as an adulterant for olive oil. The stearine which remains in the press is known as "lard stearine," and is used in making "Compound Lard," and for similar purposes. Lard Substitutes On account of the cost of pure lard, and because of a growing prejudice against animal fats, a large number of substitutes have been proposed, and some have found a very extensive use. These are carefully made of clean, wholesome material, and are usually sold under various well-known trade names. Vegetable fats and oils are by many believed to be more whole-some than lard and they contend that lard substitutes are really better for general use from a hygienic standpoint. Compound lard, which is sold under various trade names, is a mixture of such materials as cotton-seed oil, lard stearine, beef stearine and some times lard. The cotton-seed oil used is purified, then bleached by filtration through Fuller's earth before being mixed with the |