This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
Fresh bears' fat is white and very similar to lard in appearance. The flank fat is softer and more transparent than the kidney fat, and its odor recalls that of fresh bacon. Bears' fat differs from the fats of the dog, fox, and cat in having a lower specific gravity, a very low melting point, and a fairly high iodine value.
Bone fat, which is principally obtained from horse bones, is very dark colored in the crude state, and of an extremely disagreeable smell. To remedy these defects it may be bleached by the air or chemicals, the former method only giving good results when the fat has been recovered by means of steam. It consists in cutting up the fat into small fragments and exposing it to the air for several days, the mass being turned over at intervals with a shovel. When sufficiently bleached in this manner, the fat is boiled with half its own weight of water, which done, about 3 or 4 per cent of salt is added, and the whole is boiled over again. This treatment, which takes 2 or 3 weeks, sweetens the fat, makes it of the consistency of butter, and reduces the color to a pale yellow. Light seems to play no part in the operation, the change being effected solely by the oxygen of the air. The chemical treatment has the advantage of being more rapid, sufficient decoloration being produced in a few hours. The fat, which should be free from gelatin, phosphate of lime, and water, is placed in an iron pan along with an equal weight of brine of 14° to 15° Bé. strength, with which it is boiled for 3 hours and left to rest overnight. Next day the fat is drawn off into a wooden vessel, where it is treated by degrees with a mixture of 2 parts of potassium bichromate, dissolved in 6 of boiling water, and 8 parts of hydrochloric acid (density 22° Bé.), this quantity being sufficient for 400 parts of fat. Decoloration proceeds gradually, and when complete the fat is washed with hot water.
Instead of exposing to the sun, -which is always attended with danger of rendering fats rancid, it is better to liquefy these at a gentle heat, and then add £ in weight of a mixture of equal parts of kaolin and water. The fatty matter should be worked up for a time and then left to separate. Kaolin has the advantage of cheapness in price and of being readily procured.
Freshly burned animal charcoal would perhaps be a more satisfactory decolorlzer than kaolin, but it is more expensive to start with, and not so easy to regenerate.
Exposure of tallow to the action of steam under high pressure (a temperature of 250° or 260° F.) is also said to render it whiter and harder.
A simple method for the detection of the addition of coloring matter to fats is here described. Ten parts, by measure, of the melted fat are put into a small separating funnel and dissolved in 10 parts, by measure, of petroleum ether. The solution is then treated with 15 parts, by measure, of glacial acetic acid and the whole shaken thoroughly. The addition of coloring matter is known by the red or yellow coloration which appears in the lower layer of acetic acid after the contents of the funnel have been allowed to settle. If only a slight addition of coloring matter is suspected, the acetic acid solution is run off into a porcelain basin and the latter heated on a water bath, when the coloration will be seen more readily. This test is intended for butter and margarine, but is also suitable for tallow, lard, etc.