The Purification of Fats and Suets.
The task that devolved upon the authorities of Paris during the late siege of that city by the Germans, of obtaining food for the many thousands who were cut off by the iron circle of their enemies from their usual sources of supply, was a difficult, and, as the event proved, an impossible one. Towards its accomplishment, however, great efforts were put forth by French savans, and for a time the whole current of scientific investigation was turned towards securing increased effectiveness in warlike weapons, the enforcement of the sanitary regulations best suited to the abnormal state of affairs, and the discovery and utilization of previously unknown or unused alimentary substances.
Among the many memoirs presented to the French Academy with the last-mentioned object, were some that treated of a subject not without interest to pharmacists,—the purification of fats and suets,—of which the following is a résumé.
M. A. Boillot communicated a method which he stated had yielded excellent results, and for which he claimed the merits of simplicity and moderate cost. (Comptes Rendus, lxxii, 36.) Two litres of lime-water is added to one kilolitre of the fat or suet, mixed well together, and kept over the fire two or three hours. It is then left to cool, and, when it has become pasty and acquired a sufficient consistence, it is decanted, placed in flannel or linen, and submitted to an increasing pressure, when water and oleic acid, containing besides some solid fatty acids, from which it can readily be freed afterwards, passes through. The oily mass, after two or three days, acquires a whiteness which leaves nothing to be desired; and when freed from the little lime that it contains by treating it with water slightly acidulated with sulphuric acid, may be used for purposes of illumination. Fat thus prepared loses its bad odor, and acquires a remarkable hardness and whiteness; (The use of lime for the purpose of blanching lard has already been reported, from America. There, however, it appears to be left as an impurity in the lard. See Pharm. Journ., 1st ser., vol. i, p. 1043.) and if run into water to which a small quantity of sulphuric or acetic acid, or vinegar, has been added, it will be thoroughly purified, and may be employed for all purposes to which the best fats are applied.
M. Dubrunfaut states (Comptes Rendus, lxxii, 37.) that the most tainted fat may be deprived of its characteristic odor by submitting it to the operation of frying; and that, after being thus treated in a manner specified, it may be used for all culinary preparations, and even for pastry. For this fact he furnishes the following scientific explanation.
M. Dubrunfaut has practically ascertained, by laboratory and manufacturing experiments, that fish oil is radically deprived of its odorous principle by simply heating it to a high temperature (330 C.) He has also found that the fatty acids are volatilized in a current of steam at a temperature above 100° C., whilst the neutral fats remain perfectly fixed. Finally, he has found that the neutral fats comport themselves in a similar manner to the fatty acids under the influence of a current of steam, if they have previously been heated to a temperature of from 300° to 330° C.
The manner in which the purification is effected is by heating the fat in a frying-pan or other suitable utensil to a temperature of about 140° to 150° C., then cautiously sprinkling upon it small quantities of water. The vapor so caused traverses the fat, decomposes the neutral fatty substances,—which, as shown by M. Chevreul in the case of hircine, yield fatty acids,—the whole of the fatty acids are volatilized, and the purification is accomplished. These conditions, he says, unite all the elements which are favorable to the elimination of the volatile fatty acids, which are generally the material cause of the odors of fat substances. The product thus obtained is as perfectly purified as the finest lard.
M. Dubrunfaut had so much faith in the efficacy of this method of purification, that he called attention to the large quantity of candle tallow still in the city, and stated that by a modification of the process to suit the known constituents of the tallow, the whole of it might be so purified as to fit it for use in cooking various kinds of coarse flours, such as buckwheat flour, and thus secured for the purposes of alimentation. The same method might also, he stated, be applied to the large stock of colza oil.
In a second note presented to the Academy, (Comptes Rendus, lxxii, 57.) M. Dubrunfaut again called attention to the facility with which the large stocks of tallow and colza oil might be utilized for food, while the mineral oils would suffice for the purposes of lighting. On this occasion he pointed out the similarity of the origin of the kitchen fats and the tallow of commerce, and said that the absence from the kitchen fats of the repulsive odor of the tallow was due to the method of preparation. In the operation of roasting meat especially the conditions necessary for the purification of the fat—the high temperature and the superheated vapor—were realized in perfection. And although they were present in a less degree in the operation of boiling, still there was a real purification. This opinion is supported by the fact that tainted fat, undergoing ebullition in a melting-pot in the presence of salt water, is purified in proportion as the boiling is prolonged.
As the result of various experiments in which colza oil was treated according to M. Dubrunfaut's method, he reported that the oil lost its characteristic taste and odor, preserving only a slight savor that was not repulsive, and would not prevent its use in culinary operations.
MM. Wurtz and Willm reported (Ibid., lxii, 57.) that they had found that when colza oil was submitted to a current of steam at a temperature of from 116° to 120° C., an odorous and acrid principle was carried off without sensibly saponifying the oil,—an inconvenience which followed the employment of steam too highly heated. Washing with a feeble warm solution of carbonate of soda takes away all traces of the fatty acids that may have been formed, or have pre-existed, in oil of bad quality but the separation of the soap so formed presents some difficulties. (Some idea of the importance of this subject to the Parisians under then existing circumstances may be inferred from the fact that the stock of colza oil in the reservoirs at St. Ouen and La Valette was estimated at from 12,000,000 to 13,000,000 kilograms. This enormous quantity had been accumulated by speculators who, anticipating a great demand for illuminating purposes, had obtained the oil from all the markets of Europe. It was the ordinary colza oil of commerce, prepared by warmth from the seeds of Brassica Napus, and had not undergone sulphuric purification which, while rendering it combustible, would have unfitted it for alimentation.)
M. Fua suggested (Comptes Rendus, lxxii, 59.) a modification of M. Dubrunfaut's method, which consisted in melting the fats at so high a temperature that the residue of the cellular and vascular tissues were thoroughly exhausted. He also expressed an opinion that these methods for the purification of fats were preferable to the introduction of either acids, alkalies, or substances, as these foreign bodies had always to be removed afterwards.—Pharm. Journ., Lond., Oct. 21, 1871.