FOOD PRESERVATION in a technical sense relates to the processes adopted for the preservation of organic substances used as food, either animal or vegetable. It is.gener ally understood that the "spoiling° of foods and food materials is due to the activities of bacteria, and the various preservative processes are therefore contrived to prevent bacterial action. They may be considered under the fol lowing heads: (1) Preservation by cold; (2) Preservation by drying; (3) Preservation by salting; (4) Preservation by smoking; (5) Preservation by sterilization by heat and the exclusion of air; (6) Preservation by chemical or antiseptic substances; (7) Preservation with sugar and with brandy, and by pickling with vinegar in the customary household processes.
1. Cold.— The application of cold for the preservation of meat and vegetables may now be conducted under modern methods of apply ing this agent, at temperatures varying from 0° F. (— 18° C.) to 40° F. or more. In the large cold storage plants now established in many cities, in which the expansion of liquid ammo nia is chiefly used for the production of vari able degrees of cold, it is customary to provide several large compartments or rooms for the preservation of food in which different tem , peratures are maintained, fruit being kept at temperatures a little above the freezing point, and meats, fowl and especially fish at consid erably lower temperatures.
In densely settled countries like England, where the land area is insufficient to produce the;necessary amount of meat for the food of the people, frozen meat from other countries forms a considerable part of the food supply. If the meat is frozen before rigor mortis (ri gidity following death) supervenes the meat keeps well, but if it is frozen later it rapidly decomposes after thawing. Freezing arrests putrefaction and has a tendency to conceal the or of decomposition. Hence bad condition frozen fish may not be detected until the at necessary for cooking is applied. Meat itch has been frozen is often unusually ten ? on account of the loosening of the inter iscular tissue by freezing; bacteria can more idily penetrate into the interior of thawed tat, and bring about rapid decomposition.
ozen meat and fish, especially when thawed 3 suddenly, lack the flavor of fresh meat. icteria in general and especially those which e concerned in the production of putrefac seem to be endowed with extraordinary wers of resistance to the action of cold. demann and Mickendrick kept flesh six urs in hermetically sealed boxes at temper ures from — 21° to — 202° F., but in every stance the flesh after being removed to a ghtly warm temperature, though protected om infection, began to decompose in from 10 12 hours. But cold, though it may not de coy all micro-organisms, prevents the devel anent of putrefactive bacteria. There are, >wever, certain bacteria which are capable of nreloping in frozen meat, and especially in iat which is kept at about 32° F. Lafar ttributes to this cause the unpleasant flavor 3metimes acquired by meat which has been ept in a refrigerator for several days. This confirmed by Popp, who says that the walls such ice chambers when moist swarm with acteria, which in his opinion produce the ob ectionable flavor often developed in stored nat. The ordinary household refrigerator as been found ineffective, less than 20 per cent egistering 45° F., the degree of cold required 3 preserve food. Of 100 pounds of ice placed i such refrigerators 80 pounds was consumed i cooling the air which leaked in.
The Detection of Freezing in Meat.—Mal :an describes a method of detecting freezing meat by microscopic examination of the lood of the meat. A drop of the blood is ex ressed from the suspected meat upon a glass ide, covered with a thin glass, and examined s soon as possible to preclude solidification. he juice of fresh meat shows numerous red orpuscles of normal color and shape floating 1 a nearly colorless serum. But the corpus les of meat which has been frozen are more ? less distorted in form and are completely ,ecolorized, while the surrounding fluid is rela ively dark in color. On placing a fragment of uch meat in a test tube, containing some water, he liquid becomes colored more rapidly and ntensely than in the case of fresh meat.