Articles of food (see Aliment) are very complex in their chemical constitution, and are exceedingly prone to return to the simpler and more stable compounds called inorganic. (See Eremacausis, and Fermentation.) The principal promoters of such decomposition are moisture, oxygen, and certain minute organisms. The art of preserving food in a manner to retain its flavor and natural qualities is chiefly modern, as the ancients only understood rude methods, the principal of which were drying and salting. - Fruits may be preserved in six principal ways: 1. In the natural state. Most fruits, such as berries, peaches, and plums, can be kept in the natural state only a short time, except when frozen or near the freezing point. In a good refrigerator, kept cool by a circulation of cold dry air, these more perishable fruits may be kept in a natural state for many days. This is also the best method of preserving melons and oranges. Apples and pears may be kept in cool dry apartments put up in barrels. Well selected apples, enclosed in compact tissue paper and carefully packed in barrels, may be preserved for nearly or quite a year.
Pulverized charcoal dust is a very good material in which to pack the fruit. 2. Boiling and adding sirup, or the method of making what are commonly called " preserves." These are in three forms: whole or sliced fruit, jam, and jelly. When preserved whole or sliced, they may be boiled in a sirup made of two pounds of sugar to one of water, the quantity of sirup varying in particular cases, but as a general rule being about once and a half the volume of fruit. They may also be heated alone with sugar, or packed in sugar without heating. Their keeping properties are of course increased by the coagulation of the albumen by heat and the destruction of ferments. Jams are made by reducing the fruit to a pulp (sometimes removing the skin and the seed, but often allowing them to remain in the mass for flavoring), and conducting the subsequent processes on the same principles as for whole fruit, excepting that jam is always cooked, and should as a rule contain rather more sugar. Jellies are made by boiling the fruit in a small portion of water, straining, and adding sugar, usually in quantities equal to the juice.
All these preserves are better kept in glass jars, because they allow inspection to detect incipient fermentation, which may be arrested by immediate reboiling and reduction of mass by evaporation. The jars may be covered with air-tight caps fitted with gum elastic, or, what is quite as good, with white paper glazed with white of egg. A tough leathery mould after a time usually forms upon the surface of the preserves, which is considered by good housekeepers as a protection against fermentation. 3. Boiling and sealing in air-tight cans, with little or no sugar added, the principle of preservation being the destruction and exclusion of ferments, and also the exclusion of air. The jars are sealed with screw and gum elastic covers, or with solder, while they are filled with the fruit and steam. When the steam condenses, a vacuum remains.
This method is carried on to a great extent in the principal fruit-growing districts, millions of cans being sent annually to the great markets. 4. Fruits are dried in various ways. Berries are simply exposed, on boards or coarse cotton cloth or gauze, to the heat of the sun, or in the shade to a current of warm dry air. Apples, pears, and peaches may be cut into pieces and dried in the same way. When they reach the requisite degree of dryness, indicated by a tough condition well known to the experienced housekeeper or fruiterer, the juice has become sufficiently inspissated to resist the action of ferments; and they may be protected from mould for many months by keeping them in a cool dry atmosphere. 5. Fruits may be frozen and their qualities retained for a long time in this condition, and in the absence of good refrigerating apparatus the crude process of freezing may be resorted to; but keeping them in refrigerators at or a little above a temperature of 32° F., and considerably above the freezing point of the juices, is to be preferred.
South American and West Indian fruits, and those raised in the southern states and California, are now commonly sent north in refrigerators. 6. By immersion in strong brine and subsequent preserving in vinegar, or by primary immersion in vinegar, alcohol, or brandy. The method with brine and vinegar is known as pickling, and is generally employed with those articles which are termed vegetables instead of fruits, although peaches, plums, cherries, and berries are often preserved in vinegar. (See Pickles.) - Animal food may be preserved by several methods, of which the following are the chief: 1. By immersion in a solution of common salt, to which a small portion of saltpetre is often added, called brine. This acts by abstracting the juices from the meat, and also by preventing the development of organic germs and lessening the tendency to molecular change. 2. By packing the meat in salt, whereby the juices are abstracted; then removing it and allowing it to dry, and packing in boxes or barrels. 3. By rubbing with common salt, and drying in the sun, or in a current of dry air. 4. By salting and smoking, by which means, in addition to the abstraction of moisture by the salt, pyroligneous acid and creosote act upon the flesh, causing it to contract and harden, and also preventing the development of mould. 5. By drying in a current of warm air at about 140° F., or in the open air at even a lower temperature, when the air is comparatively free from ferment germs.
The latter method has long been practised, especially for "jerked beef," throughout Spanish America and in the warmer parts of the United States. This dried meat may be reduced to powder, packed in air-tight cans, and preserved for a long time. When mixed with fat, it forms the pemmican used in arctio voyages. Spices and dried berries are sometimes added to it. (See Pemmican.) 6. By cooking, to coagulate the albumen, and then enclosing in air-tight cans with exclusion of air, after the manner of canning fruits. 7. By cooking and pickling in vinegar, a common method of preserving oysters, lobsters, and fish. Cooking and seasoning, and covering with melted lard or olive oil, is a common method of preserving very small fish. (See Sardine.) 8. By refrigeration and freezing, a process now extensively practised in all civilized countries, fresh beef being carried from South America to all parts of the world, and in the United States from the Pacific to the Atlantic coast. The trade in frozen herring from the coast of Maine and the bay of Fundy has recently grown immensely. (See Freezing-, Artificial.) Milk is preserved by evaporating it to the consistency of thick sirup, in which condition it resists the motion of ferments; or by reducing it to a solid state, and adding a portion of salt. (See Milk.) There are several special methods, having particular names, which might be classified under some of the above heads.
Appert's method, introduced in France about 1810, for which he received a prize of 12,000 francs from the board of arts and manufactures in Paris, and which was afterward patented in England and improved by Donkin, Hall, and Gamble, consists principally in cooking the meats at a temperature of about 240°, and sealing in air-tight jars. The process has been further improved by McOall and co., who add a small quantity of sulphite of soda (12 grains to every pound of meat), to absorb traces of oxygen which may have been left. Still another improvement is the application of entrance and exit tubes, the exhaustion of air through these by an air pump, and subsequently the passing through the can of nitrogen gas to remove all oxygen, and then of a small quantity of sulphurous acid, and after this of nitrogen; after which the can is hermetically sealed. The merit claimed for this process is that the meat may be preserved without cooking. The process of Prof. Morgan of Dublin consists in forcing into the aorta of the recently slaughtered animal, and thence throughout the capillary and venous system, a strong brine, containing a small portion of saltpetre, by which means the blood is forced out of the system at the same time that the meat is salted.
It may then be cut into pieces, and dried and smoked, or preserved in brine. One objection to this process is that it washes out nutritive material. By Dr. Endemann's process the meat is cut into thin slices and dried in a current of warm air not exceeding 140° F. It may then be ground into powder, kept in airtight cans, and used for making soup. M. Laujorrois has lately communicated to the French academy a method of preserving food by the use of fuchsine (aniline red, rosaniline, or magenta). A vessel containing a solution of gelatine treated with a minute quantity of fuchsine 11 months before, and open to the air ever since, was exhibited, and was found in a perfect state of preservation. %