EVERYDAY ACTUALITIES.—NO. XX.
ILLUSTRATED WITH PEN AND GRAVER.
BY C. T. HINCKLEY.
PRESERVATION OF FOOD.
THE various organic substances furnished by the animal and vegetable kingdoms, which constitute the food of man, are, from the nature of their chemical structure, liable to change and decay; they are also irregular in their supply; hence arises the necessity of storing up the abundance of one season to meet the deficiencies of another. The art of preserving food as much as possible in its original state is therefore of great importance; it has been improved by gradual steps, depending, in great measure, as in so many other cases, on chemical discovery and the diffusion of chemical knowledge among persons engaged in the useful arts; so that, at the present time, the deprivations suffered by our forefathers may be prevented; the commonest articles of food may be enjoyed at all seasons; and even the delicious fruits of our gardens may be made to contribute to our health and refreshment at a season when the trees which produced them are covered with snow. The mariner, too, is not now necessarily confined to salt meats; he may, on the longest voyage, and in the severest clime, as easily enjoy fresh meat and vegetables as when he is in port.
The necessity for adopting means for the preservation of articles of food arises from the complicated structure of organic compounds, and their tendency to resolve themselves into simpler or inorganic compounds. Although the comprehensive history of the animal and vegetable kingdoms is written with a very brief alphabet; although the elements which enter into the composition of organic bodies are only carbon, hydrogen, and oxygen—often, but not always, nitrogen—and occasionally minute portions of sulphur and phosphorus; yet their extraordinary powers of combination are such that there appears to be no limit to the number of definite substances which they are capable of producing, each substance having a character peculiar to itself, and often a crystalline form. It is very different with the fifty-eight other members of the list of elements; the compounds which they assist in forming are inorganic, and they are formed by the union of pairs of elements, or pairs of binary compounds.
It is a consequence of this complicated structure that organic compounds are unstable in their character, and liable to decomposition, or, in other words, to resolve themselves into simpler compounds. An inorganic substance, on the contrary, however complex its formula may appear, is actually built up of binary compounds, the simplest that can be formed. But in the organic substance the carbon and hydrogen have a strong tendency to form carbonic acid; the hydrogen and oxygen to form water; the hydrogen and nitrogen to form ammonia; or, the hydrogen and the sulphur to form sulphuretted hydrogen, &c. In popular language, these changes are expressed by such terms as decay and putrefaction. Liebig, however, has given precision to them by limiting the term decay to the decomposition of moist organic matter freely exposed to the air, the oxygen of which gradually burns and destroys it without sensible elevation of temperature.[1] The term putrefaction is limited to changes which occur in and beneath the surface of water, the effect being a mere transposition of elements or metamorphosis of the organic body.[2] The conversion of sugar into alcohol and carbonic acid is a simple illustration of the term. The contact of oxygen is, however, first necessary to the change, which, when once begun, is continued without the aid of any other external substance, except perhaps water, or its elements. Every instance of putrefaction begins with decay; and if the decay, or its cause, viz., the absorption of oxygen, be prevented, no putrefaction occurs. In short, if the access of oxygen be prevented, there is no decay; if the access of water be prevented, there is no putrefaction. The exclusion of air and moisture forms the basis of some of the best methods of preserving food.
There are certain substances named Antiseptics (from ἀντὶ, against, and σήπομαι, to putrefy), from their property (exerted, however, very unequally) of preventing the putrefaction of organic substances. Thus, alcohol, and common salt in certain proportions, check all putrefaction and all the processes of fermentation by depriving the putrefying body of water. Nitre, vinegar, spices, and sugar are also antiseptics. The antiseptic effect of a very low temperature is caused by the solidification of the water and other juices, which, in their usual fluid state, allow the molecules to move freely on one another.
We will first notice the various methods of preserving animal food. These are: 1, by drying; 2, by cold; 3, by salting and by sugar; 4, by smoking; 5, by vinegar; 6, by parboiling and excluding air; 7, by potting; 8, by alcohol.