PRESERVATION OF FOODS
This subject is of ever-growing importance. The study of the preservation of foods has added much to the store of human knowledge. By this means it is possible for those living in districts remote from the supply, those who cannot afford to buy them fresh, and those who have no cellars in which to store them, to have vegetables and fruits at all seasons of the year.
Nutritious foods can be prepared in such small bulk and of such excellent keeping quality that explorers, whether to the arctics or the tropics, can be kept in first-class physical condition, enabled to withstand fatigue, and be removed to long distances from the base of supplies without great hardship.
The decomposition of food is occasioned by bacterial action. Air is necessary to the growth of bacteria. If the air is excluded the ordinary bacteria are prevented from exerting their deleterious action.
Heat, as in canning, prevents the formation of bacterial products.
Cold, in refrigeration, by inhibiting bacterial activity is also an excellent preservative.
Other methods in use are smoking, salting, drying, sterilizing, various antiseptics, and the exclusion of the air, as in coating eggs or meat for transportation to other countries.
Eggs are preserved for a long period by excluding the air, which otherwise penetrates the shell. A solution of water glass (silicate of sodium), dry oats or salt are used for this purpose.
All food intended for preservation should be kept in a clean, cool, dry, dark place.
Drying, cooking, and sealing from the air will preserve some meats and fruits, while others require such preservatives as sugar, vinegar, and salt. The preservative in cider vinegar is acetic acid, in wine vinegar tartaric acid.