FOOD PRESERVATION.
The art of preserving food in a fit condition for human consumption has probably occupied men's minds from very early times ; but it is only within quite recent years that the subject has attracted scientific attention, and has grown from a domestic to a commercial scale. The curing of bacon, the preserving of fruit, and the making of pickles, are all strictly included under the heading of this article ; but the object here will be to avoid such matters as may be found in any handbook of cookery, and to confine attention to the processes which have been devised and executed on a wholesale basis, and which, collectively, exercise a most important influence upon the food-supply of the United Kingdom. For convenience of reference, the subject may be divided into the following heads :—Dairy Produce ; Fish ; Fruit, Grain, and Vegetables ; and Meat.
Dairy heading embraces eggs, milk, and butter.
EGGS.—The best method of preserving eggs in a fresh state for an indefinite period is by the exclusion of air and moisture, and the application of an antiseptic. The eggs, as taken from the nest, are coated with butter (or other sweet animal fat) containing 2-3 per cent. of salicylic acid, applied by a little wool. Each egg is then placed in a box containing sawdust, which has been dried, even to scorching, then poured into the box, and allowed to cool perfectly. The eggs should not touch, and should be quite covered with the sawdust, and the box should be nearly air-tight. Ordinary methods are:—(l) Scalding ; (2) short immersion in silicate of soda.
Mn.x.—Milk may be kept sweet in the pans for a short time by the addition of a little borax. For its preservation for lengthened periods, several processes are in vogue.
Condensed Milk.—The compound known as " condensed milk" is an illustration of the application of the drying or desiccation theory, accomplished by evaporating the excess of moisture, adding sugar, and packing in hermetically sealed vessels. The milk, as received from the dairies, is placed in vessels having a capacity of 750-1000 gal., where it is maintained at a slightly raised temperature,
by means of steam-heat, and undergoes evaporation in vacuo. The duration of the process varies from 2 to 5+ hours. Refined sugar in powder is added in the proportion of about + by weight of the total condensed product ; and when the mass assumes the consistency of thick honey, it is put into tin boxes, and hermetically sealed. The proper conduct of the operation is by no means easy. There is much danger of a decomposition of the casein in the presence of heat and sugar, especially if the milk has been in the slightest degree " turned " ; also much of the fatty constituents will distil with the water, if the temperature is allowed to exceed 38° (100° F.). Attention has recently been called, in the Analyst and elsewhere, to the fact that these unfavourable conditions do frequently come into play, and that the loss of nitrogenous matter by decomposition, and the loss of equally important fat, partly volatilized, partly decomposed, so generally sustained by condensed milk, render it unfit to replace new milk in the nursery. Small quantities are prepared (almost solely for the American market) without the addition of sugar, in which case the evil is lessened ; but the product does not keep so well.
Mabrun's process.—This simple process was probably the foundation of the preceding. The milk is warmed at a moderate temperature, in a tin vessel, furnished with a leaden tube, for the expulsion of the air. The tube is then compressed, and the orifice is soldered up. After 6 months' keeping, the milk is as good as new. The process received a prize of 1500 fr. from the French Academy of Sciences.
fforfies process.—In 1 gal. of milk at 55°-60° (130°-140° F.), is dissolved 1 lb. of gelatine ; the mixture is left to cool to a jelly, when it is cut into slices, and dried. The compound is used to gelatinize more milk, and this is repeated till the gelatine is in the proportion of 1 lb. to 10 gal. of milk.