butter-fat had a tendency to become rancid before many months. But improvements are constantly being made and milk powders of every degree of richness bid fair to take the place of fresh milk on board ships and in other places where milk must be kept a long time before being used.
In many new food preparations of value, milk powder is filling a long-felt want. Dissolved in 8 or 9 times as much water, milk powder makes a liquid almost identical with pasteurized fresh milk.
It has already been mentioned under the chapter on "Cream" and under "Ice Cream" how skim milk powder and unsalted butter, emulsified in a suitable amount of water or milk, make an excellent material for ice cream.
CONDENSED AND EVAPORATED MILK
Milk cannot be boiled down in a common open kettle or steam boiler without being scorched. Evaporating or condensing is therefore usually done in a vacuum pan at a low temperature. Condensed to one-third of its volume and excluded from the air by canning, milk will keep well for months, and has many uses as a substitute for fresh milk. Often sugar is added as a preservative, and where sugar would be added anyway, as in coffee, ice cream, etc., this is unobjectionable.
For purposes where sugar is not wanted, unsweetened condensed or evaporated milk is on the market, so carefully made that the taste of the original milk is hardly changed at all by the process. When water is added in the proportion of two parts of water to one of the evaporated milk, the fluid obtained excels even that from milk powder in its resemblance to fresh milk.
