Milk should be kept in a cool, clean place, free from odors, in a perfectly clean, covered vessel of suitable material - earthen, porcelain, glass or tin. The sanitary condition of milk is of the utmost importance as it easily becomes a medium for the distribution of disease germs, readily absorbs odors, flavors, and impurities, and undergoes fermentation.

To clean the vessels in which milk is kept, rinse out first with cold water, then wash with hot water and soap, adding a little borax or washing soda to the water. Scald well, rinse with clear water and let the bottles cool. To sterilize the vessels, fill with cold water and heat to the boiling point, boiling 20 minutes. Let vessels stand in the sun 2 to 3 hours when possible.

Because of the danger from disease germs in impure milk or of the development of lactic acid bacteria in milk, it is often necessary to apply heat to kill all bacteria in order to make it safe for use as food or to keep it for even a short time.

Pasteurization is the most desirable method of preserving milk, the disease germs are destroyed, the milk will keep sweet from one to four days and the digestibility of the milk is but little affected.

Sterilization is the most effective method of preserving milk, as both bacteria and their spores are destroyed but the taste of the milk is altered by sterilization, the emulsion of fat is destroyed, the lact-albumen is coagulated and the casein is rendered less easy of digestion.

Cream separates from the heavier liquid in the milk by the force of gravity when standing or by centrifugal force in the separator - this separation is more complete when the milk is a few days old. The older cream also whips more easily.

Acids cause the casein in the milk to curdle. This action takes place when lactic acid is produced in sour milk or by the addition of vinegar, lemon juice, or tartaric acid to milk.

Milk is coagulated by the action of rennin, a ferment of the gastric juice, especially abundant in the infant's stomach. This action takes place if the milk has not been heated over 120 degrees. Rennet is rennin artificially prepared for commercial use from the fourth part of the stomach of a calf, in the form of tablets by the addition of milk sugar.

Milk is sometimes altered in order more nearly to resemble human milk. For this purpose the protein must be decreased, the carbohydrate increased, the milk given an alkalin reaction and the fat retained in relatively the same proportion. This is called "Modified" milk.

Cooking of Milk

When milk is heated the albumen becomes coagulated at 158 degrees and the casinogen is changed. A scum consisting of coagulated lact-albumen, some dried casein, lime salts, and fat, forms on the bottom and sides of the kettle and over the top of the milk.

The taste of milk changes as it is heated and it is easily scorched, growing darker in color. Because of the danger of scorching milk and of the effect that too high a degree of heat has on the albumen, making it more difficult of digestion, milk should be heated in a perfectly smooth vessel and whenever possible it should be heated over hot water in a double boiler. When a skin forms on top with bubbles around the side, milk is said to be scalded and is hot enough for most purposes in cooking.

All utensils which have held milk should be rinsed in cold water before being put in hot. Salt should not be added to milk when it is to be heated for some time, for it may cause milk to curdle.

Reasons for Heating Milk

Milk is heated for the purpose of preservation; to introduce heat into the body; and to combine it with other foods. Milk forms the basis of many cooked dishes, for example cocoa, cream soups, white sauce, custards, and other puddings. Either whole milk or skimmed milk may be used for cooking. In many recipes water may be substituted for the milk, but one must then take into consideration the reduction in food value of the dish.

Sterilized Milk

When it is necessary to preserve milk in order that it may be kept for some time, the temperature should be raised to the boiling point and kept there 10 to 20 minutes. The milk should then be strained and quickly cooled. Milk sterilized in this way and put into clean utensils, carefully covered, can be kept for many days.

Pasteurized Milk

Fill sterile bottles or jars full of milk, cork them with cotton that has been baked in the oven and place on rings in a deep pan. Fill the pan with cold water so that the water may be as high outside the jars as the milk is inside, place the pan over the fire and heat until small bubbles appear around the top of the milk (158 degrees F), and keep at this temperature 20 to 30 minutes, then reduce temperature as quickly as possible.

Rennet or Junket

1 quart milk 2-tablespoons sugar

1 tablespoon rennet or 1 tablet (dissolved in 1/4 cup lukewarm water)

Heat the milk until lukewarm, add sugar, and stir until sugar is dissolved. Add rennet, stir slightly, pour into glass dish, and leave in a warm place until firm. Sprinkle with nutmeg and chill. Serve with sugar and cream. Do not jar. Rennet should be handled carefully, so as not to break mass, as curd and whey separate. Rennet may be improved by addition of such fresh fruits as strawberries, raspberries, etc. Serves 8.