In pasteurizing milk it is heated to a temperature of 60° C. (140° F.) for a period of twenty minutes. This destroys the so-called pathogenic germs, yet does not destroy the ordinary milk ferments. It does not change its digestibility nor alter the taste or appearance.
All of the so-called pathogenic germs, such as tuberculosis, typhoid, dysentery and diphtheria, for example, are completely destroyed by pasteurization, but the ferments are not destroyed and the milk is in no way altered. This process may be accomplished on a large scale and thus furnish as safe milk for commercial consumption. Pasteurized milk should be rapidly cooled after heating, and if kept cool furnishes a clean, healthy milk entirely safe and satisfactory for infant food as well as for adults.
Pasteurization furnishes a purified milk but not a pure milk. It is undoubtedly the best means of preservation and may be considered as bearing the same relation to purification of milk as filtration bears to purification of water.
The use of formaldehyde, borax and boracic acid is as objectionable in artificial preservation of milk as in the preservation of meat and other foods and should not be tolerated.
Condensed Milk
Milk is condensed by removing some of the water. It is made either from skim or whole milk. It may be unsweetened or sweetened with cane sugar. Condensed and evaporated milk should contain a label stating the grade of milk used. Condensed and evaporated milk are poor in vitamin C.
Dry Milk
It has been found that by certain processes it is possible to dry milk, taking all the water out and leaving a powder. This may be accomplished and still retain most of the nutritive value of the milk. Vitamin fat soluble A and water soluble B remain practically the same, but water soluble C vitamin is diminished. Babies fed on dried milk will thrive, but orange juice or some other food containing antiscorbutic properties must be given to compensate for the loss of vitamin C. Dried milk provides an adequate supply to many parts of the country and to the cities, where it is difficult to obtain fresh milk.
Butter
Butter is produced by placing cream in a proper apparatus and agitating or churning it until the fat globules coalesce into lumps. These lumps are then taken out of the serum known as the buttermilk and the water and milk worked out until it becomes more or less solid. When butter has had the milk and water worked out of it the constituents should be in about the following proportions: Fat, 83.5%; curd, 1.0%; ash, 1.5%; milk sugar, 1.0%; water, 13.0%. By weight butter should never contain more than 16% of water and should contain at least 80% of fat.