Page:Popular Science Monthly Volume 40.djvu/790

768 to be in it, and it will so decrease the numbers of the other bacteria that the milk will keep sweet for a long time.

All methods of sterilization that are in use in this country have the disadvantage of giving to the milk the taste which is peculiar to boiled milk, and also of rendering it less easily absorbed by the body. In France and Germany a method has been adopted which accomplishes the purpose without injuring the taste of the milk. Machines are in use in Paris and some other cities which will heat great quantities of milk to a temperature of about 155° Fahr. for a few minutes, and then cool it rapidly to a low temperature. The method has been called the pasteurization of milk. It does not kill all the bacteria, but it does destroy so many of them that it greatly increases the keeping properties of the milk. Moreover, it almost entirely destroys the danger from disease-germs in milk, since nearly all forms likely to occur in milk are killed by this temperature. The advantage of this method is that the temperature of 155° Fahr. does not give to the milk the taste of boiled milk, which most people find unpleasant, and does not render the milk difficult of digestion. These pasteurizing machines have not yet been introduced into this country, and the opportunity exists for some one to develop a thriving business by furnishing pasteurized milk in our large cities. A little experience with its superior keeping properties, and a little knowledge of its greater wholesomeness, would soon create a demand for it in America as it has already done in the larger cities of France and Germany.

—If bacteria are the enemies of the milkman, they are the allies of the butter and cheese maker. The last few years have shown us that butter owes at least its flavor to bacteria growth in the cream. Butter is made by allowing the cream to separate from the milk by means of its less specific gravity, and then by shaking the cream vigorously until the butter collects in lumps. Now, it has been for a long time recognized that it is a difficult matter to churn sweet cream. It may be shaken for a long time without the separation of the butter, and a smaller amount of butter can be obtained from it than from cream that has been allowed to sour or "ripen" for a time before churning. This, at all events, is true of cream which is separated from the milk by the ordinary method of setting, though it seems less true of cream separated by means of a centrifugal machine. It has also been generally recognized that the butter made from sweet cream lacks the delicate flavor or aroma which is such an important factor in a first-class butter. Sweet-cream butter has a flat, creamy taste, which is not generally desired.

For these reasons butter-makers have learned not to churn cream when fresh, but to allow it to stand awhile and sour, or