768 THE POPULAR SCIENCE MONTHLY. 



to be in it, and it will so decrease tlie numbers of the other bac- 

 teria 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 ab- 

 sorbed 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 pas- 

 teurizing machines have not yet been introduced into this coun- 

 try, 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 de- 

 mand for it in America as it has already done in the larger cities 

 of France and Germany. 



Butter. — 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 impor- 

 tant 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 



