PASTEURIZATION OF MILK. 1 87 



in a continuous stream at the bottom of the machine, 

 and heat it by revolving the milk with suitable discs 

 or paddles against a steam-heated surface, and deliver 

 it at the top, are known as continuous. This class is 

 suited for creamery practice, or for handling a large 

 quantity of milk in a short time. The other class 

 heats a limited quantity of milk at a time, and is suit- 

 able for small dairies, as the results are got by adopt- 

 ing lower temperatures for a longer time. Time and 

 temperature are two important factors in deciding the 

 effect on germ life. The object of pasteurization is to 

 kill most of the germs or bacteria in milk or cream by 

 means of heat. 



As regards the method of driving, two classes of 

 pasteurizers are found on the market belt- driven and 

 turbine, or steam applied directly. The former have 

 proved more satisfactory, as it is more difficult to 

 regulate the temperature in turbine pasteurizers. 



The chief advantages of pasteurization for butter- 

 making are : 



1. It destroys the germ life of milk or cream to a 

 large extent, especially when heated to 185 degrees, 

 which is the temperature to be recommended. A 

 clean seed-bed is thus prepared for the proper germs 

 to give fine flavor to the butter. 



2. It tends to eliminate stable and feed flavors from 

 milk and cream, especially with milk in winter. 



3. The ripening of the cream may be controlled by 

 the buttermaker, which is the most important point in 

 making good butter. 



4. In case of bad-flavored milk, it enables the but- 



