BUTTER-MAKING 313 



the buttermilk from a churning in which the butter has been 

 of excellent flavor. A skim-milk starter is usually preferred, 

 because it will contain the desirable bacteria in a larger pro- 

 portion than either of the others. 



Another kind of starter is called commercial starter. It con- 

 sists of a preparation containing the desired kind of bacteria. 

 The preparation is made in special laboratories where every- 

 thing is favorable to producing the right kind of bacteria. In 

 liquid starters the bacteria are put up in sterilized bouillon, or 

 milk. In powder starters the bacteria are contained in a 

 powder of milk-sugar. Both kinds are good while fresh, but 

 the liquid starter deteriorates more quickly than the powder. 

 Commercial starters are used mostly in creameries, and full 

 directions for use come with each package. 



Cream and milk are pasteurized by heating to a tempera- 

 ture between 140° F. and 212° F., usually 160° F., for five 

 minutes. Or temperatures of 155° F. for ten minutes or 

 150° F. for fifteen minutes or 140° F. for thirty minutes 

 may be used. These temperatures kill practically all the 

 germs commonly found in milk or cream. Having killed the 

 germs of all kinds, the butter-maker can introduce by means 

 of the starter just the kind of germs desired. Some of the 

 advantages claimed for pasteurization are: (1) A more uni- 

 form quality of butter can be made; (2) many of the bad 

 taints in the milk or cream are removed; (3) most of the 

 germs are destroyed, and therefore the danger from disease 

 germs, like scarlet fever, typhoid fever, etc., is lessened; 

 (4) the keeping quality of the butter so made is increased. 

 Pasteurization cannot be properly done without expensive 

 machinery, and it is little used except by creameries and 

 large milk plants. 



