DAIRYING 



starter as soon as possible. The spore-bearing bacteria do not 

 grow well in milk containing a large number of lactic acid bac- 

 teria. 



Making the Starter. 



530. The common method of making a starter as practiced 

 by butter makers is about as follows : For the foundation, or 

 soil in which to grow the bacteria, sweet skim milk* is selected 

 from the separator or gravity skimming when the cleanest milk 

 is being skimmed. This is pasteurized** by heating it in either 

 the modern starter-can or by setting a can of it into a larger 

 can or tank of hot water. While being heated, the milk is 

 stirred occasionally to prevent its burning onto the tin. The 

 temperature to which the milk is heated will depend somewhat 

 on its purity and cleanliness. When exceptionally clean, the 

 few bacteria which the milk may contain will be destroyed by 

 heating to 150 degrees Fahrenheit. 



This is a sufficiently high temperature to kill a large number 

 of the fully developed bacteria, but if the milk has been more or 

 less contaminated, by careless milking and dirty handling at the 

 farms, a large number of spores from the spore-making bacteria 

 will survive this temperature and make it necessary to heat the 

 milk higher. Heating to 185- degrees Fahrenheit for one-half 

 hour is the temperature usually recommended for preparing the 

 seed bed or foundation skim milk in which the pure culture of 

 bacteria is to be grown. 



531. Necessity of Thorough Heating. It is very essential 

 that the foundation skim milk should be nearly germ-free, as any 

 undesirable bacteria that may have been left alive in it after 

 heating will grow and multiply as fast as the desirable ones 

 whic^t have been added in the form of a pure cculture ; the pr,od- 

 ucts formed by the growth of these undesirable bacteria may be 



* Besides skim milk, whole milk, and thin cream, such milk product* 

 us unsweetened condensed milk and milk powder may be used for th 

 foundation material in starter making. 



.Sterilizing and Pasteurizing. The proper use of the words "steril- 

 izing" and "pasteurizing" is not understood by all butter makers. They 

 are likely to use either word as a name for heating milk to some temper- 

 ature near scalding. This is not correct, as each word has a meaning of 

 Us own and should indicate a different treatment of milk. 



