BUTTER-MAKING 239 



" In practice two kinds of starters are used ; the commercial 

 and the natural. The commercial starters are pure cultures of 

 bacteria prepared by bacteriological methods. They are put up 

 in milk, milk-sugar, beef broth, and other substances. Those 

 in the dry form maintain their vitality longer. The milk cul- 

 tures show their age or ripeness by the coagulation of the milk. 

 They are sold in packages of one to several ounces and are a 

 staple commodity, like yeast. The creameries usually order 

 these cultures to be sent them periodically by mail. 



"There are two steps in the preparation of a commercial 

 culture for use in the creamery : The ' building up ' and the 

 'carrying on,' or propagation. Directions for these are sent 

 with the cultures. A great deal has been said and written about 

 the kind of milk that is best for starters. In the earlier days 

 many butter-makers preferred milk from fresh cows, or from 

 cows getting good feed. The period of lactation can have only 

 an indirect and unimportant effect on starters. The fitness of 

 milk for starters depends upon the number and kind of bacteria 

 that it contains. The fewer the numbers of bacteria, and espe- 

 cially of spores, the better the milk for starters. The presence of 

 a few lactic acid bacteria in milk that is to be pasteurized is not 

 a great defect because they are easily killed by pasteurization. 

 The butter-maker has not the means of knowing what kind of 

 bacteria the milk contains. A bacteriological analysis or a fer- 

 mentation test would show this, but the results would come so 

 late that they would not be applicable to the lot of milk that has 

 been examined. These methods are of value in finding which 

 patron's milk is best, but the quality of a patron's milk some- 

 times varies daily. The senses and judgment of the butter- 

 maker are the most practical guides. The sweetest and cleanest 

 milk is the best in the long run. 



"A natural starter is derived from a natural fermentation 

 of milk. A very important step in the preparation of such 

 starters is their selection. The most conspicuous characteristic 



