BUTTER-MAKING 241 



the milk instead of taking some of the mixed milk. If the 

 benefit of the selection is to be realized, the milk should be 

 skimmed separately and handled in clean utensils. This in- 

 volves a great deal of extra work. Moreover, the fat in the 

 whole milk does not interfere with the growth of the bacteria. 

 In the cream the bacteria have to grow in the presence of much 

 greater quantities of fat. The fat, however, cloys the sense of 

 taste and makes it somewhat more difficult to judge the quality 

 of the flavor. 



" In pasteurizing milk for starters it is best to apply the heat 

 for thirty to sixty minutes. A temperature of 150 F. kills all 

 the sporeless bacteria. Higher temperatures, up to 212 F., do 

 not kill the spores, but they are so weakened by the higher heat 

 that they germinate more slowly and their harmful effect is re- 

 tarded. This fact, and the results of experience, indicate a 

 temperature of about 185 to 200 F. as best. The heating and 

 cooling can be done in cans immersed in water. Stirring hastens 

 the process, but is not necessary when the heating surface is 

 not hotter than about 200 F. Where the heating is done by 

 steam, stirring is necessary to prevent scorching. Starter cans 

 are a great convenience (see Fig. 48). 



" The building up of a starter consists in adding a culture to a 

 quantity of pasteurized milk and ripening it. Then it is in- 

 oculated into a still larger quantity of milk and so on until the 

 desired amount is obtained. The best results are obtained when 

 the quantity of milk used for a culture is such that it is ripened 

 in forty-eight hours or less; twenty-four hours is still better. 

 When the fermentation has once developed in milk, it grows more 

 vigorously and gives the best results when the ripening period 

 is not over twenty-four hours. When the quantity of milk in- 

 oculated is so large that it takes more than twenty-four hours 

 to ripen, the spores that withstood the pasteurization and the 

 bacteria that may accidentally get in have a better chance to 

 develop. Pasteurized milk, if kept long enough, will ferment 



