DAIRYING 



the cause of some defects in the butter. If, on the other hand, 

 the skim milk is very clean, heating to a temperature of 150 de- 

 grees Fahrenheit is sufficient to kill all the bacteria in it. Re- 

 peated heating to a high temperature will aid in reducing the 

 number of bacteria and of spores. Some of the spores will sur- 

 vive one heating. This is especially true of the putrifactive 

 bacteria which may be the cause of serious defects in butter if 

 they are not held in check. 



532. When the foundation skim milk (or milk free from 

 weeds) is made as nearly germ-free as possible by heating, it is 

 covered with an over-lapping cover and left to cool. 



Cooling the Skim Milk. The cooling is done in any conveni- 

 ent way, either by allowing cold water to run around the hot 

 can or by setting the can in a refrigerator ; stirring while cooling 

 will hasten matters, and the more quickly the cooling is done 



Plate 1 Covered Milk Bottle for Propagating Starter 

 the better it will be for the starter, as sudden cooling checks the 

 development of the spores which may have lived through the 

 heating. 



When the skim milk has cooled to 80 degrees Fahrenheit, 

 the pure culture is added to it. This pure culture may be a small 

 quantity of some sour milk which has been selected and allowed 



