Bacteria and Butter Making. 155 



rooms and in storage at ordinary temperatures deterior- 

 ation goes on more rapidly than would have been the 

 case when the butter was fresh. At the temperature of 

 an ordinary refrigerator the changes go on much more 

 rapidly. This fact has often been looked on as indicat- 

 ing that the factors causing the changes are biological 

 ones. The influence of temperature in accelerating the 

 changes would be the same if no biological factor were 

 active. 



That biological factors are of importance is indicated 

 by the fact that the keeping quality of the product is 

 profoundly affected by the quality of the cream. But- 

 ter made from sweet, fresh cream, that has been thor- 

 oughly pasteurized, has the best keeping quality, while 

 butter made from such cream, but not pasteurized, has 

 the poorest keeping quality, especially when no salt is 

 added. Every process by which the desirable lactic bac- 

 teria are increased in proportion to other kinds has a 

 marked effect in enhancing the keeping quality of the 

 butter. Thus, the use of pure cultures in raw cream, and 

 pasteurization together with the pure cultures, have a 

 marked beneficial effect. 



The addition of preservatives exerts an effect on keep- 

 ing quality. Borax is the chemical most frequently em- 

 ployed for this purpose. Its use is allowed in Australia 

 and New Zealand in butter that is shipped to England, 

 but the use of all preservatives is forbidden in the 

 United States. 



The size of the package also has an effect on the keep- 

 ing quality; the smaller the package, the greater is the 

 surface exposed to the air and the more rapidly the but- 

 ter deteriorates. Butter used in the United States Navy 

 is packed in hermetically sealed cans so as to exclude the 

 air as far as possible. 



