344 MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



pasteurized and ripened with a pure culture of Bact. lactis acidi, has 

 the best keeping qualities. It is asserted from very limited data that 

 if fresh, sweet, clean cream is pasteurized, the butter will have better 

 keeping qualities than when made from the same cream pasteurized 

 and ripened with a pure culture. If this is true, it is evidence that not 

 only the bacteria other than Bact. lactis acidi are harmful, but that 

 this organism, that has been considered without influence on the keep- 

 ing quality, must be classed as one of the factors in the decomposition of 

 butter. 



It has been shown that the bacterial content of the water used for 

 the washing of the butter has an influence on the keeping quality. If 

 the water is of surface origin and contains the bacteria peculiar to these 

 types of waters, its influence may be marked and some method of treat- 

 ment must be followed. Filtering or heating the water has been resorted 

 to, the latter with marked success. A pure water will contain so few 

 bacteria that they will not exert any noticeable influence on the keeping 

 quality of the butter. 



Storage temperature also has a marked influence on the deterioration 

 changes in butter. Modern butter-storage rooms are kept below 

 o F.; the butter is quite unchanged on removal from storage, but 

 deteriorates much more rapidly than would have been true at the same 

 temperature before storage. Another factor that is of influence in the 

 keeping of butter is the amount of salt used. In salted butter, the con- 

 tained water is a concentrated brine; in such a medium most forms of 

 bacteria are unable to grow. Small packages deteriorate more rapidly 

 than large ones, because the proportion of the mass of butter exposed to 

 the air is relatively greater. Exposure to light is also claimed to exert 

 a harmful influence. Antiseptic substances such as borax and boric acid 

 have a marked effect on the deterioration changes. The New Zealand 

 and Australian butter exported to the English markets is treated with 

 preservatives. 



A large amount of experimental work has been done in order to 

 determine the effect of specific organisms on the keeping quality of butter. 

 The results obtained have not been definite and it is not certain that the 

 organisms employed are constantly concerned in the deterioration 

 changes. It is very probable that both bacteria and molds exert an 

 influence. The chemical changes that take place in the spoiling of butter 

 are no better known than are the causal factors. It has been asserted 



