RELATION OF MICROORGANISMS TO BUTTER 483 



DECOMPOSITION PROCESSES IN BUTTER 



Butter is a finished product at the time it is removed from the mod- 

 ern churn and all subsequent changes are likely to cause more or less 

 deterioration. The specific causes of these changes are not well known 

 but it is very evident from a study of the conditions that favor or retard 

 the appearance of the flavors, characterizing these changes, that biolog- 

 ical factors are concerned. When raw cream is used, sweet-cream butter 

 has very poor keeping qualities. As the proportion of acid-forming 

 bacteria in butter is increased, either by the fermentation of the cream, 

 by the addition of pure cultures, and through the use of the latter in 

 connection with pasteurization, the keeping qualities are enhanced. 

 Of the butter made from ripened cream, that prepared from cream, 

 handled in a clean manner, and thoroughly pasteurized and ripened with 

 a pure culture of Bact. lactis acidi, has the best keeping quality. If. 

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

 keeping quality than when made from the same cream pasteurized and 

 ripened with a pure culture. This is evidence that not only the bac- 

 teria other than Bact. lactis acidi are harmful, but that this organism, 

 that has usually been considered without influence on the keeping 

 quality, must be classed as one of the factors hi 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 re- 

 sorted 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 

 oF.; the butter deteriorates slowly during storage at these tempera- 

 tures, but on removal undergoes change much more rapidly than 

 would have been true before storage. Another factor that is of influence 

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

 contained water is a concentrated brine; in such a medium most forms 

 of bacteria are unable to grow. Small packages deteriorate more 



