138 Dairy Bacteriology. 



than milk, yet the changes due to bacterial action are slower 

 so that it usually spoils sooner than cream. For this same 

 reason, cream will sour sooner when it remains on the milk 

 than it will if it is separated as soon as possible. This fact 

 indicates the necessity of early creaming, so as to increase 

 the keeping quality of the product, and is another argu- 

 ment in favor of the separator process. 



Ripening Of cream. If cream is allowed to remain at 

 ordinary temperatures, it undergoes a series of fermenta- 

 tion changes that are exceedingly complex in character, the 

 result of which is to produce in butter made from the 

 same the characteristic flavor and aroma that are so well 

 known in this article. We are so accustomed to the de- 

 velopment of these flavors in butter that they are not gen- 

 erally recognized as being intimately associated with bac- 

 terial activity unless compared with butter made from per- 

 fectly fresh cream. Sweet-cream butter lacks the aromatic 

 principle that is prominent in the ripened product, and 

 while the flavor is delicate, it is relatively unpronounced. 



In the primitive method of butter-making, where the but- 

 ter was made on the farm, the ripening of cream became a 

 necessity in order that sufficient material might be accumu- 

 lated to make a churning. The ripening change occurred 

 spontaneously without the exercise of any especial control. 

 With the development of the creamery system came the 

 necessity of exercising a control of this process, and there- 

 fore the modern butter-maker must understand the prin- 

 ciples which are involved in this series of complex changes 

 that largely give to his product its commercial value. 



In these ripening changes three different factors are to 

 be taken into consideration: the development of acid, flavor 

 and aroma. Much confusion in the past has arisen from a 



