WHAT IS CREAM RIPENING? 185 



enzymes capable of producing chemical changes in the milk 

 entirely independent of the agency of bacteria. There is no 

 proof that these enzymes may not have a part to play in the 

 cream ripening, and the changes which occur during this 

 process may be in part due to their agency. On the other 

 hand, there is no proof that they can produce any consider- 

 able action in such a short time, since it is their nature to 

 act quite slowly. They certainly do produce changes in milk 

 after a time, and also in cheese which is ripened slowly for 

 several weeks, but their action is not sufficiently rapid to lead 

 us to believe that they can produce much effect upon cream 

 ripening for a few hours. At all events the prodigious 

 growth of bacteria indicated by the figures above given is 

 such as to show, beyond question, that they must produce the 

 most profound changes in the cream, and that the chief 

 phenomena of cream ripening must be due to the action of 

 bacteria rather than the action of milk enzymes. Moreover, 

 the changes which occur in the cream are exactly such as we 

 have learned are produced by the growth of bacteria. The 

 cream becomes acid from the development of lactic acid; it 

 also becomes thick and acquires a peculiar odor, indicating 

 a variety of decomposition products. Such changes are the 

 very ones found to be produced by the growth of bacteria, 

 and thus the general nature of the changes during cream 

 ripening is quite in accordance with the belief that bacteria 

 are the primary agents in the change. 



Why Ripening Affects the Yield of Butter. There is no 

 difficulty in understanding how the growth of the bacteria 

 increases the yield of butter. A microscopic study seems to 

 show that churning is a process of shaking the fat drops into 

 contact with each other, causing them to adhere in larger and 

 larger lumps. This process can be understood from the ex- 

 amination of Fig. 25, which is taken from cream at different 

 intervals in churning. When the lumps become large enough 

 to be removed from the liquid the churning is stopped, and 



