76 THE STORY OF GERM LIFE. 



is desired, and the cream is subjected to a process 

 known as "ripening" or "souring" before it is 

 churned. In ripening, the cream is simply al- 

 lowed to stand in a vat for a period varying 

 from twelve hours to two or three days, accord- 

 ing to circumstances. During this period certain 

 changes take place therein. The bacteria which 

 were in the cream originally, get an opportunity 

 to grow, and by the time the ripening is complete 

 they become extremely numerous. As a result, 

 the character of the cream changes just as the 

 milk is changed under similar circumstances. It 

 becomes somewhat soured; it becomes slightly 

 curdled, and acquires a peculiarly pleasant taste 

 and an aroma which was not present in the origi- 

 nal fresh cream. After this ripening the cream 

 is churned. It is during the ripening that the 

 bacteria produce their effect, for after the churn- 

 ing they are of less importance. Part of them 

 collect in the butter, part of them are washed off 

 from the butter in the buttermilk and the subse- 

 quent processes. Most of the bacteria that are 

 left in the butter soon die, not finding there a 

 favourable condition for growth ; some of them, 

 however, live and grow for some time and are 

 prominent agents in the changes by which butter 

 becomes rancid. The butter maker is concerned 

 with the ripening rather than with later processes. 

 The object of the ripening of cream is to render 

 it in a better condition for butter making. The 

 butter maker has learned by long experience that 

 ripened cream churns more rapidly than sweet 

 cream, and that he obtains a larger yield of butter 

 therefrom. The great object of the ripening, 

 however, is to develop in the butter the peculiar 

 flavour and aroma which is characteristic of the 



