GROWTH OF BACTERIA IN CREAM. IQI 



For the first few hours there is a gradual growth of bac- 

 teria, all species probably increasing somewhat in numbers. 

 The lactic bacteria are commonly few in numbers in the per- 

 fectly fresh cream, but these grow more rapidly than any 

 other species, and slowly increase in proportion until they 

 become as numerous as all of the other species put together. 

 After this the lactic bacteria grow more rapidly still; the 

 other species are gradually crowded into the background, 

 and either disappear entirely, or become relatively so few as 

 to play practically no part in the further cream ripening. 

 Fully ripened cream contains little besides lactic bacteria. 



It is evident, therefore, that the study of the growth of 

 bacteria in cream shows that the ripening of the cream is 

 divided into two distinct stages. The first period consists of 

 the first few hours after the cream is separated from the milk, 

 the exact number of hours depending chiefly upon the tem- 

 perature, but also upon the other conditions. During this 

 time there is a development of many different species. In all 

 cases the peptonizing bacteria increase in numbers, and the 

 same is true of most of the bacteria which were found in the 

 original cream. At the close of this first period of ripening, 

 although the lactic bacteria have become relatively more 

 abundant than at the outset, the peptonizing and the many 

 miscellaneous species have also increased rapidly and have 

 become very numerous. The second period in cream ripening 

 is that in which the lactic organisms gradually replace the 

 others, becoming more and more abundant and producing 

 lactic acid which sours the cream and slightly curdles it. 

 When this occurs the cream is ready for churning. 



These two periods are passed through in all cases of cream 

 ripening. Sometimes the first period is completed before the 

 cream has been brought to the creamery, and sometimes, 

 ' indeed, the cream is fully ripened when brought to the 

 creamery. In other cases the whole of the process may go 

 on in the creamery vat. 



