RELATION OF BACTERIA TO DAIRY INDUSTRY. 79 



with desired flavours, while others, under identical 

 conditions, produce decidedly poor results with 

 undesired^ flavours (Figs. 21-23). If the butter 

 maker obtains cream which is filled with a large 

 number of bacteria capable of producing good 

 flavours, then the ripening of his cream will be 

 satisfactory and his butter will be of high quality. 

 If, however, it chances that his cream contains 

 only the species which produce unpleasant fla- 

 vours, then the character of the ripening will be 

 decidedly inferior and the butter will be of a 

 poorer grade. Fortunately the majority of the 

 kinds of bacteria liable to get into the cream 

 from ordinary sources are such as produce either 

 good effects upon the cream or do not materially 

 influence the flavour or aroma. Hence it is that 

 the ripening of cream will commonly produce 

 good results. Bacteriologists have learned that 

 there are some species of bacteria more or less 

 common around our barns which produce unde- 

 sirable effects upon flavour, and should these be- 

 come especially abundant in the cream, then the 

 character of the ripening and the quality of the 

 subsequent butter will suffer. These malign spe- 

 cies of bacteria, however, are not very common in 

 properly kept barns and dairies. Hence the pro- 

 cess that is so widely used, of simply allowing 

 cream to ripen under the influence of any bacte- 

 ria that happen to be in it, ordinarily produces 

 good results. But our butter makers sometimes 

 find, at the times when the cattle change from 

 winter to summer or from summer to winter feed, 

 that the ripening is abnormal. The reason ap- 

 pears to be that the cream has become infested 

 with an abundance of malign species. The ripen- 

 ing that they produce is therefore an undesirable 

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