BACTERIA IN BUTTER-MAKING. 185 



butter, others a turnip-tasting, or putrid butter. In general, it is the 

 lactic bacteria which produce the desired results, while other types, 

 if excessively abundant, give rise to the abnormal flavors. 



Since the bacteria are so varied in their action, it may be a matter 

 of surprise that cream-ripening, if left to itself, so commonly results 

 favorably. The primary reason for this is the superior vigor of the 

 lactic acid bacteria. Since, in the ordinary bacterial growth in 

 cream, the lactic bacteria finally get the upper hand and grow at the 

 expense of all the others, it ordinarily happens that the ripening 

 produces a good flavor, and a satisfactory butter is obtained. Un- 

 fortunately, however, the favorable species of lactic bacteria do not 

 always get the upper hand in the cream-ripening. Sometimes large 

 numbers of other bacteria are present in the cream, just as vigorous 

 and just as capable "of rapid growth as the desirable lactic acid 

 germs. In such cases the unusual bacteria may develop abundantly 

 and produce a variety of uncommon changes in the cream, with the 

 result of giving an undesirable flavor to the butter. Such a phe- 

 nomenon explains the occasional appearance of bad-tasting butter. 

 The fact that such improper ripening does sometimes occur clearly 

 points to the need of some control over the ripening, especially in 

 creameries where a uniformly good product is necessary for financial 

 success. 



CONTROL OF CREAM-RIPENING. 



The butter-maker has no control over the kinds of bacteria that 

 get into his cream, and a creamery must take cream filled with 

 whatever bacteria chance to be most common in the dairy furnishing 

 it. But though he cannot control this factor, he can, more or less 

 satisfactorily, regulate the growth of the bacteria. 



Temperature of Ripening. At a temperature of from 65 to 

 70 the favorable lactic acid bacteria get the upper hand of other 

 species more readily than at either a higher or a lower temperature. 

 At temperatures above or below this, different species, mostly un- 

 favorable, are more likely to gain the upper hand. Hence, by 

 keeping the temperature at about 65, the undue development of 

 mischievious bacteria is more likely to be prevented. 

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