BACTERIA AND BUTTER-MAKING 2OI 



50 to 75. In earlier years, higher temperatures have been 

 adopted. There are certain important reasons for the higher 

 temperature. In a well-ripened cream there must be an abun- 

 dance of lactic acid bacteria, and these do not grow well below 

 60. Certain other species of bacteria, which produce a bitter 

 taste, are more likely to develop at low temperatures than at 

 high. If, therefore, cream is ripened at too low temperatures, 

 the acid organisms do not grow so well, and there is a greater 

 chance for the bitter bacteria to develop sufficiently to produce 

 an undesirable flavor. On the other hand, at too high temper- 

 atures other types of bacteria, especially gas-producing forms, 

 and others equally undesirable, are particularly favored. A 

 temperature from 65 to 70 appears, on the whole, most likely 

 to avoid both of the difficulties, and under ordinary circum- 

 stances the best results can be obtained by a temperature from 

 65 to 70. In warmer weather it may be desirable to use a 

 lower and in cold weather a somewhat higher temperature. 



2. Duration of Ripening. The duration of the ripening varies 

 very much with the conditions. Sometimes cream when brought 

 to a creamery is already nearly sour and has, therefore, become 

 ripened even before the butter-maker receives it. In other 

 cases, especially in winter, it will be not only very sweet, but 

 will contain small numbers of bacteria, requiring a much longer 

 ripening. Moreover, milk produced under good dairy conditions, 

 clean and fairly free from bacteria, will ordinarily require 

 longer ripening than milk that has been produced under less 

 favorable conditions, and that consequently already contains 

 bacteria in great numbers. The length of time will vary also 

 with the temperature, being, of course, longer at lower temper- 

 atures. To determine when the cream is sufficiently ripened 

 the butter-maker has two methods. One is the general appear- 

 ance to his eye and taste, the other is by determining the acidity. 

 The production of the acid may not be the whole of cream 

 ripening, inasmuch as it has little to do with the flavor and 



