BACTERIA IN BUTTER-MAKING. 233 



of their meaning and experimented with them quite widely. 

 At the outset too great expectations were raised as to the 

 value of such cultures, and dairymen were naturally disap- 

 pointed in the results. As a consequence, the use of such 

 commercial cultures has not advanced very much in the last 

 few years. But one thing has resulted from the attempt to 

 introduce the use of pure cultures for cream -ripening among 

 American dairymen. Nearly all butter-makers, at least all 

 who have a pride in the quality of their product, have learned 

 of the absolute necessity of greater attention to the process of 

 cream-ripening, and nearly all have adopted such means as are 

 easily within their power for controlling this ripening. 



PREPARATION OF PURE CULTURES. 



The first step in the preparation of pure cultures must be 

 taken by the bacteriologist, who obtains, from some lot of 

 milk or cream, a certain species of bacterium which experi- 

 ment has indicated produces the desired results. Different 

 bacteriologists have proceeded differently in searching for such 

 a culture, and the various "cultures" placed on the market 

 show much variation. They are commonly pure cultures, i. e., 

 consist of a single species of bacterium, but in some cases 

 they consist of mixtures of several species. In practically all 

 cases a lactic bacterium is the basis of such cultures. It must 

 be admitted that none of the cultures which have been used 

 have been found to be perfectly satisfactory, for, although they 

 ripen the cream normally and produce a proper amount of 

 acid, they all appear to be lacking in flavor. 



The bacteria as obtained from the bacteriologist are in the 

 form of a pure culture but in small quantity, insufficient to use 

 directly in the cream, and they must consequently be " built up." 

 For this purpose the butter-maker sterilizes a small amount of 

 milk by heat, and, after it is allowed to cool, the commercial 

 culture is placed in it. The mixture is then allowed to stand 

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