BACTERIA AND BUTTER-MAKING 



ever, that it requires some skill on the part of the butter-maker 

 to know whether the starter that he thus obtains is of the best 

 character, and whether it should be used or thrown away, and 

 another obtained. Starters made in this way are not sure to 

 be uniform, inasmuch as the different samples of milk may 

 contain different types of bacteria, and experience is needed 

 on the part of the butter-maker to know whether the starter 

 thus obtained is satisfactory. 



Starters from Commercial Cultures. In the last few years 

 there has been placed upon the market quite a variety of com- 

 mercial cultures for the purpose of controlling butter-making. 

 These are prepared by bacteriologists and consist of many types 

 of bacteria that have been found by experiment to produce a 

 satisfactory ripening. The bacteria have usually been isolated 

 from ripening cream, and have been chosen from a large num- 

 ber of tested species which promise to produce a desired type 

 of ripening and, consequently, the best grade of butter. These 

 commercial cultures are commonly called pure cultures, which 

 means that they consist of one species of bacteria only. We 

 have already noted that the flavors, aromas and acidity are 

 probably not produced by the same organisms. Probably no 

 bacterium combines in itself the requisite powers of producing 

 all three factors. Pure cultures, therefore, might not be ex- 

 pected to give all the qualities desired in a first class butter. To 

 meet this difficulty some of these commercial cultures consist 

 of a mixture of bacteria of two or more* kinds, in order to 

 produce a starter which will furnish at the same time flavor, 

 acidity and aroma. These bacteria cultures, whether pure or 

 mixed, are developed in a bacteriologist's laboratory until the 

 organisms are in great abundance, and are prepared for market 

 in various ways. In some cases they are mixed with some inert 

 powder and sold in a dry form. In other cases they are sent in 

 the form of a bouillon culture much like those described on 

 page 295. Others again are cultivated in milk and sent out as 

 milk cultures. 



