Bacteria and Butter Making. 145 



from their own by-products, to which they would be ex- 

 posed if maintained in liquid cultures. The keeping 

 quality, therefore, of dry cultures, is much better than 

 that of liquid cultures. 



By the use of the pure-culture starters, the butter 

 maker is able to add to his cream the same kind of bac- 

 teria from day to day, and the butter will be more uni- 

 form than when the less constant home-made starter is 

 employed. In cream to which the starter is added, there 

 are present a greater or less number of acid-forming 

 bacteria, depending upon the age of the cream, and upon 

 the condition under which it was produced. These will 

 grow during the ripening process, and the flavor of the 

 product will be the result of the mixture of the bacteria 

 in the cream. The maker can not, therefore, be certain 

 that the addition of a pure culture to raw cream will 

 effectively control the type of fermentation. This can 

 be secured only by first destroying the existing bacteria 

 in the cream, before the selected culture is added. Heat- 

 ing the cream accomplishes this; and in cream thus 

 freed from the various kinds of bacteria, the butter 

 maker can insure the dominance of the desirable types, 

 contained in the pure-culture starter. If the cream can 

 be obtained in a sweet condition, the maker through this 

 process of pasteurization, and the use of pure cultures, 

 secures almost perfect control over the type of fermenta- 

 tion that occurs in the cream, and thus exercises control 

 over the degree and kind of flavor of the product. This 

 most scientific type of butter making is now used by the 

 most progressive butter makers in the leading butter- 

 producing regions of the world. 



Pasteurization of the cream also distinctly improves 

 the keeping quality of butter, a condition doubtless due 

 10 



