30 THE STORY OF MILK 



In a Continuous Pasteurizer a constant stream of 

 milk is fed into the machine, heated by flowing over 

 a metal surface with steam or hot water on the opposite 

 side, and cooled by running over a cooler furnished 

 with a stream of cold water or ice water. 



PURE CULTURES 



Before 1890 it was supposed that the flavor of fine 

 butter depended upon certain volatile oils and acids 

 peculiar to butter-fat. In the early 

 nineties Professor V. Storch of 

 the Danish Experiment Station 

 showed, however, that it was 

 due rather to the products of 

 bacteria and he isolated the lactic 

 acid bacilli which would produce 

 such exquisite flavor even when per- 

 fectly neutral and tasteless butter- 

 fat was churned with milk acidified 



Professor V. Storch, . i -ii ix £ 



originator of pure cul^ cr ripened With a pure culture of 

 tures for ripening these bacilli. In this country Dr. 

 cream and milk n Y/ Conn of Wesleyan University, 



Storrs, Conn., did much to advance the theory and 

 practice of ripening cream with a pure culture starter. 



''Pure cultures" are produced in the bacteriological 

 laboratory by picking out under the microscope col- 

 onies of the desired species of bacteria, planting them 

 in a sterilized medium and allowing them to grow under 

 the most favorable conditions and with the exclusion 

 of all other germs. 



When such a culture has reached its maximum growth 

 it is transplanted into a larger quantity of a sterilized 

 medium containing proper nourishment for the par- 



