No. 4.] USE OF PURE CULTURES. 171 



therefore milk should be cooled at once to a low tempera- 

 ture, for germs are })ai'tially paralyzed by the process, and 

 milk keeps much longer cold. 



Sterilization by heat is sometimes practised to destroy 

 bacteria in milk and prevent change by souring and putre- 

 faction. 



Pasteurization, or partial sterilization, is also resorted to, 

 and secures freedom from change for a time, without ren- 

 dering the milk so ol)jectionable and unwholesome to weak 

 stomachs as sterilizing does. 



Unwelcome as these ferments and the changes they pro- 

 duce are in milk, they are essential to the profitable manu- 

 facture of 1)utter and cheese. The ripening or curing of 

 cheese and flavor developed depends almost entirely on 

 bacterial growth. The different kinds of cheeses, Cheddar, 

 Stilton, Gloucester, etc., owe their diflerence in a measure 

 to diflerent organisms involved in ripening. In butter-mak- 

 ing they are not less important. 



The production of a desirable and uniform flavor in butter 

 has been the subject of a great deal of study and careful 

 investigation in the last decade. The earlier work on this 

 subject was performed by the Danish scientist, Storch. In 

 1890 he found that the production of a first-class flavor 

 in butter was dependent on the kind of bacterial life that 

 was present in the cream. If sweet cream was pasteurized 

 and made into butter, it lacked the delicate aroma that was 

 so much desired. In studying the diflerent species of bac- 

 teria that were isolated from ripening cream, he finally suc- 

 ceeded in separating a form that had the property of 

 producing a highly agreeable flavor when introduced into 

 pasteurized cream. Storch's experiments opened up a 

 practically new field for investigation, which has since been 

 assiduously cultivated by several Danish investigators, by 

 Weigmann in Germany and Conn in this country. 



Previous to the discovery of the function of bacteria in 

 ripening cream, and the separation and cultivation of those 

 forms calculated to produce highly agreeable flavors, the 

 manufacture of beer had enlisted the talents of some of the 

 most distinguished scientists. It is a curious fact that beer 

 has been more carefullv studied, with a view to increasing 



