248 BACTERIA IN CHEESE MAKING. 



tion appearing to have some influence upon the milk which 

 prevents it undergoing the normal changes. The pasteuriza- 

 tion destroys or injures the enzymes present in the milk, and 

 inasmuch as the ripening is produced in considerable degree 

 by the action of these enzymes, it is easy to understand that 

 cheese made from pasteurized milk would not normally 

 ripen. 



Nevertheless, the work of most recent times has given 

 more promise of success in these lines. It has been found 

 that certain of the soft cheeses and some of the sour milk 

 cheeses can be made in a perfectly normal way by pasteuriz- 

 ing the milk and subsequently inoculating it, either with 

 pure cultures of certain microorganisms or with soured 

 milk, or with freshly made cheese. Such pasteurized milk 

 cheeses undergo a normal ripening. Moreover, in some of 

 the hard cheeses more recent experiments have indicated that 

 a proper ripening can be produced by the agency of pure 

 cultures added to the pasteurized cream (270, 284). But, 

 nevertheless, pasteurization does injure the enzymes in the 

 milk and this makes it uncertain whether it will ever be pos- 

 sible to treat milk in this manner and be sure subsequently of 

 a normal ripening by the simple addition of pure cultures of 

 bacteria. 



But in cheese-making, as in^ butter-making, it is becoming 

 apparent that pure cultures may be used successfully even 

 without the previous pasteurization, and for similar reasons. 

 Lactic bacteria have a marked power of checking the growth 

 of other organisms. A few years ago Lloyd used certain 

 species of a pure culture of lactic bacteria for inoculating 

 milk to be made into the Cheddar cheeses, and claimed to 

 have obtained satisfactory results both in quality and uni- 

 formity. 



The extension of this use of bacteria has proved to be one 

 of the most promising applications of bacteriology to cheese- 

 making. In the last few years manufacturers of the Cheddar 



