16 THE BOOK OF CHEESE 



fermentation takes place first, and later other fermenta- 

 tions or changes begin, which, after a time, so decom- 

 pose the milk that it will not be suitable for cheese- 

 making or human consumption. 



The following grouping of the organisms in milk is 

 based on their effects on the milk itself l : 



I. Acid-producing types. 

 II. Peptonizing types. 



III. Inert types. 



IV. Alkali-producing types. 

 V. Butyric fermenting types. 



Each type of bacteria produces more or less specific 

 changes in the milk. As a general rule, the predominance 

 of one of these types is an aid in the interpretation of the 

 quality of the product at the time of analysis, such as 

 the age, the temperature at which it has been held, the 

 conditions under which it was produced and, in some 

 cases, the general source of the contamination. The 

 reaction due to certain bacteria is utilized in the manu- 

 facture and handling of dairy products; other groups 

 have deleterious effects. (See Fig. 2.) 



1 Conn. (Storrs) Exp. Sta. Kept. 1899, pages 13-68. 



Conn. (Storrs) Exp. Sta. Kept. 1903, pages 33-98. 



Conn. (Storrs) Exp. Sta. Kept. 1904, pages 27-88. 



Esten, W. M., and C. J. Mason, Sources of bacteria in milk, 

 Conn. (Storrs) Exp. Sta. Bui. 51, 1908. 



Rogers, L. A., and B. J. Davis, Methods of classifying the 

 lactic acid bacteria, U. S. Dept. Agr. Bur. An. Ind. Bui. 154, 

 1912. 



Bergey, D. H., The colon-aerogenes group of bacteria, Jour. 

 Med. Research, Boston, Vol. XIX, pages 175-200, 1908. 



Conn, H. W., Classification of dairy bacteria, Conn. (Storrs) 

 Exp. Sta. Rept. 1906. 



Rogers, L. A., Bacteria in milk, U. S, Dept. Agr., Farmers' 

 Bui. 490, 1912. 



