THE MILK IN ITS RELATION TO CHEESE 19 



initial presence of these bacteria in milk is indicative of 

 fecal contamination or unclean conditions of production. 

 These organisms, however, grow and develop in milk 

 very rapidly at high temperatures of handling. The 

 total acidity produced by these forms is less than that by 

 the Bacterium lactis-acidi group. Of the acid produced, 

 less than 30 per cent is lactic acid; the other acids are 

 formic, acetic, proprionic and succinic. The large per- 

 centage of these acids, with comparatively large amounts 

 of certain alcohols, aldehydes and esters, invariably im- 

 part undesirable flavors and odors to the milk. Mem- 

 bers of this group uniformly ferment the lactose with the 

 production of the gases, carbon dioxide and hydrogen. 

 The milk is coagulated into a lumpy curd, containing gas 

 pockets. 



25. Acid peptonizing group. These are often as- 

 sociated with colon organisms. The group includes 

 those bacteria which coagulate milk with an acid curd 

 and subsequently partly digest it. They grow and mul- 

 tiply rapidly at a temperature between 65 and 98 F. 

 They impart undesirable flavors and odors to the milk, 

 which appear to be due to the formation of acids other 

 than lactic acid, and to action on the milk proteins. 



26. Bacillus bulgaricus group. These organisms grow 

 best at a temperature of 105 to 115 F. They will de- 

 velop at lower temperatures, but not so rapidly. They 

 survive heating to 135 F. without loss of vigor, as occurs 

 in Swiss cheese-making. They produce from 1 to 4 per 

 cent of acid in milk, which is practically all lactic acid. 

 They do not produce gas. They impart no undesirable 

 flavors to the milk. 



27. Acid cocci or weak acid-producers. This group 

 of organisms is not very well defined. It consists mostly 



