THE GRADING OF MILK 



165 



acid bacteria predominate ; b v b 2 and 6 3 indicate progressive degrees 

 of intensity of gas evolution. While there is only a difference of 

 a degree between g 3 and 6 l5 all the casein will have been driven 

 to the surface in b 3 . The spongy types, s v s 2 and 3 , differ from 

 the blown types in being finer in curd texture. In s i the coagulum 

 forms so fine a network that it may easily be mistaken for g r 

 Milk which is poor in true lactic acid bacteria often becomes 

 spongy in the fermentation test, owing to the gas production 



FIG. 68. Spongy Types. 



FIG. 69. Cheesy Types. 



being in full swing before coagulation occurs. In this case the 

 gas-producing organisms may sometimes be lactose fermenting 

 saccharomycetes. The cheesy type is distinguished by a well- 

 marked separation of clear whey, due to organisms which secrete 

 rennet-like enzymes, especially peptonising lactic acid strepto- 

 cocci ; c l5 c 2 and c 3 indicate progressive degrees in the contraction 

 of the curd. If at the same time much gas has been formed, this 

 type cannot well be distinguished from the spongy or the blown 

 type. In actual practice distinction is only made between the 



