iqoo-i.] The Ripening of Cheese. hi 



bacteria seems to indicate that these phenomena are causally related. 

 This view is further strengthened by the fact that cheese made from 

 pasteurised milk in which the lactic acid bacteria have been destroyed 

 fail to ripen in the normal manner, while the addition of a pure lactic 

 acid ferment to the pasteurised milk permits the usual changes to occur 

 in a probably normal way. 



Schirokich took up the study of this problem by preparing in milk 

 pure cultures of some peptonizing bacteria as well as of lactic bacteria 

 and then investigating by means of chemical analysis the changes 

 which took place in the milk in the course of the development of the 

 micro-organisms in it. The change in the composition of the milk was 

 studied as to (i) the quantity of the casein of the milk converted into 

 soluble form ; (2) the amount of ammonia found in the cultures, and (3) 

 the amount and kind of fatty acids produced by the micro-organisms. 



With reference to the first point, it was found that while the 

 peptonizing bacteria converted during the first fifteen days of their 

 culture almost all of the casein of the milk into proteids soluble in 

 water, and the remainder into products of decomposition, the lactic 

 bacteria did not alter in the slightest, the amount of nitrogen in the 

 soluble protein matter after thirty days of culture. In other words, 

 while the bacteria of the former group acted very energetically on the 

 casein, those of the latter group did not affect it at all. The fungus 

 OidiiDii lactis was also found very active in changing the casein, 

 although in a lesser degree than the peptonizing bacteria. 



Further, the author found in the cultures of the Oidiuni lactis less 

 ammonia than in those of the peptonizing bacteria, and none whatever 

 in the cultures of the lactic bacillus. 



Finally, on comparing the nature of the fatty acids formed in cheese 

 (the author experimented with hard Gruyere and soft Brie cheese) and 

 those produced by the bacteria in pure cultures, he found that the 

 mi.xture of the volatile acids caused by the bacteria not liquef\'ing 

 gelatine did not correspond to those which are formed either in the hard 

 or in the soft cheese. On the contrary, the volatile acids produced bv 

 the peptonizing bacilli were found to be very similar to the mixture of 

 these acids produced in the ripening of Gruyere cheese. And, lastly, 

 great similarity was observed between the volatile acids of the soft Brie 

 cheese and those produced by the fungus Oidiiun lactis. 



Thus, all three lines of investigation pursued by the author lead to 

 the conclusion that the bacteria of lactic fermentation, though present in 



