BACTERIA AND CHEESE-MAKING. 261 



Sour-milk Cheese. The former method is mainly applied 

 in the manufacture of so-called sour-milk cheese (" Dutch 

 cheese "), prepared by the spontaneous souring of milk and 

 subsequent heating, by which processes the casein is com- 

 pletely coagulated. In the making of this cheese the lactic- 

 acid bacteria are offered as favorable conditions as possible. 

 When the casein is precipitated the cheese is pressed, and 

 it is then often considered ready for consumption. At some 

 places the pressed cheese is allowed to ripen for a few days, 

 during which time all kinds of fermentations arise. The 

 office which the bacteria fill in the manufacture of this cheese 

 is then twofold: (1) the casein is precipitated and (2) the 

 cheese is ripened by them. In the former work only lactic- 

 acid bacteria take part ; in the latter such bacteria appear 

 as use the casein as fermentation material. The former 

 decompose the milk-sugar and precipitate the casein by 

 the ferment which they produce; the latter decompose the 

 precipitated casein. The latter group of bacteria are 

 usually only allowed to develop to a limited extent, there 

 being otherwise a danger that the fermentation processes 

 will progress too far under the very favorable conditions 

 present, in'which case the bacteria would give rise to harm- 

 ful or undesirable fermentations, producing a bad flavor 

 and taste in the cheese. This kind of cheese will therefore 

 only keep for a short period. 



The sour-milk cheese is the oldest kind of cheese in 

 Finland (as in most other dairy cduntries), and forms an 

 important and rich article of food on the table of most 

 farmers. Among other kinds of cheese in the making of 

 which the lactic-acid bacteria play an important part, may 

 be mentioned green Swiss cheese, cottage cheese, etc. 



Cheese Prepared by Means of Rennet. Considering 



