BACTERIA AND OTHER MICROORGANISMS IN CHEESE 517 



case the soft cheese. The raw material so obtained is still simply curd 

 and becomes cheese only after going through a process of ripening 

 with various changes depending upon the activity of bacteria and other 

 microorganisms. In addition to the proteids, the curd contains a 

 variable amount of fat, depending upon whether it has been obtained 

 from whole or from partially or more completely skimmed milk. 



Ripening of Curd into Cheese. The ripening of the curd into cheese 

 consists in a partial or more or less complete conversion of the insoluble 

 casein into simpler and soluble proteid or albuminoid bodies and in 

 the production of certain bodies which give to the ripe cheese the 

 peculiar taste and characteristic flavor which vary greatly in different 

 varieties. The change of the casein which resembles that brought 

 about by gastric juice is due to enzymes secreted by bacteria and 

 other microorganisms, which multiply enormously during the process 

 of ripening. It is still a much disputed point to what extent certain 

 bacteria are responsible for the ripening of the cheese. It is believed, 

 however, by many that the hay bacillus (Bacillus subtilis), which 

 secretes a strong proteolytic or peptic ferment, plays an important role 

 in the conversion of casein into soluble albuminoids. In some soft 

 cheeses the presence of Bacillus subtilis in enormous numbers has 

 been established. Ducleaux has shown that peptonizing bacteria 

 which he has named Tyrothrix tenuis, distortus and geniculatus, are 

 important factors in the ripening of certain French cheeses, and 

 Adametz proved the presence of bacteria likewise endowed with 

 proteolytic enzymes in soft and hard Swiss cheeses. It has also been 

 shown that lactic-acid bacteria which at the same time possess the 

 power to produce certain changes in casein likewise play an important 

 role in the ripening of cheese. Liquefying cocci have been found in 

 cheese by von Freudenreich. Thoeni and Weigmann and Jensen 

 have shown that their peptonizing enzyme is an important factor in 

 the early changes in curd. Von Freudenreich and Jensen have also 

 found in Swiss cheese anaerobic bacteria which decompose lactate of 

 lime into propionic acid, some acetic acid and carbon dioxide, and 

 which produce holes in the cheese, improving its flavor and taste. 

 Rodella and Weigmann have discovered anaerobic butyric acid 

 bacilli in Swiss cheese and Paraplectrum fcetidum in Limburger 

 cheese. Weigmann gives the following summary of the activity of 

 bacteria and other microorganisms in the ripening of cheese: 



"The lactic-acid bacteria, such as Streptococcus Guentheri and 

 others, which remain in the curd with the larger or lesser amount of 

 whey contained therein, multiply and form lactic acid, this prevents 

 the immediate activity of putrefying bacteria originally contained 

 in the milk and present in the curd. The bacilli most susceptible 

 to acid, such as the Bacillus coli, some of the hay bacilli, and some 

 of the anaerobics present, are much reduced in numbers, liquefying 

 cocci and lactic-acid bacteria, which can decompose casein without 

 peptonization, however, multiply considerably. After the activity 



