BACTERIA AND CHEESE-MAKING 203 



cover the cheese, which in due time is placed in a maturing 

 " cellar " at a constant, low temperature, where the • growth of 

 mould is stopped or retarded, and bacterial growth becomes rapid. 

 Thus new products are formed which give to the cheese its fully 

 ripened flavour. If the bacterial ripening is carried too far, or 

 progresses at too high a temperature, the result is an ill-flavoured 

 cheese. Undesirable bacteria such as are found in cheese seem 

 unable to grow at a temperature of 38° R, and consequently bad 

 flavours in cheese, caused by bacteria, do not increase in cold- 

 storage. The long life of lactic acid bacteria in cheese seems to 

 have an important bearing on the question of ripening, in check- 

 ing the development of bacteria which produce bad or undesirable 

 flavours. The exact temperature at which cheese will best cure 

 has yet to be ascertained. It is obvious that in such a manufac- 

 ture there is ample scope for many and wide variations in detail, 

 which in fact take place and give rise to the different types of soft 

 cheeses. The differences are based upon empirical knowledge and 

 general experience. The scientific rationale is not at present 

 understood, nor do we know the various species of moulds and 

 bacteria which give the different flavours. Even less is known as 

 to the exact bacteriology of hard cheeses. Moulds, however, play 

 no part in their ripening, which is due to bacteria. Some have 

 held that the peptonising or casein-digesting organisms ripen hard 

 cheeses, but the majority of dair>^ bacteriologists look upon the 

 lactic acid species as that chiefly responsible. 



Freudenreich and Marchal have shown that in certain Swiss 

 and Belgian soft cheeses the principal part in the ripening is due 

 to Oidiuin ImHs ; various budding fungi also seem to aid in the 

 process. Another example of the soft cheeses, the Roquefort, is 

 ripened, at least in part, by the Penicilliuni glauaun, which filamen- 

 tous fungus occupies all the cracks and fissures which abundantly 

 intersect the cheese. There it consumes the acid produced by 

 the lactic acid bacteria, and retards the development of the albumin- 

 digesting organisms. ThQ penidllium flavour has become so much 

 appreciated that the mould is now often sown in the first curd, and 

 aerating holes are pierced in each cylinder of cheese. The coatings 

 of mould appearing in Gorgonzola, Brie, and Stilton cheese have a 

 similar action. Edam cheese, on the other hand, appears to be 

 ripened by Streptococcus Hollandicus, an organism which possesses 

 the property of making milk or whey ropy. It is employed by 

 adding 2 per cent, by volume of ropy whey to the milk to be set 

 for cheese. 



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