RIPENING OF CHEESE. 439 



acid organisms, which increase rapidly and transform the milk- 

 sugar into lactic acid. Freudenreich and Lloyd have both come 

 to the conclusion that these organisms are the chief, if not the 

 only, factor in the ripening of cheese. While it cannot be denied 

 that they have some influence, it is hard to realise that lactic 

 acid bacteria, which, when grown in sterilised milk, do not 

 convert the proteins into albumoses and amino-compounds, 

 should acquire this property in cheese. It appears to be an 

 established fact, however, that the lactic acid organisms develop, 

 rise to a maximum, and then diminish gradually. The acid 

 they produce appears to be inimical to the growth of other 

 organisms. The ripening of cheese goes on concurrently with 

 the growth of the lactic acid organisms, and continues at an 

 even rate while the organisms are decreasing. This shows that 

 the ripening of cheese is not due to the direct action of micro- 

 organisms. 



B,6le of Moulds. C. Thorn has shown that for the ripening 

 of Camembert cheese three organisms are necessary. 



Lactic acid bacteria, which rapidly multiply, and produce 

 acid, which inhibits the action of other bacteria. 



A special mould, Penicillium Camembertii, which secretes an 

 alkaline substance, and a peptonising enzyme ; the latter diffuses 

 into the curd, and produces the texture of the cheese. 



Oidium lactis, which gives the cheese its characteristic flavour. 

 For Roquefort cheese the only organisms necessary are lactic 

 acid bacteria and the Penicillium Roqueforti ; the latter reduces 

 the acidity, digests the curd, and produces the characteristic 

 flavour. 



The Roquefort Penicillium is also found on Stilton, Gor- 

 gonzola, and other cheeses. The common green mould, 

 Penicillium glaucum, does not appear to play any part in cheese 

 ripening. 



R&le of Enzymes. Duclaux has recognised this, and 

 attributes the ripening of cheese to enzymes (called by him 

 " diastases ") secreted by various organisms to which he gives 

 the name Tyrothrix ; the enzyme would remain and be active 

 after the organisms had died off. 



Babcock and Russell have shown that milk itself contains a 

 peptonising enzyme. By treating milk with a quantity of an 

 antiseptic, such as chloroform, to check all microbial action, 

 they found that a digestion of the proteins was still going on. 

 They have isolated the enzyme from milk, and, finally, have 

 prepared cheeses, which have been ripened under aseptic con- 

 ditions. Though perfectly sterile, these cheeses show that the 

 proteins are converted into albumoses, peptones, and amino- 

 compounds in the same manner as in normal cheeses. 



