RELATION OF MICROORGANISMS TO CHEESE 503 



this important French cheese made from cow's milk by the addition 

 of rennet. The milk is ripened to an acidity of 0.20 to 0.25 per cent 

 before the addition of the rennet. The curd, which thus contains 

 many acid-forming bacteria, is neither cut nor heated so that the 

 maximum amount of whey is retained. The curd is placed in small 

 hoops and allowed to drain without pressure. Salt is applied to the 

 surface of the cheese. 



The milk sugar is rapidly fermented and the resulting acidity 

 is high, for the cheese contains 60 to 70 per cent of moisture when 

 fresh and 50 per cent when ready for consumption. The high moisture 

 content of the cheese and the humidity and temperature conditions 

 of the curing room favor the rapid development of microorganisms 

 on the surface of the cheese. Both molds and bacteria thrive under 

 the influence of these favorable conditions, changing the cheese to 

 a soft, smooth and butter-like mass, while a characteristic flavor is 

 developed. 



In three or four days the cheese becomes covered with the growth 

 of Oidium lactis; the characteristic mold of Camembert cheese, Peni- 

 cillium camemberti, appears later, within five to six days. These 

 molds reduce the acidity of the curd, and through the enzymes, which 

 they produce and which gradually diffuse into the cheese, proteolyze the 

 curd very completely. The appearance of the cheese when cut in- 

 dicates the depth to which the enzymes have penetrated; when the 

 entire mass is acted upon, the cheese is ready for use. The reduction of 

 the acidity by the molds exposes the cheese to the attacks of putre- 

 factive bacteria and it soon becomes unfit for use after it is completely 

 ripened. Several kinds of bacteria are found in the slimy surface 

 layer, but their role is not known. 



The development of the characteristic flavor and aroma is dependent 

 on a certain relation between the various biological agents concerned 

 in the ripening. This balance is dependent on very narrow conditions 

 of temperature and humidity; slight changes in these environmental 

 conditions favor or retard the individual types in varying degrees. If 

 the equilibrium essential for the development of typical flavor is 

 destroyed, this cheese fails to ripen properly and is of low value. The 

 manufacture of Camembert cheese is a delicate problem in the ecology 

 of microorganisms, and because of this fact the manufacture is attended 

 with greater difficulties than is the case with most types of hard cheese. 



