362 MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



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 addi- 

 tion of the rennet. The curd, which thus contains many acid-forming 

 bacteria, is neither cut nor heated in order to retain the maximum amount 

 of whey. The curd is placed in small hoops and allowed to drain with- 

 out 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, PenicUlmm 

 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 indicates 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 putrefactive bacteria and it 

 soon becomes unfit for use after it is completely ripened. A number of 

 different 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 microorgan- 

 isms, and because of this fact the manufacture is attended with greater 

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



