RIPENING PROCESSES OF CHEESES 147 



rod bacterium, and yeast) ; in view also of the results set out in 

 the table on p. 146, there can hardly be any doubt as to the 

 cause of the thorough-going decomposition processes which take 

 place in this cheese. A similar flora will also develop on the rind 

 of hard cheeses if they are kept damp, and it will be understood 

 how the ripening of these cheeses may be modified so as to conform 

 with the type generally associated with Limburger cheese. The 

 ammonia formed on the surface gradually diffuses into the interior, 

 and not only does it neutralise the lactic acid, thereby rendering 

 possible the activity of the bacterial enzymes, but it also converts 

 the casein into the readily soluble ammonium caseinate. The 

 ripening of the soft smeared cheeses involves further complexities. 

 In the ripe state these cheeses contain appreciable amounts of 

 valerianic acid, an acid which is only produced by the above- 

 mentioned bacteria in very small amounts, while on the strongly - 

 smelling surface there are formed various typical products of 

 putrefaction, such as hydrogen sulphide and indole. It is obvious 

 that under normal conditions organisms other than those mentioned 

 above participate in the process Weigmann mentions Plectridium 

 fcetidum but whether their activity is to be regarded as at all 

 desirable may be an open question ; it is quite possible that Lim- 

 burger cheese might have a wider market if it contained no 

 products of putrefaction. According to Laxa 1 , Oidium lactis 

 participates in the ripening of certain Bohemian cheeses, which 

 resemble Limburger cheese (Harrach and Knoppist) ; these 

 cheeses therefore form a link with the mouldy cheeses. 



The moulds play a part in the mouldy cheeses similar to that 

 of the peptonising bacteria in the smeared cheeses. As a type we 

 may take Camembert, which, thanks to the researches of Roger, 

 Maze 2 , and Thorn 3 , is one of the most thoroughly investigated 

 cheeses. The moulds which develop in this cheese are Oidium 

 lactis (according to Maze, Oidium camemberti, other oidium species, 

 and a mycoderma), Penicillium camemberti, and P. candidum. 

 The moulds of the Oidium group grow the quickest, while the 

 Penicillium group first begins to develop after five to six days, 

 when the surface has become a little drier. The chief difficulty 

 lies in maintaining the proper humidity. If the air is too damp, 

 the surface of the cheese becomes too slimy, as in the case of the 

 smeared cheeses, and bacteria, yeasts, oidium, and even certain 

 mucors, gain the upper hand ; if too dry, on the other hand, the 

 Penicillia grow too freely, causing the rind to shrivel ; all the green 

 Penicillia which develop (not excepting P. roqueforti) produce 



1 " Centralblatt f. Bakt.," 2 Abt., 1899, Bd. V., p. 755. 



2 " Annales de 1'Institut Pasteur/' 1910. 



3 U.S. Dept. of Agric., Bureau of Animal Industry, Bull. 115, 1909. 



102 



