RIPENING PROCESSES OF CHEESES 141 



ripening of these cheeses. Similarly, it is probable that it assists 

 in the ripening of Gouda cheese, which is made on the smaller 

 Dutch farms from perfectly fresh milk without the addition of 

 lactic acid bacteria ; under such conditions these organisms will 

 have ample opportunity for development. Boekhout and de 

 Vries have shown that the peptonising bacteria do not assist to 

 any appreciable extent in the ripening of Edam Dutch cheese, 

 which is nowadays generally made with a lactic acid starter 1 , and 

 they have not succeeded in demonstrating other specific ripening 

 bacteria 2 . As Edam cheese is on the whole poor in typical pro- 

 ducts of bacterial action (amino acids and volatile acids), it would 

 appear that the bacteria here play only a subordinate part, and 

 that the principal changes are due to the rennet, as is indicated by 

 van Dam's researches 3 . "Salt stone" is occasionally found in 

 Edam cheese, but in this case it consists of calcium lactate and 

 phosphate. Again, in Cheddar cheese, the peptonising bacteria 

 do not bring about any changes of importance ; here also a great 

 deal of the action is due to the rennet, and the main feature in the 

 making of this cheese is the production of a curd having a fairly 

 high acidity at the outset, so that when the curd is pressed against 

 a hot iron it can be drawn out into long silky threads (the hot- 

 iron test). American investigators have found the flora in 

 Cheddar cheese to consist almost exclusively of the true lactic acid 

 bacteria, chiefly streptococci. The bacterial count reaches its 

 maximum immediately after the cheese has been made and then 

 decreases steadily, the rate of decrease being quicker the higher 

 the temperature at which the cheese is kept 4 . By allowing the 

 curd to become strongly acid through the agency of different 

 streptococci, the author has succeeded in producing cheeses resem- 

 bling Cheddar in texture and taste, so that there can be no doubt 

 that in this case such bacteria actually accomplish more than the 

 mere production of acid 5 . . The streptococci cannot, however, be 

 responsible for the large amounts of amino acids found in ripe 

 Cheddar, so that here also we have evidence of the action of lactic 

 acid rod bacteria. As a matter of fact, the author has never met 

 with any kind of cheese in which lactic acid rod bacteria (strepto- 



1 " Kevue generate du lait," 1910, vol. 6, p. 1. 



2 " Centralblatt f. Bakt.," 2 Abt., 1905, Bd. XV., p. 323, and 1906, Bd. 

 XVII . , p. 1 49. These authors have described a diplococcus-like rod bacterium 

 which converts lactic acid into acetic acid, carbon dioxide and hydrogen, 

 and which is said to have some significance in the formation of eyes in 

 Edam cheese. It will stand 4^ per cent, of salt, and its optimum tempera- 

 ture is 21 C. (ibid., 2 Abt., 1918, p. 130). 



3 "Centralblatt f. Bakt.," 2 Abt,, 1910, Bd. XXVI.. p. 189. ' 



* Harrison, " Centralblatt f. Bakt.," 2 Abt., 1904, Bd. XI., p. 637. Sub- 

 sequently Harding and Prucha made a thorough study of the flora of 

 Cheddar cheese (New York Agric. Exp. Station, Bull. No. 8, 1908). 



5 " Centralanstalten's 97 Meddeise." 



