338 MILK AND MILK PRODUCTS. XIV. 



If the cheese be wanted to cure rapidly, the rennet should 

 cause coagulation in about 20 minutes ; if a slow curing be 

 desired, in about 40 minutes. When the curd is solid the 

 temperature is raised to about 37 and kept constant until a 

 hot iron placed in contact with the curd and drawn away pulls 

 off threads about half an inch in length. This usually occurs 

 in about one or two hours after the milk is heated to 37. 



The whey is then run off and the curd stirred and turned to 

 allow the whey to escape. The curd is next reduced in a mill, 

 salted, and pressed in moulds. The cheeses are then stored 

 away at a temperature of 15 to 18 and allowed to ripen. * 



The changes which occur during ripening are little under- 

 stood, although recently an enormous number of researches 

 have been made on the subject. Considerable loss of water 

 occurs, the milk sugar of the whey left adhering to the curd is 

 converted into lactic acid, but the most obscure changes are 

 those which affect the proteid matter. 



The original casein is converted into other more digestible 

 and palatable nitrogenous bodies, consisting probably of pep- 

 tones and albumoses. Exactly how these changes are brought 

 about is still a matter of uncertainty. 



Freudenreich f asserts that the lactic bacteria are able to 

 decompose casein and thinks that these organisms play the 

 most important part in the ripening of cheese. This view has 

 been supported by the investigations of Lloyd J and Campbell . 

 On the other hand, Babcock and Eussell announced in 1897 the 

 discovery of a proteolytic enzyme or unorganised ferment, to 

 which they have given the name yalactase and to which they 

 ascribe the chief share in the ripening of cheese. This enzyme 

 is present in the milk of all animals, possesses the power of 

 peptonising casein, and in many respects resembles trypsin, 

 the enzyme of the pancreatic juice. It is more active in alka- 

 line than in acid solutions. By its action on casein, albumoses, 

 peptones, amides, and ammonia are formed. || Freudenreich 

 has repeated and confirmed Babcock and Eussell's experi- 



* For a detailed account of Cheddar cheese making see a Report by Lloyd, published 

 by the Board of Agriculture, 1899. 



t Landwirtschaf Miches Jahrbuch der Schweiz, 1897 ; also 1898, 279. 

 j Board of Agriculture, Report on Cheddar cheese making, 1899. 

 Transactions of the Highland and Agric. Society of Scotland, 1898. 

 || Jour. Chem. Soc. 1900, abst. ii. 712. 



