vm] RENNET AND ITS ACTION 141 



and in the above period of time, more than three 

 million parts of milk. 



Difference between Rennet -Curd and Acid- 

 Curd. The nature of the action of rennet is a point 

 regarding which our knowledge is still very imperfect. 

 If the coagulation of curd produced respectively by the 

 formation of lactic acid or other acid (and this curd 

 may be distinguished by calling it " acid-curd," and 

 that produced by rennet " rennet-curd ") are examined, 

 it will be found that these two curds differ in many 

 respects in their properties and composition. Eennet- 

 curd, for example, is an elastic substance scarcely 

 soluble in water, and not in the slightest extent 

 sticky or greasy. Acid- curd, on the other hand, is 

 not elastic, is less insoluble in water, and is sticky 

 and greasy. Again, acid-curd, will be found to 

 exhibit a strongly acid reaction; while, although 

 the reaction in rennet-curd is also acid, it is only 

 slightly so. It is for ' this reason that acid-curd is 

 not so suited for the manufacture of such a wide 

 variety of cheese as rennet-curd, since its acid re- 

 action is not favourable to the development of a large 

 variety of micro-organic life. On the other hand, in 

 rennet-curd the conditions for bacterial development 

 are much more favourable. Hence in cheeses made 

 from acid-curd, with very few exceptions, the process 

 of ripening resembles in general the process of putre- 

 faction, inasmuch as it goes on from outside to inside. 



