CAUSES OF RIPENING CHANGES 363 



(i) When no acid, or acid salt, is present in the 

 cheese-making process, practically no changes take 

 place in the protein of the green cheese, even in the 

 course of a year; the different classes of compounds 

 remain about the same in amount at the end of a year 

 as in the fresh cheese. Rennet-enzym, in the ab- 

 sence of acid or acid salts, has practically no dissolv- 

 ing eft'ect on the protein of green cheese and, there- 

 fore, does little or no work in the formation of water- 

 soluble protein in the process of cheese-ripening. 



(2) When lactic acid was added to milk at the 

 rate of 0.2 per cent, the results were in marked con- 

 trast with those given when no acid was used. Thus, 

 we have (a) a considerable amount of brine-soluble 

 protein in the fresh cheese, and (b) a large increase 

 of water-soluble nitrogen compounds at the end of 

 12 months. It is noticeable that the increase in these 

 water-soluble compounds is largely confined to the 

 paranuclein, caseoses and peptones; the amount of 

 amino acids remains small as compared with a normal 

 cheese of the same age. 



That rennet-enzym acts like pepsin in dissolving the 

 protein of fresh cheese-curd has been shown by 

 experimental work. Heated milk (lOO cubic centi- 

 meters), treated with chloroform to prevent bacterial 

 action, was put into sterilized bottles ; 0.22 cubic cen- 

 timeter of Hansen's fresh rennet-extract was added 

 to some bottles, and to others 0.06 gram of aseptic 

 scale-pepsin for each 7 grams of protein in milk. In 

 the case of one-half of the bottles, 0.5 cubic centimeter 

 of pure lactic acid was added. The bottles were kept 

 at 60° F. The germ content was shown to be insig- 

 nificant. In one set of experiments milk was used 



