364 CHEESE 



are never at any time abundant, and their bitter flavour 

 appears to be removed by common salt in a manner not 

 yet understood. 



(iii) Causes of the ripening of Cheese. While the 

 general facts of the ripening process are fairly clear, the 

 causes which operate in the production of the chemical 

 and physical changes involved in the process are still 

 imperfectly understood, and much controversy has arisen 

 in regard to them. It is, however, agreed on all sides 

 that ripening is due chiefly, if not altogether to the 

 activity of bacteria and fungi. The process only 

 goes on when these are present, and cheese prepared 

 from sterilized milk, or kept under conditions which 

 destroy living organisms, do not ripen. Russell and 

 Babcock state that they found cheese would ripen when 

 immersed in chloroform, and suggested that the process 

 was due to the action of galactase, a trypic enzyme 

 normally present in milk and capable of hydrolysing 

 casein. It is very doubtful, however, if the action of 

 bacteria was precluded in their experiments, and careful 

 investigations by other workers do not support Russell 

 and Babcock's view. It is probable that galactase plays 

 some part in the breaking down of proteins in cheese, 

 but its influence is small. Another proteolytic enzyme, 

 namely pepsin, is introduced into cheese in the rennet 

 used for curdling the milk, and this no doubt also takes 

 a share in the ripening process. An increased addition 

 of rennet is followed by an increment in the amount 

 of those soluble nitrogenous compounds which are 

 characteristic of peptic digestion. Moreover, pure pepsin 

 added to cheese hastens the ripening process, more 

 particularly in Cheddar and similar varieties, where 

 considerable acidity is developed in the early stages of 



