CHAPTER VII 



RELATION OF BACTERIA TO CHEESE 



In the making and curing of cheese of all kinds, micro- 

 organisms, and especially the bacteria, function as essential 

 factors. Both cheese made with rennet, as well as that pro- 

 duced from curd precipitated by acid, are markedly affected 

 by the activity of these organisms. 



Ripening of cheese. Cheese differs from butter in that it 

 must undergo a profound series of changes, physical and 

 chemical in nature, before it is fit for consumption. These 

 changes, collectively known as the curing or the ripening, 

 are exceedingly complex, and differ in details in various tyj efl 

 of cheese, but possess in common certain characteristics, the 

 most important of which are (1) the gradual change of the 

 insoluble paracasein to a series of compounds more or less 

 soluble in water, and hence more readily digestible than the 

 original paracasein ; (2) the production of substances having 

 more or less distinctive flavors and odors. 



Our knowledge relating to the exact nature of these proc- 

 esses is yet far from complete. Moreover, they are of such a 

 complex nature that they cannot be readily demonstrated 

 by laboratory exercises. Consequently only the general prin- 

 ciples here involved can be outlined. 



The gradual change of the insoluble paracasein to soluble 

 compounds is a process related to digestion, and undoubtedly 

 produced by proteolytic enzymes from various sources. Ren- 

 net is added to milk primarily for the purpose of curdling 



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