i82 MILK AND DAIRY PRODUCTS PART 



The chemical composition of the many varieties of cheese is 

 naturally very different. Where the cheese has been made 

 from a rennet curd, the majority of the undissolved substances 

 in the milk fat, di- and tri-calcium phosphates, as well as the 

 lime which is in combination with the casein are carried down 

 with the coagulated casein. This rennet curd has the same 

 reaction as the milk, or it may be slightly alkaline. The sour 

 milk or acid curd on the other hand contains no insoluble lime 

 salts, because during the formation of the curd the lime salts 

 pass into the soluble form, owing to the distinctly acid character 

 of the medium. The difference in reaction between rennet and 

 acid cheeses is of fundamental importance with regard to the 

 ripening of the two varieties. 



Owing to the less acid character of the rennet curd the 

 various classes of micro-organism do not meet with such an 

 adverse medium as is the case in the sour milk cheeses. A free 

 development of one or more of the groups is therefore possible ; 

 and the way in which the cheese has been made, the pressing, 

 the salting, and the storing, determine which of the micro- 

 organisms shall predominate. From rennet curd it is therefore 

 possible to prepare cheeses with very varying properties and 

 chemical composition. In the case of sour milk or acid curd 

 the state of affairs is different for then the lactic acid 

 bacteria predominate from the beginning. It is only possible 

 also for those bacteria which can flourish in an acid medium 

 to take part in the ripening of cheese of this class. This being 

 so, ripening proceeds in a one-sided manner, and for that reason 

 all sour milk cheeses are more or less alike. 



Apart from the above-mentioned chief differences in the 

 composition of rennet and sour milk cheese, a difference which 

 begins with formation of the curd, there are also variations in 

 the amount of fat which the mass of coagulated casein contains 

 according to the richness of the milk. 



During ripening soluble substances are gradually formed 

 from the insoluble paracasein, and the original porcelain-like 

 elastic curd, thereby becomes transformed by degrees into 

 a yellowish, homogeneous, plastic mass the cut surface of which 

 somewhat resembles butter. 



At first substances which hold a position between paracasein 

 and peptones, e.g. caseoglutin are formed, and afterwards, 



