CASEIN 17 



has obtained a substance from milk called fibrin. These 

 latter substances, however, are present in minute portions, and 

 are believed by some of the best scientists to be the same as^Hie 

 albumen. Their presence in the filtrate is due to incomplete 

 precipitation of the albumen in the first place. 



Casein. Casein is by far the most important of all of the 

 albuminoids. It is the substance which forms the curd in cheese- 

 making. In fresh milk, as is now understood, it is in chemical 

 combination with lime salts. It is on this account that fresh milk 

 shows the amphoteric reaction, which will be explained under 

 the " Properties of Milk." The coagulation of casein by the 

 addition of rennet or dilute acids is thought to be due to this 

 union between the casein and lime. Fleischmann refers to this 

 as the " caseous matter " of milk. The viscosity of normal milk 

 is believed to be due in a large measure to this condition of casein 

 in milk. It causes the casein to be present in a colloidal condi- 

 tion. When milk coagulates by natural or by artificial means, 

 the union between the casein and lime phosphate is largely 

 broken. 



Casein and albumen -differ in composition, in that the casein 

 contains phsophorus and less sulphur than does albumen. 

 Fleischmann maintains that a substance called nuclein is asso- 

 ciated with casein, and is not found in albumen. 



Casein is precipitated by the use of rennet and dilute acids, 

 and coagulates spontaneously, due to the acid formed in the milk. 

 The precipitates formed by the use of different precipitating 

 agents are not alike. The curd coagulated by rennet contains 

 more fat and calcium phosphate than the curd which is precip- 

 itated by dilute acid or by the spontaneous souring of the milk. If 

 milk stands at air temperature for any length of time after milk- 

 ing, the caseous matter (or the nitrogenous matter combined with 

 lime) tends to separate. The caseous matter of milk is not com- 

 pletely precipitated by heat, although heat partially destroys the 

 union between the casein and lime. This largely destroys the 

 action of rennet. Instead of getting a smooth solid coagulum, a 

 more flaky precipitate is obtained. For this reason milk for 

 cheese-making should not be heated to a high temperature. By 



