PASTEURIZATION 207 



In normal milk the larger proportion of the fat droplets 

 agglutinate into tiny globules or masses. At a temperature 

 of 65° C. or above, these clusters are broken down and the 

 globules are more homogeneously distributed throughout 

 the fluid. 



The cooked or scalded taste appears at about 70° C, 

 and becomes more pronounced the higher the temperature. 

 This is due perhaps to a decomposition of certain of the 

 proteids in the milk. The loss of certain gases also alters 

 the taste, so that milk heated in closed vessels has a much 

 less pronounced flavor than if heated in open vessels. 



The coagulation of milk depends upon several factors, 

 among which are time, temperature, degree of acidity, 

 quantity and solubility of the calcium salts, etc. 



Milk curdles when it is heated to 130 or 150° C. It may 

 also be coagulated by about twelve hours heating at 100° 

 C. 



The presence of acids favors coagulation of milk at or 

 below the boiling-point, due to the fact that very small 

 quantities of acid liberate the casinogen and render the 

 calcium salts normally present in' milk available for its 

 coagulation. 



Milk sometimes curdles in the process of pasteurization. 

 This is due to the amount of acid and calcium salts which 

 it contains. In order to avoid such accidents, Kastle 

 advises that the only safe rule to follow is to determine 

 the effect of heating on small samples of the milk in ad- 

 vance. 



It has been observed that cooked milk coagulates with 

 rennin more slowly than raw milk. This effect is noted 

 often at temperatures of 80° to 90° C, but it has not been 

 observed in milk heated to 60° for twenty minutes. The 

 curd produced by rennin coagulation in cooked milk is 

 softer, less tough, and more flocculent, than that produced 

 by rennin coagulation in raw milk. This is believed to be 

 an advantage favoring the digestibility of heated milk. 



