THE MILK CONTRACTOR 



279 



Physical and Chemical Changes Induced in Milk by Pasteurizing. 



It is charged that pasteurizing milk changes its physical and chemical 

 properties to its detriment. It is true that milk is altered by heating but 

 careful investigation by many observers has established the fact that the 

 changes that are induced depend on the degree of heat applied and on the 

 length of the heating period. North has compiled the results reported by 

 many students of the subject and has made a graph, Fig. 41, illustrating 

 the most important changes that take place in the milk and the effect of 

 heating on certain disease germs. It appears that the salts begin to be 



30' 40' 



Time in Minutes 



FIG. 41. Time and temperature for milk pasteurization, C. F. North. 



affected when the milk is heated to 170F. for 40 min. and in less time as 

 the temperature of heating rises till at 176F., heating for 1 min. affects 

 them. The principal changes that occur are the precipitation of calcium 

 and magnesium salts and a great part of the phosphorus together with a 

 decrease in organic and an increase in inorganic phosphorus. The albu- 

 min is more sensitive to heat; it is injured by heating it for 30 min. at 

 149F., or for 10 min. at 158F. and in correspondingly less time at higher 

 temperatures. 



The enzymes, the figure shows, may be heated to 149F. for 20 min. 



