12 



at equal cost with reference to its ability to stimulate growth, 

 both of the bony and muscular structure, are not affected by 

 heat; they remain entirely normal and unchanged. I say, 

 even if these changes of the physical and chemical properties 

 of the milk constituents do occur, it does not necessarily 

 follow that the milk so changed is less digestible than raw 

 milk. 



But these changes are possible only when heating to tem- 

 peratures near the boiling point. Boiling milk and pasteurizing 

 it are two different processes. Boiling is not pasteurizing. 

 Pasteurization as now understood and practiced refers to heat- 

 ing to 145° F. and holding for twenty to thirty minutes. At 

 this temperature these changes do not occur, or, at the most, 

 only to a very slight extent, nor is the activity of the enzymes at 

 this temperature destroyed. Pasteurization properly executed, 

 therefore, does not impair the digestibility of market milk and 

 does not render such milk less suitable for infant feeding. 



Commercially the greatest objection to pasteurization of 

 market milk has been that the pasteurized milk loses its cream 

 line. Since the consumer judges the richness of the milk 

 largely by the depth of the layer of cream that forms in the 

 neck of the bottle, and since many families desire to use that 

 cream separately on the table, by pouring it off the top of the 

 bottle, the cream line is a commercially important feature that 

 cannot be overlooked. Its absence loses trade. The fact that 

 pasteurization at temperatures near the boiling point does 

 cause the cream line to disappear has led to the popular con- 

 clusion that all heating diminishes the cream line. This is 

 erroneous. Heating to very high temperatures does retard, if 

 not destroy, the formation of the cream line. This is an es- 

 tablished fact. But heating to 14:5° F. and holding for twenty 

 to thirty minutes does not diminish it, but actually enhances 

 its formation, and tends to produce a deeper cream line if 

 anything. This point was experimentally demonstrated by Dr. 

 Burri of Switzerland, whose results conclusively showed that up 

 to 145.4° F. the cream line formed more rapidly and was deeper 

 than in the raw milk of the same batch. 



The reason for this lies in the well-known fact that heat 

 destroys the viscosity of the milk. It makes milk more fluid. 



