PASTEURIZATION 213 



f erences were observed, in some cases calves fed on boiled 

 milk developed a diarrhoea which disappeared when raw 

 milk was substituted. 



5. Ferments or Enzymes. In the opinion of some 

 authorities, the ferments or enzymes contained in milk 

 play a very important role in its digestion and assimila- 

 tion. From this standpoint the effect of heat on these 

 substances is therefore an important consideration in 

 connection with the pasteurization of milk. Most of the 

 ferments in milk can withstand a temperature of from 

 60 to 65 C. (140 to 149 F.) for some time, while higher 

 temperatures weaken or destroy them. 



6. Taste. Milk does not acquire a cooked taste un- 

 less it is heated to 158 F. (70 C.) or above. 



7. Cream Line. If milk is exposed to a temperature 

 of 70 C. (158 F.) or above, the cream will not sepa- 

 rate. A temperature of 65 C. (149 F.) for 10 min- 

 utes has no effect on the separation of the cream, but 

 as the time of exposure to this temperature is increased 

 beyond this period the separation of the cream is de- 

 layed more and more until finally, after 40 minutes ex- 

 posure, it does not separate at all. A temperature of 

 145 F. (62.8 C.) for 30 minutes and 60 C. (140 F.) 

 for as long as 50 minutes has no effect on the formation 

 of the cream layer. In the commercial pasteurization 

 of milk, the pumping and stirring necessary to force 

 the milk through the heater and to bring it in contact 

 with the heated surfaces may have the effect of breaking 

 up the fat globules and thus interfere with cream sepa- 

 rating even when the temperature has not been suffi- 

 ciently high to alone affect the cream line. 



Summarizing the facts which have been definitely 

 established regarding the effects of pasteurization, we 



