THE PASTEURIZATION OF MILK 



through a commercial pasteurizer and heated to 

 different temperatures, and held for varying lengths 

 of time. The results obtained indicated that when 

 an attempt was made to heat this milk in a com- 

 mercial pasteurizer to a temperature of 140 F., and 

 then hold it for twenty minutes, there was a con- 

 siderable unavoidable variation in the actual tem- 

 perature to which the machine was capable of 

 heating the milk. This was due to the difficulties 

 of both hand and automatic temperature control. 

 Even with the best automatic controller, it is 

 probable that the real variation of temperature is 

 greater than is indicated upon the record charts. 

 Thermometers are not usually sufficiently sensitive 

 to record rapid fluctuations in temperature. It is 

 also true that thermometers indicate average tem- 

 peratures only, and it is possible that certain por- 

 tions of the milk, the temperature of which is con- 

 siderably below this indicated average, pass 

 through the apparatus. 



In regard to the time held also, especially when 

 a continuous or flow type holding apparatus is 

 used, great uncertainty exists. It is impossible to 

 be sure that the time is the same as intended. The 

 rate of flow varies, and there is also more or less 

 26 



