558 MANUAL OF MILK PRODUCTS 



able on account of the cooked taste produced in the milk, and 

 because of the reduction of the cream line and the possibility 

 of some chemical alteration of the milk. With the lower tem- 

 peratures of the holder process no cooked taste is produced, 

 there is no noticeable reduction of the cream line, and only 

 slight chemical changes, if any at all, take place. Finally, the 

 use of lower temperatures is preferable, from a financial stand- 

 point, as they effect a saving in the cost of steam for heating 

 and in refrigeration for cooling. 

 Temperatures and methods to be used. 



It is essential to use an accurate thermometer when heating 

 milk. Many of the ordinary thermometers may register a 

 number of degrees away from the correct reading, so the ther- 

 mometer in use should be tested against a thermometer known 

 to be correct. 



As previously stated, the best method of pasteurization at the 

 present time, and the one which should be used, is the holder 

 process, in which the milk is held for thirty minutes. For this 

 process a temperature of 145° F. is to be advised, since that 

 temperature gives a margin beyond that sufficient to destroy 

 pathogenic organisms, while at the same time it leaves in the 

 milk the maximum number of lactic acid producing organisms 

 which cause the souring of the milk. When using the flash 

 process, the milk should be heated to at least 160° F. Since 

 there is almost always a fluctuation in the temperature during 

 pasteurization, care should be taken to see that the tempera- 

 ture never drops below 160° F. in the flash process. 



The pasteurization of milk in bottles may, in the future, 

 prove to be the best method when suitable machinery is 

 devised for the process. 



If the process of bottling pasteurized milk while hot proves 

 satisfactory on a commercial scale, it will undoubtedly be an 

 important improvement on the present system of pasteurizing 

 milk. 



