156 MANAGEMENT OF DAIRY PLANTS 



that such steam enters the pasteurizer at a point close to the 

 inlet of the cold milk. 



E. Milk Moving too Slowly Over the Heating Surface. If 

 the milk is moving rapidly over the heating surface there is no 

 part of the milk solids that will remain long enough in touch 

 with the heating surface to burn on. It is therefore essential 

 that the heating surface is smooth; rough places either due 

 to imperfect metal or to burned-on particles retard the speed 

 of small parts of milk and therefore at such places more or 

 less burned-on milk solids will be found. Higher speed of the 

 agitator may prevent the milk particles from burning on. 



The Danish Experiment Station 1 (Fig. 28) placed horizontal 

 plates on the agitator of a pasteurizer of the continuous type. 

 This caused the milk to move over the heating surface at a 

 higher rate of speed and as a result less milk solids burned on to 

 the heating wall. The horizontal plates on the dasher further- 

 more assured uniform heating of all particles of milk pasteurized 

 by preventing milk just entering the pasteurizer from splashing, 

 whereby some of the cold milk might be discharged with the 

 milk properly pasteurized. More particles of the milk will 

 come in direct contact with the heating surface of the pasteur- 

 izer and the economic efficiency of the machine is thereby in- 

 creased. 



III. Purchasing Equipment for Pasteurization. 



1. Pasteurizer. When purchasing a pasteurizer the buyer 

 should request that the manufacturer furnish a guaranty as to 

 its economic efficiency. If a machine is represented to be of 

 1,000 pounds capacity per hour the temperature of pasteuriza- 

 tion should be considered, as it takes about twice as long to 

 pasteurize a given amount from 60 F. to 185 F. as is required 

 to pasteurize the same amount from 60 F. to 145 F. The 

 pasteurizer should be constructed from material of sufficient 

 strength and the heating surface should be smooth. 



2. Cooler. The cooler should be of a size sufficient for cool- 

 ing the milk or cream to within 2 to 4 F. of the temperature of 

 the water. If a tubular cooler is used the tubes should be con- 



1 Bulletin 43, Danish Experiment Station, 1899. 



