PASTEURIZATION 203 



avoided. The tendency of abnormal curdling is especially pro- 

 nounced in the case of cream very low in butterfat. 



In the case of sweet cream, or sour cream neutralized to 

 about .25 per cent acid, there is no danger of the formation of 

 an abnormal curd. The neutralizer should be added after all 

 the cream of one batch is in the vat pasteurizer and before the 

 heat is turned on. The neutralizer should be distributed uni- 

 formly throughout the cream in the vat while the coil is revolv- 

 ing. If sweet milk is added to the cream it should be added im- 

 mediately after neutralization and before pasteurization. 



Speed of Revolving Coil. The coil in the vat pasteurizer 

 should be run at the speed indicated in the directions furnished 

 by the manufacturer of the vat. The exact speed desired varies 

 with the size of the vat and the size of the coil, ranging from 

 about 25 to 40 revolutions per minute. The higher speed ap- 

 plies to the smaller coils and the lower speed to the larger 

 coils. A coil with a 24 inch diameter should revolve about 35 

 to 40 revolutions per minute, while a coil with a 29 inch diam- 

 eter should make about 28 to 30 revolutions per minute. 



Insufficient speed of the coil fails to produce adequate agita- 

 tion which in turn makes the control of the temperature difficult, 

 retards the heating and cooling and may augment the coating 

 of the coil with cooked cream. 



Too high a speed of the coil causes excessive foaming of 

 the cream and the beating of air into it. The foaming is 

 objectionable because it renders difficult the emptying of 

 the vat without the use of excessive volumes of water and usual- 

 ly incurs excessive loss of fat. The beating of air into the cream 

 is undesirable because the incorporated air invites oxidation 

 which later may lead to butter defects. 



Fullness of Vat Pasteurizer. The best results are obtained 

 when the vat is full enough to completely submerge the revolv- 

 ing coil in the cream. The heating and cooling proceeds faster 

 when the coil is submerged than when part of it projects above 

 the cream, because with a submerged coil the entire coil is active 

 at all times while, in the case of an exposed coil only part of 

 the coil does duty. The portion of the coil that is exposed to 



