86 SWEETENED CONDENSED MILK CONDENSING 



sure permissible must be governed by the amount of heating sur- 

 face, the capacity of the vacuum pump and the temperature and 

 amount of water available for use in the condenser. Under aver- 

 age conditions about fifteen pounds of steam pressure may be safely 

 used. 



During the early stages of the process, when the milk is of 

 low density, the evaporative duty is high, probably about twenty- 

 five to thirty-five pounds per square foot of heating surface with 

 ten pounds of steam pressure. This gradually decreases and is 

 lowest toward the end of the process. 



When enough milk is in the pan to completely cover the jacket 

 and coils, the milk intake should be reduced and regulated in ac- 

 cordance with the rate of evaporation. The milk is drawn into the 

 pan continuously, but only as fast as it evaporates. It should be 

 kept as much as possible at a constant level, and this level is prefer- 

 ably as low as is consistent with complete covering of the upper coil. 



In order to secure maximum rapidity of evaporation, the 

 vacuum pump should run at the proper speed and its operation 

 should be uniform, a uniform vacuum and temperature should be 

 maintained and the milk should be prevented from rising to an ab- 

 normally high level in the pan. 



Prevention of Accidents. The operator should pay strict at- 

 tention to the pan in order to avoid loss of milk due to accidents. 

 He should watch the water supply and govern its use accordingly. 

 If the water supply becomes exhausted, air is liable to be drawn 

 into the pan through the condenser. This will cause the milk to drop 

 suddenly and then rise in a body, threatening to escape through the 

 condenser. Whenever air in considerable quantities is allowed to 

 enter the pan while in operation, be it as the result of lack of water, 

 or through any other cause, or when the vacuum pump is allowed to 

 stop and live steam is turned into the milk in the pan, as is the case 

 when the milk is superheated, the escape of milk may be avoided by 

 immediately shutting the steam inlet to the jacket and coils, by clos- 

 ing the milk intake and by slightly opening the blow-down valve 

 whenever the milk rises dangerously high. By skillful manipulation 

 of the blow-down valve until the milk again settles down to uniform 



