Condensed Mixk and Mii,k Powder 65 



be governed by the amount of heating surface, the capacity of the 

 vacuum pump and the temperature and amount of water available 

 for use in the condenser. Under average conditions about fifteen 

 to twenty 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 pref- 

 erably as low as is consistent "with complete covering oi the upper 

 coil. 



In order to secure maximum rapidity of evaporation, the 

 vacuum prmip 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, 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 careful manipula- 

 tion until the milk again settles down to uniform boiling, loss can 

 be avoided and the process can be continued in the normal way. 



By the time all the milk is in the pan, condensation is nearly 

 completed, and from ten to twenty minutes further boiling usually 

 gives the milk the desired density. Toward the end of the process 



