Condensed Milk; and Milk Powder 63 



denser to maintain a high vacuum. As soon as the steam pres- 

 sure in the jacket and coils reaches the point where the water in the 

 condenser fails to promptly reduce the vapors, the vacuum drops, 

 the temperature in the pan rises and evaporation is checked. 



If the water supply were unlimited and the water available 

 were cool (about 50 degrees F. or below), condensing with twenty 

 to twenty-five pounds of steam pressure in the jacket and coils would 

 result in the maximum rate of evaporation' consistent with good 

 quality of the product. 



The condensing of milk requires immense quantities of water; 

 experience has shown that it takes from two to three gallons of 

 water to condense one pound of fresh milk. The water supply is 

 one of the weakest points in most condenseries, so that economy of 

 water is one of the important factors to be considered. The steam 

 pressure in the jacket and coils should therefore be so regulated, as 

 to make it possible to maintain the maximum vacuum consistent 

 with reasonably economic use of water. The experience of the best 

 pan operators is that about fifteen pounds of steam pressure in the 

 jacket and coils and a vacuum of twenty-five inches is practically the 

 maximum that can be maintained under average conditions without 

 taxing the usual water supply beyond its capacity. With a vacuum 

 of twenty-five inches the temperature in the pan is about 135 degrees 

 F., the temperature varying somewhat with the altitude of the fac- 

 tory. In some condenseries the temperature of the pan is kept at 

 150 degrees F. This practice may economize the water a trifle 

 better, but the rapidity of evaporation is considerably lower. 



Condensing at temperatures lower than 130 degrees F., without 

 reducing the steam pressure in the jacket and coils, increases the 

 rapidity of evaporation, but taxes the water supply beyond the reach 

 of most condenseries. So much water has to be used in the con- 

 denser that it is not used economically, as is shown by the relatively 

 low temperature of the water discharging from the condenser. The 

 temperature of the condenser discharge bears a direct relation to 

 the temperature of the vapors in the pan. Observations made in 

 various factories and under different conditions by Hunziker and 

 others showed that the condenser discharge was anywhere from 5 to 

 25 degrees F. lower in temperature than the vapors in the pan, the 

 difference averaging about 15 degrees F. 



