CONDENSED MILK HEATING 55 



to lessen the tendency of the sugar to crystallize in the finished 

 product. Undissolved sugar crystals in condensed milk act in a 

 physical way much as bacteria in fluid milk do in a bacteriological 

 way. They multiply rapidly, and such condensed milk usually 

 precipitates its sugar before the product reaches the market. The 

 presence of excessive sugar crystals makes the product gritty and 

 causes the formation of a sediment in the bottom of the cans ; this 

 is objectionable to the consumer. When the milk is heated to the 

 proper temperature before condensing, the solution of the cane 

 sugar is facilitated and the tendency toward grittiness is minimized. 



PREVENTION OF BURNING MILK ON HEATING SURFACE. If cold 

 milk comes in contact with a steam-heated surface and is not agi- 

 tated vigorously, it bakes or burns onto this heating surface. The 

 milk in the vacuum pan is heated or kept hot by means of the steam 

 jacket and coils. These radiators are charged with steam under 

 pressure and consequently give off a high degree of heat. If cold 

 milk is drawn into the vacuum pan, the milk remains calm for a 

 considerable length of time. During this time it is bound to bake 

 or burn on the heating surface, giving the product a burnt flavor, 

 causing it to contain brown specks and retarding the process of 

 evaporation. If the milk is hot when it enters the pan, the reduced 

 pressure in the pan causes it to boil violently at once, avoiding all 

 danger of sticking to and burning on the heating surface and making 

 possible maximum rapidity of evaporation. 



Temperature. In most factories the milk is heated to from 

 180 degrees F. to 200 degrees F. This temperature is sufficient to 

 accomplish the three purposes. Heating the. milk to the boiling point 

 tends to give it a rather pronounced cooked flavor, which is objec- 

 tionable. However, in the case of danger of contamination of the 

 milk with resistant types of undesirable bacteria, it may become 

 necessary to practice boiling the milk. 



Manner of Heating. Thorough, efficient and rapid heating of 

 large volumes of milk to temperatures near the boiling point is a 

 problem that requires careful consideration. The tendency of the 

 milk to stick to the heating surface is a permanent obstacle and 

 efforts to overcome this frequently result in sacrificing thoroughness 

 of heating. 



