Condensed and Evaporated Milk 49 



pan. The temperature of the pan should be about 

 130° F. with a vacuum or about 25 to 26 inches of 

 mercury. 



It is desirable to have the heating surface in the 

 pan as large as possible in order to make high steam 

 pressure in the jacket and coils unnecessary, and in- 

 sure complete condensation of the steam. Otherwise 

 too high milk temperatures or waste of steam results. 

 Steam gauges should be placed just after the valves 

 connecting the jacket and coils with the main steam 

 line. Twenty-five pounds' pressure is considered as 

 high as can be safely used, and many condenseries 

 operate with twelve to twenty pounds' steam pres- 

 sure. Taking into consideration the ordinary water 

 supply, fifteen pounds' steam pressure and twenty- 

 five inches' vacuum are about the best conditions that 

 can be steadily maintained. The temperature is 

 about 135 degrees at this vacuum. 



The milk is drawn into the pan by vacuum. After 

 enough has been drawn in to boil well, a constant 

 stream maintains the same volume in the pan. Care 

 must be exercised or the milk will boil over the top. 

 The usual practice is to concentrate a trifle too much 

 and then standardize by the addition of distilled 

 water. This can only be done when the milk has 

 been standardized in the holding tanks. 



It is very important for the successful operation 

 of the pan that, it be equipped with an accurate 

 thermometer and vacuum gauge. A thermometer 

 which is constructed so that the bulb may be well 

 submerged in the milk is more sensitive to tempera- 

 ture changes and at the same time makes it possible 

 to place the indicator where it is convenient to read. 

 Such a thermometer is known as a long-distance type 

 thermometer. 



