310 CITY MILK SUPPLY 



Cost of Pasteurization. The average cost of pasteurization is difficult 

 to determine because it varies a good deal in different localities, being- 

 dependent on the price of labor, of coal, on the capital invested in machin- 

 ery, on the temperature of the milk when received at the plant and on 

 other factors of moment. Bowen for the U. S. Department of Agriculture 

 investigated the cost of pasteurizing milk at five representative milk 

 plants and of cream at four cream-pasteurizing plants. All of the city 

 milk plants used the holder process whereas but two of the cream- 

 pasteurizing plants did so. 



Some of Bowen's results at the city milk plants are given in Table 86. 



Bowen also made tests of the cream-pasteurizing apparatus at four creameries. 

 The apparatus represented both the flash and holder type of machines and pasteuriza- 

 tion was accomplished by using (1) live steam, (2) exhaust steam from the engine or 

 from steam-driven pumps and (3) hot water heated by exhaust steam from steam- 

 driven auxiliaries. The acutal cost of pasteurizing cream at each of the four plants 

 was $0.0456, $0.0701, $0.765, and $0.1101. 



The conclusions reached by Bowen were that : 



"1. The flash process requires about 17 per cent, more heat than the holder, 

 process, consequently the milk or cream must be cooled through a wider range, 

 hence both add to the cost of pasteurizing. 



"2. The proper design and arrangement of the heater, regenerator, cooler, 

 piping and refrigerating apparatus have much to do with the efficient operation 

 of the plant. 



"3. The loss in heat from poorly arranged apparatus and leaky piping may 

 amount to approximately 30 per cent, of the total amount of heat required to 

 pasteurize and it is practicable to reduce this loss to a negligible amount. 



"4. It is practicable to use exhaust steam from the engine and steam-driven 

 auxiliaries, or water, heated by exhaust steam, to furnish heat wherewith to pas- 

 teurize both milk and cream. Milk plants usually waste enough heat in the 

 exhaust to do the pasteurizing. 



"5. For every 400 Ib. of milk pasteurized per hour with exhaust steam ap- 

 proximately 1 hp. is taken off the boiler plant. 



"6. The average cost of pasteurizing 1 gal. of milk is $0.00313 and 1 gal. of 

 cream $0.00634." 



These figures of Bowen's deal with the pasteurizing cycle proper, that 

 is, starting with the initial temperature of the raw milk and raising its 

 temperature to the pasteurizing point and then cooling the milk to the 

 initial temperature of the raw milk. They show the additional expense 

 of producing pasteurized milk over the raw product. The results of 

 Bowen's tests have been quoted only in part and the reader is advised 

 to consult the original paper. 



With regard to the present use of pasteurization it may be said that 

 butter and cheese makers have wisely adopted the flash process. In the 



