12 BULLETIN 85, U. S. DEPARTMENT OF AGRICULTURE. 



it becomes necessary to put them all on an equal basis, so far as it is 

 possible to do so, and for this purpose it is assumed that the pasteur- 

 izing cycle consisted in raising and lowering the temperature of the 

 cream through a range of 100° F., all other conditions remaining the 

 same. The cost of pasteurizing 100 pounds of cream in the different 

 plants, corrected as above, is $0.0459, $0.0650, $0.0726, and $0.1056 

 for tests Nos. 1, 2, 3, and 4, respectively. 



The amount of cream handled will, of course, affect the unit cost 

 to a great extent, as may be gathered from the summary of tests. 



Referring to test No. 4, the power required for driving the pasteur- 

 izing equipment was excessive, as a considerable amount of line 

 shafting was uselessly driven while pasteurizing. This, together with 

 taking steam from the boiler through a reducing valve instead of 

 using the heat from the exhaust steam, accounts for the high cost of 

 pasteurizing at this plant. 



CONCLUSIONS. 



The conclusions drawn from the foregoing tests are as follows : 



1. The flash process of pasteurization requires approximately 17 

 per cent more heat than the holder process. There is a correspond- 

 ingly wider range through which the milk or cream must be cooled, 

 both adding extra cost to the pasteurizing cycle. 



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. With poorly arranged apparatus and leaky piping the loss in 

 heat may reach approximately 30 per cent of that required to pas- 

 teurize, which it is practicable to reduce 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 with which to pasteurize both milk and cream. 



5. Usually there is sufficient heat in the exhaust steam which is 

 allowed to waste in milk plants and creameries to do the pasteurizing. 



6. For every 400 pounds of milk pasteurized per hour with exhaust 

 steam, approximately one horsepower is taken off the boiler plant. 



7. The average cost of pasteurizing 1 gallon of milk is shown to be 

 $0.00313. 



8. The average cost of pasteurizing 1 gallon of cream is shown to be 

 $0.00634, or $0.0756 per 100 pounds. 



9. It must be understood that the cost of pasteurizing as figured 

 in this paper deals only with the pasteurizing cycle, viz, starting with 

 the initial temperature of the raw milk and raising its temperature 

 to the pasteurizing point, then cooling the milk down to the initial 

 temperature of the raw milk. In other words, it has been attempted 

 to show the additional expense encountered in producing pasteurized 

 milk and cream over the raw product. 



o 



