BULLETIN OF THE 



No. 85 



Contribution from the Bureau of Animal Industry, A. D. Melvin, Chief. 

 April 27, 1914. 



(PROFESSIONAL PAPER.) 



THE COST OF PASTEURIZING MILK AND CREAM. 



By John T. Bowen, Technologist, Dairy Division. 

 INTRODUCTORY. 



In the pasteurization ot inilk and cream there are two systems in 

 use at the present time, known as the "holder" and the "flash" 

 processes. The holder process consists in holding the milk or cream 

 for about 30 minutes after it has been heated to the pasteurizing 

 temperature of 140° to 150° F. ; either in the same apparatus in which 

 the pasteurization takes place or in separate holding tanks arranged 

 for the purpose, after which it flows to the coolers. In the flash or 

 continuous process the milk or cream flows from the receiving tank 

 to the pasteurizer, where it is heated to a temperature of from 160° 

 to 165° F. in from 30 seconds to 1 minute, and from thence direct to 

 the coolers, where it is cooled. 



It is obvious that there is more heat required to pasteurize a given 

 amount of milk or cream in the latter process than in the former; 

 for example, assuming that the initial temperature of the incoming 

 milk is 60° F. and that in the holder process it is heated to 150° F. 

 and in the flash process to 165° F., then for every 1,000 pounds of 

 milk to be pasteurized by each of these processes the actual number 

 of heat units required to raise the temperature of the milk to the 

 pasteurizing temperature is: 



B. t. u. 1 =l,000X0.95 2 (150-60)=85,500, holder process. 

 B. t. u. =1,000X0*95 (165-60)=99,750, flash process. 



It will be noted from the above figures that the flash process of 

 pasteurization requires 16.6 per cent more heat to pasteurize a given 



1 B. t. u. (British thermal unit) is the quantity of heat required to raise 1 pound of pure water 1° F. at or 

 near its maximum density, 39.1° F. For practical purposes, however, it may be considered the heat 

 required to raise the temperature of 1 pound of water 1° F. 



2 The specific heat of milk is taken as 0.95. The specific heat of any substance is its capacity forabsorbing 

 heat compared with that of water taken as unity. 



Note. — This bulletin deals with the cost of pasteurization from an engineering point of view. It con- 

 tains desirable information for proprietors of creameres and milk plants and for designers and manu- 

 facturers of pasteurizing apparatus. 

 33347°— 14 



