PASTEURIZATION 211 



bottle are sometimes not as hot as the bottom, or require a 

 much longer time to heat up. 



Commercial pasteurization 



Pasteurization of milk on a conunercial scale often 

 leaves much to be desired. But although it is not always 

 thoroughly carried out, it is by no means a fraud, as we are 

 sometimes told. With a little sanitaiy supervision on the 

 part of the health officer and education on the part of those 

 in charge of the process, it may be made efficient. It is 

 much easier to pasteurize milk on a large scale than on a 

 small scale in the household. 



Commercial pasteurizers at first were popular with dairy- 

 men, not because of the public health interest, but on 

 account of the economic advantages in improving the keep- 

 ing qualities of the milk. It is estimated that the expense 

 of a pasteurizer would pay for itself in the course of 

 about a year. This estimate is based mainly on the saving 

 of losses from sour milk. The cost of pasteurization in 

 bulk varies from about one tenth to one half of a cent a 

 quart. 



There are three ways in which milk may be pasteurized 

 commercially: — 



(1) By the flash method, which is sometimes improperly 

 called commercial pasteurization. 



(2) By the holding method, which is also known as per- 

 fect pasteurization. 



(3) Pasteurization in the bottle or final container. 

 Each of these requires consideration. The flash method, 



in which the milk is momentarily heated to 70° or 80° and 

 then at once chilled, cannot be depended upon to kill the 

 tubercle bacillus, and is known to give irregular and unreli- 

 able results. It is difficult to be sure that eveiy particle of 

 the milk is heated to the desired temperature; in fact, it is 

 quite sure that some of the milk escapes, and the results, 

 therefore, are irregular and unreliable. Flash pasteuriza- 



