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UNITED STATES DEPARTMENT OF AGRICULTURE 
f BULLETIN No. 342 J 
jtu^*^-t^ 
Washington, D. C. 
Issued January, 1916; revised June, 1932 
THE PRESENT STATUS OF THE PASTEURIZATION 
OF MILK 
By S. Henry Ayers, 1 Bacteriologist, Bureau of Dairy Industry. Revised by 
R. P. Hotis, Associate Market Milk Specialist, and C. J. Babcock, Market 
Milk Specialist, Division of Market Milk Investigations, Bureau of Dairy 
Industry 
CONTENTS 
Page 
Meaning of the term pasteurization 1 
Past and present theories of pasteurization 1 
Value of pasteurization.. 2 
Extent of pasteurization in the United States.. 6 
Electrical and ultra-violet-ray treatment of milk 10 
Methods of heating milk 11 
Advantages of low-temperature pasteurization. 14 
Temperatures and methods most suitable for 
pasteurization 14 
Supervision of the process 15 
Pa^e 
Handling of milk after pasteurization 17 
Cost of pasteurizing milk 17 
Bacteria that survive pasteurization 17 
Survival of streptococci 20 
The colon test for effectiveness of pasteurization 20 
Pasteurization and vitamins 21 
Pasteurized milk for infants 22 
The necessity for pasteurization 23 
Literature cited.. _ 23 
MEANING OF THE TERM PASTEURIZATION 
The term " pasteurization" originated in the experiments of Louis 
Pasteur in France. In the period 1860-1864, in experiments on the 
" diseases" of wine, he found that heating for a few moments at 
temperatures of 122° to 140° F. was sufficient to prevent abnormal 
fermentations and souring in wine. A little later he found that by 
similar heating beer could be prevented from souring. The appli- 
cation of the process gave rise to the term "pasteurization." 
As applied under commercial conditions, pasteurization is the 
process of heating liquids for a short or a long period, as the different 
processes demand, at temperatures usually between 140° and 185° F. 
As applied to milk for direct consumption, pasteurization should mean 
a process of heating every particle of milk to a temperature not lower 
than 142° F. for not less than 30 minutes. The process is followed 
by rapid cooling. 
PAST AND PRESENT THEORIES OF PASTEURIZATION 
Pasteurization is at present favorably regarded by most medical 
men, sanitarians, dairymen, and consumers, but the use of the process 
has not been developed without opposition. Most of the objections 
to pasteurized milk have been based upon theory or upon experiments 
in which milk was heated at high temperatures. 
1 Mr. Ayers resigned from the department in 1923. 
113363°— 32 1 
