STATUS OF PASTEURIZATION OF MILK 
safety when milk is Pasteurized at 
140° F. for 30 minutes, and the com- 
mittee expressed the following opin- 
ion : 
The committee feels that while enough 
has been done to indicate clearly that a 
proper application of heat to a temperature 
of 140° F. for a minimum period of 30 
minutes will destroy substantially all the 
pathogenic bacteria in milk, still they be- 
lieve, as already expressed, that a margin 
of safety for biological reasons calls for 
the use' of higher temperatures of not 
lower than 145° F. 
The United States Department of 
Agriculture, since 1910, (2) has ad- 
vised the use of a temperature of 145° 
F. for a period of 30 minutes for the 
Pasteurization of milk. Besides in- 
suring an ample margin of safety, a 
temperature of 145° F. causes a con- 
siderably greater destruction of bac- 
teria in milk than 140° F. when held 
for the same period of 30 minutes. 
Extensive experiments (3) in the re- 
search laboratories of the Bureau of 
Dairy Industry have shown that the 
thermal death point of a considerable 
number of bacteria lies between 140° 
and 145° F. ; therefore an increase of 
5° above 140° F. produces a great in- 
crease in the destruction of bacteria. 
There is a marked tendency in com- 
mercial work to Pasteurize at or near 
the minimum temperature require- 
ment necessary to destroy pathogenic 
organisms, namely. 140° F. Such 
seems to be the case because of the 
fear of injuring the cream line. In 
fact, the opinion is often expressed by 
milk-plant operators that a tempera- 
ture of 145° F. can not be used be- 
cause of the marked loss in cream line. 
Whittaker, Clement and others (19) 
have studied the effect of temperature 
on the cream line in a number of dif- 
ferent plants throughout the country, 
and have come to the following con- 
clusion : 
Milk heated to 143° F. for 30 min- 
utes showed practically no decrease 
in the cream volume, and in some 
cases an increase resulted. 
Pasteurization at 145° to 146° F. 
for 30 minutes reduced the cream 
volume an average of approximately 
8 per cent, with considerable varia- 
tions above and below. 
Pasteurization at approximately 
148° F. for 30 minutes caused a de- 
crease in cream volume of from 18.5 
to 41.7 per cent, with an average de- 
crease of approximately 31 per cent. 
It may be said, however, that there 
are plants in this country, including 
some of the largest, in which milk is 
successfully Pasteurized at 145° F., 
and this temperature is maintained for 
6552°— 26 2 
30 minutes. It is also interesting to 
note that at the 1921 meeting of the 
International Dairy and Milk Inspec- 
tors' Association, Pease reported ex- 
periments carried on by Heulings and 
him which showed that Pasteurization 
at 145° F. for 30 minutes did not de- 
crease the cream line when the milk 
was properly heated and cooled. 
The method of Pasteurization, 
whether it is the holder or in-the- 
bottle process, is not so important pro- 
vided the process is such that the milk 
is heated to 145° F. and that all of it 
is held for 30 minutes. The great 
majority of plants Pasteurize by the 
holder process, and it is gratifying to 
observe that the flash process is but 
little used. Replies to a question- 
naire sent to numerous cities in this 
country showed only 33 plants using 
the flash process in 18 cities out of the 
266 which supplied information on this 
subject. Five cities reported that the 
flash process was not allowed, while 
one permitted its use but would not 
allow the milk to be labeled " Pas- 
teurized." 2 
SUPERVISION OF THE PROCESS 
Intelligent supervision of the Pas- 
teurizing process is absolutely neces- 
sary and can not be provided unless 
there is a thorough knowledge of the 
primary object of Pasteurization and 
the bacteriological principles involved. 
The primary object is the destruc- 
tion of any disease-producing bacteria 
which may be in the milk and the 
handling of the Pasteurized milk in 
such manner that it can not be rein- 
fected. When this object is accom- 
plished it is found that a large percen- 
tage of the bacteria in the milk are 
destroyed and its keeping quality 
greatly improved. 
The primary object can be accom- 
plished by heating all the milk to 145° 
F. and holding it for a period of 30 
minutes. It is then only necessary to 
cool the milk immediately over thor- 
oughly cleaned and steamed coolers, 
to run into thoroughly cleaned and 
steamed, or otherwise sterilized, bot- 
tles through a thoroughly cleaned and 
sterilized bottle filler, then to cap the 
bottles with sterilized caps and place 
the milk in low-temperature refriger- 
ators. 
This process seems relatively sim- 
ple, yet at every step problems are en- 
2 For information on Pasteurizing equip- 
ment the reader is referred to United 
States Department of Agriculture Bulletin 
No. 890, 3Iilk-Plant Equipment. 
