PRESENT STATUS OF THE PASTEURIZATION OF MILK 15 
there for twenty minutes it will kill tubercle, typhoid, and diphtheria bacilli. 
Our experiments show that milk pasteurized at this temperature for the specific 
time may not always, in practice, reach these minimum requirements. It is 
therefore evident that a liberal factor of safety is necessary in the operation of 
this type of pasteurizer under commercial conditions. 
The United States Department of Agriculture advises the use of a 
temperature not lower than 142° F. for a period of not less than 30 
minutes, for the pasteurization of milk. Besides insuring an ample 
margin of safety, a temperature of 142° causes a greater destruction 
of bacteria in milk than does 140°, when the milk is held for the same 
period of 30 minutes. 
There is a tendency in milk plants to pasteurize as near the minimum 
temperature required as possible,, so as not to injure the cream line. 
Whittaker, Clement, and others (63) have studied the effect of tem- 
perature on the cream line in a number of different plants throughout 
the country, and have come to the following conclusion : 
In the case of milk heated to 143° F. for 30 minutes there was 
practically no decrease in cream volume, and in some cases an increase 
resulted. Heating at 145° to 146° for 30 minutes reduced the cream 
volume an average of approximately 8 per cent, with considerable 
variations above and below. Heating at approximately 148° for 30 
minutes caused a decrease in cream volume of 18.5 to 41.7 per cent, 
with an average decrease of approximately 31 per cent. 
The method of pasteurization, whether it is the holder or in-the- 
bottle process, is not so important, provided the process is such that 
the milk is heated to a temperature not lower than 142° and that all 
of it is held for not less than 30 minutes at that temperature. 
Marcussen (46, p. 62-63) also presents the following conclusions : 
1. The temperature of pasteurization exerts an influence on the quantity of 
cream present on pasteurized milk. 
2. The quantity of cream present on milk pasteurized at 145 degrees F. is always 
less than the quantity of cream present on the same milk when pasteurized 
at 142 degrees F. 
3. The average volume of cream on milk pasteurized at 145 degrees F. was 13.325 
per cent less than the average volume of cream on the same milk pasteurized 
at 142 degrees F. 
Erb (21) states that agitation of either raw or pasteurized milk at 
temperatures between 42° and 100° or 105° reduced the cream layer 
from 2 to 3 per cent of the volume of the milk, while agitation at 
temperatures from 100° or 105° to 144° had no effect on the cream 
layer. 
Trout (59) reports that heating milk at 145° for 30 minutes de- 
creased the creaming ability of milk from 9 to 16 per cent, depending 
upon the temperature of creaming. 
Dahlberg and Marquardt (18) state that there is no known method 
of restoring the creaming properties of milk which has been heated 
~ above 145° for 30 minutes or momentarily to temperatures in excess 
of 165°. 
SUPERVISION OF THE PROCESS 
Supervision of the pasteurizing process is absolutely necessary, 
but it can not be fully effective unless the supervisor has a thorough 
knowledge of the primary object of pasteurization and the bacterio- 
logical principles involved. 
