PASTEURIZATION 213 
ferences were observed, in some cases calves fed on boiled 
milk developed a diarrhoea which disappeared when raw 
milk was substituted. 
5. Ferments or E'nzymes.—In the opinion of some 
authorities, the ferments or enzymes contained in milk 
play a very important role in its digestion and assimila- 
tion. From this standpoint the effect of heat on these 
substances is therefore an important consideration in 
connection with the pasteurization of milk. Most of the 
ferments in milk can withstand a temperature of from 
60 to 65° C, (140 to 149° F.) for some time, while higher 
temperatures weaken or destroy them. 
6. Taste —Milk does not acquire a cooked taste un- 
less it is heated to 158° F. (70° C.) or above. 
7. Cream Line.—If milk is exposed to a temperature 
of 70° C. (158° F.) or above, the cream will not sepa- 
rate. A temperature of 65° C. (149° F.) for 10 min- 
utes has no effect on the separation of the cream, but 
as the time of exposure to this temperature is increased 
beyond this period the separation of the cream is de- 
layed more and more until finally, after 40 minutes ex- 
posure, it does not separate at all. A temperature of 
145° F. (62.8° C.) for 30 minutes and 60° C, (140° F.) 
for as long as 50 minutes has no effect on the formation 
of the cream layer. In the commercial pasteurization 
of milk, the pumping and stirring necessary to force 
the milk through the heater and to bring it in contact 
with the heated surfaces may have the effect of breaking 
up the fat globules and thus interfere with cream sepa- 
rating even when the temperature has not been suffi- 
ciently high to alone affect the cream line. 
Summarizing the facts which have been definitely 
established regarding the effects of pasteurization, we 
