4. During epidemics of typhoid fever, scarlet fever, diphtheria, or any form of diarrhoeal disease.
What are the two methods of heating milk?
The first is known as sterilizing, in which the milk is heated to 212° F. for one hour or one hour and a half; the second is known as pasteurizing, in which the milk is heated to 155° or 170° F. for thirty minutes. A temperature of 155° F. continued for thirty minutes is sufficient to kill the germs of the diseases above referred to.
Will milk which has been thus treated keep indefinitely?
No; for although all the living germs may be killed, there are many undeveloped germs, or spores, which are not destroyed, and which soon grow into living germs. Milk heated to 212° F. for an hour will keep upon ice for two or three weeks; that heated to 155° F. for two or three days.
Is milk which has been sterilized always a safe food?
No; for the reason that the milk may be so old, so dirty, and so contaminated before sterilizing that it may be still unfit for food, though it contains no living germs.
Is cow's milk rendered more digestible by being heated in this way?
Sterilizing milk does not improve its digestibility but rather the contrary. Sterilized milk should be modified for infant feeding in the same way as milk which has not been heated.
Is milk in any way injured by heating to 212° F. for an hour?