144 EVAPORATED M11,.K—S'TERILIZING 
ture to 70 or 80 degrees I. in twenty minutes for gallons and in 
ten to fifteen minutes for small size cans. The water pipe should 
be so arranged as to distribute the water uniformly over the 
entire length of the sterilizer. 
If the process is to be successful, the processer must have 
as nearly perfect control of the heat as possible. This means 
especially, that there must be plenty of water available to insure 
rapid cooling and the water must be distributed over the cans 
uniformly. Insufficient water supply and uneven distribution 
of the water in the sterilizer, means that some of the cans are 
exposed to the sterilizing heat longer than others, causing lack 
of uniformity in the smoothness and color of the milk of different 
cans of the same batch. Delayed cooling, owing to insufficient 
water supply. has the further disadvantage of causing the cans 
to bulge badly, owing to the difference in pressure between the 
interior and exterior of the cans. This is especially noticeable 
in gallon-size cans, the ends of which may become badly dis- 
torted, present an unsightly appearance and their seams and 
seals may be weakened to the extent of producing “‘leakers.”’ 
Excessive bulging and injury to the cans can be avoided by 
admitting to the sterilizer a sufficient quantity of compressed 
air at the conclusion of the sterilizing process, to take the place 
of the steam pressure and thereby equalizing the pressure be- 
tween the outside and inside of the cans during the cooling 
process. 
Fractional Sterilization.—In the early days of the manu- 
facture of evaporated milk the product was sterilized by frac- 
tional sterilization. This method has now been largely aban- 
doned, but is occasionally used when the milk happens to be 
in very abnormal condition. ‘The milk is heated in the sterilizer 
to considerably lower temperatures than those stated above, and 
this heating is repeated on two or three successive days. The 
principle of this process is to kill all vegetative forms of bac- 
teria during the first heating. his gives the spores a chance 
to develop into vegetative forms by the second and third days. 
which forms are then destroyed during subsequent heating. This 
system of sterilization is not practical for general use. It is too 
great a tax on the capacity of the average factory and increases 
