144 EVAPORATED MILK STERILIZING 



ture to 70 or 80 degrees F. 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. This 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 



