17 
and the framework is stationary. lr any case it must be so 
_ arranged that the milk slowly revolves during the process, 
. which is necessary to insure even heating and to prevent the 
‘formation of 2 scum on top of the milk in the cans. The 
sterilizing Las proved the most delicate part of the whole pro- 
cess of maxing evaporated milk. On it many new untried 
_ ventures broke down and it is the cause of occasional losses in 
all factories. This heating process has really two purposes. 
' In the first place its object is to sterilize the milk, i.e., to kill 
all living organisms, the vegetative bacterial cel's as well as 
~ the very resistant spores. To assure this the milk must ¥e 
subjected to a temperature of at least 220°F. for about 30 to 
40 minutes. But a second object of the heating process is the 
following. Evaporated milk is not condensed to so high a 
degree as the sugared milk and its viscosity is not enhanced 
ky the addition of sugar. When it enters the cans it is still a 
white and comparatively thin liquid. We have noted before 
that heat precipitates or coagulates the casein in milk. In 
‘sterilizing, the evaporated milk must be heated to such a de- 
gree that this thickening just begins. This is necessary not 
only to give the produce a nice creamy appearance, but to give 
it a “good. body.” ‘Otherwise the butter fat will rise to the 
top in the cans in the warehouse or on the shelves of the 
- stores, or it may even be churned into lumps during transit. 
- Such milk, though sound, is unmarketable as it cannot be used 
. for the ordinary purposes it is intended for, e.g., in coffee, tea 
or on fruit. But the heating must not go beyond that point 
or else the coagulation will reach such a degree that the milk 
becomes grainy or lumpy, so that the precipitated protein will 
not dissclve any more. Such a milk is equally unmarketable. 
A slight grainyness may be shaken out and for that purpose 
all factories are fitted with special shaking apparatus, and 
_ some even put all evaporated milk through this shaking pro- 
cess. No amount of shaking, however, will make a smooth 
. soluble milk again if it has been precipitated in large or hard 
grains or lumps. The important point, therefore, is to deter- 
just what the milk “will stand,” e.g., to adjust time, mode of 
applying the heat and temperatures in such a way that the 
milk is thoroughly sterilized and that it arrives just at the 
-proper stage of thickening. Now the fact is:that no definite 
point car be fixed for that. As indicated at the beginning of 
