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EVvAporaAteED MiLnK—MojJONNIER CONTROLLER l 
milk may be expected to withstand the sterilizing heat without 
danger of curdling in a manner that would render the product 
unmarketable. 
The purpose of the viscosity test, of sample cans having 
passed through the pilot sterlizer or controller is, to determine 
whether the evaporated milk of the entire batch, without treat- 
ment will safely pass through the adopted, standard sterilizing 
process, or to what extent this process must be modified, or to 
what extent the product, before sterilization must be treated 
with bicarbonate of soda to secure a good body, and at the same 
time insure freedom from the formation of a permanent curd 
when applying the standard sterilizing process. 
A certain degree of viscosity in evaporated milk is desirable 
and necessary in order to give the product a good body and to 
prevent the separation of the butter fat. 
But. as the viscosity increases a point is reached beyond 
which it is not safe to go, because of the danger of the formation 
of a permanent curd that renders the product unmarketable. 
The increasing viscosity is due to a change in the physical 
properties of the protein constituents of evaporated milk result- 
ing from the action of heat. The earlier stages of these changes 
are desirable, because they result in a product of good body and 
of increased stability of emulsion. An excessive continuation 
of these changes precipitates the proteins in the form of visible 
particles of curd which, if permanent, spoil the product for the 
market. 
Factors which Influence the Viscosity and their Correlation 
to the Sterilizing Process.—The extent to which heat increases 
the viscosity of evaporated milk 1s dependent on many and vary- 
ing conditions, such as acid of milk, natural stability of proteins 
in milk as related to their behavior toward heat, degree of con- 
centration of evaporated milk, degree of heat apphed in fore- 
warmer, amount of extraneous water in evaporated milk, degree 
of heat in the sterilizer, duration of exposure to sterilizing heat. 
The resistance of the proteins to heat, as affected by these sey- 
eral conditions and factors, can be modified and largely con- 
trolled if necessary, by the treatment of milk that has an ab- 
normally low resistance to heat, with definite, small quantities 
of bicarbonate of soda, 
