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Bureau of Dairy Industry, Agricultural Research Administration, U. S. D. A.
ABSTRACT
Quantitative determination of the deterioration of evaporated milk during storage showed that the pH and viscosity decrease and the color increases with an increase in the temperature of storage. Commercial evaporated milk of heavy body remained acceptable for 2 yr. when held in undisturbed storage below 60° F. Physical deterioration was rapid during storage above 70°.
Determination of the reaction of evaporated milk afforded a means for evaluating its previous storage conditions. The reaction of fresh evaporated milk was about pH 6.1. The product remained of good quality until the reaction became more acid than pH 6.0. The product was unacceptable when it was more acid than pH 5.9.
Separation of fat and protein in a commercial evaporated milk of heavy body was negligible during storage for 2 yr. below 60° F. At higher temperatures, protein not associated with milk fat gradually settled and the precipitate thus formed became an insoluble gel. The fraction of protein that was adsorbed on the fat phase slowly rose with the fat, and redispersion of this gel-like fat layer became almost impossible.
It is suggested that to attain improved stability in evaporated milk, the fat globules might be further subdivided to create new surfaces for adsorption of protein. If very small fat-protein particles could be formed, a balance might be obtained which would retard separation regardless of the viscosity of the milk.
The results presented here were from a single batch of commercial evaporated milk but this was considered to be representative of a large group of laboratory and commercial milks that were studied. Milks manufactured under a variety of conditions, particularly those sterilized by continuous methods, could be expected to yield data in general, but not in close agreement with the results reported here. Since this work indicates the nature of the changes through which all evaporated milks pass during storage it may serve as a guide for additional studies on a wide variety of samples.
1 Present address: National Bairy Research Lab., Oakdale, Long Island, N. Y.
3 Present address: Department of Dairy Husbandry, Texas A. & M. College, College Station.
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