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"Viscolized" Milk and its Detection^*

F. J. Doan

Department of Dairy Husbandry, Pennsylvania Experiment Station, State College

ABSTRACT

When fluid milk or cream containing sufficient fat (8 per cent or more) is homogenized at a pressure of 2000 to 3000 pounds per square inch a peculiar structure in the fat is created. The globules are greatly reduced in size and the myriad of small globules formed tend to clump together while the clumps themselves show a tendency to arrange themselves in such a fashion as to occupy the greatest possible space. Such milk or cream, will not separate a cream layer. If it be mixed with normal raw whole milk or skimmilk, however, a deep cream layer is formed on standing. The depth of the layer depends more on the volume of the homogenized milk or cream which was mixed with the normal skim or whole milk than on the actual amount of fat that was homogenized.

These phenomena make possible the preparation of "viscolized" milk, a product which has been and possibly is being sold in some localities, either openly or without admission. The process produces a greater cream volume on the held bottled milk than normal milk of the same fat content, and therefore deceives the purchaser who is apt to judge the richness of the product by the depth of the "cream line."

Pasteurization of such processed milk does not destroy the clumped structure of the fat although the clumps are seemingly smaller and more individual globules are present. The cream layer while considerably diminished in volume by pasteurization is still in most cases greater by far than similar normal milk.

A simple, accurate, means of detecting "viscolized" milk is described, the only apparatus needed being a microscope. A limited amount of experience, however, in judging the appearance of normal and "viscolized" milk is necessary for highly dependable results.

^* Published by permission of the Director of the Agricultural Experiment Station. Contribution from the Department of Husbandry, The Pennsylvania State College. No. 441.

Assistance with the experimental work was given by J. H. Erb and F. E. Geyer