If you are old enough, you will remember flavor changes in milk in the spring and fall, when cows switched from pasture to silage. You probably also remember the off-taste that occurred when the cows found wild onions in the spring. The following is from Research and Farming, the 1948 annual report of the North Carolina Agricultural Experiment Station, published by N.C. State College, Raleigh
Several different types of food flavors can be removed from milk by blowing air through it, according to W.M. Roberts, F.M. Haig, and M.L. Shumaker, who have completed several trials of the new method.
The process consists of heating the off-flavored milk to 150 degrees F., and blowing filtered air through it until the flavor is removed. This usually requires from 20 to 60 minutes, depending on the intensity of the off-flavor.
It is necessary to spray milk by circulation into the vat so that the foam which forms can be dispersed. After the flavor is removed, the milk is homogenized at 2,500 to 3,000 pounds per square inch pressure and cooled.
Practically all volatile feed flavors are eliminated by this treatment. The milk has normal keeping qualities. From 3 to 8 per cent of the water is lost by evaporation.