A similar defect may be due to ketosis in cows, but with more of a medicinal or chemical after taste (see cowy). The cause of this is known to be an enzymatic breakdown (microbial or milk enzymes) of milk proteins to short bitter peptides. Certain weeds ingested by cows may also cause bitterness although this is rare. Cooked Note odor and flavor. Cows who have gotten into wild onions have been known to produce milk that smells and tastes like onions.
The cows that are held for dairy production are kept on a very strict diet, and only allowed certain items in order to contain the smell and the taste.
If there is a dairy farm near your home, one could call and see if they do a day trip out. Dairy farmers are very knowledgeable about the causes and conditions of the milk that they are producing, and are mostly willing to answer any other questions that you might have as well.