MILK Flavors and Odors Ascribed to Four Main Causes
Cow’s milk invariably has a characteristic flavor and odor more or less pronounced, but comparatively little is known concerning the factors contributing to these characteristics. The flavors vary from those which make the milk pleasing to others which make’ it objectionable and unpalatable.
Flavors and odors in milk result mainly from four causes: (1) The internal or physical condition of the individual cow, (2) highly flavored feeds, (3) odors absorbed by the milk after production, (4) biological changes in the milk.
Flavors and odors of the first and second classes are noticeable just after the milk is drawn and usually do not increase with time. Those of the third class may develop when the atmosphere to which the milk is exposed is permeated with pronounced odors, while those of the fourth class become more apparent after some time has elapsed.
Milk of pleasing quality can be produced only when the factors deleteriously affecting thé flavor and odor of milk are controlled. In 1921 the department began investigations, considering principally the factors of the second and third classes. Throughout the investigations the department has endeavored to suggest methods of assistance to dairymen in the production of milk reasonably free from feed taints frequently found in market milk.
The objects of the investigation are as follows: (1) To determine whether or not certain feeds affect the flavor and odor of milk, (2) if they are found to do so, to determine how these feeds may be used and the milk handled so as to minimize their effect on the quality of the product.
For this work cows are selected giving milk relatively free from abnormal flavors and odors when fed a basic hay and grain ration. These are known as check cows. In addition to the basic hay and grain rations, the other cows receive varying quantities of the experimental feed at different stated times before and immediately after milking. The cows in the various groups are interchanged at frequent intervals in order to equalize any abnormal results due to the milk of any individual animal. Samples are taken from the milk produced by these cows and judged for flavor and odor. The opinions of the judges determine the degree to which the feed affects the flavor and odor of the milk.
From the work thus far completed it has been shown that when corn silage, legume silage, green alfalfa, cabbage, and turnips are fed to dairy cows one hour before milking, the flavor and odor of the milk are seriously affected. Green rye, green cowpeas, potatoes, dried beet pulp, and carrots affect the milk only to a slight degree; whereas green corn, green oats and peas, pumpkins, and sugar beets have practically no effect on the flavor and odor of the milk produced.
Throughout the work certain facts have been proved, namely:
While feed-tainted barn air may have some effect on the flavor and odor of milk, it is of relatively small importance even under extreme conditions; for feed flavors and odors are imparted to milk mainly through the body of the cow and not by absorption from the surrounding atmosphere.
Highly flavored feeds may be fed immediately after milking with- out seriously affecting the flavor and odor of the milk produced at the next milking.
Most feed flavors and odors are more pronounced in cream than in the milk from which the cream is skimmed.
Proper aeration reduces strong feed flavors and odors in milk, and slight feed flavors and odors may be eliminated.
In order to obtain further and more definite information concerning the time required for feed flavors and odors to enter the milk and the time required after consumption before the flavor and odor will have disappeared, as well as the methods by which the flavor
and odor may enter the milk, experimental work was carried on
with garlic, and the following conclusions were reached:
Garlic flavors and odors may be detected in the milk when the samples are taken one minute after feeding one-half pound.
The intensity of the garlic flavor and odor increased as the time interval between feeding the garlic and taking the milk samples increased, until at 10 minutes a high degree of intensity was reached. This intensity remained to an objectionable degree for 4 hours, after which there was a decrease, and at 7 hours it had practically disappeared.
Strong garlic flavor and odor were found in milk drawn 2 minutes after the cows inhaled garlic odor for 10 minutes. The inhalation took place in such a manner that it was impossible for the cows to eat any of the garlic. The cows were then milked in an atmosphere free from garlic odor. The garlic flavor and odor imparted to the milk in this manner practically disappeared in 90 minutes.
Garlic odor was readily perceived in samples of blood drawn 30 minutes after feeding the cows 2 pounds of garlic tops, and strong garlic odor was present in the blood drawn 45 minutes after such feeding.
These data indicate that the feed flavor and odor are absorbed by the blood from the stomach, or, in cases where the feed has a pronounced odor, to some extent from the lungs and thence transmitted to the milk.
Milk is often rendered unsalable by feed flavors, while a product of pleasing taste extends the market by increasing the quantity consumed. Feed flavors may be avoided by controlling the time of feeding, for in most cases feed flavors are not imparted to milk except for a few hours after feeding. For this reason dairy cows should be fed highly flavored feeds immediately after and not just before milking.
Pastures should be cleared of weeds which cause objectionable flavors and odors in milk. Until this is done, cows should be removed from infested pastures as long as possible before milking. The longer the interval between removing the cows and milking, the less the intensity of the undesirable flavors. Some weeds, however, have a tendency to impart objectionable flavors several hours after consumption. When such weeds are present it may be necessary to forego pasturing until the weeds are exterminated.