FEED - The feed a cow eats may impart certain odors to milk. Some stronger feeds will carry through more noticeably than others. Odors resembling green grass, silage, turnips, and alfalfa hay are outstanding examples. Feed odor can be minimized or eliminated by taking the cows off offending feeds at least four hours before milking. Certain feeds can be detected in milk if fed to the cow even 15 to 30 minutes before milking.

BARNY - This odor is caused by cows breathing in foul air due to poor barn sanitation and/or ventilation. Proper ventilation, good sanitation, and proper milking procedures will correct this problem.

FOREIGN - Any serious objectionable odor foreign to milk, such as sanitizer, fly spray, paint, oil, kerosene, creosote, or a medicinal substance, will render the milk unacceptable or unfit for use. Such an odor may be caused by direct contamination of the milk or may be absorbed from the air. Sanitizers are included in this category because the residue of sanitizer, such as hypochlorite and iodophor, if left on dairy equipment, may be absorbed by milk and impart a foreign odor. Phenolic compounds used in udder ointments may combine with iodophor or hypochlorite sanitizers to form a highly objectionable foreign odor that is detectable in very low concentrations.

GARLIC/ONION - This obnoxious weed flavor, imparted to milk when the cow eats garlic, onions, or leeks, is not classified as one of the usual feed flavors described above. The garlic/onion flavor is recognized by distinctive odor suggestive of its name. It may be so objectionable as to render the milk undesirable for use.

MUSTY - This odor is suggestive of musty or moldy hay. It may be absorbed directly by the milk but is more likely to come from feed or stagnant water consumed by the cow.

RANCID – Oxidized rancidity gives off odors usually described as cardboardy, metallic, or tallowy. It is usually more noticeable during the winter months when cows are on dry feed. The most frequent cause of oxidative rancidity is the contamination of milk with small amount of copper or iron from milk contact surfaces. Hydrolytic rancidity found in milk will give off odor resembling spoiled nutmeats. It is more noticeable during winter, when cows are on dry feed, or during late lactation. Agitation of warm raw milk in the presence of air, causing foaming, will result in a rancid type of odor within a few hours.

SOUR - Sour milk will have a malty odor and will be found when bacteria grow in poorly cooled milk. It also may result from bacterial growth due to unsanitary milking practices and/or unsanitary equipment.

WEEDY - The weedy odor is not included among the usual feed odors. It may include obnoxious odors resembling such plants as ragweed, bitterweed, or peppergrass, and may become a very troublesome flavor defect. It can be eliminated or minimized by keeping cows away from weed infested pastures or by not offering feeds containing such weeds until after the cow is milked.

The odors gather just below the cover of the bulk tank. To check properly for off-odor, remove the small port opening and smell the milk through this opening. Never open the lid, as this will let the odors escape into the air. The detection of off-odors can be affected by a few external factors. The hauler should strive to eliminate these factors: