Milk exposed to various forms of radiant energy develops off-flavors. For
example, off-flavors may develop when milk is exposed to sufficient direct sunlight,
fluorescent light, or even diffused daylight. The light-induced flavor has two distinct
components. One is a burnt or "sunlight" flavor which develops rapidly and has been
attributed to the degradation of protein components. The second component is similar
to oxidized flavor which seems to develop more slowly. Recently, the widespread use
of plastic milk containers has increased the incidence of the light-induced flavor.
Several terms have been used to describe this flavor. Rancid, the most
commonly used, is ambiguous since it is also used to describe the flavor defect
resulting from lipid oxidation. The descriptive terms goaty, soapy, and butyric also have
been used. It is recommended that lipolyzed flavor be used to denote the lipase-
induced flavor defect.
Serious flavor defects in both raw and pasteurized milk may result from an
accumulation of the products of bacterial metabolism. These are produced by the
actions of contaminating organisms on the constituents of milk. See paragraph 4-10d
for additional information.
This undesirable flavor is often in milk and results from a reaction between
oxygen and fats. Milk varies considerably in its susceptibility to this defect.
Milk flavors may arise by passage of substances from the cow's feed or
surroundings while the milk is still in the udder. This transfer may be via the respiratory
system and/or digestive system and bloodstream. Some of these off-flavors are
described as feed flavor, weed flavor, cowy flavor, and barny flavor.
a. Definition. This group of flavors includes those flavors that either cannot be
attributed to a specific cause or cannot be specifically defined in sensory terms.
b. Absorbed Flavor. The term absorbed is applied to those flavors (odors) that
are absorbed from the environment. The evidence indicates that fat-soluble
substances, such as turpentine, are absorbed readily. The milking and milk storage
areas should be kept free of these odors.