b. Examination of Product. You must examine the product for abnormal
color(s), abnormal odor(s), abnormal flavor(s), and abnormal texture or consistency
which may indicate microbial deterioration. Microbial spoilage may be caused by
bacteria, mold, and/or yeasts. The particular color, odor, flavor, or texture/consistency
change(s) involved will depend upon the type or species of microorganisms involved. If
microbial spoilage is suspected, DO NOT TASTE THE PRODUCT. You should contact
the veterinary officer for further examination of the product.
c. Color Changes. The following color changes may indicate microbial
spoilage: blue, bluish gray, pink, yellow, red, and brown.
d. Odor and Flavors. The following odors and flavors may be associated with
microbial deterioration of dairy products: sour or acid, bitter, burnt or caramel, soapy,
malty, rancid, fishy, fruity, oxidized, alcoholic, and putrid. Although bacteria may be
responsible for a number of different flavor defects in both raw and pasteurized milk,
only those defects described as acid, malty, and fruity can be recognized as being of
microbial origin by sensory perception alone. The flavors described as stale, barny,
unclean, bitter, foreign, rancid, and feedy (like animal feed) can be caused by bacteria,
but determination of the actual cause is often difficult without bacteriological analyses
because of the similarity of these flavors to flavors due to other causes.
(1) Acid flavor. Because of the universal distribution of Streptococcus lactis
in the environment of milk production, most milk is unintentionally inoculated with this
organism immediately after milking. If the milk is not cooled immediately to 4.4C (40F)
or below, it eventually will develop an acid taste due to proliferation of the organism and
its conversion of lactose to lactic acid. The development of lactic acid in milk is
accompanied by an odor usually described as sour. Since S. lactis is destroyed by
proper pasteurization, acid development in milk subsequent to pasteurization is not
likely. However, pasteurization will not improve the flavor of raw milk if acid already has
(2) Malty flavor. A flavor and aroma which in the past has been described
as cooked, burnt, caramel, or malty, may develop in raw milk as a result of the
metabolism of S. lactis subspecies maltigenes. This organism enters milk through
contact with improperly sanitized equipment during production.
(3) Fruity flavor. The aroma, which may develop in pasteurized milk and
other processed dairy products as a result of Pseudomonas fragi, has been described
as strawberry-like or fruity. P. fragi, a psychrotrophic water and soil organism, is
distributed widely in dairy environments. The organism is very heat sensitive, and its
presence in pasteurized products is due to post-pasteurization contamination. Strains
of Bacillus have also been isolated from milk with a fruity flavor. These spore-forming
organisms may be the cause of flavor defects in aseptically packaged "sterilized" milk
and fluid milk products.