(4) Unclean, bitter, and putrid flavors. Unclean and bitter flavors may be
due to other causes. However, unclean, bitter, and putrid flavors are often caused by
growth of psychrophilic organisms in pasteurized milk. The resulting flavor defects
usually become evident upon extended storage of milk.
e. Defects of Butter. One of the main defects of butter is rancidity. This can be
due to oxidation as well as to microbial growth. Molds are able to grow on the surface
of butter. Putrid, proteolytic, and fruity flavors in butters are caused by psychrophilic
bacteria. Surface taint and yeasty butter are other defects of this product caused by
f. Defects of Cottage Cheese. In cottage cheese, the flavor defects of milk
may be accompanied by a gelatinous or tapioca curd formation. Pseudomonas fragi
and Alteromonas putrefaciens have been associated with a slimy curd defect on the
surface of cottage cheese. A fruity, putrid, or rancid odor and a fruity or bitter flavor may
accompany this defect. Surface discoloration of cottage cheese may occur due to the
growth of the pigment Flavobacterium. E. coli can cause barny or unclean flavors and,
if the cottage cheese is held at room temperature, the organism can cause a gassy
defect. The yeast Rhodotorula produces pink spots which may become a pink slime.
Torulopsis also produces a slime, but it is yellow. Geotrichum produces off-white, tan,
or yellow surface discolorations.
g. Defects of Italian Cheese. A pink discoloration of Romano and other Italian
cheese varieties occurs as a uniform band of color near the cheese surface or as
discoloration throughout the entire cheese. This discoloration is due to Lactobacillus
helveticus and L. bulgaricus.
h. Summary. A summary of microbial conditions of dairy products may be seen
in figure 4-1.
Rancidity, Ropy or Slimy, Sour, Bitter, Fruity
Slimy Curd, Putrid Odor, Gelatinous, Fruity
Figure 4-1. Microbial conditions of dairy products.