In both SPC and coliform tests, a q

In both SPC and coliform tests, a quantity of prepared
samples is placed aseptically into a petri dish
containing nutrients or selective agar. The bacteria are
dispersed throughout the agar and after a period of
incubation, the plate is examined for colonies, which
are counted and multiplied by the dilution factor to estimate
the original bacterial concentration. The psychrotrophic
organisms (cold surviving) have become
increasingly important over the past years with the increase
in bulk storage under refrigerated conditions.
This is now widely adopted in testing of milk and
dairy product manufacture as a quality and safety test.
In some product manufacture, thermophilic bacterial
counts are tested. In some cases such as yogurt and
cheese, yeast and mould counts are also determined
as a quality and safety test.
Direct microscopic count is useful for routine examination
of milk. This test is useful for its ease and
speed and its ability to detect anomalies in the milk
such as leucocytes in mastitis, and so forth. However,
it is not a viable count and dead organisms are
also counted, which results in unreliable estimates of
some products, such as pasteurized milk