Sayed Mohammad Naim KHALID
A low level of
contamination by microorganisms is the first aim. To achieve this, the sources
of contamination should be known. Some contamination occurs before milking, especially in housing (clean
cows) and fodder production (butyric acid bacteria). Cleaning and disinfection
of the milking equipment is essential. It is specifically meant to remove and
kill bacteria. Bacteria originating from inadequately cleaned equipment usually
have no lag phase and can grow rapidly in milk.
Cooling is the main
means of slowing down the growth of bacteria in milk. The maximum storage time
of milk closely depends on the storage temperature. Satisfactory operation of
refrigerated milk tanks on the farm is essential. However, cooling of milk
kills no bacteria, and it cannot remedy unsatisfactory hygiene.
In dairy factories,
the raw milk received often is not simply stored before processing, but is
thermalized and then cooled to below 4°C. Thermalization is a mild heat
treatment, e.g., 15 s at 65°C. It kills nearly all psychrotrophic bacteria,
which are not at all heat-resistant. In this way, growth of these bacteria to
harmful numbers during cold storage of the milk in the factory is prevented, as
is the formation of heat-resistant enzymes (lipases and proteinases).
Thermalization kills some of the other bacteria too, including many lactic acid
bacteria.
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