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95
I have for many years advocated the pasteurisation of
all milk which, if carried out in the manner laid down in
the "Special Designations" Order, will destroy pathogenic
organisms and render the milk safe for humantion.
An increasing number of consumers is coming to rely
upon pasteurised milk as a safe milk. Unfortunately, much
of the milk now labelled and described as "pasteurised"
is, in fact, nothing of the kind.
A number of pasteurising plants are defective in design
or construction, and frequently they are inefficiently
operated. As a result the milk treated in them is not
satisfactorily pasteurised. The legal bacterial standard of
100,000 bacteria per millilitre is of no value whatever as
a control of the efficiency of pasteurisation. It is possible,
without much difficulty, to attain such a standard at any
reasonably well-conducted farm, especially during the
winter months, without resort to heating the milk at all.
As Professor Wilson has pointed out the best bacteriological
control of the efficiency of the pasteurising process
is the coliform test, but this test has its limitations.
B. Coli should not be present in appreciable numbers in
properly pasteurised milk immediately after pasteurisation,
but their absence does not necessarily demonstrate efficient
pasteurisation.
What is required, therefore, is a reliable test which will
establish whether the milk has been treated in accordance
with the requirements of the Milk (Special Designations)
Order, i.e., that it has been retained at a temperature of
not less than 145° and not more than 150° F. for at least
30 minutes.
Details of a test which, it is claimed, will meet these
conditions has been published by Professor Kay of the
Institute for Research in Dairying, Reading.
The test is based upon the fact that the enzyme phosphatase,
which is a constant constituent of raw milk, is
almost completely destroyed when the milk is held for a
period of half an hour at the minimum temperature required
by the regulations for officially pasteurised milk.