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107
In Circular 1533, issued in connection with the Milk
(Special Designations) Order, 1986, the Minister of Health
refers to this test in the following terms:—
" The Minister is advised that there is evidence that
milk subjected to the pasteurising process may in fact be
improperly pasteurised on account of the pasteurising
plant being imperfect in design and construction, or
improperly and inefficiently operated and controlled. It
has also been asserted that in cold weather milk which has
not been through the pasteuriser at all may be sold as
' Pasteurised,' Improperly pasteurised milk has not
the advantage, which pasteurisation is designed to secure,
of the destruction of pathogenic bacteria, and the
Minister is therefore pleased to learn that a test for
pasteurised milk (the phosphatase test) has recently been
devised.
A detailed description of this test and its method of
operation is given in the Journal of Dairy Research
(Vol. VI, No. 2, p. 191, 1935). Present experience of
the test shows that a positive result, i.e., the demonstration of the presence of phosphatase in the milk, is conclusive
evidence that the milk has not been properly
pasteurised or that milk which has not been pasteurised
has been added to it. A negative result, i.e., failure to
demonstrate the presence of phosphatase, does not
necessarily indicate that the milk has been properly
pasteurised, as it may not be possible to demonstrate
indubitably the presence of phosphatase in milk which has
been heated to slightly below the pasteurising temperature or for a slightly less period than 30 minutes, or to
which a small proportion of raw milk has gained access.
Nevertheless, it is claimed that even relatively small
errors in pasteurisation technique, e.g.. heating at 143°F.
instead of 145°, or heating for 20 instead of 30 minutes
at 145°, or the addition of 0.3 per cent. (or even less)
of raw milk to the pasteurised bulk may be detected by
this test.