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33
The time taken to decolourise methylene blue dye will depend upon the amount
of bacterial contamination present. Ice cream samples may be divided into four
grades; grade 1 showing, according to the test, the least contamination and grade IV
the maximum.

It will be noted that nearly 50 per cent. of the samples examined were placed by
the bacteriologist in Grade IV.
Where ice cream manufacturing firms regularly produced ice cream in Grade IV
detailed attention was given by the staff to the methods of production, with a view
to producing ice cream which was hygienically safer. It did not always prove an
easy matter to track down the particular mode by which bacterial contamination
was introduced. But, generally speaking, it was found possible, sometimes only after
considerable enquiry and by paying special attention to detail, for a higher grade of
ice cream to be manufactured.
Samples taken prior to the introduction of these Regulations (1/5/47) numbered
5:—Very Good 2. Good 2 and Fair 1.