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The high proportion of samples shown this year as
unsatisfactory is due to the new grading system adopted
experimentally by the Bacteriologist at the Public Health
Laboratory Ealing. Together with Brentford & Chiswick
Southall. Acton. Hayes&Harlington and Heston& Isleworth,
we agreed to accept these unofficial standards.
Prior to 1956 ice cream was placed in the top grade
if it passed the Methylene Blue Test. The presence of
faecal and other organisms in any quantity did not affect
the grading.
In 1956, the Methylene Blue Test was discontinued and
a plate count was carried out on all samples. The presence
of faecal organisms automatically placed the sample
in the lowest grade, and the number of other organisms
present was considered in grading other samples, Plate
counts of less than 500 are graded 1, 500-20 000 Grade 2,
20,000-100,000 Grade 3 and over 100 000 Grade 4. On the
old system at least 11 of our unsatisfactory samples this
year would have been graded as satisfactory.
The following-up of the unsatisfactory samples of ice
cream manufactured in Ealing involved the testing of
various constituents and equipment and the contamination
was traced in all cases - in one case an unsatisfactory
ingredient was being used, in another case the sterilizing
agent was not doing its work and in a third case the
sterile ice cream was being contaminated by a container
after manufacture, Unsatisfactory samples of ice cream
manufacturered outside Ealing were reported to the Local
Authorities concerned for investigation. Repeat samples
subsequently proved to be satisfactory in all cases.
Ice Cream Heat Treatment Regulations, 1947 1952,
There are 6 premises registered for the manufacture
of ice cream but only two of these are in regular use.