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A portion of the above was removed at the request of the owners.
TINNED LOGANBERRIES.
An endeavour was made during the year to solve one of the difficulties associated with
the tinned fruit trade. Attention was first directed to the problem by the surrender in
one of the Metropolitan Boroughs of a quantity of tins of loganberries which were assumed
to be unsound on account of their " blown " condition.
Difficulty occasionally arises in deciding whether a tin of loganberries or other fruit
containing " pips " (such as raspberries) is fit or unfit for human consumption.
The principal method of distinguishing a sound from an unsound tin of foodstuffs is
by examination of the flat metal ends of the container. Tinned products are submitted to
various processes during preparation, and are finally sealed while hot, which fact results
in the creation, after cooling, of a vacuum or partial vacuum inside the tin. Against this
vacuum atmospheric pressure causes a depression, or concavity, of the ends of the container.
When the product decomposes gas is evolved and the vacuum is replaced by an internal
pressure which may result in the ends of the container becoming convex.
Cylindrical tins containing foods which show this convex condition are always regarded
with grave suspicion and condemned if the convexity is found to be accompanied by much
internal pressure. Occasionally, however, bad packing or a low degree of vacuum may
cause such convexity, or at least absence of concavity of the ends. In these instances confirmatory
evidence one way or the other is usually obtained by opening a few tins of the
consignment.
With loganberries and certain other fruits, however, it has been observed that the
tins in which they are contained may first show the desirable concavity of the ends, and
accordingly be passed as sound, but after a few months, and whilst the contents should still
be sound—and, moreover, generally are sound—the concavity is replaced by a convexity,
and a suspicion of unsoundness is aroused. When opened, the contents of the tins, so far
as the usual criteria of taste and smell are concerned, show no decomposition changes to
account for the gas production which has undoubtedly taken place.
The position—obviously a difficult one—appeared to call for investigation. Six tins
of loganberries showing convex ends and apparently " blown," were submitted to Sir
Frederick Andrewes, K.B.E., City Bacteriologist, to whom the circumstances were explained.