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91
TIN IN CANNED FOODS.
In my Annual Report for 1908 reference was made to an endeavour to
persuade packing firms in New Zealand to agree upon a scheme for marking
tinned foods in such a way as to indicate where and when they are packed.
The age of a tin of preserved food is a matter of considerable importance by
reason of the liability of the contents to metallic contamination.
In the early part of 1909 the Local Government Board published Reports
by Dr. G. S. Buchanan and Dr. S. B. Schryver, D.Sc., on "The Presence of
Tin in certain Canned Foods, together with some investigation on the
Toxicology of Tin," and one of the conclusions arrived at by the former
was that—
"The inquiry illustrates the advantage which would be gained, from
"the administrative point of view, if the persons or firms by whom
"canned foods are prepared were in a position to determine by marks,
"labels, or otherwise the date and place of preparation, and could be
"required to furnish such particulars, on reason shown, to public health
"authorities concerned with food inspection and wholesomeness of foods."
The following other conclusions were arrived at in the Report:—
That practically all ordinary canned foods are contaminated with tin as the
result of contact of the food with the tin-plate of the can.
More tin is found in meat extracts and essences than in other meat foods,
owing to the acidity of the meat extractives. Certain canned fruits, vegetables,
and food made as soups are also liable to take up tin in consequence of their
natural acidity. These include canned peaches, cherries, pears, apricots,
pineapples, tomatoes, asparagus, canned fruit puddings, and tomato soup.
Canned lobster has been found to contain notable quantities of tin.
As time goes on the quantity of tin taken up from the can increases. Meat
essences and extracts, six years old, returned from South Africa, usually
contained from l½ to 3 grains of tin to the pound.
Canned carrots, apricot jam, and fruit puddings of the same age contained
2 to 3 grains of tin per pound.
Flesh foods of that age, however, such as brawn, curried rabbit, sausages,
tongues, sliced bacon, etc., contained considerably less, ranging between ½ and
1½ grains per pound.
The cheaper quality of tin plates are most liable to erosion, causing solution
of the tin, than those more thickly coated with tin. If solder (containing
both tin and lead) finds its way into a can, a very conspicuous solution of tin
may take place. Owing to this cause, the contents of one tin examined was
found to contain no less than 20 grains of tin to the pound.