In a post-apocalyptic but non-nuclear world, how long would canned food remain edible?
Pat French
Longdon-upon-Tern, Shropshire, UK
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It depends on the can, the food in question and the method of storage before, during and after the apocalypse. Reactions can occur between substances within the tin, whether that is between the food contents or with the tin’s inner surface. Canned sardines in brine are more likely to degrade due to chemical reactions within the food than, say, canned peanut butter powder or sardines in oil.
Food cans are made of different alloys and other materials and have different internal coatings. The coating is often specific to the food contained and is sufficient for the intended shelf life with a good margin for safety. Famously, members of John Franklin’s Arctic expedition in 1845 seem to have been seriously affected by lead poisoning from the solder in their unlined tins of provisions at a time when canning was poorly understood (see page 15 for new findings about the expedition).
The way in which cans are stored will affect the contents and the container. Mechanical damage and temperature extremes will also exacerbate can failure and food deterioration.
Cans abandoned over a century ago by Ernest Shackleton have been tested by scientists and found to be safe to eat
Should an apocalypse typical of the Hollywood film industry ever happen, though, none of this will matter because all our surviving tinned food is likely to be consumed within the first year.
Mike Follows
Sutton Coldfield, West Midlands, UK
Scientists have tested food that was canned over a century ago, including cans abandoned by Antarctic explorer Ernest Shackleton. Although safe to eat, it had lost much of its flavour and nutritional value.
Canned low-acid foods like baked beans remain reliably edible for up to five years, while high-acid foods like fruit, tomatoes and pickles shouldn’t be left in cans for longer than one-and-a-half years. Cool, dark and dry environments extend the shelf life of food, even when it is canned.
Damage to the can, like dents or rust, reduces the shelf life of the food inside. Indeed, such cans should be discarded as they can harbour botulism if the seal is compromised. Bacteria like Clostridium botulinum – the cause of botulism – don’t produce an odour, so the smell of canned food shouldn’t be used as a reliable guide that it is safe to eat.
Honey has an indefinite shelf life if properly sealed: 3000-year-old honey from the tomb of King Tutankhamun is still edible. Of course, we wouldn’t be able to survive on honey alone.
Dehydrating, freeze-drying and vacuum sealing are other methods of extending the life of food. Freezing food depends on a power supply or living in a very cold place, which would introduce its own survival issues.
Many so-called preppers store food in a cool, dark and low-humidity environment. They label food and rotate their stocks so they always consume the oldest food first, before it exceeds its shelf life.
Will Higgs
Gilsland, Northumberland, UK
While hiking in north-east Greenland in the 1980s, I came across tinned food left by prospectors searching for a site for a lead mine. The Blyklippen mine opened in 1956, so the food was presumably older than that.
We ate the contents of a few tins stored in a hut without ill effect. I also found a crate of tins of sweetened condensed milk lying out in the open. Their bottoms had rusted away, but I can assure you the stuff at the top was perfectly edible!
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