Cans and aluminum in fridge: safe?
September 22, 2010 8:32 PM   Subscribe

I used to live in a co-op, and our kitchen managers always stressed not putting cans or aluminum in the fridge. They said that it could cause botulism to grow. Fact or fiction?

I've never heard anyone else bring this up so I'm a bit skeptical, but they studied bio and seemed pretty convinced. In addition, our kitchen was certified and routinely inspected, and apparently this was one of the things the inspectors looked for.
posted by archagon to Food & Drink (29 answers total) 1 user marked this as a favorite
Opened cans of food? I think that an open can left in the fridge long enough risks botulism. But it should be slower than leaving the can out in the open. I'm pretty sure the bacteria responsible for botulism toxin don't like the cold... but your fridge isn't cold enough to stop them completely (only slow them down).

I think the general idea here is that people tend to open cans of food, stick the leftovers in the fridge, and then forget about them. Certainly I'm guilty of it. In a communal situation that could be dangerous. It's just easier to have a rule that says no leftover cans in the fridge than to enforce labeling and a discard policy.
posted by sbutler at 8:44 PM on September 22, 2010

No cans at all? That's pretty ridiculous. Do they drink warm coke?

The only way this makes any sense would be if you had a can, say, of chickpeas that was already infected with botulism, opened it, ate half, put the other half back in the fridge still in the can, and left it there for the bacteria to sit and create even more toxins in the already-infected chickpeas. Botulism doesn't just magically appear on cans after the fact, and putting it in the fridge or not putting it in the fridge isn't going to affect it at all.

It is good practice, however, to transfer any unused contents of a can to a tupperware if you're going to be keeping it in the fridge for more than a day.
posted by phunniemee at 8:55 PM on September 22, 2010 [1 favorite]

My high school biology teacher told us this very thing. He seemed very credible, he had an entire freezer full of dead mice.
posted by hermitosis at 8:59 PM on September 22, 2010 [3 favorites]

Mr. Sill didn't include aluminum soda/beer cans in his warning.
posted by hermitosis at 9:00 PM on September 22, 2010

Most foodstuff cans have a warning on them which directs the consumer to "promptly refrigerate unused portion in separate container" or something similar.
posted by easy, lucky, free at 9:03 PM on September 22, 2010

Response by poster: What about covering things with aluminum foil, then? Is that safe?
posted by archagon at 9:06 PM on September 22, 2010

Response by poster: (And putting it in the fridge, obviously.)
posted by archagon at 9:06 PM on September 22, 2010

What about covering things with aluminum foil, then? Is that safe?

It's fine. Just follow safe food procedures (i.e. don't leave it sitting on the counter at room temp).

(And putting it in the fridge, obviously.)

Yeah, then it's fine.
posted by phunniemee at 9:13 PM on September 22, 2010

The only danger with aluminum foil appears to be that since botulism grown anaerobically, you could tightly wrap a baked potato and that could give the toxin a place to grow. Slightly more on botulism here. Nothing about open cans, a lot about canning.
posted by jessamyn at 9:14 PM on September 22, 2010

I think most commercial food is botulism-free when you get it, ideally at least, it gets pasteurized and that destroys the spores... water-bath canning doesn't kill 'em.

Personally I find tins in the fridge cumbersome and easy to spill. I find that acidic foods do get a bit of a tang to them but I am likely just imaging it. I reckon it's make-believe to keep people from filling fridges with opened tins.
posted by glip at 9:22 PM on September 22, 2010

I'm still skeptical. This FAQ from the CDC does not mention storing food in metal or aluminum cans as a risk.

Storing food in opened metal cans is not a great idea for other reasons. The cans can't be sealed very well and the food sometimes starts to taste tinny.

"Home-canned food" is a notorious source of botulism poisoning, but that has nothing to do with it being in metal cans; most home-canned food is stored in glass jars, actually. The problem is that some home canning methods don't get the food hot enough to kill the Clostridium botulinum bacterium, and the anaerobic environment inside the sealed jars makes a good home for the it.

What about covering things with aluminum foil, then? Is that safe?

I am not a food safety expert, but look: botulism is caused by a toxin generated by the Clostridium botulinum bacterium. The bacterium doesn't come from aluminum foil or metal cans; it has to be present in the food itself. My understanding is that it typically comes from field soil, which would be why that CDC FAQ mentions potatoes baked and stored in aluminum foil: it's not that the foil causes botulism, it's that traces of field soil on the skin of the potato carry the bacterium. It may be that the foil creates a better environment for the bacterium to multiply or produce toxin, but your average lasagna (for example) is not going to suddenly start growing Clostridium botulinum just because you put foil on top. (It could make a lasagna cell, though.)
posted by Orinda at 9:24 PM on September 22, 2010 [4 favorites]

Nonsense. Clostridium botulinum, the bacterium responsible for botulism, does not have an affinity for aluminum. Unless someone can produce actual data-based references to back this assertion up, testimony from high-school teacher "experts" on food safety is really just urban myth and superstition.

The only problem I see is that it can be harder to seal canned goods than, say, food in tupperware. However, it's still no more dangerous than pizza* in a pizza box, or uncovered food on a plate. And if the bacteria gets established while the food is uncovered, no container on earth will stop its growth.

Heat and acidity stop it. Boiling-level temperatures for 10 minutes is the general rule for destruction of the bacterium (although this won't destroy the spores; this is why pressure canning was invented). Moderate levels of acidity will inhibit the bacteria - this is why beer, wine, pickled veggies, and tomato sauces are fairly safe foods at room temperature.

*Actually, the acidity of the tomato sauce on pizza may help ward Clostridium botulinum off from pizza, but that isn't really the point.
posted by IAmBroom at 9:26 PM on September 22, 2010

Sigh, I wrote a whole thing up and folks beat me to most of it. So, just a couple bullet points, then.

* There has only been one case of botulism from canned good in the US in the past 30 years and it was from an off brand with baaaaad practices.

* From what I've just read on (yes, I know) Wikipedia, Clostridium botulinum is a soil bacteria, so it is probably fairly happy at 4 degrees C AKA fridge temperature. But since your food probably is fine to begin with and you're presumably not sprinkling it with topsoil, should be fine.

* In the end, you're a lot less likely to spill a closed tupperware container than an opened can AND they stack better, so that's the best logic for transferring containers, IMHO. Oh, and avoiding Aspergilus niger AKA bread mold and other lovely fungus. They won't kill you, but they don't improve the tomato sauce you're trying to save.
posted by maryr at 9:27 PM on September 22, 2010

for the it = for the bacterium
posted by Orinda at 9:28 PM on September 22, 2010

Also, on post-view, when I said "hot enough to kill the Clostridium botulinum bacterium," I should have said "hot enough to kill the Clostridium botulinum spores"
posted by Orinda at 9:32 PM on September 22, 2010

FWIW, I've heard this aluminum/botulism thing before, though certainly not in any context that didn't smell like an urban legend.
posted by desuetude at 9:44 PM on September 22, 2010

I'm looking at a Food Handler's Manual her and it warns about acidic foods, saying after opening transfer to a glass, plastic or stainless steel container. This is because metals can leach into the food.

It doesn't say anything about potential contamination, but open containers are a big no-no and certainly present a possibility for cross contamination. In addition there have been cases of botulism linked to baked potatoes cooked in aluminum foil (& held at room temperature).

Part of what the inspectors are looking for is general attitudes to, and common practices to food hygiene. Having open cans around would be a sign of sloppy attitudes and practices, and once opened present an opportunity for contamination food traces clinging to exposed metal. essentially you are storing stuff in unwashed, and unsterilized containers.

Botulism doesn't just magically appear on cans after the fact

Except that is sort of does. Large scale and commercial kitchens present many more opportunities for cross contamination than domestic ones, as well as much greater danger when contamination does occur — not just because they feed more people, but because bacteria growth occurs at different rates (and quantities) with larger amounts of food. Clostridium botulinum is a soil bacterium and can easily travel in from outside on unwashed vegetables etc.
posted by tallus at 9:53 PM on September 22, 2010

If you put a metal container with something acidic in it and cover it with foil, there's a chance the foil will be eaten away. This was on America's Test Kitchen recently, and I'm too lazy to google a source.
posted by elpea at 10:05 PM on September 22, 2010

Take a look at the actual cutting edge of your can opener.

If it's not the dirtiest thing in your kitchen outside of the drain in your sink, you're doing better than I am.

Using that thing inoculates the sterile contents of whatever can you open with it with a very nice mixture of the organisms that can grow on the stuff that was in the last six months of cans you opened.
posted by jamjam at 10:31 PM on September 22, 2010 [2 favorites]

I've been told that you shouldn't store unopened cans in the fridge because that could mask the swelling of the can that would have otherwise occurred at room temperature and given you a pretty reliable clue that there is spoilage going on.
posted by halogen at 11:54 PM on September 22, 2010 [1 favorite]

You're not going to be growing much botulism in your refrigerator, wrapped in foil or not once you've opened the can. It's an anaerobe and isn't likely to do well in an open container no matter how carefully you wrap it before you put it in there. (Unless you keep your kitchen under an argon atmosphere or something.)

That's not to say that there aren't scads of things that will grow (albeit slowly) at 4 degrees under air, but none of them need metal. Well, not any more metal than other forms of life and that's probably in your food anyway.

I can talk to the guys downstairs about the growth conditions for this, but I'm pretty sure they don't throw a tin can into the bioreactor. (It's Clostridium histolyticum and not botulinum, but they're not radically different.)
posted by Kid Charlemagne at 12:18 AM on September 23, 2010

Botulism? No more than any other kind of container. Assorted organic compounds of aluminium and/or tin, formed where acidic food meets metal meets air? Certainly, and not very good for you.
posted by flabdablet at 1:21 AM on September 23, 2010 [1 favorite]

I think this may be a modern confusion (because both have become rare) of lead poisoning from tin cans (specifically, from the solder). In large part modern manufacturing has eliminated this risk (I get indications that lead solder was banned in food cans, but no confirmation of when this took place).

This used to be a major problem. The lost Franklin expedition may have failed in part due to lead poisoning via improperly soldered tins. The problem was medically recognized by the end of the 19th century. But someone raised before ca. 1975 may well remember these warnings.
posted by dhartung at 1:53 AM on September 23, 2010

I actually just googled something about botulism in cans last night...don't ask. Anyway, the consensus seems to be that bulging cans are a bad sign and should be discarded. You should also be careful with dented cans, since it might have been hit hard enough to create a small hole and other potentially harmful bacteria could enter and thrive that way. As long as the can is intact, refrigeration makes no difference to the quality of the food.
posted by deep thought sunstar at 8:36 AM on September 23, 2010

After doing a little research on you, I think we lived in the same coop system (Cal?) and I think the no cans in the refrigerator was because we were inspected in the same way as commercial kitchen. We couldn't have a regular toaster either, it had to be an industrial one. So while I think some of the rules were valid (like separate sponges for the bathroom and the kitchen) the cans in the fridge was overkill.
posted by Duffington at 10:16 AM on September 23, 2010

It might be a worry about the metal in the can contaminating the food:
Don't store food in an opened tin can, or re-use empty cans to cook or store food. This is because when a can has been opened and the food is open to the air, the tin from the can might transfer more quickly to the can's contents.

nightwood, there's no tin in modern "tin cans".
posted by IAmBroom at 12:03 PM on September 23, 2010

Yes there is; the steel is plated with it. But can seams are now crimped, not soldered, so there's no lead in them. Also there's often, but not always, a lacquer coating inside to keep food and metal apart.

Metal transfer into food in opened cans still happens, though. If you can taste metal in your food, it's probably not good for you; and food stored in opened cans in the refrigerator frequently, in my experience, does end up tasting metallic.
posted by flabdablet at 6:43 PM on September 23, 2010

IAmBroom - google tin-coated steel food cans - lots of articles about tin still being used, for instance:
eHow: Many steel cans used for food storage today still contain tin, which is coated on both sides of the steel prior to forming the can.
posted by nightwood at 7:44 PM on September 23, 2010

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