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April 16, 2009 11:48 PM   Subscribe

[MythFilter]: Grandmothers always say never buy a dented can from the supermarket. Is there any truth to this today?

From faint memory, I recall people were not supposed to buy dented cans as there was lead which could be ingested, however I am not sure if this was baloney or part of the myth.

What are the origins and does a dent in the can matter today?
posted by Funmonkey1 to Food & Drink (34 answers total) 3 users marked this as a favorite
To me dented or otherwise misshapen cans indicate possible botulism, not possible lead. I will readily admit I also learned this from my grandmother, though. It seems more plausible to me than lead...I really doubt there's lead in the cans used to package modern food.
posted by crinklebat at 11:55 PM on April 16, 2009

The FDA says don't do it.
posted by grouse at 12:01 AM on April 17, 2009 [5 favorites]

I have no idea whether grandmothers today buy dented cans from the supermarket :)

I was told that a dented tin removes the coating on the inside of the tin. So the question becomes: "do we need a coating on the inside of a tin?"

Also a dented tin may mean a broken seal.
posted by devnull at 12:20 AM on April 17, 2009

My paternal grandfather lived through the depression with his farm family, clipped coupons like religion, split his shopping list between the stores with the best deals in that week's circular, and completed the list at the local "grocery salvage"...

..and he'd never, ever buy a dented can because of the threat of botulism.

Nothing to do with lead, everything to do with a painful (and potentially fatal) foodborne illness.
posted by batmonkey at 12:28 AM on April 17, 2009 [2 favorites]

It depends. Can you press the top or bottom of the can in? As in, you can make it "wobble" when you press on it? Like there's a bubble underneath? Then no, definitely not - it means the seal is broken.

If the can seems otherwise rock solid, and is only lightly dented in a cosmetic sort of way, then you probably can. Even so, keep in mind that the can itself is designed to be intact, and that any serious dents will compromise the freshness or safety of the food inside. In other words, if you are going to buy a dented can of food, eat it immediately. Don't store it in your cupboard for six months and think you can eat it.

My uncle used to be part of a commune/living cooperative that was freegan before it was called that... when we'd visit him as kids, we'd eat all sorts of things from dented cans that were chucked out. But again, use your common sense.
posted by Grrlscout at 1:02 AM on April 17, 2009

My interpretation of this rule was that the dented can could have small ruptures and tears along the dent, meaning that its contents are exposed to the air.
posted by TheOtherGuy at 1:11 AM on April 17, 2009

Botulism is the risk, and this is most definitely not a myth.

The problem is that a dent might result in a tiny rupture that is just large enough to let some clostridium botulinum spores in, but too small to allow air to circulate freely. Especially if the contents are thick and viscous (e.g. canned mushroom soup). This results in a contaminated, anerobic environment inside the can -- exactly what c. botulinum needs to thrive. Moreover, many canned foods (especially canned vegetables) are pre-cooked, therefore not cooked again (or not cooked thoroughly, merely re-heated), therefore the botulinum toxins are not destroyed before the food is eaten.
posted by randomstriker at 1:45 AM on April 17, 2009 [1 favorite]

The wikipedia page on tin cans does not cover the issue of dented cans - but it does highlight a couple of changes to their fabrication which may have changed since your Grandmother's day:

1. From what I can make out cans no longer use solder as a closure mechanism - rather they use pressure in the construction mechanism to force the top onto a rim. At one time lead solder was used and sometimes (as allegedly in the case of the Franklin expedition) this could cause lead poisoning. The longer the food had been in the can the greater the chances of problems - and dents might be one of the few signs of an old can.

2. Since the 60s an increasingly large proportion of cans have been constructed from aluminium rather than tinplate steel. Aluminium is more resistant to corrosion so could probably withstand a dent of a given size with less chance of breaking the seal.
posted by rongorongo at 1:57 AM on April 17, 2009

My friend once got a bunch of soup cans with dents from somewhere. When I was moving the bunch of them around, one of them fell down, broke open and emitted the foulest smell I have ever witnessed, bar none. I don't think I tried eating from any of the other ones, not because of botulism, but because I don't like the taste of canned foods in general, except for olives.
posted by rainy at 2:05 AM on April 17, 2009 [1 favorite]

I opened a dented can once, where it didn't seem from the outside like the dent had had much effect. On the inside, though, the lining had separated, and it looked blackish, possibly like some sort of mold. Didn't eat that one.
posted by alexei at 2:06 AM on April 17, 2009

I hope this isn't too much of a derail, but if everyone agrees it's dangerous, and the FDA says it's dangerous, why are supermarkets allowed to sell them so casually?

I feel like I've seen dented can bins in our supermarket. And it's not like they open the case and throw out the can of tomatoes with the dent in it--they just put it on the shelf. I assumed they were safe, though I read recently that the plastic liner of some cans contains BPA.
posted by A Terrible Llama at 2:59 AM on April 17, 2009

Botulism - it is particularly dangerous because it is odorless and colorless and cannot be detected without laboratory tests.
posted by Lanark at 3:47 AM on April 17, 2009

I was taught to look for dents when buying anything with acidic contents: canned tomatoes, pinapples or almost any other fruit.

The body of the can is (or used to be) made of steel, with a thin inner coat of something else (probably galvinised?). If you expose steel to even a mild acid it will corrode amazingly fast, releasing iron ions into the acid and hydrogen gas.

So the argument was that a bad dent in a can could disrupt the inner coating, exposing the steel to the acidic juices. This would lead to lots of iron dissolved in the juice, which would taste bad but is probably not toxic. More importantly, you get a buildup of hydrogen gas in the can combined with an increasingly weak spot in the can wall. This means it could conceivably burst while sitting on your shelf, or much more likely just suddenly fizz up and make a mess when you open it.

alexi - That black powder was probably carbon left behind when iron ions were leaving the steel. You can see the same thing happening if you drop a (non-galvanised) steel nail into smething acidic - vinegar, lemon juice, etc.
posted by metaBugs at 4:48 AM on April 17, 2009

Nthing what everyone else has said, that a dent in a can could mean that there's been a microscopic crack in it that's big enough to let in botulism or other air-borne bacteria that could contaminate the contents of the can. Lead has nothing to do with it.
posted by EmpressCallipygos at 4:49 AM on April 17, 2009

Yeah, I was taught (in school) not to buy dented or bulging cans to avoid risk of botulism
posted by winston at 5:08 AM on April 17, 2009

I read an article asking people not to donate dented cans to the food bank. It said that a single large dent causes "2 miles" of microscopic fissures in the metal. Supposedly there is a problem with supermarkets (and people) offloading huge quantities of dented cans that the food bank can't safely hand out and has to pay for disposal of.
posted by bonobothegreat at 5:14 AM on April 17, 2009

Supermarkets put the dented cans on the shelf because their margins on canned goods are razor-thin. The profit for an entire case can be ruined by one bad can.

At least, that's what the manager at a grocery store I worked at long ago told me.
posted by Shohn at 5:35 AM on April 17, 2009

No! No! Don't do it! The local newspapers are full of people dying of botulism from eating dented tins! Or maybe not.

The US Government Centers for Disease Control and Prevention says:
"In the United States, an average of 145 cases are reported each year. Of these, approximately 15% are foodborne, 65% are infant botulism, and 20% are wound. Adult intestinal colonization and iatrogenic botulism also occur, but rarely. Outbreaks of foodborne botulism involving two or more persons occur most years and usually caused by eating contaminated home-canned foods. The number of cases of foodborne and infant botulism has changed little in recent years, but wound botulism has increased because of the use of black-tar heroin, especially in California. "

So I make that 22 people in the US get sick from any food-borne botulism a year, and if the numbers due to dented tins exceeded the small number due to home canning, they would presumably be mentioned. Notice the stories others have told of bad contents were about stuff you wouldn't eat anyway, so couldn't get sick from. As A Terrible Llama says, supermarkets don't sell stuff they can be sued for.
posted by Idcoytco at 5:44 AM on April 17, 2009 [1 favorite]

It seems pretty rational to me: if a can is dented, it is more likely that that can's seal was broken. Whether this happens often or not is not the point; it's just that, if the package appears broken, why buy it?

I have no idea how this could be construed as a myth.
posted by koeselitz at 5:51 AM on April 17, 2009

Idcoytco: No! No! Don't do it! The local newspapers are full of people dying of botulism from eating dented tins! Or maybe not... So I make that 22 people in the US get sick from any food-borne botulism a year...

The data you cite would be conclusive and final if botulism were the only food-borne illness. It's not. Botulism is probably the rarest food-borne illness. Using the numbers listed in this Wikipedia link, between 1996 and 1998 25.3 million people per year contracted food-borne illnesses. 'Botulism' is awful and sounds bad, but it's hardly representative of the larger problem.
posted by koeselitz at 5:58 AM on April 17, 2009

posted by koeselitz at 5:58 AM on April 17, 2009

22 in 350 million is pretty good odds that you'll be ok.
posted by electroboy at 6:19 AM on April 17, 2009

Former Grocery Manager here: I am in the backroom denting your 100% organic, free-range, gluten-free cans!

Botulism and other food borne bacteria are the reason you don't eat from a dented can. The Botulism toxin causes slurred speech, vomiting, difficulty breathing, muscle paralysis, and whatever happened to Janice Dickinson's face. None of these are good things.

When a can is dented with enough force, the seams and seals are not always structurally sound. They may be open just enough to allow bacteria in, but not let food out. While most food-borne bacteria can be killed by cooking, typically with canned food, you do not heat it hot enough to kill bacteria because you're making it hot enough to eat, not hot enough to cook a second time.

To kill botulism, you apparently have to hold food at 121°C for 3 minutes. This doesn't remove the toxin that actually makes you sick though. So you're still risk looking like Janice Dickinson.

Dented cans end up on the shelf for a variety of reasons... mostly it's either stocked too fast and the stocker wasn't paying attention or a customer drops it and it just gets put back on the shelf. I have never had a problem with returning product to or getting credit for product from my distributors, but some stores might not be on as good terms or may feel they should make a profit on that can rather than just zero it out.

All this being said, I've eaten tons of food in dented cans because they would never sell to customers. So I'd get credit on my next case & have lunch. Yum! :D I've never gotten sick from eating canned food, even if it was dented or past the expiration date.

Did you drop the can? Eat it.
Is it a small dent in the middle of the can? Eat it.
Is the can alright in other respects (no weird bulges at the seams, no rust)? Eat it.
When opened, does the food look & smell alright? Eat it.
Are you old enough to be out of Kindergarten but not yet old enough for the Senior Center? Eat it.
posted by aristan at 7:02 AM on April 17, 2009 [7 favorites]

My understanding is that the risk, as others have stated, is there in all dented cans BUT you really (mostly) should be worried if the dented can is bulging or swollen (for lack of a better word), indicating that contamination has taken place.
posted by misha at 7:09 AM on April 17, 2009

What aristan says. I always assumed that dented cans in the supermarket were dropped by customers and put back, and that the store's staff had not yet removed them. I don't buy dented cans, but if I find one on my own pantry shelf, I assume that it got dented rolling around in the trunk of my car. Not a big deal for me, YMMV.
posted by Robert Angelo at 7:11 AM on April 17, 2009

This is all interesting. Does anyone know how much time would need to elapse between the denting of a can and the appearance of a botulism colony (is that the right word?) in the can?
posted by adamrice at 7:34 AM on April 17, 2009

I've never even heard about this and having been happily eating out of dented cans for the last thirty years. Do you only get botulism in the US or is there a conspiracy of silence trying to kill me in the UK?
posted by ninebelow at 7:51 AM on April 17, 2009

I always assumed that dented cans in the supermarket were dropped by customers and put back,

See, the problem with this is that in my entire life, I can't remember ever dropping and denting a can. I probably have, but I don't think it's something that occurs easily (quick! everyone! go into your kitchen and drop a can!) because if it were, if people were really that droppy and supermarket floors that hard, the supermarket would be filled with broken jars of pickles* and the like. It seems to me like something that happens in the presence of heavy machinery or other heavy items, crushing together.

*instead of just occasional broken jars of pickles
posted by A Terrible Llama at 7:52 AM on April 17, 2009

Last night my husband opened a dented can of cat food. The contents were definitely not in the edible category (it was a god-awful color and smelled much worse than usual). Don't risk it.
posted by killy willy at 8:22 AM on April 17, 2009

For two years I've bought nonperishables at a local Amish bent-and-dent store, usually between 15 and 50 cents for a can.. I've picked up plenty of boxes of cereal that had gone stale, but zero cans that we have in any way been unable to use (seal broken or contents spoiled).

Anecdotal evidence is not real evidence, of course, but I've got a number of friends who have all done the same thing for years, and no bad experiences.
posted by relucent at 8:24 AM on April 17, 2009

If you really think there is an entirely secret epidemic of death from dented tins, that is just great for the rest of us who can buy cheap.

The reason why botulism is cited as the key deadly danger is because it is the famous one that grows without visible food spoilage. As I said, you won't get sick from eating damaged stinky cans because you have more sense than to eat the contents.

Of course food tainted with salmonella is not always visibly bad either. So you have to leave to me and people like me all eggs, and all things made with mayonnaise unless you know their history. Never buy a sandwich when you are away from home -- statistically a far more important message than "don't buy dented cans".

I am not minimizing the risk of illness and death from food poisoning. They are very, very real. But avoiding dented cans while wiping your child's face and hands with the cloth you just used to wipe your kitchen surfaces is not conducive to their health. Work on the major dangers -- make sure your family/employees wash their hands properly after going to the toilet and be careful in the handling of raw meat and everything it might have contaminated. (Don't forget those raw eggs either.)

And we ought to give a mention to campylobacter which is actually the major threat in the developed world. Grandmother probably hadn't heard of it, but sadly it may kill her in a care home.
posted by Idcoytco at 8:29 AM on April 17, 2009

but I don't think it's something that occurs easily (quick! everyone! go into your kitchen and drop a can!) because if it were, if people were really that droppy and supermarket floors that hard, the supermarket would be filled with broken jars of pickles* and the like.

Oh, believe me, there are.

Peanut Butter, Pickles, Mayo, it is ALL on the floor. Stores do this neat thing where they... get this... mop the floors! Customers are not individually nasty, but together they are a force. Seriously. Your experiment would be more accurate if you included the following:

- Give all the cans to a pair of 3 year olds who have done nothing buy mainline sugar and spongebob cartoons for 48 hours.
- Throw a 60lb bag of dog food on top of the cans.
- find out exactly how many cans fit on the shelf in your pantry. Oh... 8? yeah... you need to put 12 in there. CRAM them in as hard as you can and then have random people (might I suggest a couple of earlier mentioned 3 year olds?) pull one from the back. Because it's fresher or full of magic ponies.
- Stack all of your cans in a large pyramid. Reenact the plot line to many black and white sitcom episodes.

Repeat this daily until a can actually gets dented or one of your neighbors comes over and gives you 50 cents for it.

Seriously, you guys may think there are a lot of dented cans, but remember that one can came out of a case of 12 where 11 were perfectly fine.
posted by aristan at 9:12 AM on April 17, 2009 [2 favorites]

I think I've had a few cans which came home from the store OK, sat undisturbed on the shelf for a few months and then dented inward.

When I opened them the food in a couple of them, but not all, did not smell right, as if some organism had sucked up all the gas in the can and caused it to dent rather than giving off a bunch and making it bulge.

I assume many cans are sealed hot, and those are going to be lower than atmospheric pressure inside anyway, and it would only make sense to minimize materials cost by making the cans only just a strong as they need to be, so it might not take much to make them dent.
posted by jamjam at 10:07 AM on April 17, 2009

nthing the botulism worry
posted by Acer_saccharum at 6:49 PM on April 17, 2009

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