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I'd been taught growing up that you should never store canned food in the fridge in the open can. Is there any scientific basis to this, or is it just an old wives tale?

What types of foods should not be stored in their can once open? Would olives, for example, be harmed from this sort of storage? Or only more acidic foods like tomato paste or pineapple be affected?

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You seem to assume that it is a matter of food safety. I was taught that you should close cans because else the smells will mingle and you will get olive-smelling milk. Also, solid food like cheese will dehydrate. I can attest to both, but also curious whether there are other reasons too. –  rumtscho Jan 28 '13 at 23:58
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Seems everybody has a different explanation for this; I've always understood that refrigerating open cans - or just generally speaking, using the cans for food storage - is ill-advised because the cans themselves are reactive (some more than others, depending on material) and become oxidized by all the available oxygen, which of course affects the food. Not sure if that's authoritative, though. –  Aaronut Jan 29 '13 at 1:10
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The materials cans are made from are reactive (since they are usually made of aluminum or steel, despite the phrase "tin can"); but the cans are lined. The lining is obviously able to stand up to the canning process itself, then the long shelf life--it is unlikely to be in danger from a few days in the refrigerator. I think the "no good way to close them" story is more likely to be closer to the heart of the idea. –  SAJ14SAJ Jan 29 '13 at 1:30
    
@Aaronut what I was taught is to not store anything open in the fridge. For preserved vegetables, it doesn't matter if they are in a tin can or in a non-reactive glass jar. Cheese went into tupperware, batter/dough got a foil cover over the bowl, etc. I don't close plastic-cup-closed-with-foil containers for yogurt, cream, etc., but if they stay open for a few days, the contents get a stale smell, slightly reminiscent of more smelly fridge contents (which have some smell leakage through the container). –  rumtscho Jan 29 '13 at 14:08
    
@SAJ14SAJ To cover a can you can buy plastic lids specifically designed to fit standard size cans. They make a nice, airtight seal. They're commonly used to cover dog food cans, so can usually be found where pet supplies are sold. –  Carey Gregory Jan 29 '13 at 15:36
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1 Answer 1

up vote 10 down vote accepted

Short answer: storing food in an open can is normally safe for a short period, but inadvisable.

Longer answer: There are three main issues with storing foods in an open can. They are metal oxidation, contamination, and funk.

(1) Oxidation. As commenters have observed, cans used to be made of tin, which is toxic. Modern cans are made from either steel or aluminum. If the contents of the can are acidic, cans are lined with a polymer (plastic) inner layer. If that layer is broken -- say, by a major dent in the can or by using a knife to scrape out contents -- then the acid can get to the metal and, over time, corrode it, and some of the now-oxidized metal will dissolve into the food. As far as we know, the oxidized metal is not toxic, but it tastes horrible.

(2) Contamination. Any open container of food can become contaminated when an airborne water droplet (tiny -- microns wide) containing a nasty microbe drips or settles into it. The major biological culprit here is Listeria, which can grow in any moist environment, including spaces refrigerated below 40F (5C). Also, if juices from your raw meat drips onto an upper shelf, which later gets wiped inadvertently into your container of ready-to-eat food, you are likely to get Salmonella or E coli. This risk can be mitigated if you keep your raw meats on the lowest shelf, but not eliminated. Also, it is worth noting that contamination through this pathway is a relatively rare event -- but even so, it is not worth the risk.

(3) Funk. Have you ever put an ice cube in your beverage and notice your beverage tastes strange? The chemical compounds that give food their flavor tend to be volatile (meaning they will readily leave the food into the surrounding air). Also, the mustiness of a refrigerator/freezer is due to volatile compounds produced by mold and mildew. Foods that are wet and/or fatty can be molecular velcro to these compounds.

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