Is it ok to store open cans in the fridge?
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?
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.
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.
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.
@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).
@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.
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.
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.
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.
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.
Now clumsy-dancing white folk are going to put open cans of food into their fridges in a futile attempt to get da funk. I won't down-vote you for it, though.
Am I correct in my reading that (1) is an issue only if the lining of the can is broken, and (2) and (3) are issues for any uncovered container of food, but not for cans covered in plastic wrap? If that's the case, it seems that storing food is a convenience that entails a small amount of risk, and it's not necessarily inadvisable.
I have the same question as @Patrick. #2 and #3 apply to storing food in the refrigerator in general and don't seem to have anything to do with cans in particular. Just cover the can. Also, re #1: Wouldn't a major dent in the can be a problem regardless of whether it was stored in the fridge? If so, the scrape of a knife on a lined can seems like the only issue ... since it is introduced by the consumer after the can is opened. Since this is non-toxic and easy to detect by taste, it seems like an extremely low risk. I'd love to know if my thinking is correct on this.
Okay... I've done some more research. Here is what I now believe: (1) Opening the can introduces *oxygen* which in combination with any acid in the can, will react with the metal of the can. (2) In a lined can, opening the can exposes the *metallic top edge* of the can to the acidic contents which will oxidize over time.