The Reason You Shouldn't Store Food In An Open Can
We've all done it. Time is short, you're in a rush, or you just don't have any clean storage containers on hand; so you cover that half-used can of tomato sauce with aluminum foil and stick it in the refrigerator for a few days. When you need to use the rest of that sauce in a new recipe, you notice something doesn't taste quite right. It may be subtle or it may be dominant, but the sauce now has a distinctive tinny taste.
That metallic flavor is due to oxidizing metal. All metals (except silver, platinum, and gold) form metal oxides when exposed to oxygen. Cans of food are airtight so no oxidation can occur — oxidation happens with food as well as metal. Once you open a can, you let oxygen in and it starts to interact with the metal (and the food), making it less palatable. This is why you shouldn't store food in an open can.
Is food stored in a metal can safe?
If food doesn't taste right, it is a red flag alerting us it might not be safe to eat. This is why your first instinct is to toss that half-can of tomato sauce — it doesn't taste right, so it must not be safe to eat.
However, according to the U.S. Department of Agriculture (USDA), "Unused portions of canned food may be refrigerated in the can." In other words, if you need to store food in the refrigerator using the can that it came in, it doesn't create an immediate health risk. But the USDA does state that these unused portions are only good for up to four days, so you can't let them linger for long.
If you want food that is safe to eat and tastes great, you need to remove the unused portion from the can and place it in a food-grade glass or plastic container, preferably one that is airtight (which is better than using plastic wrap or aluminum foil, anyway). This quick and easy solution is the best option for storing food in your refrigerator — whether it was initially canned or not.