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A: Chopped or sliced onions can be stored in a sealed container in your refrigerator at the proper temperature of 40Â°F or below for 7 to 10 days (Source: USDA). For pre-cut fresh or frozen products, always use and follow manufactures use by dates.
Refrigeration is only necessary when trying to extend the shelf life of sweet or mild onion varieties with high water content, but be sure to use a low humidity setting, they must be kept dry. 1  Whole peeled onions should be refrigerated after purchasing. 2  Cut onions can be stored in a sealed container for up to 7 days.