Bananas can turn from green-accented yellow to brown-speckled yellow in two or three days. If you keep unripe bananas near fully ripened ones, they’ll ripen fast themselves because the ripe fruit gives off a gas called ethylene, which hastens the ripening process. Many sources warn against refrigerating bananas, and their skins will generally turn brown faster when subjected to cold, though the fruit inside may not be affected. Bananas that are refrigerated, however, might take longer to ripen, or not ripen at all, when brought back to room temperature. Note that bananas whose flesh has become very soft and brown are still perfectly edible: They may not work in the usual peel-and-eat way, but are good in desserts, banana bread, cocktails, etc.
The problem with berries — especially soft-skinned raspberries — is that they’re very susceptible to mold and mildew. Refrigerating them in unopened plastic containers (or with their paper baskets tightly sealed with plastic wrap) will usually keep them edible for about a week. Rinse them only just before eating to avoid increasing mold-generating moisture. Once mold starts to form on a few berries, it’s safest to discard them all, as it spreads fast and can be hard to see.
Unless it’s the supermarket variety that’s loaded with preservatives, bread is extremely perishable. Mold spores form quickly on it, especially once it’s been cut into, and particularly in humid climates. Most kinds of bread mold are not dangerous, but because invisible mold cells can permeate the loaf, and because some mold can produce harmful mycotoxins, the USDA advises tossing the entire thing if it develops blue- or green-and-white splotches. While it isn’t considered spoilage, strictly speaking, the other problem with bread (the kind not loaded with preservatives), of course, is that its crumb hardens and dries out progressively and it becomes stale. At this stage, it is best cut into croutons or turned into breadcrumbs.
As long as it doesn’t get damp and isn’t invaded by weevils or rice mites (those tiny but mobile black specks that can find their way into grains kept in unsealed containers), white rice will last almost indefinitely. Brown rice, however, can go rancid in six to eight months, or slightly longer if refrigerated. That’s hardly overnight, but faster than most people would suspect. This is because the bran, which is polished off white rice but coats the brown variety, contains oils that start to spoil with time. Leftover cooked brown rice, even when refrigerated in a sealed container, should be eaten within five days or discarded.
Corn on the cob
As with most fruits and vegetables, corn on the cob is susceptible to mold and mildew. They usually start at the pointed tip of the cob, and if that is cut off, the corn is still fine to eat. If the mold extends below the tip, the whole cob should be discarded. Unshucked corn will last for four to six days if refrigerated in sealed plastic bags. But there’s another problem with corn. It’s not exactly spoilage, but when sweet corn is first picked, it’s high in sugar and low in starch, and the balance starts reversing almost as soon as it’s off the stalk. Grocery store corn may have been picked weeks before it’s sold, so it can be starchy and nowhere near as sweet as expected. Farmers’ market corn is a better bet — but no matter where corn is purchased, it should be eaten as soon as possible for maximum flavor and good texture.