Molds, which look like mini-mushrooms under a microscope, are actually a type of fungi, with visible spores on the surface and a network of microscopic roots that twist deep below that are often invisible to the naked eye. So a mold's penetration into a piece of bread may be greater than a quick look-over suggests, says Gravely.
You might have slightly more leeway when it comes to sliced bread in a bag: If after careful inspection of the interior and exterior of the bread on a long loaf, you can tell one end is unaffected, keep it, Gravely says. But otherwise, it should be tossed — the fact that bread is sliced is no guarantor that mold hasn't spread.
"I have seen mold spread from one slice to the next," she says.
What's more, by the time mold has moved in, other harmful kinds of bacteria associated with food spoiling may also have infiltrated the food.
Some molds, like those used for Gorgonzola cheese, are safe to eat. But the mold dotting bread isn't a benign source of extra fiber. Gravely says people who eat moldy food may suffer allergic reactions and respiratory problems. Even inhaling mold can be dangerous. To avoid breathing mold, the USDA recommends putting food in a plastic bag and then in a covered trashcan, out of the reach of children and animals.
"I'm sure some people would really want to press the situation, but bread is cheap," says Gravely. "Go buy some more."
Soft fruits, lunch meats and jams also must be tossed once moldy, she adds. But for those who mourn their castaway croissants, there's some good news: Tougher foods are salvageable even after fungus has invaded. Hard cheeses, salamis and vegetables like carrots, bell peppers and cabbage have tougher surfaces, making it more difficult for a mold's roots to move through. So you can excise the mold at the surface before it ruins the food's interior. For such foods, Gravely recommends cutting the mold out with a clean knife, allowing an inch of buffer on each side of a fuzzy patch.
Of course, the best way to cut down on funeral dirges for food past its prime is not to let the food get moldy in the first place. Gravely advises inspecting produce sold in plastic containers before buying it at the store. If shoppers discover a couple of moldy strawberries once at home, no need to jettison the entire bunch — just wash the other strawberries well and make sure the mold hasn't spread. The U.S. Department of Health and Human Services also has an app that helps consumers know how long different types of food generally last. Refrigerating food keeps it fresh longer, and cleaning the refrigerator every few months helps purge any food beginning to mold.
"They're pretty clever and adaptable," Gravely says of mold spores. "They prefer moist environments and warm temperatures, but they can grow in the refrigerator, and they can grow in sweet things or salty things."
But consumers shouldn't feel overwhelmed by the puny kitchen invaders, she says. After all, she adds, remember who's in charge: "Food in your kitchen is completely within your control."
Gnawing Questions is a semi-weekly column answering the food mysteries puzzling us and our readers. Got a question you want us to explore? Let us know via our contact form.