Is It Safe to Eat Moldy Bread—and How Can You Stop It From Going Bad So Fast?

You’re all ready to eat your sandwich when you notice the golden brown of your roll now has a…decidedly green tint. So you wonder: Is it safe to eat moldy bread—you’d cut off the bad stuff, of course—or do you need to rethink lunch?

It’s an unfortunately all-too-common question, because, well, mold has a way of sneaking up on you. Within the span of a few days, an innocuous speck can turn a loaf of bread from prime sandwich material into a hideous mass of blue-green fuzz—an appetite-killing sight if ever there was one. “Bread is a pantry staple, but it’s also a prime target for mold, which raises both quality and safety concerns,” Darin Detwiler, PhD, a food safety expert and associate teaching professor at Northeastern University’s College of Professional Studies, tells SELF.

So is it safe to toss the fuzzed-up slices but eat the rest? Or do you need to trash the entire loaf? And what’s the best way to stop bread from molding so fast in the first place? Read on to find out more about all things mold, because this is your best shot at making sure your sandwich plans are never foiled by fungi again.

Why is bread such a mold magnet?“As simple as bread may seem, it is practically a dream food for mold,” Dr. Detwiler says. Soft, a little moist, neutral in pH, rich in sugars and starches, and typically stored at room temp, bread makes the perfect incubator for those sly little spores, according to Dr. Detwiler. And thanks to their ingredient makeup, some types are more susceptible than others.

What’s more, mold is inescapable. Even though it isn’t always visible with the naked eye, it’s all around us, lurking in the soil, floating in the air, and even entering your airways (BRB, hopping in the shower). Whenever you take bread out of the bag, you expose it to the surrounding environment, offering an opportunity for drifting spores to settle on the surface. Under the right conditions (think warmth and humidity), those spores will then start to proliferate—“almost invisibly at first,” Dr. Detwiler says. As the mold colony grows, you’ll see those familiar fuzzy spots starting to form.

Of the more than 1.5 million species of mold estimated to exist, a few are especially likely to blame for your spoiled slice. “One of the most common culprits is Rhizopus stolonifer,” Dr. Detwiler says. Better known as “black bread mold,” R. stolonifer starts off as fuzzy white spots that then turn gray or black, hence its name, according to Dr. Detwiler. Other top suspects include Penicillium molds, which often manifest as blue-green patches, and Cladosporium molds, which are olive green to black in color. In some cases, Aspergillus molds (white, yellow, green, brown, or black) can also grow on bread.

Is it ever safe to eat moldy bread?Unfortunately, the answer is a hard no. By the first hint of discoloration on any slice, your entire loaf is a goner. “Once mold forms, just throw it out,” Martin Bucknavage, MS, a senior food safety extension associate at Pennsylvania State University, tells SELF. “It’s just not worth it.”

Before you ask, that rule of thumb holds true even if you take a knife to the bad parts. “What many people don’t realize is that once mold appears, it’s not just on the surface,” Dr. Detwiler says. Instead, root-like structures known as hyphae penetrate deep into the interior, compromising the entire thing. Thanks to these hyphae, it’s impossible to tell just by looking at your loaf how far the contamination has spread and whether any portion is still untouched, so it’s always better to err on the side of caution. Same applies to sliced loaves. Even if only the slices on the end are visibly moldy, the risk extends to every single one, since mold spores can travel between the individual pieces, according to Dr. Detwiler.

Not only will moldy bread probably taste bad—it usually brings a characteristic musty flavor, “like funky dirt,” Bucknavage says—it could pose some real health risks too. Some types of mold can cause respiratory issues and allergic reactions. What’s more, a few molds produce mycotoxins (toxic substances that can bring about a range of health issues), including certain strains of Aspergillus and Penicillium. Certain Aspergillus mycotoxins can cause birth defects, increase your liver cancer risk, and trigger kidney and immune system problems, for instance, according to the FDA. Of course, serious side effects are rare, so a one-off moldy bite isn’t likely to do you in, but it’s not worth taking the risk. Basically, mycotoxins are “just really bad players,” Bucknavage says. “Why mess with that?”

Not only will cutting off moldy spots fail to salvage your loaf, cooking won’t work, either, so you can forget about sticking your slice in the toaster or microwave for a lil’ heat treatment. “Heat may kill the spores, but it doesn’t destroy potential mycotoxins,” Dr. Detwiler says. The takeaway: Once mold appears, it’s game over.

What’s the best way to store bread to deter mold?Mold might be all around us, but you’re not completely defenseless: Storing your loaf correctly can prevent it from spoiling before its time. So should you let your bread chill on the kitchen counter? Is refrigeration a better bet? What about freezing? Turns out the correct answer depends on a few different factors.

First, you need to consider your bread type. By “bread type,” we’re not referring to the specific variety (say, rye, pumpernickel, ciabatta, whole wheat, or multigrain). Instead, we’re talking about the manufacturing process: commercial (think a mass-produced sliced loaf you’d find in a supermarket aisle) versus artisanal or homemade (like a fresh-baked loaf you could buy at a bakery or your grocery store’s baked goods section, or one you bake yourself).

Most commercial bread is made with preservatives—like calcium propionate and sorbic acid—that deter mold development and extend the product’s shelf life, Bucknavage says. On the other hand, artisanal and homemade bread isn’t formulated to last, according to Bucknavage. It “usually lacks these additives, so it can mold within just a few days at room temperature,” Dr. Detwiler says. Because of this difference in staying power, storage is a far more pressing concern for artisanal and homemade bread than commercial bread. (For an option that lasts slightly longer than most, you might want to go with sourdough: The lactic acid bacteria found in its starter are known to produce compounds that can help resist mold, so it shouldn’t spoil quite as quickly.)

Second, you need to ask yourself how long it will realistically take to finish the whole loaf. Thanks to the preservative content, commercial bread can stay mold-free at room temperature for a week or more (keep it sealed within its original plastic bag), Dr. Detwiler says, but artisanal and homemade bread is a different story. Confident you can polish it off within a few days? Store it in a cool, dry place like a bread box within a breathable container like a paper bag, according to Bucknavage. Just make sure to give the bread box a thorough cleaning in advance, especially if you’ve previously had mold issues, Bucknavage says. Otherwise, lingering spores could “hasten the development of mold” on new tenants, he explains. (And for best quality, keep it whole until you’re ready to eat—slicing increases the surface area, creating more opportunities for it to dry out, Bucknavage says.)

Meanwhile, the loose covering ensures that moisture doesn’t get trapped against the surface of the bread, according to Bucknavage. “You have to let that moisture escape,” Bucknavage says—remember, mold thrives in hot, damp environments. In fact, it’s for this reason that paper bags are specifically recommended: Tightly tied plastic bags can “trap moisture and can actually accelerate mold growth,” Dr. Detwiler says. (This doesn’t really apply to commercial bread, though, because the preservatives counter the effects of the plastic sealing, so there’s really not much of a point in transferring it to a paper bag, he adds.)

Betting you’ll need more time? Freezing is your best option regardless of bread type: “It halts mold growth entirely and preserves quality,” Dr. Detwiler says. You can freeze commercial bread in its original bag if the duration will be less than two weeks, but if it’ll be any longer, take extra protective measures by wrapping the loaf (or individual slices) “in an extra layer of aluminum foil, freezer paper, or a zip-top freezer bag, as this prevents freezer burn and flavor loss from long exposure to cold, dry air,” Dr. Detwiler says. Likewise, artisanal and homemade bread should be tightly wrapped before freezing to reduce any loss in quality. Per the University of Wyoming, the best method is to apply plastic wrap to your loaf, stick it in a zipper-top freezer bag, press to release any excess air, and seal. You might also want to preemptively cut it into slices if you anticipate only eating a small amount at a time.

Notice we didn’t mention the fridge here? That’s because while the colder temps might slow mold growth, they’ll also trigger changes in starches that hasten staling, “causing the bread to harden and kind of dry out,” Bucknavage says. Stale bread might not pose a health risk like the moldy stuff, but it’s still not exactly a desirable outcome. And if you’re spending $7 on high-end rye or pumpernickel, you want the best experience possible—meaning stuff that’s not only safe to eat, but that also tastes good.

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