Mold on Food

We all grow up learning mold is gross. But is it just unpleasant, or is it actually dangerous? Isn’t it mold that makes blue cheese blue? And wasn’t penicillin first discovered in moldy bread?

Are we wasting perfectly safe food when we throw it out? Or are we gambling our health when we shrug our shoulders and eat that piece of cheese that had a dusting of white fuzz?

Let’s look at the facts.

What is mold on food?

Mold is a microscopic fungus, and yes, spoiler alert: some of it can make you sick. Like its cousin the mushroom, there are thousands of different species.

A few are used on purpose (think blue cheese and Brie). Others can produce mycotoxins, which Health Canada describes as toxic chemical products formed by fungi, and some people are allergic to mold. So mold on food is worth taking seriously. If you’re in the Montreal area and suspect a mold problem in your home, our Montreal Mold Busters team can help you address it.

Why does mold grow on food?

Mold requires three things to grow: organic matter, water and oxygen. Food provides the first two ingredients. Exposed to air, mold has everything it needs to grow.

How does mold grow on food?

Tiny mold spores are carried in the air. When these spores land on food, they take root and grow until they produce patches of mold visible to the naked eye. Once they mature, they produce new spores and release them into the environment and the cycle continues.

How long does it take for mold to grow on food?

Many factors affect the rate of growth of mold: the specific type of mold, the food it’s growing on, and the ambient temperature and humidity. Many species of mold like warmer temperatures and mold growing on fruit on your counter may develop in very few days, especially in the warm humid summer months. Other mold growing on food with less water content in the cool of a refrigerator might take several weeks.

How to handle mold on food?

Mold can grow on most types of food, but not all food is the same.

Red Flag Food

Red flag food items should be automatically discarded when moldy. These items include most food items, particularly soft and moist foods:

• Luncheon meats, hot dogs, bacon, etc.
• Cooked leftover meat, poultry and fish
• Cooked pasta and cooked grains
• Casseroles
• Sour cream and yoghurt
• Soft fruits such as tomatoes, berries, cucumbers, etc.

Some other drier, harder foods fall into this category as well:

• Nuts and legumes
• Bread, baked goods and other highly porous items

In general, softer food with more moisture content is more prone to molding, and can’t be safely salvaged. In addition to the mold itself, soft moist food can provide an ideal environment for dangerous bacteria to grow. For these foods, it’s important not to assume the problem is limited to the mold you see.

Throw away the moldy food, and carefully inspect other nearby food, especially food in the same package. Don’t sniff moldy food: USDA food safety guidance warns it can cause breathing trouble. Wrap the spoiled items in plastic to contain the spores, and discard. If you’re based in Ottawa, our Ottawa Mold Busters team is ready to assist you in dealing with mold issues.

Cheeses made with mold

Cheese often incorporates mold as part of its production. However, it’s crucial to distinguish between intentional and potentially harmful molds. Here’s a guide to some popular cheeses and their relationship with mold.

The mold used in making these cheeses is safe for consumption. However, if other mold that is not part of the manufacturing process is present, these items should be discarded just like any other red flag food item. Some blue cheeses may be hard enough to be treated as a Yellow Flag item (see below for care). However, if you are unsure where to draw the line, remember: when in doubt, throw it out.

Note that while the mold that forms the blue veins inside blue cheeses is harmless when deprived of oxygen inside the cheese, the same strain of mold can form harmful mycotoxins if allowed to grow on surfaces exposed to air. Be careful of cross-contamination with these cheeses and keep them wrapped in cellophane while storing them.

Yellow Flag Food

Other foods, particularly harder and drier foods, can sometimes be kept once the mold is carefully removed. These include:

• Hard cheese
• Firm fruits and vegetables (cabbage, carrots, bell peppers, etc.)
• Hard salami and dry-cured ham

If you’re going to cut away mold rather than discard the item, it’s important to remember that there is more mold present than what you can see. Below the surface, mold will have penetrated up to 2cm or more. For these food items, mold can be cut away but you should cut at least 2.5cm (1 inch) outside of and underneath any visible surface mold. Be careful to keep the knife clear of the mold to avoid contaminating the rest of the food as you cut.

Note that surface mold is a normal occurrence on certain hard salamis. In this case, scrubbing the mold off the surface is sufficient. Again, it never hurts to be cautious. When in doubt, throw it out.

Keep, cut or throw out: food by food

Here’s the whole list in one place, based on USDA Food Safety and Inspection Service guidance.

Types of mold on food

There are numerous types of mold that can grow on food. Some food molds are beneficial and used in producing certain foods, like blue cheese. However, molds prefer warmer temperatures and can grow on various foods, from soft cheese to bell peppers. It’s crucial to recognize and differentiate between harmless and harmful mold. For instance, while some molds on hard cheeses can be scrubbed off, moldy soft cheese should be discarded immediately.

Here’s a breakdown of common mold colours on food and what to do about each.

Black mold on food

Various strains of mold can have a black appearance. Homeowners tend to worry about black mold, Stachybotrys chartarum, but that one grows on water-damaged building materials such as drywall, not usually on food.

The black mold you find on food is usually something else, such as Rhizopus stolonifer, also known as black bread mold. You may also see black mold on the rubber seals of your refrigerator. That doesn’t mean you have Stachybotrys in your house, but play it safe: discard the food, scrub the refrigerator clean, and look for other signs of black mold in your home.

Can black mold grow on food?

Yes, black mold can grow on food. While it’s commonly found on walls and ceilings, it can also grow on food, especially if the conditions are right. Foods with high moisture content, like green and mixed salads, are particularly susceptible. If you spot black mold on any food item, it’s best to discard it immediately.

Did you know?

Stachybotrys is the 3rd common toxic mold type found in homes we tested?! Find out more exciting mold stats and facts inside our mold statistics page.

Pink mold on food

Pink moldy formations on food may not be mold at all, but rather bacteria growing. Aureobasidium and Fusarium are also two common fungi that grow with a pinkish colour.

Pink mold is most often seen on bread, dairy products and meat. Whether it’s mold or bacteria, the answer is the same: throw the food out. Pink growth on soft food isn’t something to cut around.

White mold on food

White mold is seen on a variety of foods, from the white mold purposefully grown on the outside of certain cheeses, to fluffy white mold appearing on berries and other fruit.

Many strains of mold can appear white, and to complicate matters many coloured strains of mold go through a phase where they look white before developing the spores that give them their colour. Unless white mold is a purposeful part of a food’s production (e.g. Brie and Camembert cheese, or the white coating on some dry salamis), treat it like any other mold and handle the food accordingly.

Green mold on food

Green mold is commonly found on citrus fruit and bread, and it’s usually a Penicillium species. Cladosporium, which looks olive green to almost black, also turns up on food.

Green mold often has a strong musty smell, and people with mold allergies may find it irritating. Some Penicillium species can produce mycotoxins, so don’t sniff it, and throw out anything soft it’s growing on.

Orange mold on food

Orange mold on food is often Neurospora, sometimes called orange bread mold, and some orange growth is bacteria or yeast rather than mold. You’ll also find orange molds around the house, on damp wood and in bathrooms, but those are different organisms.

Treat orange mold on soft food like any other mold: throw it out, and check anything it was touching.

Red mold on food

While various molds can look red, red mold on bread is most often Neurospora, the same group as orange bread mold. Some mycotoxin-producing molds can also look reddish, or grow alongside it, so treat red mold on food with the same caution as any other mold.

Blue mold on food

Blue mold on bread and the blue mold deliberately cultivated to make blue cheese are strains of the genus Penicillium. And yes, some species of Penicillium (but not all!) produce penicillin. Many species of Penicillium are innocuous, but some are not.

And while the blue mold in blue cheese, deprived of oxygen, is safe for consumption, that same strain of mold can produce mycotoxins when it grows on an outside surface exposed to air. So, eat that blue cheese but treat other blue mold as potentially toxic.

What happens if you eat mold?

It depends on three things you can’t see: which mold it was, whether it had time to produce toxins, and whether you’re allergic to mold. That’s exactly why the standard advice is to throw soft moldy food out rather than taste-test it.

Is it dangerous to inhale mold spores from food?

It’s best not to. USDA food safety guidance says sniffing a moldy item can cause breathing trouble, and some people are allergic to mold. A musty smell is still a useful clue before you can see anything (on dishcloths and sponges, for example), but once you’ve spotted mold, keep your nose out of it.

Can mold on food make you sick?

It can. USDA food safety guidance notes that some molds cause allergic reactions and breathing problems, and a few produce mycotoxins, poisonous substances that can make people sick. The World Health Organization says most mycotoxins are chemically stable and survive food processing, which is why moldy soft food goes in the garbage rather than the oven. If you have questions about your own symptoms, talk to a healthcare provider. And if food keeps going moldy fast, the problem may be your kitchen rather than the food: our virtual inspection services can help you find the source.

What should you do if you ate moldy food?

Taking a bite before you notice the mold happens. Here’s what to do next:

• Stop eating it, and throw out the rest along with anything soft it was touching in the same package.
• Don’t try to rescue what’s left by toasting, boiling or microwaving it. Heat won’t remove toxins that some molds leave behind.
• If you feel unwell afterwards, or you have a mold allergy, call a healthcare provider. In most provinces, including Ontario (Health811) and Quebec (Info-Santé), you can dial 811 to reach a nurse at any hour.
• Call 911 right away if someone has trouble breathing or signs of a severe allergic reaction.
• Find where it came from. Mold on fridge seals, shelves or the bread box will keep seeding new food until you clean it.

Food mold facts and questions

Which food will mold fastest?

Storage conditions will have a significant effect on how quickly a given food turns moldy. However, all things being equal, food with a high moisture content will mold first. Thus, in the fridge, fruits such as strawberries or cucumber might get moldy before other foods. Stored at room temperature, natural bread (with no preservatives) can get moldy quite quickly.

Is it safe to eat fruits with mold on a peel you discard?

It may be tempting to think that for fruit with a peel, simply removing and discarding the peel may be enough to protect you. In the case of a firm fruit like a pineapple, it can indeed be treated as a “yellow flag” food, carefully cutting away the affected area.

Fruits with a softer peel like oranges or bananas should be treated as “red flag” foods and discarded, because the mold may have gone through the peel into the fruit inside. In the case of an avocado, the skin is quite tough but mold can still get underneath and into the fruit. Play it safe and discard it.

Can you kill mold by cooking it?

Cooking kills most mold, but it doesn’t make moldy food safe to eat. Some molds leave behind mycotoxins, and the World Health Organization notes that most mycotoxins are chemically stable and survive food processing. USDA research adds that some molds make heat-resistant spores that can survive heat treatment. So cooking won’t rescue moldy food: throw out soft and moist foods, and only cut and keep the hard ones in the table above. Afterwards, clean the spot where the food was stored so the mold doesn’t move on to the next batch.

Does heat kill mold?

Yes, heat kills most mold, but that’s only half the answer. The toxins some molds produce can survive cooking. Grain and nut crops are the classic example: heat can reduce the mold, but the toxins may stay. That’s why Health Canada advises people to avoid eating mouldy nuts or other mouldy foods, and the World Health Organization says to discard nuts and grains that look mouldy, discoloured or shrivelled.

Mold response to heat

To understand how heat affects mold, let’s look at common heat treatment methods and their impact on mold and mycotoxins.

Does boiling water kill mold?

Boiling water kills most molds, but it won’t make moldy food safe. Most mycotoxins survive food processing, and some molds make heat-resistant spores. Boiling water is great for cleaning utensils and jars, not for rescuing food that’s already moldy. Throw out perishable food with visible mold.

What temperature kills mold spores in food?

There’s no single safe number. USDA research says most molds are destroyed at 60 to 71°C (140 to 160°F), but notes that some make heat-resistant spores that can survive heat treatment, and heat has to reach the middle of the food, not just the surface. Most important, the mycotoxins certain molds produce survive food processing, so moldy soft food isn’t safe to eat no matter how hot you heat it.

Will cooking moldy cheese kill bacteria?

Cooking can kill the mold and bacteria, but it doesn’t get rid of the toxins they’ve already produced. Soft cheeses like cream cheese and Brie mold quickly; if they have mold that isn’t part of how they’re made, throw them out. Hard cheeses like cheddar or Parmesan can be saved by cutting off at least 1 inch (2.5 cm) around and below the spot. When in doubt, throw it out.

Does heat kill mold on bread?

Toasting kills mold on the surface, but it doesn’t make moldy bread safe. Bread is soft and porous, so mold roots run deeper than the spots you can see, and toasting doesn’t remove the toxins some molds leave behind. Once you see mold, throw out the loaf.

Does freezing kill mold on food?

No. USDA food safety guidance explains that freezing to -18°C (0°F) makes bacteria, yeasts and molds inactive, but once the food thaws they can become active again. Freezing also does nothing to toxins that are already there. So the freezer is great for prevention (Health Canada recommends keeping yours at -18°C or lower) and useless for rescuing food that’s already moldy. Cold doesn’t solve mold in the house either; see our guide to mold in cold storage rooms.

How to prevent mold on food?

Of course, far better than throwing out moldy food is avoiding having your food get moldy to begin with! Fortunately there are steps you can take to keep your food fresh and mold-free:

• It takes one moldy food item to get the whole basket covered in mold! This is very important rule to remember the moment you are at the market. If you are buying nonpacked items, ensure each of them is fresh. If you notice mold on any single piece, simply don’t buy it. Examine each item for bruising, softness, oxidation or signs of mold before you buy it and avoid any items that look overly ripe.
• On the other hand, when buying pre-packed food you cannot examine every single piece, meaning that moldy items can go unseen. In that case, ensure you checked the date and chose the one that was most recently packed. Instead of buying processed or pre-packed food, where you often don’t have control of the freshness (the story of wrong dates is not rarely heard), choose local markets and stores you can trust.
• Once you buy your delicious food, especially fresh fruit and veggies, it is important to keep it covered until you’re ready to eat it to minimize the risk of cross-contamination with bacteria, mold, dust and debris from the environment. Use plastic wrap to cover foods you want to keep for longest, such as fresh fruits, vegetables, salads and cheese.
• Once a can is open, move what’s left into a tightly sealed plastic or glass container in the fridge. Refrigerate leftovers and use them within 3 to 4 days.
• Consume early to avoid mold. The first step you can take to prevent food going bad is to eat it before mold has time to take hold. Especially for moisture-rich and porous food like fruits and breads, buy in smaller quantities so you can eat it within a few days.
• Keep food cold: the cooler the better. Keep food, especially soft moist food like fruit, in the refrigerator rather than at room temperature, and only take it out while you’re using it (under two hours). Health Canada recommends a fridge at 4°C or lower and a freezer at -18°C or lower. To keep food mold-free for longer periods, store it in the freezer rather than the fridge.
• Use heat to kill mold. High acid foods such as fruits, jams and jellies can be made safe to preserve through heat treatment. A boiling water bath is a common practice to prepare them for a long shelf-life. The amount of time required for a water bath will vary depending on what and how much you’re canning, so be sure to adapt your method to the specific food you’re treating.
• Keep kitchen tools and surfaces clean. Mold may thrive on food, but it can be found anywhere. The less mold in your kitchen, the less your food will get exposed. Wipe your refrigerator and other kitchen surfaces with 1 tablespoon of baking soda dissolved in about 1 litre (1 quart) of water. Watch out for black-coloured mold on your fridge’s rubber seals and scrub carefully to clean it out.
• Keep your dishcloths, tea towels, sponges, mops and other kitchen tools clean. Give them the sniff test: if they smell musty, they may be harbouring mold. Any item that you can’t get clean and fresh-smelling, discard and replace.

Food storage recommendations

Proper storage is key to preventing mold growth on food. Here’s a handy guide on how to store various food items to maximize their shelf life and keep them mold-free.

Mold proofing kitchen and cleaning tips

Since food is stored in the kitchen (most of the times), keeping your kitchen clean and well-aired will also have a big impact on your food’s life. For example, mold will develop anywhere where there is a leak, and if you are storing food close to that it can easily transfer from a corner and attack your favorite otherwise fresh food.

In order to prevent mold on food you will have to work on overall kitchen mold prevention. In most cases it includes either ensuring there is enough fresh air or regular cleaning. Here are a few tips that can help you prevent mold in the kitchen.

• As we said above, mold can grow in the fridge, so keep the inside clean. Every few months, wash it with the baking soda mix, rinse with clean water and dry it thoroughly before putting food back.
• Ensure your food is still fresh by checking it every day or two. Toss away anything that has a sign of mold or that started rotting away.
• Replace sponges at least once a week and always use clean dish cloths and towels. If you notice a musty smell coming from a sponge or towel, replace it immediately.
• Wash the dishes at least once a day. Don’t leave food leftovers in your sink behind you once you are done with the meal. Throw them away immediately. If you are in a rush, keep your dishes under water to prevent food stains from hardening until you can wash them properly.
• Mold can be found in your dishwasher and garbage disposal. It can be the reason behind the odors, so keeping them clean should be a priority. At least once a week, pour baking soda, salt and vinegar (or lemon) down the sink and leave it for 10 minutes. You can add lemon or orange peels for a nicer smell. Then flush it with boiling water, and your disposal and sink will be clean and fresh.
• Kitchen tools, especially wooden ones, should be washed and dried well before you put them away, because wood is one of mold’s favourite foods. Leave them somewhere dry with fresh air and light. If you’ve just finished cooking and the stove is still warm, setting them next to it works well.
• Don’t forget about unused kitchen appliances. They are often sealed and if not well dried, mold can form due to water evaporation inside. The best way to prevent mold from developing inside is to ensure it is well dried before storing and, if there is a possibility, keep it open.
• And last but not least, keep the relative humidity in your home below 50% (ideally around 40%), especially in the warmer months when mold grows fastest. Run your kitchen and bathroom fans, open windows when it’s drier outside than in, and use a dehumidifier if you can’t get the level down. Keep your air vents clean and unblocked too.

Additional recommendations

Mold is a type of microscopic fungus, and there are many species in our environment. While some molds are used on purpose in food production, others can be harmful. Store food properly to keep mold growth down: eat processed food before its best before date and keep animal products refrigerated. Regular cleaning of your kitchen and cleaning tools helps too. Some foods can be saved from mold, but when you spot it on soft cheese or any other soft food, the general rule is to throw it out.

Conclusion

As with mold in general, there are many strains of mold that can be found on food. While some are innocuous, many are not. While mold that’s purposefully introduced into certain cheeses can be safe, always treat other mold on food as a dangerous substance. Treat “yellow flag” foods with caution and for “red flag” foods, play it safe and discard it.

And remember, the same mold that spoils food can grow anywhere in your house that stays damp. Keep watch for mold in your kitchen and the rest of your home, and if you spot signs of mold, learn the steps needed to remove it safely.

Resources

• USDA Food Safety and Inspection Service: Molds on Food, Are They Dangerous?
• Health Canada: Safe food storage
• Health Canada: Natural toxins
• World Health Organization: Mycotoxins fact sheet

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Published: May 19, 2020 Updated: October 19, 2026

Written by:
John Ward
Account Executive
Mold Busters

Fact checked by:
Michael Golubev
CEO
Mold Busters