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?
Mold is a microscopic fungus, and yes—spoilers!—consuming it can be bad for our health. Like its cousin the mushroom, there are thousands of different species.
Some are safe to consume, but many produce poisonous mycotoxins that cause illness and even death. Additionally, some people are allergic to mold and need to steer clear of it. So dealing with mold on food is serious business.
Why does mold grow on food?
Mold requires three things to grow: organic matter, water and oxygen. Food provides the 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.
On which types of food does mold usually grow, and how should you handle it?
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
- 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. Do not sniff moldy food: spores might get into your respiratory system. Wrap the spoiled items in plastic to contain the spores, and discard.
Special case: Cheeses made with mold
- Blue cheese
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: Hard and Less Moist
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 pepers, 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.
Different types of food mold
Black mold on food
However there are many non-toxic strains of black mold as well, including Rhizopus stolonifera, also known as black bread mold. You may encounter black mold on the rubber seals of your refrigerator or on food. While this doesn’t prove you have black toxic mold in your house, you are best to assume it may be harmful and discard the food item in question, meticulously scrub clean the refrigerator, and look for signs of black mold in your house.
Pink mold on food
Pink mold is most often seen on bread, dairy products and meat. Dangers of pink mold include infection of the respiratory, gastro-intestinal or urinary tracts.
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 may go through a phase where they appear 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), assume it is toxic and handle affected food accordingly.
Green mold on food
It can have a potent smell and be particularly irritating, particularly for people with mold allergies. This can lead to respiratory problems such as wheezing and coughing, as well as vomiting. Clodosporium mold can produce mycotoxins as well, so avoid exposure.
Orange mold on food
A variety of mold can take on an orange colour, including Fuligo septica and Aleuria aurantia. These orange molds commonly have a slimy texture.
While they may be less dangerous than some other colours of mold, they can still cause respiratory problems, and where orange mold is present, bacteria are also likely to be found.
Furthermore, orange mold is particularly prone to growing on wood. So not only is orange mold a threat to your food, it is a threat to the wood in your house.
Red mold on food
While various strains of mold can be red, red mold on food is most commonly Neurospora. While this type of mold is typically less dangerous than other types of mold, some mycotoxin-producing molds might appear red in certain conditions, or might be present alongside red mold. It’s therefore wisest to treat red mold on food with the same caution as 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.
Health effects of eating mold on food
Is it dangerous to inhale mold spores from food?
Inhaling mold visible on food is risky and should be avoided. It may cause allergic reactions or problems with the respiratory tract. When mold isn’t visible, sniffing may be a useful way to detect it—e.g. smelling dishcloths. However, once you’ve spotted mold, avoid inhaling.
Can mold on food make you sick?
Mold on food can be harmful in various ways. Some people are allergic to mold and could have a potentially serious reaction. However, even if you don’t have allergies, mold can cause irritation in the respiratory, gastro-intestinal or urinary tracts. And the mycotoxins created by some molds are poisonous carcinogens that can prove fatal.
What are health symptoms you can get by eating mold on food?
Allergic reactions to mold can include sneezing, runny or stuffy nose, coughing, postnasal drip, irritated eyes, nose and throat and dry, scaly skin. Those with asthma may experience coughing, wheezing, shortness of breath and tightness in the chest.
Those without allergies may still experience respiratory problems such as wheezing, sneezing, tightness in the chest and difficulty breathing. In more severe cases, this can lead to respiratory infection and even hypersensitivity pneumonitis.
A particular concern is ingesting mold that produces mycotoxins. Signs of mycotoxin poisoning include reduced appetite, a general feeling of malaise, acute illness or death in rare cases.
Interesting 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—underneath the visible mold, it may have penetrated the peel to the flesh of the fruit inside. In the case of an avocado, while the skin is quite tough mold can still get underneath and infect the fruit inside. Play it safe and discard it.
What temperature kills mold spores in food?
Most molds are killed off by temperatures of 60-70°C (140-160°F). Thus, boiling water is generally enough to kill off mold. Remember, though, that mold doesn’t just grow on the surface: heat will have to penetrate into whatever the mold is growing in to kill it. Also keep in mind that the mycotoxins produced by certain mold can survive intense heat: boiling may kill the mold but leave its poisons still intact.
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:
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 consume it within a just 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. Only take it out while you’re using it—under two hours. 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. Clean your refrigerator and other kitchen surfaces with a mixture of 5ml of baking powder to 1L 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.
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 concerns about mold allergies and mold toxicity that applies to food mold also applies to other mold in your house. Keep watch for mold in your kitchen and whole house, and if you detect signs of mold, get informed as to the steps needed to eradicate it safely.