Is it safe to eat mouldy food?

When you spot a blue corner growing on a block of cheese, should you toss the entire thing? Or can you scrape off the offending bit of mould and keep using that cheddar?

According to experts on BBC’s Trust Me, I’m a Doctor, it’s actually pretty safe to cut off the mould and keep using some foods — but not all.

Here’s a rundown of what you can keep, and what you should toss.

Keep

Mouldy hard, dry cheese. Hard cheeses like cheddar and Parmesan are too dry to allow mould to thrive, so mould rarely spreads too deeply into the cheese. Cut off the mould — removing an extra centimetre or so below the visible mould — and you’re good to go. And make sure to rewrap the cheese in fresh packaging.

Mouldy blue cheese. Moulds that are part of the manufacturing process are fine. If surface mould starts growing on hard cheeses like Gorgonzola and Stilton, cut it off and the surrounding area before using.

Mouldy firm vegetables. If the vegetable is firm, like a carrot or pepper, cut off the mould and the surrounding area before using it. Keep your knife out of the mould to prevent cross-contamination.

Mouldy dry-cured meats. This mould is generally harmless. A thin white coating “gets the OK,” while anything else should be cut out.

"[In] some of the hard salamis, mould is actually added to produce a special flavour,” Michael P. Doyle, PhD, the director of the Center for Food Safety at the University of Georgia tells Health magazine. “In general those types of moulds are considered to be safe.”

Up for Debate

Mouldy bread. If you find small amounts of white and blue mould on your sandwich bread, you’re probably fine to just cut off those parts — as long as you toast what’s left, says mould expert Dr. Patrick Hickey.

Because mould can easily spread through the porous loaf, be sure to “cut off a good few centimetres beneath the mould before eating the rest.” If the mould is black or takes up a large surface area, then it’s garbage time.

The U.S. Food Safety and Inspection Service, however, advises people to throw out their mouldy bread and baked goods, as porous foods “can be contaminated below the surface.”

Mouldy jam. If you discover that a jar of jam is growing mould in the refrigerator, scoop out the mould and the surrounding area — you want to get rid of any nearby spores — and the jam should be safe to spread on that toast you just salvaged, Hickey suggests.

It should be noted that this is an “area of some debate.”

Doyle disagrees with Hickey, warning that mould spreads easily through soft, sugary foods like jam.

“Moulds tend to be more adaptable than bacteria in many cases, and can grow in these types of foods that might have ingredients that would be inhibitory to general bacteria growth,” Doyle tells Health magazine.

Mouldy fruit. If a piece of fruit is very mouldy, toss it. Otherwise, the acid in the fruit should prevent bacteria from growing once you’ve cut out the visible mould, Hickey says.

The U.S. Food Safety and Inspection Service actually recommends tossing out mouldy soft fruits, but concedes that “small mould spots can be cut off FIRM fruits and vegetables with low moisture content. It’s difficult for mould to penetrate dense foods.”

Toss

Mouldy apples. While some fruit with tiny amounts of mould is still edible, the BBC One show warns against apples, as they can produce a toxin when mouldy.

"Apples will keep for ages," says Hickey, “but if there’s a puncture in the skin, fungi can get in. There have been serious outbreaks in the past, incidents of people being poisoned by drinking bad apple juice, which contains a toxin called patulin.”

Mouldy soft cheese. Soft cheeses are more likely to house harmful bacteria like listeria or salmonella, so it’s best to toss them once they show signs of mould.

Mouldy nuts and seeds. Never eat mouldy nuts. If your nuts taste bitter or are soft or powdery, it’s time to ditch them. Mould on nuts can be “seriously dangerous,” as they harbour a fungus called Aspergillus flavus, which produces a toxin that can eventually build up in the liver and cause liver cancer. This also applies to mouldy peanut butter.

"The genus Aspergillus, which grows on peanuts and peanut products, produces a group of toxins called aflatoxins. They can cause liver cancer – and cooking won’t destroy them,” warns Philippa Hudson, senior lecturer in food safety at Bournemouth University.

Slimy vegetables. If your vegetables are covered in a slimy substance, it’s time to toss them — unless you really enjoy stomach cramps and diarrhea.

Mouldy meat. If you spot a mouldy hot dog, slice of lunch meat or package of bacon in the fridge, steer clear. Bacteria is likely growing alongside the mould.

"Mould grows more slowly than bacteria, so that’s why it may take several days or weeks for mould growth to develop," says Doyle.

Mouldy cooked leftover meat and poultry should also go straight into the compost bin.

Mouldy casseroles and pasta. These dishes have a high moisture content. Mould has likely contaminated more of the food than is visible so it’s best to toss the whole thing.

Mouldy sour cream or yogurt. These products make it too easy for mould to spread.

Mould in a “semi-moisture or liquid product could more easily diffuse [toxins] into the product,” says Doyle.

What mouldy foods do you salvage? Or do you toss it all?