It’s a conundrum we’ve all faced.
Opening up the cupboard or fridge to grab something to eat, only to find that item is dotted with white, blue or grey mould.
Can you eat around it? Or does it need to be chucked out straight away?
There are no official guidelines when it comes to what is or isn’t safe to eat—and everyone has different red lines.
But eating mouldy food can come with serious health consequences past just an upset stomach, say experts.
Consuming spoiled food exposes the body to range of microbial toxins and biochemical by-products that can cause anything from mild food poisoning to liver cancer.
And, says toxicology professor Dr Brad Reisfeld, cutting around it won’t protect you.
While certain foods may give you a better chance of being able to consume a non-mouldy part unscathed, others are almost certainly ridden with toxic—and invisible— spores.
Because bread is porous, mould structures are able to grow throughout it and not just on the surface
So, from apples to bread to soft cheese and yoghurt, here’s which foods you can just cut the mould off—and which needs to be binned immediately.
Meat
It’s perhaps the most obvious one to avoid.
But meat of any form should not be eaten past its sell-by date, says Professor Reisfeld.
While mould tends to be the primary concern for fruits, vegetables and dairy, bacteria is responsible for decomposing meat.
Spoiled meat may develop a slimy texture, and greenish or brownish discolouration as it begins to rot.
But the harmful bacteria that most commonly grow on meat don’t always produce a noticeable change in smell – making it hard to assess whether it’s gone off or not by sensory cues alone.
The smell of rotting meat is instead caused by chemicals released later in the decomposition process – which themselves can cause nausea, vomiting and abdominal cramps, as well as headaches, flushing and a sudden drop in blood pressure.
The most famous meat contaminant is Escherichia coli – or E coli (pictured) – a common beef contaminant that produces a toxin which can cause severe gastrointestinal illness
Spoiled meat can contain a number of harmful – and potentially deadly – strains of bacteria, says Prof Reisfeld.
The most famous of these is Escherichia coli – or E coli – a common beef contaminant that produces a toxin which can cause severe gastrointestinal illness and, in some cases, a dangerous kidney disease called haemolytic uremic syndrome.
Poultry, meanwhile, tends to carry a bacteria called Campylobacter jejuni, which produces a toxin that invades gastrointestinal cells, causing diarrhoea, abdominal cramps and fever.
In rare cases, it can even cause the body’s immune system to attack its own nerves, leading to temporary paralysis.
Salmonella is another fear when it comes to gone-off meat – as well as raw eggs and undercooked chicken.
The bacteria works by releasing toxins into the lining of the intestine that drive painful inflammation.
And Clostridium botulinum produces the botulinum toxin – deadly even in tiny amounts – and can lurk in improperly stored or tinned meats.
If a piece of meat – cooked or raw – shows any signs of spoilage, or simply has been sitting in the fridge for too long, don’t risk it.
When fruit becomes overripe, and eventually rots, it produces fungi – the fuzzy patches of green, yellow, black or white mould
Fruits
Fruits are not immune from toxins, says Professor Reisfeld.
‘When they become bruised or overripe, or are stored in damp conditions, mould can easily take hold and begin producing these harmful substances,’ he wrote in a piece for the Conversation.
When fruit becomes overripe, and eventually rots, it produces fungi – the fuzzy patches of green, yellow, black or white mould that are so horrifying to find on the underside of your apple.
This fungi can give off a musty smell and produce toxic chemicals called mycotoxins.
Exposure to mycotoxins, through eating, drinking, inhaling, or skin contact, can cause poisoning – called mycotoxicosis – with effects ranging from mild symptoms like flu-like illness to serious complications like organ damage and cancer.
A major type of fungi – known for infecting apples, as well as pears, cherries and peaches – is a blue mould called Penicillium expansum.
This fungus produces a toxin called patulin, which works by infecting key enzymes in cells that impair normal cell functions and harm DNA, proteins and fats in the body.
In large amounts, patulin can even cause damage to major organs like the kidneys, liver, digestive tract and immune system.
‘It is tempting to just cut off the mouldy parts of a fruit and eat the rest,’ said Prof Reisfeld.
‘However, moulds can send out microscopic rootlike structures called hyphae that penetrate deeply into food, even in seemingly unaffected bits.
‘Especially for soft fruits, where hyphae can grow more easily, it’s safest to toss mouldy specimens. Do it at your own risk, but for hard fruits, I do sometimes just cut off the mouldy bits.’
Bread is one of the most tempting foods to cut a little patch of mould off and eat
Grains
Bread is one of the most tempting foods to cut a little patch of mould off and eat.
But doing so risks liver damage and even cancer, says Professor Reinsfeld.
Two of the most common fungi found on grains and nuts are Aspergillus flavus and A. parasiticus.
These can release mycotoxins called aflatoxins, which can trigger mutations when the molecules they produce bind to DNA.
Repeated exposure to aflatoxins can damage the liver and as even been linked to liver cancer – especially for those with existing risk factors like hepatitis B infection.
Another group of fungal pathogens that grow as mould on grains like wheat, barley and corn are called fusarium.
These tend to grow in humid environments and can make grains appear discoloured, or have a pinkish hue.
Fusarium can produce toxins that also damage cells and irritate the digestive tract, as well as disrupting how cells in the body build and maintain their outer membranes.
And bread is particularly risky.
As it’s porous, or has a lot of gaps, mould could easily have spread to other areas beyond the visible patch.
These growths may not be as visible to the naked eye — but are still present.
Says Prof Reisfeld: ‘If grains or nuts look mouldy, discolored or shriveled, or if they have an unusual smell, it’s best to err on the side of caution and throw them out.
‘Aflatoxins especially are known to be potent cancer-causing, so they have no safe level of exposure.’
Some cheeses are prized for their tangy flavour caused by chemicals produced by certain fungi – Roquefort and Stilton among them
Cheese
Mould on cheese is by no means always bad.
In fact, some cheeses are prized for their tangy flavour caused by chemicals produced by certain fungi – Roquefort and Stilton among them.
Others, like brie and Camembert, are coated in a soft, white rind—made of fungi— that contributes to their flavour and texture.
But that doesn’t mean that a bit of fuzzy mould on your block of cheese is safe to eat, says Professor Reisfeld.
Unwanted forms of mould tend to look fuzzy or powdery and can come in unusual colours, like greenish black or red.
These can be caused by the Aspergillis species, and should be immediately discarded.
Another species common in cheese, called Penicillium commune, is known for producing cyclopiazonic acid – a toxin that can impair nerve and muscle function.
At a high-enough level, the toxin can even cause tremors and nervous system symptoms.
Though rare, the fungus will usually produce a sharp, sour rank odour.
‘As a general rule, discard soft cheeses such as ricotta, cream cheese and cottage cheese at the first sign of mold,’ says Prof Reisfeld.
‘Because these cheeses contain more moisture, the mould’s filaments can spread easily.
‘Hard cheeses, including cheddar, parmesan and Swiss, are less porous.
‘So cutting away at least one inch around the moldy spot is more of a safe bet — just take care not to touch the mold with your knife.’