What Happens When Things Go Mouldy?
The moulds we find on bread, cheese and other foods are fungi, like the mushroomy substances that grow on the ground and on trees. They appear when certain little organisms in the air find the moist conditions they need in substances such as bread. The microscopic fungi that we call mould can survive cold, dry or acidic conditions that make bacteria curl up their toes and die.
They spread their threads through everything from meat and fruit to bread, vegetables, cheese and jam. They’re the culinary equivalent of dry rot. Moulds have many other uses. Some fungi produce the fermentation needed to brew beer or turn grape juice into wine. Others are used in making bread or delicious cheeses. Fungi also perform the important action of turning dead leaves and animal bodies into useful components of the soil.
Fungi are very important on account of the great good or harm the different kinds can do. One particular green mould has proved of tremendous benefit in medical treatment because Sir Alexandar Fleming discovered in 1928 that it stops the growth of certain bacteria.
Doctors have used this mould Penicillium, of course, Penicillium notatum, which is called penicillin and others like it as “antibiotics” to destroy more serious bacteria which cause disease. Such moulds have been cultivated on a gigantic scale to produce substances of unequalled curative power.
But its less glamorous siblings are good friends to the food industry. Penicillium camemberti (again) is sprayed on to camembert and brie to age them and create their white rinds, while Penicillium roqueforti gives blue cheeses such as stilton and roquefort their veins.
Another mould, Botrytis cinerea, is essential to dessert wines such as Sauternes and Trockenbeerenauslese. Grapes attacked by the “noble rot” become partially raisinised, reducing their water content and increasing their sweetness. Many wine-makers will deliberately spray Botrytis spores over their vineyards.
Does this mean we should be more relaxed about mould? Yes and no. Impressively thorough advice from the US Department of Agriculture says you can rescue hard cheese and firm fruit and vegetables by cutting out at least an inch around and below the mould spot, but advises you to chuck out whiskery hot dogs, cooked meat, casseroles, grain and pasta, soft cheeses, yoghurt, sour cream, jellies, soft fruit and vegetables, bread, baked goods, peanut butter, legumes, nuts and many more.
Philippa Hudson, senior lecturer in food safety at Bournemouth University, backs up that advice about cheese – though she’d only remove a centimetre or so beyond the surface mould. This will usually be our old friend Penicillium. “But it’s important to say that not all of the Penicillium moulds are safe,” she adds.
“Some of them do produce toxins and you can’t necessarily tell which the bad ones by looking at them are. It’s not as if all green moulds are good, all white moulds are good and all brown ones are to be avoided.” Mind you, she admits, that’s not totally useless as a rule of thumb: “You’re moving along the right tracks.”
How dangerous can moulds be? “Seriously dangerous,” she says. “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.”
That’s a message that Peter Wareing endorses. He’s the editor of the handbook Common Yeasts and Moulds in Foods, and a food safety expert at Leatherhead Food Research, which carries out independent scientific studies. As well as peanuts, brazil nuts and almonds, all of which can harbour aflatoxins, he warns about apples, where moulds can produce a toxin called patulin.
But there’s some good news. According to Wareing, most jam mould can safely be spooned away with no further threat to life and limb, while patulin is destroyed by fermentation. All of which means that so long as you stick to a diet of cider and marmalade, you should be entirely safe.