Can you cut mould off food and still eat it?

Monday, June 5, 2006
It's a pretty common occurrence for people to find a corner of mould growing on their block of cheese, or slice of bread at home, to cut off that affected spot, and continue consuming the remainder, believing that they've gotten rid of the contamination.

But is it safe to do so? Let's find some answers.

Before the test, Leila takes her mouldy-looking cheese sandwich to Dr Ailsa Hocking, one of Australia's leading experts in the field of mould.

Dr Hocking is a little worried, and there's a reason for that. Mould is a growth of minute fungi which typically forms on food which has been left alone for too long.

But what if Leila were to just cut off the mouldy bits she can see? There is still risk: as the cheese has a lot of mould and varying sorts of mould, the mould can make toxics that diffuse into the cheese. So while it might look safe and not mouldy there might still be toxins in the food.

So after allowing a loaf of bread, a jar of jam, and block of hard cheese to go partly mouldy, Leila removes the mouldy portion then it's off to the testing lab to find out what is lurking in Leila's food.

The food is tested for:

  • Yeast and mould count
  • Standard plate count (bacteria)
  • Water activity
  • PH

A sample of each food is tested fresh to be used as a comparison.

The aim of the test is to find out whether or not the remainder of the food contains mould/microorganism activity if the mouldy portion is removed.

So can we cut the mould off cheese and still eat it? And how much mould is actually in a sandwich once the mouldy portion has been removed?
The lab results (and mouldy sandwich) are taken back to Dr Hocking.

At Leila's first visit, after removing the mouldy parts from her cheese sandwich, mould spores were present in the rest of the sandwich, but they hadn't yet started to grow.

They sure have grown — at an alarming rate!
So how much mould is in it? The lab reports said there were about 300,000 moulds per gram. The normal amount for a cheese sandwich is less than 200 moulds per gram. The mould in the food left in the fridge for too long has multiplied more than a thousand times.

Therefore contaminating anything it is put near.

"In the past when I've chopped the mould off my bread and eaten the rest I've been eating these things ... I don't think I'm going to do that anymore," says Leila.

Cutting mould off food in the fridge is a really bad idea. Therefore if there's any mould anywhere on your food, the best place for it is in the bin.

It is possible to remove the mould from some foods and eat the remainder without harm, however, to do so does pose some risk in most cases and is therefore not advised.

Dr Hocking: "The problem with mould toxins is they don't make you sick straight away like bacterially toxins. Like food poisoning, they can be longer acting, they can be carcinogenic and so while it may be fine, it may not make you sick, it's probably not good to do this sort of thing on a frequent basis because every time you are exposed to a carcinogen you have a greater chance of eventually developing some sort of problem."

  • Did you know that jam will keep in your fridge for much longer than bread or cheese? It's because jam has a very high concentration of sugar, but a low water content. On the other hand, tomato paste will only keep a week or two as it's got a high water content — but freezing it will make it last longer.

  • What about all those soft cheese we eat which are already mouldy? This is a case of good mould versus bad mould. A very small amount of penicillin rochefort (yes, that's what we make antibiotics from) is mixed into a thousand litres of cheese. This will produce enough live spores in the milk so that when the blue cheese is punctured later in its life, all those spores will grow into the little veins that grow through the cheese.

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