Different types of moulds grow on food, from Penicillium in blue cheese to Botrytis on strawberries. Moulds are fungi, some of which produce poisonous substances called mycotoxins. Several hundred mycotoxins have been identified, but about a dozen have a reputation for causing serious health effects, including tremors, muscle weakness, fever and vomiting.
Aflatoxins, produced by Aspergillus moulds in cereals, spices and tree nuts, are among the most poisonous. They can damage DNA to cause cancer, while large doses can kill by damaging the liver. Thankfully, most mycotoxins are only a health risk if we eat them over long periods.
If the conditions are right for moulds to grow, harmful bacteria may also multiply. Moulds thrive in moist, soft foods, such as peaches. They also spread quickly through porous items like bread, creating a network of roots invisible to the human eye, making it best to throw these mouldy foods away.
It is generally advisable only to eat mouldy foods that are designed to be that way, such as blue cheeses. However, there are some exceptions when you can safely slice away mould, including hard cheese, hard salami, and firm fruit and vegetables like carrots and pumpkin.
Hard cheese has a low moisture content and a dense structure, meaning that mould is less likely to spread far below the surface. If you are brave enough to remove mould from cheese, slice away a good margin. If a soft blue cheese begins to grow different types of mould, throw it away.
Read more:
- What is slime mould (Physarum polycephalum)?
- I’m in my 30s and I never follow the nutrition labels on food. Am I about to die?
- Does eating blue cheese contribute to antibiotic resistance?
- Why is rice such a food-poisoning culprit?
Asked by: Jenny Walker, Sheffield
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- This article first appeared in issue 374 of BBC Science Focus Magazine – find out how to subscribe here