Can I cut the mould off food and eat the rest?

The visible mould is only the fruiting body. Underneath it, a network of threads runs through the food, and some moulds also produce toxins that spread further still and are not destroyed by cooking. How far all that travels depends almost entirely on how easily it can move — which is why hard cheese has an exception and a loaf of bread does not.

Safety

Step by step

1. Sort the food into hard or soft.Hard and dense means the threads cannot penetrate far — hard cheese, firm vegetables like carrots, cabbage and peppers, and firm dry salami with an intended surface mould. Everything else is soft, wet or porous, and that is the majority of a fridge.
2. For hard cheese, cut generously.At least 2.5cm around and below the spot, with a clean knife that does not touch the mould. Rewrap in fresh wrapping. This works for cheddar, parmesan, gruyère and similar. It does not work for anything soft or crumbly.
3. For firm vegetables, do the same.A mouldy patch on a carrot, a cabbage or a firm pepper can be cut well away and the rest used. Soft, watery vegetables such as cucumber, courgette, tomatoes and mushrooms cannot — bin those.
4. Throw away all soft and wet foods entirely.Bread and baked goods, soft cheese, cream cheese, cottage cheese, sliced or grated cheese, yoghurt, soured cream, jam, soft fruit, cooked food and leftovers, casseroles, nuts, and any opened cured meat that is not meant to have surface mould. The whole item, not the mouldy end.
5. Bin the whole loaf, not the mouldy slice.Bread is porous, so the threads run through the crumb well beyond the visible spot, and the slices in a bag share air. One mouldy slice means the loaf goes.
6. Do not sniff it to check.Bringing mouldy food to your nose releases and inhales spores. It is an irritant for anyone and a genuine problem for people with asthma, allergies or a compromised immune system. Bag it and put it out rather than examining it.
7. Know the deliberate exceptions.Blue cheese, brie, camembert and salami with a white bloom are meant to be mouldy, with specific cultivated moulds. That does not extend to a different, unexpected mould appearing on them — a fuzzy green patch on a brie is not part of the plan.
8. Wash the container properly and check the neighbours.Wash the container in hot soapy water and wipe the shelf, because spores spread. Look at whatever was next to it — mould in a fruit bowl or a bread bin usually has company.
9. Be stricter for anyone vulnerable.For pregnant women, young children, older people and anyone immunocompromised, do not apply the hard-cheese exception at all. Throw it away.

Tips

• Store bread in a bread bin rather than a warm sealed plastic bag, or freeze half the loaf on the day you buy it. Bread mould is nearly always a storage problem.
• Fruit moulds fast in a bowl because one soft berry infects the rest. Take out anything soft as soon as you see it and eat the rest quickly.
• Fridge shelves and the seal around the door are where mould spores persist. A wipe-down every few weeks makes a noticeable difference.
• Jam and preserves that grow mould should not be scraped — jam is soft and wet, and the old advice about scraping the top predates any understanding of mycotoxins.

Common mistakes

• Scraping mould off yoghurt or jam — Both are soft and wet, which is the ideal medium for threads and toxins to spread. What is visible is a small fraction of what is present. The pot goes in the bin.
• Cutting the mouldy corner off a block of soft cheese — The 2.5cm rule applies to hard cheese only. Soft, crumbly and sliced cheeses are penetrable, and shredded cheese has enormous surface area, so those go entirely.
• Assuming cooking it makes it safe — Heat kills the mould but does not destroy the mycotoxins some moulds produce. Baking, frying or boiling mouldy food does not make it safe to eat.

Questions people ask