Is it safe to cut mould off food? Experts answer

By Alisa Hocking, Tom Ross

What should you do when you find mould on food?
Photo / Thinkstock
What should you do when you find mould on food? Photo / Thinkstock

The short answer is that it's a lot safer than not cutting it off.

Some moulds make and release poisons, called mycotoxins, into the food that could, over time, make you very sick. Why they do it is not especially well understood but that doesn't make it any safer.

Some mouldy foods should simply be discarded (ideally, to compost). For others, though, you can salvage and use the unaffected parts without exposing yourself to a health risk. That's good if your mouldy food is an expensive, vintage cheddar cheese!

The life of moulds

Moulds are fungi. They're related to mushrooms, and the yeasts we use to make bread, or convert sugars to alcohol. They are heterotrophs, meaning they can't make their own food (unlike plants). Instead, they degrade complex organic molecules in their environment into smaller molecules they can absorb to meet their energy and nutrient needs.

In nature, mould's ability to break down detritus (waste) ensures that dead matter doesn't accumulate. It also enables the release of minerals that are chemically tied up in detritus to the plants that need them for their primary production.





What to do?

Many moulds can grow on, and spoil, our foods. Among those we are likely to encounter on foods in our homes are Penicillium ("cousins" of those used to make antibiotics, or to ripen some cheeses), Aspergillus, and on fruits, Botrytis.



A good rule of thumb to judge whether a mouldy food can be "saved" is its moisture content or firmness. Foods with a high moisture content such as cooked casseroles, soft fruit and vegetables, pastes/sauces and soft cheeses can have invisible hyphae growing below the surface and producing mycotoxins.



The United States' Department of Agriculture's website is a good source of advice for dealing with mould contamination on a wide variety of foods.

* Tom Ross is Associate Professor in Food Microbiology, Food Safety Centre, School of Agricultural Science at University of Tasmania. Alisa Hocking is an Honorary Associate, School of Biological Sciences, University of Sydney; Honorary Fellow, Division of Animal, Food and Health Sciences at CSIRO. The authors do not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article. They also have no relevant affiliations.

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