Is it ever safe to scrape the mould off your food?

You’re doing food storage wrong and we want to help

Image: Steven Depolo

Do your nectarines always go squishy before you can eat them? Try keeping them away from bananas. Image: Steven Depolo

Alas, not all microbes are confined to Petri dishes. We’ve all experienced the horror of discovering a long forgotten morsel lurking deep within the recesses of our fridge. What are the secrets to avoiding these delightful surprises and when is it safe to risk it? Are there any foods that will never let you down?

For general storage, a sealed Tupperware box will stop any new bacteria getting and a cold fridge will slow the growth of what’s there. This method will keep pretty much anything safe to eat for about 3 extra days.

Fresh berries make a nutritious addition to breakfast but it’s easy to be put off by their pathetic shelf-life of 2-3 days. Cyclospora bacteria builds up on the surface and the recognisable furry Botrytis mould quickly breaks berries down into surgery goo. However, all is not lost – rinsing in weak vinegar solution (1:10 vinegar and water) will decontaminate berries without leaving a taste and extend the shelf life to 2-3 weeks.

Baked spuds are a student staple but all too often they develop into terrifying accidental bonsai trees. The sprouts are toxic; they contain high concentrations of glycoalkaloids, a natural fungicide with effects ranging from stomach upsets neurological damage. While it is safe to excavate the growths salvaging the rest of your spud, it’s best to avoid them. Ethylene released from apples and bananas inhibits the growth of sprouts and keeps potatoes healthy for up to 5 weeks. The same ethylene causes fruit to over ripen so storing apples and bananas with the spuds, away from the rest of your fruit, is a win-win.

Hard cheeses like cheddar are rare in that it’s safe to just cut mould off. The density and lack of moisture inside the cheese prevents the filaments from penetrating. As long as you cut an inch around and below the mould, you’re good to go. In porous moist foods, however, the structure of the mould extends far beyond what you can see. Bread, yoghurt, cream cheese – once you can see the mould, ditch the lot.

Sealed honey will last forever – jars found in Egyptian tombs are still edible. Honey’s natural state is very low in moisture due to the high sugar content so very few bacteria can survive. Other sugary foods like molasses do this too. Honey has the added bonus of a small amount of hydrogen peroxide generated in the bee’s stomach. Combine that with its natural acidity and nothing can survive.

Finally, the alcohol content of hard liquors keeps them safe from any life forms. These wondrous liquids have long been used to preserve fruit cakes though ‘feeding’ them a spoonful of brandy every week and storing in an airtight container. This trick keeps cakes moist and delicious for years.

So if all else fails, you should be able to eke out a living on nubs of hard cheese, ancient honey and some very tipsy cake. At least until the shops open and you can pick up a sandwich.

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