How to store half a lemon – and 17 other ways to keep leftover food fresh

Using lemon or lime juice on the cut side, or wrapping the whole thing in clingfilm, can also help to minimise oxidation, which is what causes avocado flesh to turn grey and mushy.

James Cooper, the deputy director of food policy at the FSA, advises emptying leftover contents into a bowl or airtight container before storing it in the fridge.

“Once cut, I keep cucumber in an airtight container, lined with a little kitchen paper or a clean tea towel [in the fridge],” says Melissa Hemsley, the author of cookbooks including Feel Good and the forthcoming Real Healthy.

Photograph: Yulia Naumenko/Getty Images From roquefort to red leicester, Hemsley has useful advice about open packets of cheese: “Beeswax wraps or silicone reusable bags are really handy, or seal the packaging with elastic bands,” she suggests.

Photograph: Anna Pustynnikova/Getty Images For me, this comprises almost an entire fridge shelf: harissa, tomato puree, pesto, gochujang and curry pastes can all sit for weeks – perhaps longer – used once, then abandoned.

I refuse to let them go to waste and yet, according to Leonard Tanyag, the executive chef at Los Mochis London City, I am doing it all wrong if I want them to remain fit for consumption: really, they shouldn’t be left in their jars at all.“Once opened, transfer to an airtight container to maintain their freshness and add some oil on top to prevent air exposure, which makes it last for weeks,” he says.