Blueberry

Sit with a bowl of blueberries and look closely. Good ones have a soft grey-blue bloom on the skin, that powdery haze you can wipe off with a thumb. Rub it away and the colour underneath is deep, almost black-blue. That is the berry you want: plump, firm, dry to the touch, with no give when you press it gently between your fingers.

Taste before you buy if you can. A good blueberry is sweet with a sharp little bite right after, and the skin should pop cleanly between your teeth. Blueberries don't get sweeter after picking, so what you taste in the shop is what you'll get at home. Choose by feel over smell — a faint scent is normal and tells you little either way.

Some people say a heavy bloom means the berries are fully ripe. No! Go by colour and feel, not by the bloom alone. A berry can wear a thick haze and still taste thin and sour underneath. Squeeze gently, taste one, and trust your fingers and tongue over the look of the skin, or you'll end up with a bowl of pale, sharp fruit.

Wash blueberries only just before you eat them. Wet berries turn soft and mouldy far sooner than dry ones, so never wash the whole batch for storage.

A hundred grams gives you about 64 kilocalories, with 14.57 grams of carbs, 0.7 grams of protein and 0.31 grams of fat.