Considerable areas of our memory are taken up with food: it might be the taste of Mother’s sponge, the melting texture of an aunt’s buttery pastry or something recent, like the flavour of the first spoonful of a sour and nutty south-east Asian dish. Especially good meals are recalled with the same clarity as revolting school dinners and the stench of stale fish — we can conjure aromatic memories with ease thanks to the olfactory nerve, the brain’s cache of stored eating experience that helps us to tell good from bad when choosing what to eat.