The elusive white truffle cannot be farmed and grows spontaneously in the roots of poplars, oaks, willows and linden in northern Italy, only between October and December. It is impossible to preserve, except in paste form (most truffle oils are synthetic), and the real thing expires after about a week, or three at best if kept under light soil in a jar. The large white truffle that a consortium, including Gwyneth Paltrow, Mick Jagger and Roman Abramovich, bought for £28,000 legendarily shrivelled in a locked fridge before its owners managed to eat it. White truffles are, in short, a goldmine under the oak trees of Piedmont, either FedExed to restaurants around the world in polystyrene boxes, or held in situ for international gourmands taking truffling holidays near Alba.