“This isn’t so much a harvest, as a hunt for grapes,” said French winemaker Jean-Jacques Robert, with a rueful laugh as he unloaded grapes still warm from his vineyards around Fuisse in Burgundy. “It’s a catastrophe, the worst harvest for 30 or 40 years,” said the normally cheery 64-year-old owner of Domaine Robert-Denogent. The organic winemaker lost between two-thirds and three-quarters of his harvest in one hailstorm in April. He is not alone. For thousands of French winemakers, 2016 will go down as an annus horribilis, with vines destroyed by frost, heavy rain, hailstones “as big as ping pong balls”,...