(Bloomberg) -- As my boots crunch through snow, Pierre-Marie Luneau hands me a chunk of serpentinite rock in his vineyard on La Butte de la Roche. Like all the best Muscadet producers, Luneau is obsessed with how soil affects a wine’s quality. Muscadet is typecast as a gulpable, fresh, crisp white wine ideally paired with oysters. And in this huge region in the west of France’s Loire Valley there’s always been plenty of plonk