A French blackmailer attempted to extort one million euros from the estate of Romanée-Conti, the world's most expensive wine, by threatening to poison the vines, it has emerged.Producers of the Burgundy wine, which can fetch more than £15,000 a bottle, received a letter from the man earlier this year in which he promised to spread poison on the vines unless he received the pay-off, which amounts to almost £850,000. "I didn't really know what to make of the first letter," said Aubert de Villaine, co-manager of the estate. "But when a second arrived shortly afterwards, I took the affair very seriously," he said.