France, Aug. 20 -- "It's very intense," says Francois, who is picking Muscadet grapes at the Huchet wine estate in the Loire-Atlantique department. The work is a race against the heat.

"You have to work well under pressure. You have to be responsive, you have to be present."

Less than 10 years ago, grapes at this estate were picked in September. Now the harvest takes place in August.

"This is unprecedented, and it's likely to happen again," says owner Jeremie Huchet.

"Winegrowers who used go on holiday at the end of August will have to change their habits," he says - one of the many ways soaring temperatures are changing the wine industry.

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The F...