Workmen swarmed the grounds of Buena Vista Winery one recent morning, taking advantage of a break between storms to resume this Sonoma, Calif., property’s massive makeover.

A crew labored on the asphalt road leading up to the estate while stonemasons laid cobblestone and landscapers trimmed a boxwood maze. At the far end of a newly cobbled courtyard, a large fountain sprayed fine arcs of water, the droplets glinting like glass beads in the sun.

Thanks to a deep-pocketed Frenchman, California’s oldest winery is undergoing some much-needed surgery.

In the three years since Jean-Charles Boisset, son of a prominent Burgundian wine negociant, bought the troubled winery, Buena Vista has been buffed, earthquake-retrofitted and repositioned for the future.

“It’s an absolute emotional pursuit,” says the ebullient 44-year-old, who heads Boisset Family Estates, the U.S. arm of his family’s holdings. Despite his background in finance – he has an MBA from the University of San Francisco – Boisset insists that this investment is an affair of the heart, an obsession he has nurtured for more than three decades.

On his first trip to California, as an 11-year-old, Boisset visited Buena Vista with his French grandparents, both schoolteachers. He soaked up the story of the swashbuckling Hungarian Count Agoston Haraszthy, who had built a stone winery on the property in 1857. Later, his grandparents poured him a taste of Buena Vista chardonnay.

“I was totally enamored and wanted to stay here,” Boisset recalls. “I went home and told my parents, ‘This is where we need to spend time.’ ”