The co-founder of one of the nation's fastest-growing wine companies, 585 Wine Partners, is stepping down from the Sonoma-based firm.

Industry veteran Dan Leese declined to say why he is leaving the company he co-founded in 2005 and grew into one of the 30 largest wine groups in the United States.

It is not a health-related issue, but a business decision, he said.

"Everyone's health is good. I've just got to work out a couple of things," Leese said.

585 Wine Partners purchased a controlling interest in popular Red Truck Wines from Sonoma's Cline Cellars in 2005. The launch of additional brands — including Picket Fence, Bivio Italia and Steelhead Wines — have helped push the winery's sales over 500,000 cases.

A former executive at Foster's Wine Estates Americas, Leese and his wife Kathy, who is also leaving the company, founded 585 Wine Partners with Doug and Becky Walker and a small group of investors.

Doug Walker, the company's chief operating officer and also a former Foster's executive, remains with the company. Leese said he plans to remain involved in the development of the brands as an owner.