Daniel Roberts, a soil scientist, reworks old vineyards using modern techniques to make them more productive and improve wine quality. (Dave McIntyre)

The first of two columns on viticulture in Sonoma County, Calif.

The Platt Vineyard rises steeply — so steeply that its one-lane road has a small stoplight to warn ascending arrivals about vehicles careering down the hillside. Once we got to the top, about 800 feet above sea level, Daniel Roberts showed me the vista.

We were facing south. To the west, we could glimpse the Pacific Ocean, just seven miles away. From there and across to our left, we could see the Petaluma Gap, a channel that draws ocean wind inland to bounce off Sonoma Mountain and then down to San Pablo Bay. The gap’s wind is a major factor in grape growing around here; the federal government is considering a petition to designate the Petaluma Gap as an American Viticultural Area. For now, it is part of the Sonoma Coast AVA, a large and disparate portion of Sonoma County that lacks consistency in soil, climate or even coast — characteristics that elsewhere would define a wine-growing region.

Roberts, 68, holds a doctorate in soil science and is one of California’s leading vineyard consultants. He helped Kendall-Jackson Wine Estates develop its extensive vineyards throughout California during the boom of the 1980s and 1990s before he went independent. Today, he works for exclusive vineyard owners willing to spare no cost to make the highest-quality — and high-priced — wine. His clients include Virginia’s RdV Vineyards.

When I contacted Roberts and asked him to show me how he’s helping shape Sonoma County’s modern viticulture, I quoted an old wine industry joke. “Let’s pretend I have a large fortune I want to make into a small one by owning a vineyard,” I said. He chuckled and replied, “You’d need an extremely large fortune to afford one of my vineyards.”

After I met him and toured several vineyards, I realized that wasn’t a boast but a reflection of how intensive modern viticulture can be.

So when I met Roberts at his modest ranch-style home in Sebastopol, he took me first to Platt. For wine lovers in Sonoma, the drive west toward the coast is thirst-inducing. The “west Sonoma Coast” produces some of this country’s most exhilarating pinot noirs and chardonnays. Along the way, he pointed out important landmarks, such as the Wild Flour bread bakery in Freestone, a don’t-blink-or-you’ll-miss it crossroads amid the coastal fogbanks.

Platt Vineyard grows pinot noir, chardonnay, Riesling and syrah for highly sought-after producers such as Littorai, David Ramey, Radio-Coteau and Red Car. The vineyard rises from 400 to 800 feet above sea level on Goldridge soils, a mix of sandy loam and sandstone from an ancient seabed that helps control vine vigor. Vines are planted densely, at 1,815 per acre, covering 32 acres of a 502-acre estate owned by Joan Platt, widow of Lewis Platt, former chief executive of Hewlett-Packard and later Kendall-Jackson. The entire estate, including an 8,000-square-foot mansion, is on the market for $19.5 million, according to an online listing.

When I visited in mid-February, a few buds of chardonnays on Ramey’s plots were unfurling small yellow-green leaves, an extremely early bud break for Northern California. Early bud break typically signals greater frost danger in spring, but Roberts wasn’t worried. “This vineyard never frosts,” he said.

“If you were planting this vineyard now, we would do soil work in ’15, plant vines in ’17, and you’d get your first crop in ’19 with a full crop in ’21,” he explained.

That’s a lot of labor-intensive and technology-intensive work. At Iron Horse Vineyards, in Sonoma County’s Green Valley, winery partner and chief executive Joy Sterling calls Roberts “my hero” for his work a decade ago in reworking 110 acres of vineyards originally planted in the early 1970s.

“We dug 160 soil pits and had 12 PhDs analyzing the soil,” Sterling recalled. “We even had someone chasing the fog to map where it settled in the vineyards.” They mapped the vineyard by GPS and other techniques according to soil type, moisture retention and mineral makeup. The new vineyards were planted with various chardonnay and pinot noir clones, on different rootstock, more densely and with a different trellising system.

Roberts calls his company Integrated Winegrowing. Iron Horse calls his practice precision viticulture, based on lessons learned and technology developed over the decades. “Where we had one block, we now have five,” Sterling said. “We pick different vine rows at different times, and ferment the juice separately until we make the final blend.”

The expense is worth it in an industry that does not easily forgive mistakes, said Rutger de Vink, who hired Roberts to create a world-class vineyard at RdV Vineyards in Delaplane, Va. “There’s a huge cost to do all this stuff,” de Vink said. “But you only get one chance to plant a vineyard.”

Next week: Efforts in Sonoma County to preserve historic vineyards and grape varieties.

McIntyre blogs at dmwineline.com. On Twitter: @dmwine.

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