Can Winemakers Take the Heat?

It's harvest time in California's Napa Valley, and the rows of vines that line the meandering Silverado Trail are laden with fat, lush clusters of grapes. Dozens of pickers, their wide-brimmed hats shielding their faces from the late-afternoon sun, fill their sacks as quickly as they can. I've always associated Napa with leisurely afternoons lingering over a glass of Cabernet, but it is these few, frenzied weeks of early fall that forge the valley's reputation as one of the world's premier wine-producing regions. This year's grapes, harvested at the peak of their flavor, will become the sought-after vintages of the future through an alchemy that fuels the area's $11 billion wine industry.

Napa owes its success to a rare climatic confluence: cool air wafts in from the Pacific Ocean and mingles with warm currents moving up from the hot and arid Central Valley, creating unique microclimates in each valley and on each hillside. Over the next century, the average temperature here could rise by as many as seven degrees Fahrenheit, making Napa as hot as present-day Fresno, 200 miles to the southeast. If that happens, some vintners may reach a point of diminishing returns, producing wines that do not stack up to today's vintages. In 2006, cabernet sauvignon grapes grown in Napa sold for more than $4,100 a ton; the same variety grown near Fresno fetched just $260 a ton -- less than a tenth of the price. As climate change threatens Napa's wine-making primacy, vintners are looking for ways to adapt. The question is how, and the answers vary.

My first stop is Opus One Winery in Oakville, where I meet with the company's CEO, David Pearson. He was one of the first members of the Napa Valley Vintners' Climate Study Task Force, formed in 2006 to help winemakers plan for the challenge of higher temperatures. Opus One's immaculate headquarters is an architectural mélange that strikes me as a cross between a Tuscan palace and the Millennium Falcon from Star Wars. Pearson and I sit down in his airy, light-filled office overlooking Opus One's sprawling estate, where 169 acres of premium grapes routinely yield vintages that sell for more than $100 a bottle. But even small fluctuations in climate can contribute to the difference between a $100 bottle and a $10 one.

Pearson tells me that his growing and processing strategies will adapt to suit the climate. "It's too early to be immediately worried," he says. "In warm years, people can grow their grapes differently."

As grapes ripen, they accumulate sugar and lose acid in roughly equal measure. Warm days and cool nights maintain this balance, but when the temperature soars, sugars dominate. The yeast that drives the fermentation process feeds on sugar, which means that ultrasweet grapes produce wines that are too high in alcohol to meet today's standards, which dictate that quality wine should contain only 12 percent to 15 percent alcohol by volume.

There are plenty of tricks for balancing finished wines, Pearson says. Alcohol can be extracted through various filtration methods. Or, he adds, "let's say you've got rugged flavor compounds in your wine because of the heat -- rugged tannins, like sandpaper. When you put egg whites in the barrel, the albumin binds to certain sediments." The excess sediments then "fall out" of the wine, resulting in a finished product with a smoother, subtler flavor. Pearson assures me that this process, called fining, is part of the wine-making canon, something that has been done by even the best European producers for hundreds of years.

Of course, it's better to have your grapes grow just right than tinker with the finished product, so Pearson has installed special nozzles on his irrigation system that mist and cool the vines when they approach critical temperatures, typically in the mid-90s. In trials conducted by one vineyard management company, the strategy reduced the temperature beneath the vine canopy by a full seven degrees.

These misters might come in handy up the road at Larkmead Vineyards, nestled in the northern end of the valley. The next morning I head over there to meet with Dan Petroski, a lanky, affable grower with a chemist's exacting knowledge of wine. When I arrive, an intern is performing test-tube assays of wine samples. Like Pearson, Petroski is a member of the climate task force, but he seems much more worried than Pearson about the fate of his prized grapes. He leads me out into Larkmead's fields to show me why.

Continued...