Nick Goldschmidt has been lucky so far. A wildfire has burned more than 8,000 acres just north of his vineyards in Geyserville, California, but so far his vines are OK. So is his house in Healdsburg, roughly midway between Geyserville and a 36,000-acre fire that destroyed more than 2,800 homes in Santa Rosa.
But now, amid the charred, empty spaces that scar northern California’s winegrowing region, under skies yellowed by smoke, Goldschmidt has a race to win. Wildfires can ruin the flavor of wine grapes, a problem called smoke taint. “I’ve worked with smoke before,” Goldschmidt says. “It is not an easy thing to fix. But in my experience, it’s more about contact time. So the key thing is, if you have vineyards near the fire, you’ve got to get the grapes off.”
Depending on wind, smoke from the Atlas Fire could potentially reach Goldschmidt’s Napa vineyard, where about 15 percent of the fruit remains to be harvested. He now plans to harvest the rest by the weekend.
That’s typical of Napa, where 80 to 85 percent of the 2017 harvest is done. In nearby Sonoma, 90 percent of the grapes are in. But that still means that a few grapes could get exposed to smoke, and fire and heat could damage the vines. In a region key to California’s $34 billion wine industry—and that figure doesn’t even include the enormous tourist business—that’s a big deal. Fires have killed 31 people so far, destroyed thousands of homes, and consumed the efforts of more than 8,000 firefighters. And the winemakers of the area are trying to make sure the damage to their livelihoods doesn’t get worse.
Winemaking regions around the world, especially in Australia, have been dealing with the consequences of more active fire seasons near vineyards since at least the turn of the century—but the problems haven’t really hit California yet. The state’s frequent fires haven’t intersected with its vineyards. Until now.
Smoke is complicated stuff. Everyone in the Bay Area has gotten a taste in the past few days—that medicinal, ashy, burnt flavor comes from, among other ingredients, molecules called polycyclic aromatic hydrocarbons, nitrogen and sulfur oxides, other organic compounds, and even tiny particles carried aloft by heat and air currents. If you’ve ever sat near a campfire or cooked on a grill, you know it’s not necessarily an unpleasant aroma, as cognitively dissonant as that may feel when you realize it comes from blazes that have destroyed the lives of thousands.
But what’s delicious in bacon or lox generally isn’t—depending on how much you have—in wine. The actual flavor compounds are molecules called volatile phenols. “Volatile” means they evaporate, and in chemistry “phenols” are benzene rings (a hexagon of carbon atoms with hydrogen atoms sticking off like a snowflake) connected to a hydrogen-and-an-oxygen. You might know them better as the aroma of peat in some whiskies or of antiseptic or Band-Aids. Their volatility means that in your mouth, they turn into a vapor that gets sucked up retronasally, through the back of the throat to the sensitive layer of nerve endings behind your nose that translates chemicals into odors.
Smoke taint in grapes has two specific markers: guaiacol and 4-methylguaiacol. They taste like, well, smoke. Expose grapes on the vine to them, and the wine will taste smoky. Obvious, right? Except no. “The mechanism is a little bit unclear,” says Kerry Wilkinson, an oenologist who studies smoke taint at the University of Adelaide. Leaves have pores called stomata involved in respiration, “but when grapevines are exposed to smoke, the stomata close almost immediately and photosynthesis stops,” she says. “The guaiacol conjugates are getting to not only the skins but the pulp of the fruit. I think it’s just permeation, but I don’t think anyone’s done the research.”
Making things even more complicated, grapevines have their own way of dealing with a barbecue. “Those compounds, once they’re taken up, the grapevine will stick one or more sugar molecules on them,” Wilkinson says. “We think that’s to make them less toxic to the plant.” This process—it’s called glycosylation, and the sugars are called glycosides—turns the volatile phenols non-volatile. Which means you can’t taste them in the grape juice.
But ferment that juice into wine, and acids in it will break those sugars off. Poof: Smoke gets in your wines.
I don’t mean to be flip here; smoke taint from the Canberra bushfires of 2003 cost Australian vineyards more than $4 million; fires in 2004 cost another $7 million. Once grapes are tainted, the wine isn’t easy to fix. Those ashy flavors are too strong; you can’t just try to blend in other, untainted wine to cover it up. Efforts to filter it with activated charcoal and reverse osmosis can filter out flavors you might want in the wine, too. Heck, guaiacol and 4-methylguaiacol are markers for oak-barrel aging, too. Nobody ever describes…