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Smoke Taint: What We Know

By Karen MacNeil
October 27, 2017

By Karen MacNeil

October 24, 2017

N95 meant nothing to me three weeks ago. But then the menacing smoky wildfires ringing Napa and Sonoma began. By the third soupy gray day, I owned an N95 respirator mask. The local Home Depot had them floor stacked on pallets over an area bigger than my living room.

Vineyards with their green foliage and irrigation lines are natural firebreaks. So even though these fires were the worst in California’s history, the vast majority of vineyards did not burn. More worrisome was the smoke that engulfed Napa and Sonoma for days and could be smelled as far away as San Francisco. Like everyone else who lives here, I wondered what effect the smoke would have on vineyards and on the grapes that were still hanging when the fires swept in.

Luckily, there weren’t a lot of the latter—an estimated 90% of the grapes had already been picked. But what about the ones that hadn’t? And what about the tender new juice that was only starting to ferment? Usually at this time of year, the whole Napa Valley takes on the heady, intoxicating aroma of fresh grapes being transformed into grapey new wine. Now the valley smelled like scorched tar.

In doing research for this blog, I realized that smoke taint is complex and misconceptions abound. Here is what I have found out.

Scientific Research

Although smoke taint was barely in any winemaker’s general wine vocabulary 20 years ago, the phenomenon has been widely studied recently, and not just in California wine regions beset by prolonged drought. Some of the early research comes from Australia where a warming climate has led to smoke exposure from bushfires near vineyards.

What is Smoke Taint?

Mature grapes that have been exposed to considerable smoke can lead to wines with undesirable aromas and flavors—i.e. “taint.” The density of the smoke and the duration of it are key factors in determining the severity of the taint. A wine with smoke taint can have a smell and flavor reminiscent of a dirty ashtray, smoked meat, campfires, charcoal, disinfectant, burnt rubber, or burnt leather, among other characters. Complicating the situation,   the aromas and flavors of smoke taint may not show up in the wine initially, but only become apparent months or even years later.

How Does Smoke Get into the Grapes?

Smoke contains compounds called volatile phenols. Two of the most adverse of these are guaiacol (G) and 4-methylguaiacol (4MG). These compounds are absorbed through the waxy cuticle that covers the grapes and through active pores in the leaves and then transported into the fruit. The research I read suggested that these compounds chemically bind with grape sugars in ripe grapes, forming glycosides. As a result, wine made from smoke affected grapes may initially show no signs of taint. Years later, however, as the wine evolves molecularly and the glycosides break down, the taint can appear.

How Long Do Grapes Need to Be Exposed to Smoke to be Affected?

Research suggests that smoke taint can occur after just 30  minutes of heavy smoke exposure.

Is Smoke Taint Worse at Certain Times of a Grape’s Growth?

Australian research looked at vines from flowering through harvest. Results showed that the time with the highest potential uptake for smoke is from a week after veraison (when red grapes turn from green to red) to harvest.  Early in the growing season before grape berries start to develop, the potential for smoke taint is low.

How Do Winemakers Know if Their Grapes are Affected?

Again, research suggests that the compounds that cause smoke taint get into the skins of each berry. The first thing winemakers do is to chew the berry skins and evaluate the flavor.  Most winemakers then send grapes, juice and wine samples to a laboratory for testing.

Can Anything Be Done to Smoke-Affected Grapes to Remove the Taint?

Immediately at the onset of the California fires, winemakers were advised to pick the grapes as soon as safely possible, since the effects of smoke exposure are cumulative. (Washing the grapes does not help.). Since the volatile compounds that cause smoke taint lodge in the skins and from there move into the juice, winemakers were also advised to press grapes as little as possible (difficult with red wine that depends on the skins for color, aroma,  flavor, and structure).

Can Smoke in One Year Adversely Affect a Vineyard in Subsequent Years?

It appears that smoke-exposed grapes lead to smoke taint only in the wines made from those specific grapes. In future years, grapes from the same vines aren’t affected. However some research suggests that yields may be lower the following year.

Does Smoke Taint Affect Wine That Was Fermenting or Aging in Barrels?

Probably not. First, fermenting juice is covered by a layered of CO2 gas that naturally protects the wine. As for wine in barrels or tanks, most scientists believe that concentrations of smoke inside wineries was not enough to harm those wines. (Wineries reported keeping their doors closed).

Is it Unhealthy to Drink a Wine with Smoke Taint?

I can find no evidence that wine with smoke taint is bad for you. It just tastes like hell.

What Now?

Even before the fires were fully out, scientists from all over California immediately began holding meetings and workshops to advise wineries on smoke taint and its detection. The wineries I’ve talked to are keeping grapes that may have been affected separate from wine that was already made and inside the winery. I’ve no doubt that most of the wine made from smoke affected grapes will end up down the drain or sold off at a loss as cheap  bulk wine. That bulk wine might then be put through a severe filtration regimen that strips the wine down in hopes of removing some of the smoke taint flavors, then given extra oak treatment to try to mask the smoky characteristics.

It will be interesting to taste the cheapest reds a couple of years from now.