Smoke Taint

By: Nan McCreary, Sr. Staff Writer

Wildfires have become an increasing problem in recent years, with many occurring in various wine-growing areas throughout the world. Aside from causing loss of life and extensive property damage, the wildfires pose a risk of smoke exposure to grapes in the vineyard, which can lead to off-flavors in the wine. This condition is known as smoke taint.

Smoke taint is created by volatile phenols in smoke that permeate the grape skin and bind with sugar in the grape to form organic compounds called glycosides. This process, known as glycosylation, makes the phenols non-volatile, meaning you cannot smell or taste the smokiness. However, during fermentation, the glycosides break apart and release the now-volatile phenols into the wine, making smoke-tainted flavors perceptible. This process can even happen as you sip: the enzymes in your mouth can break down any glycosides that remain, releasing unpalatable compounds into the wine. The flavors associated with smoke taint have been described as “burnt rubber,” “ashtray,” “campfire,” or “smoked meat.”

While Australia, long plagued by wildfires, has been researching smoke taint for many years, the U.S. recently felt the impact when the California wildfires of 2017 swept through the state. “This is all new to us, and it has transformed the wine industry in California,” Tom Eddy, owner of Tom Eddy Winery in Napa told The Grapevine Magazine. “In California, we really only had one wildfire event that caused problems, and that was in 2008. Then, we as winemakers were somewhat naïve — we thought, ‘Well, it’s just an act of God, and it happens,’ but we didn’t do much about it. We tried to remove it later when we discovered it. Some winemakers threw their wine away, some tried to blend it out, which they could do to some extent, and some just made it and bottled it and called it Barbecue Red.” Eddy, whose winery was at the epicenter of the Tubbs Fire, lost much of his 2017 wine, representing a $2.5 million loss.

According to Eddy, the California wildfires of 2017 were “a wake-up” call. “Now, everybody’s cognizant about smoke taint,” he said. “We’re investigating how smoke taint affects the juice and the wine, how to analyze smoke taint, and how to mitigate it.”

Researchers in the U.S., specifically at top enology programs at the University of California at Davis and Washington State University, are investigating ways to minimize the problem in the vineyard and the wine, but, as Eddy said, “We are still learning.”

While there are few definitive answers, experts have determined that the key factors influencing smoke taint are grape growth state, smoke composition, length of smoke exposure, and grape variety. Grapes are most vulnerable to smoke taint between veraison and harvest.

Once the grapes start ripening, the grape skins more quickly absorb smoke particles. As for smoke composition and duration, studies have shown that just 30 minutes of exposure to heavy smoke at a sensitive stage of vine development will cause smoke taint. Beyond that, little is known about how the specific source of the smoke affects the smoke taint composition in wine grapes.

Similarly, research is ongoing into the vulnerability of specific wine grapes to smoke taint. Some experts claim that varieties with thicker skins such as Cabernet Sauvignon are more resistant, while the thin-skinned Pinot Noir is very susceptible. In fact, there have been instances where density and duration of smoke were so intense that damage occurred irrespective of grape variety. There is a consensus on two factors related to smoke taint, however: smoke taint is not a health hazard, nor do tainted aromas pass from one harvest year to the next.

Testing and Mitigating

As concerns about the risks of smoke taint continue to grow, many research institutions and private firms are offering tests for smoke taint by measuring two of the main volatile phenols in smoke, guaiacol, and 4-methylguaiacol. Tests include pre-harvest berry testing, as well as sensory assessment of a small-scale ferment made from the same grapes. While these tests may be objective, they do not consider the arbitrary factor of whether the wine is significantly damaged. “It’s very subjective,” Eddy said. “Some can taste smoke taint right away; others can’t. Some can taste it in certain varieties, some in others. Everybody has different recognition for smoke, alcohol, sugar and other characteristics.”

Winemakers, too, are getting into the act and experimenting with winemaking practices that can mitigate smoke taint to some extent. One such method is “flash détente,” where volatile compounds are removed from the grapes by heating them to about 180° F and sending them into a vacuum chamber to be cooled. While this process may remove some volatile aromas, it is not 100% effective.

According to an American Wine Society blog, “it may remove the taint below the detection threshold of approximately five to six ppm if the level of smoke taint is slightly over that amount, but it is not going to take a 50-ppm smoke taint level and lower it to three.” Even then, adds the blog, “it is difficult to say what aromatic precursors in the wine may react with the smoke taint volatiles making the taint detectable at lower levels.” Other options for removal include using reverse osmosis, but this method is said only to be a temporary fix, and the smoke taint returns over time. Filtering and fining agents may also be effective, but the processes will remove many desirable attributes from the wine as well.

Insurance

To Eddy, one of the most significant challenges with smoke taint is how the problem is affecting the insurance industry. “Smoke taint is a problem that is new for the insurance industry,” he said. “Policies for smoke taint are not specific, so each insurance company approaches it differently.” If a grape is damaged in the field, Eddy explained, that comes under crop insurance, and few growers in California have that, as it’s designed to cover hazards such as frost damage and hail. While most wineries have insurance that covers stock loss by contamination, insurance companies haven’t yet addressed smoke taint as a contaminant.

As a wine consultant, Eddy is knee-deep in insurance research. “I’ve worked with over 100 winemakers in the last year on this issue, and there’s such a range of opinions. On one end of the spectrum, one guy says his wine is ruined, and he’s throwing it down the drain. On the other end, a guy says, ‘It’s okay, I’m making the wine.’ Insurance companies are taking the low road or the high road. They can say the wine is not damaged or agree that the wine is damaged and decide what it’s worth on the market today. When I look at smoke taint damage, part of my assignment is to determine the extent of the damage for all parties concerned.” In the future, Eddy believes, all growers will have crop insurance, and insurance companies will put smoke taint — along with specifics related to damage — in their policies. “We have never had this,” Eddy said. “This is the outcome of what happened in 2017 in California.”

Clearly, with global warming, the problem of smoke taint is here to stay. “We thought 2017 was a once-in-a-hundred-year event, but then 2018 was worse,” Eddy told The Grapevine Magazine. “There’s no reason to believe this isn’t going to continue.  Every year, we’re going to have issues.” In 2017, Napa was fortunate, because 80% of the grapes were already harvested when the fire broke out, and, according to Eddy, impact on the consumer was minimal. Next time around, winegrowers might not be so blessed. However, with leading smoke taint scientists helping the industry prepare for future wildfires, the damage may one day be contained.

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