Smoke Taint Addressed as Northwest Harvest Begins

With sensors in vineyard and hoop house, WSU researcher analyzes effects on fruit and leaves

by Peter Mitham
wine WSU smoke taint trial
A hoop house creates an environment for researchers to study smoke taint.

Sunnyside, Wash.—The first grapes of the 2016 vintage were harvested in Washington state last week, six weeks after the first signs of véraison began appearing on Red Mountain and elsewhere.

But between first blush and crush, dry weather made for a frantic wildfire season in wine country, with flames from several fires drawing near to vineyards throughout the summer.

The massive Range 12 fire near Yakima, Wash., for example, scorched close to 180,000 acres after starting July 30. The fire came within 10 feet of a block of Riesling at DuBrul Vineyard, a 45-acre property near Sunnyside.

“The fire came up to the northern edge of the Riesling,” Kerry Shiels, winemaker at Côte Bonneville, told Wines & Vines. “We haven’t had any smoke issues in the past, however, I did work in Napa in 2008, so I have experience with smoke taint.”

Shiels wanted to know if the fire—and more specifically its smoke—was going to impact her grapes, and having heard Washington State University assistant professor Tom Collins speak at the Washington Advancements in Viticulture and Enology symposium in Richland on July 14, she gave him a call.

“Most of the time when you have smoke impacts in the grapes, as a winemaker you find out about it after harvest,” she said. “If you’re going to make any modifications in your program—or you’re going to do anything to minimize the impact—it’s nice to know about it beforehand.”

Collins had just kicked off a trial smoking of Riesling grapes at WSU’s research vineyard near Prosser when the Range 12 fire erupted.

Collins had built two hoop houses enclosing about 60 vines each, with one serving as a control planting and the other equipped with an offset firebox smoking unit suitable for home barbeques, small commercial smokehouses or (as WSU would have it) simulating the effects of wildfires on vines.

Bearing in mind recent wildfire events, Collins equipped the firebox to produce a wood-based smoke typical of a burning Cascades forest with a view to determining how the intensity and duration of exposure might affect ripening grapes and finished wines. During the week of July 25, Collins put his Riesling vines through 18-hour smoking sessions. Smoke volume, temperature, particulate matter and other variables were carefully measured.

And then a real wildfire approached.

“I woke up Sunday morning (July 31) to the smell of smoke, and thought, ‘Oh great, there goes my trial,’” he said. “If we had smoke from a natural wildfire on top of the smoke we applied, we wouldn’t be able to separate the effects from the wildfire from the effects of our deliberate smoking.”

Collins hadn’t put away his monitoring equipment, however, so he set it up in the Prosser vineyard to determine how much smoke was rolling in and what effect it might be having.

“It wasn’t enough of a problem to preclude us from continuing the trial, but those fires did potentially affect other vineyards in the area,” he said.

This made the call from Shiels a welcome addition to his research. While the intensity of the smoke billowing into her block of Riesling is unknown, Collins will be able to compare wines made from grapes enveloped by this year’s Range Fire smoke with those from his trial sites. Cabernet Sauvignon grapes from WSU’s vineyard also were subject to the controlled smoke, and Collins is tracking the impact on them, too.

“We’re in the process now of doing the analysis of the fruit and the leaves,” he said. “When the fruit is ready to harvest, we’ll also look at how these compounds are extracted from the fruit into the wines.”

The end result should be a better understanding of how extended exposure to low-intensity wildfire smoke affects ripening fruit and what strategies might help mitigate the impact.

The headline-grabbing wildfires of 2015 affected fruit grown in the Lake Chelan area most, but wineries in the Yakima Valley also reported impacts as a blanket of smoke drifted south and settled over the mid-Columbia region. Some growers credited the ceiling of smoke with shading fruit during the final weeks before harvest, but the thin coat of ash that accumulated on vehicles and equipment testified to ongoing fallout.

This year, moist conditions led to lush growth early in the season. When dry conditions returned later in the summer, the grasses and sagebrush became tinder for fires south of Interstate 82 in the Horse Heaven Hills and on range land north of the highway.

“These ones made it much more apparent how (smoke) can affect them,” Collins said. “Even though the fires last year were much bigger and more spectacular, I think in the end they only affected a relatively small number of growers and wineries, whereas having the fire right in your backdoor in the middle of the Yakima Valley, Red Mountain got people’s attention.”

Collins hopes to present some preliminary results from his research, which received funding from the Washington State Wine Commission, at the Washington Association of Wine Grape Growers annual convention Feb. 7-9, 2017.

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