Think Out Loud

Research explores wine grape exposure to smoke

By Elizabeth Castillo (OPB)
Sept. 24, 2021 5:05 p.m. Updated: Oct. 4, 2021 4:25 p.m.

Broadcast: Friday, Sept. 24

Valuable wine grapes hang ready to pick on Red Mountain, near Richland, Washington.

Valuable wine grapes hang ready to pick on Red Mountain, near Richland, Washington.

Anna King


Year after year, wildfires continue to blaze through the West. How can wineries and grape growers combat smoke exposure? Tom Collins is an assistant professor at Washington State University’s Viticulture & Enology Program. He joins us with details on research about what tools can help reduce this growing problem.

This transcript was created by a computer and edited by a volunteer.

Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. As fire seasons get longer and western air gets smokier, how might grape growers and winemakers be affected? It’s actually a complicated question, because there are so many variables at play, like the time of year, the duration and intensity of smoke and the potential for growers to shield their grapes from the worst effects of that smoke. These are all things my next guest is researching. Tom Collins is an Assistant Professor in the Viticulture and Enology program at Washington State University. Welcome to TOL.

Tom Collins: Thank you, Dave, glad to be here. Thanks for inviting me.

Miller: Yeah, it’s good to have you on. How much smoke does there have to be, or for how long, before grapes are truly affected?

Collins: Well, as you alluded in your intro, it’s a complicated question, and one that we have spent several years now working on. It comes down in part to things like the time of exposure, so what time during the growing season does the smoke event happen? There appear to be differences between early season exposures and late season exposures. We’re just finishing the third year of a study looking at that.

Miller: Let’s start with that one then, because – I mean, these are ALL interesting – but do you have a sense yet for what is worse for a grape, assuming that it’s the same level of smoke, if the fruit has just set or if you’re about to harvest it? What’s the difference?

Collins: So some of the work that was done early on that prompted the work that the research that we’ve been doing, suggested that the period of time immediately following the onset of ripening, which in Oregon and Washington typically is late July early August, that period of a week or 10 days after the onset of ripening, was most likely to result in a negative outcome, all other things being equal. And then the risk dropped off a little bit towards harvest. And the risk before the onset of ripening was considered to be lower. I think what we have seen in the work we’ve done, is that the risk early in the season is higher than what we thought originally. We’ve done smoke exposures as early as fruit sets, right at the point the berries are first there after bloom finishes. And we’ve been able to see the negative outcome. Now for our research, we’re applying a fairly high level of smoke, but we still see this issue early in the season, and at levels nearly as high as what we see later in the season.

Miller: Is the big concern that the smoke is going to affect the flavor of the grape and then that flavor will, will affect the wine, OR that the vines and the fruits themselves are somehow not going to be as robust or grow as well because of the smoke? Because those seem like different things.

Collins: They are different things. And I think our primary concern is the potential for it to have a negative impact on grape and wine flavor and quality. Not every smoke exposure results in that negative effect. But when it does, it can make it really difficult to determine what to do with wines. So what’s happening is when the vineyards are exposed to smoke, the fruit is taking compounds from the smoke that have these characteristics sort of ashy, sometimes cigarette smoke kinds of aromas associated with them. Part of the vines’ response to the exposure from these kinds of compounds is to put them in the fruit and particularly in the skin of the fruit. And so when we make wine from that fruit, we can extract these compounds associated with smoke into the resulting wine. And if you get that at a high enough level, it can make the wines have these off-aromas, the smoky, ashy characteristics. So our primary concern in the research so far has been on the impact on fruit and wine quality. But we think there are also some issues associated [with] vine health and vigor, and its potential impact on how the fruit ripens as well. But those have been secondary to the effects on line quality in our research so far.

Miller: One of your research projects involves adding more air sensors. So if I understand correctly, grape growers will have a better sense ideally for how bad smoke might be, or even when it’s likely to get bad. Assuming that you could put a bunch of sensors all around Yakima Valley or the Willamette Valley or Napa or wherever, whoever wanted to use this information, what would they do with that information?


Collins: What we’re hoping to do with this, what we expect to be able to do, is develop a model using sensor data plus weather forecasting data, to determine, or estimate, or model where the smoke is headed, where the density of the smoke is likely to be higher. Because those would be the areas that might most experience a negative outcome. So that it would help the growers and help wineries understand what are the areas in their region that might be more heavily affected than others. And also to help them understand what are the regions that have not been affected. And that’s where we’re going to have less of an impact on wine quality. So it’s giving them better information to make decisions about what they’re going to do with the fruit, how they might adjust winemaking practices for example, to reduce the impact of any smoke exposure there might have been. And then we talked a little bit about the potential for barrier spray. So maybe this is a tool that growers can help growers to understand when they might want to start thinking about putting a barrier spray out, before smoke exposure reaches their area.

Miller: How might that work? So, if they look at the smoke forecast of the future and say, ‘oh, it looks like on Wednesday it could get really bad here.’ It’s Monday right now [when] they’re looking at this. What might they do with the barrier spray and what is that spray?

Collins: Well, so there are a number of materials that people are running trials with, to look at as potential barrier sprays. We’ve looked at Kaolin, which is a clay material that is registered for use in grapes for other purposes. But one of the things that Kaolin does is it absorbs compounds from the air. And so we were thinking that it can be sprayed on the fruit. The material would essentially trap some of these volatile compounds associated with the off-aromas. And then once the exposure is done, we could remove that coating and reduce the amount of these compounds that end up in the skin of the grapes. And so it may not be a tool that completely eliminates the problem, but it can reduce the extent, we think, to which these compounds end up in the fruit itself. Which, in a less severe exposure might be the difference between having fruit that is usable and fruit that is more difficult to use.

Miller: Is red wine more likely than white wine to have smoke problems because the skin, if I understand this correctly, is used in winemaking?

Collins: So that’s correct Dave. When we make red wines, we ferment the juice with the skins and the seeds, because we want to extract the pigments and the tannins,the things that [give] red wine it’s astringency and it’s color, are located in the skins as well.

And so the methods that we use to extract those compounds from the skin, are also going to extract these smoke-related compounds to a greater extent. When we’re making white wine, we typically press the juice away from the skins and seeds and ferment it separately. Because we’re not really looking for tannin or color from those grapes. And so fermenting with the skins and seeds does generally give the opportunity to extract those off-aroma and flavor compounds from the skins.

Miller: Am I right, that you’re also looking into the question of whether smoke from different kinds of wild fires could affect grapes differently?

Collins: Yes, that’s true. In Eastern Washington and in other parts of the western United States as well, we get smoke from forest fires in the Cascades or the Sierra Nevada and that’s from Douglas fir or other conifers that are burning. It’s the bark and some other fuel sources, but we also experience rangeland fires, where the plants that are burning are things like rabbit brush or sage or cheatgrass. And so we looked at the composition of smoke from different plant materials, and there are big differences in the composition of the smoke, and we think there are also differences in the likelihood that you’ll have a negative effect from a given amount of smoke based on the fuel source. So we think that what we’ve seen is that the smoke from range land plants, things like sagebrush and rabbit brush, are more likely to have a negative effect, than smoke from a Cascades forest fire, for example.

Miller: Finally, over the last few years, we’ve heard a little bit about winemakers trying to make the best of sometimes terrible situations. Basically, a wine version of ‘if life gives you smokey lemons, make smokey lemonade’. How common might that become?

Collins: Well, I think in the more severe cases, there may not be much we can do with these heavily affected wines, but in any given season, most of the smoke exposures are not going to result in a negative impact. There are some tools: you can change winemaking practices to try and reduce the amount to which these compounds are exposed. There are some tools that can help remove these compounds. Then I suppose, as you suggest, there may be some opportunities for creative approaches to how you might use wines that are maybe moderately affected, some of the ones that are more severely affected, we would struggle with ever finding a use for those other than maybe distilling them to recover the alcohol. But there may be opportunities for wines that are less heavily impacted. In general, winemakers are pretty tuned in now to the impact of smoke on their wine quality, and so we’re not likely to see some of the more heavily affected things reach the marketplace.

Miller: Tom Collins, thanks very much for joining us today.

Collins: Thanks for having me.

Miller: Tom Collins is an Assistant Professor in the Viticulture and Enology program at Washington State University.

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