Indeed, the last few years (2017 and 2020 especially) grape growing areas in Northern California and other parts of the state including the Central Coast have experienced historically large wildfires. If grapes are exposed to smoke, winemakers should be alert to the possibility of smoke taint damage to grapes and to finished wines during and after these events. You’re right — it’s an important topic for almost all of us, most particularly winemakers in Mediterranean climates where falls are warm and dry, to have a handle on the current information.
Volatile phenols (which I’ll abbreviate as VPs) are released when wood burns during wildfires. VPs exist in both free and bound forms in grapes, juice, and wine and can cause a smoke taint defect in the aroma and taste of finished wines. These sensory defects have been described as “campfire,” “medicinal,” “earthy,” or “smoky,” among other terms. While some of these descriptors are common in red wines, especially those aged with toasted oak, smoke taint is especially characterized by an ash tray sensation at the back of the throat, on the finish of the wine, and is observed retro-nasally. Please note: Smoke taint in wine is not a danger to human health and many “smoke taint markers” that can be measured are naturally-present in wines aged with toasted oak.
There is no cure for smoke taint, in the vineyard or cellar. Growers and winemakers can do their best to use the limited means of mitigation available (see more in the following paragraphs) . . . and it’s still a very evolving topic! If your vineyard is in a fire zone and/or exposed to smoke, you should assume you are at risk for smoke taint, so harvest and make wine accordingly. At the same time, there are anecdotal tales of vineyards being very close to fire zones yet still yielding perfectly normal and acceptable wines. It is extremely difficult to predict a finished wine’s final sensory and chemical analysis.
Some wine labs have “smoke taint panels” where they measure VPs like guaiacol and 4-methyl guaiacol. That’s all well and good but in my personal experience, and in the anecdotal experience of many of my winemaking friends, the numbers are truly meaningless as predictors of final wine quality and intensity of possible smoke taint.
Smoke Taint in Processing and Winemaking — Some Basic Information:
• Skin contact time: Free and bound VPs are hydrophilic and extract very quickly into musts — within a day, estimated 30%, within 5 days, over 80%. Current guidance for red winemaking is not to press off early, and shorten skin contact time, etc. Unless you can make rosé (which is not always economically possible), try to make the best red wine you can. Optimizing positive traits in a wine can help cover up volatile phenols. Whites and rosés benefit from being separated from the skins as soon as possible.
• Picking early/unripe fruit: Picking early (especially if pyrazines are present — Cab, Merlot, etc.) doesn’t help as studies are showing that pyrazines (present in unripe grapes) actually make it worse and pyrazines (bell pepper aromas) are equally a red wine defect that people are sensitive to. Pyrazines are difficult to remove as well. Now you have two wine defects, not just one.
• Aging: Studies are ongoing but some scholars believe that at one year of age the vast majority of VPs in wine will be stable, i.e., the problem will not get worse at this time.
Mitigation in the Vineyard — Can anything help?
• Minimize MOG (material other than grapes): Do everything possible to exclude MOG (leaves, stems, etc.) as smoke taint compounds are also metabolized into leaves, petioles, and stems.
• Avoid picking avenue rows and row-end fruit: In 2017, side-by-side experiments I did in one of my vineyards in Sonoma showed that not picking avenue rows (exterior facing rows) or row-end fruit helped reduce the amount of smoke taint in the final wine by a significant amount. It did not 100% prevent it of course but reduced it by about 20%. This is possibly because the avenues and row-ends carried higher levels of vineyard dust and ash kicked up by passing vehicles. This happened in the 2017 event, on the Napa Valley floor, when fire was quite close to the vineyards and it’s possible this ash was quite fresh, which is why there was a significant difference.
• Minimize time between field and press: For whites and rosés especially, VPs increase with skin contact.
Mitigation in the Cellar — Reducing perception
• Press more gently: It is clear that the maximum VPs are released into the juice (whites/rosés) and musts (reds) at greater pressure. Try to press more gently, separating out free run from press fractions, keeping pressing to a minimum. For reds, separate everything over 0.8 bar and treat press fractions separately. For whites, maximize free run and minimize rotations and length of press cycle. Wineries will have to balance acceptance of lower yields vs. higher smoke taint risk. However, don’t be afraid of maceration in reds — you’re still going to have more success by getting full extraction and “masking” by having lots of good stuff in your wine as well as potentially a little bit of bad stuff.
• 100% de-stem all reds: Destemming all red fermentations is recommended. No studies have been done regarding VPs in grape stems, but if they can be present in leaves and petioles it seems likely that VPs will be present in stems. Green stem character (pyrazines) can make smoke taint appear worse, so it seems helpful to exclude them.
• Blending: Blending smoke-tainted wine with non-tainted wine can work to reduce smoke taint character, but only if you have enough non-tainted wine to blend levels down. But be cautious — why ruin 100 gallons of smoke taint-free wine with 10 gallons of tainted wine? Do bench trials and test for free and bound VPs. Do short-term aging in bottles or bench scale if possible.
• Masking — maximize fruitiness: Using residual sugar (RS) in final blends can help. Anything that points up fruitiness, like blending with fruity wines like Zinfandel and Petite Sirah for reds or Riesling and Gewürztraminer for whites, can help lessen the sensation of smoke/ash characters. This will only work in wines with a low level of smoke taint.
• Masking — oak and tannin products: Sometimes fruity oak or tannins can mask low levels of smoke taint. Do bench trials — Oak products will never contribute to bound VPs, only free. The only time a VP can become “bound” is during the berry ripening process.
• Partial removal — activated charcoal: Activated charcoal products (available from industry-supplying companies like AEB, Laffort, and Scott Labs) can help remove lower levels of smoke taint aromas. But be aware, additions larger than 1 g/L really start to strip good things from the juice/wine as well. Again, you need to do bench trials.
Does it work? Maybe . . .
• Washing grapes: Unless there is visible ash under 24 hours old (which can release volatile phenols), washing grapes will likely not help, as most of the VPs will already have been absorbed into the grapes.
• Washing grapes with ozonated water: There are ongoing studies being done, but the anecdotal evidence so far points to it not helping. It’s also very expensive and might impact the fruit in negative manners.
What has been shown not to work?:
- Adding bentonite
- Settling out white wines to low % solids
- Adjusting fermentation temperature
- Brix/potential alcohol differences
- Enzyme treatments on juice
- Picking green/early (then you have bad/green wine on top of possible smoke taint!)
- Pressing off early for reds (in other words, make the best wine you can)
- Treating heavily smoke-damaged wine. Carbon treatments, blending, masking, etc. are all worthless against heavily smoke-damaged lots, i.e., lots that are already exhibiting bad and off aromas early.
Bottom line: If a vineyard is exposed to smoke, it is possible there will be some smoke taint risk in the finished wines made from those grapes. On the other hand, just because a vineyard experiences a smoke event, it does not mean the wines made from those grapes will all exhibit detectable or even objectionable levels of smoke taint. Decisions must be made in real time as much as possible and on a case-by-case basis. I’ve largely found that taking berry and cluster samples to a wine lab for volatile phenol analysis to be largely futile. The “numbers” didn’t seem to correlate between guaiacol levels and the final amount of olfactory smoke taint in the final wine.
As there is no cure for smoke taint, vineyard and winemaking teams alike must assess the situation as best they can and then work together on strategy and mitigation to produce the best wines possible.
I’ve been pretty lucky. In 2017 and 2020 both, I picked some Cabernet that were under very smoky conditions and, by following the advice I’ve provided, made some really great wines. The deodorizing carbon treatments, in particular, seemed to work well. It’s very important, as always, to do bench trials so you’re not adding too much and stripping the wine. I’m glad I picked those grapes as opposed to leaving them on the vine. There were a lot of winemakers in Napa and Sonoma that should’ve picked grapes in those years but didn’t.