A reader’s question about smoke, leaves, and grapes uncovers a surprising twist in smoke taint research.
A recurring annual threat
Every year, wildfires tear through wine regions such as Bordeaux, Provence, Napa Valley and Australia. The fire destroys everything in its path, but the smoke travels far beyond those burning hectares. Vineyards, many kilometres away, get caught up in it too.
That smoke settles on the skin and works its way into the juice. Wine made from tainted grapes takes on a smoky, ashy, sometimes medicinal flavour. For producers, that’s a direct hit: an entire harvest can become unsellable, even when the vineyard itself never burned.
The search for a solution
Scientists are therefore hunting for a way to break that chain. Some focus on prevention, using coatings, activated-carbon cloth and sprinkler systems designed to stop smoke phenols reaching the grape in the first place. Others look at remedies after the fact, once the damage is already done. The real sting is often in details that only surface years later.
One such detail recently came to light through a reader’s question.
‘I thought the smoke only settled on the skin and was then released during fermentation, but apparently there’s also an effect through the leaves?’
Ludo sent me that question after reading a piece in De Tijd about smoke damage in vineyards. Oenologist Sebastian Vannevel explained there that volatile phenols are absorbed not only through the grapes themselves, but also through the leaves, and are then transported on to the grape.
Ludo’s question was better than the newspaper’s explanation.
The answer, as it happens, has just changed, thanks to a study published in Food Chemistry on 1 June. That study raises serious doubts about the idea that smoke compounds travel from leaf to bunch via the vascular system.
What are phenols?
Smoke damage, usually called ‘smoke taint’, has become a structural risk worldwide in wine regions exposed to wildfires. Volatile phenols such as guaiacol, cresols and syringol can be absorbed by grapes.
Phenols form a broad family of organic compounds, built around a benzene ring with a hydroxyl group attached. Tannins are phenols. Anthocyanins, the pigments in red wine, are phenols. The smoke compounds in this article belong to the same family.
Three phenols keep reappearing in smoke taint research: guaiacol, cresols and syringol. All three are volatile, meaning they evaporate readily and travel effortlessly through the air to skin and leaf alike.
Guaiacol smells smoky and woody, like a freshly extinguished campfire. Peated single malt whisky, such as Laphroaig or Ardbeg, owes much of its character to that same compound. Cresols smell sharper and more medicinal, reminiscent of a plaster or the creosote scent of an old railway sleeper. Syringol adds a sweeter, spicier smoke note, similar to ham smoked over oak.
All three form through the incomplete combustion of lignin, the woody structural component of plants. A wildfire essentially works as one enormous, uncontrolled pyrolysis oven, and the grape captures the distillate.
From berry to glass
Inside the berry, the phenols become partly bound to sugars. As a result, they aren’t always detectable by smell or taste at first. During fermentation, ageing, and even in the mouth, they can be released again.
That’s when the smoky, burnt, medicinal and ashy notes emerge, the ones that can make a wine unsellable.
Leaf uptake of smoke
That grapes absorb smoke phenols directly is not in dispute. That leaves do the same is not in dispute either. The question is what happens next.
Since research from 2007, it had seemed plausible that compounds moved from the leaf through the plant to the grapes. In various trials, bunches were wrapped in plastic bags while leaves or shoots were exposed to smoke or guaiacol. When smoke-related compounds still turned up in the grapes afterwards, transport through the plant looked like the obvious explanation.
Logical enough. Except the experimental design had a weak spot. Volatile phenols pass straight through soft plastic.
Researchers at the University of Adelaide therefore used better shielding: activated-carbon cloth. That material adsorbs volatile compounds and keeps smoke away from the grapes far more effectively.
The outcome was strikingly clear. Leaves took up substantial amounts of volatile phenols and their glycosides, while grapes wrapped in activated-carbon cloth stayed essentially clean. No evidence of meaningful translocation from leaf to fruit was found.
Detached grapes
A further experiment made the earlier explanation even harder to sustain.
The researchers exposed grapes from so-called microvines to guaiacol vapour. Microvines are compact research vines that flower continuously, making them well suited to controlled experiments. Unprotected grapes contained 1,689 micrograms of guaiacol per kilogram after the trial. Grapes wrapped in activated-carbon cloth measured around 7 micrograms.
The researchers then repeated the experiment with detached table grapes. There, the difference was 523 versus 2 micrograms per kilogram.
Those detached grapes matter. They were no longer attached to a plant. There is therefore no way transport could have occurred via leaves, shoots or vascular bundles. If guaiacol still turned up under the plastic, that compound must have passed straight through the wrapping itself.
What had looked for years like evidence of internal transport may simply have been leakage through the packaging?
The leaf as a filter
The study contains one more striking detail.
On some vines, the leaves were removed before smoke exposure. Fewer leaves did not lead to lower levels of smoke compounds in the grapes, quite the opposite: certain smoke-related glucosides came out higher. Shortly after exposure, some values were 30 to 45 per cent higher; at harvest, several glycoconjugates were 12 to 43 per cent higher.
The likely explanation: leaves absorb volatile compounds straight from the air. That leaves less available for the grapes.
The leaf, then, doesn’t appear to act as a conveyor belt, contaminating the bunch from within. It may instead serve as a limited buffer, intercepting smoke before it reaches the fruit.
The study was confined to smoke exposure and doesn’t speak to general canopy-management advice. Bunch exposure, airflow, disease pressure and ripening all still play a role. Under smoke exposure, specifically, less leaf cover appears to work against the grower.
An old carbon bag gets a second life
The material used in the new trial looked familiar to me. Back in 2022, I wrote about an activated-carbon bag that researchers from the same university tied around grape bunches. At the time, the purpose was practical: stopping smoke phenols reaching the grape. The first results were promising, though the bags were expensive, fragile and labour-intensive.
Four years on, that same bag has proven equally valuable as a research tool. As a commercial solution, it was cumbersome. As a control in an experiment, it turned out far more reliable than plastic.
In 2024, I wrote about a different approach: a spray coating based on cellulose nanofibres, pectin, and chitosan.1 Some formulations could block guaiacol and syringol; others captured m-cresol. That technique, too, targets the outside of the grape.
That now looks even more logical than it did then. If the berry itself is the main point of entry, protection should focus on the berry.
The claim in De Tijd
The explanation given in De Tijd is, therefore, too strong. Leaves do absorb volatile phenols. That much is settled. But that those compounds are subsequently transported to the grape is precisely what the new research failed to demonstrate.
A more accurate version would read:
Both grapes and leaves can absorb smoke phenols, but contamination of the grape appears to result mainly from direct uptake by the berry itself.
Ludo was closer to the truth than he realised.
The smoke probably didn’t travel through the vine.
It travelled through the plastic.
Footnotes
- Chitosan can be sourced from crustacean chitin, but also from fungi. Fungal chitosan is used in winemaking, among other things, against Brettanomyces, and is generally considered vegan. The publication doesn’t specify the source of the chitosan used in this experimental coating. That ambiguity touches on a broader question: who actually decides where the line for ‘vegan’ wine sits. See: ‘Vegan wine: who decides where to draw the line?’ ↩
Sources
Researchers tested whether smoke compounds can be transported from leaves to the grape. Bunches wrapped in carbon cloth stayed clean, while unprotected bunches and detached grapes absorbed smoke phenols even under plastic. That points to leakage through the packaging, not transport through the plant.
Shi, T., Culbert, J.A., Ristic, R., Collins, C., Boss, P.K., Wilkinson, K.L., 2026. Exploring the possible translocation of smoke-derived volatile phenols from grapevine leaves to fruit. Food Chemistry, 513: 149009. https://doi.org/10.1016/j.foodchem.2026.149009
***
Leaves and grapes both absorbed smoke phenols during the same season, measured across multiple wildfires and a full ripening period. This study previously formed the basis for the assumption that leaf and grape are connected via the plant.
Jiang, W., Parker, M., Hayasaka, Y., Simos, C., Herderich, M., 2021. Compositional changes in grapes and leaves as a consequence of smoke exposure of vineyards from multiple bushfires across a ripening season. Molecules, 26(11): 3187. https://doi.org/10.3390/molecules26113187
***
Grapes convert volatile phenols into glycosides only after a delay. A sprinkler system above the canopy was tested as a barrier against uptake, similar in principle to the carbon cloth.
Szeto, C., Ristic, R., Capone, D., Puglisi, C., Pagay, V., Culbert, J., Jiang, W., Herderich, M., Tuke, J., Wilkinson, K., 2020. Uptake and glycosylation of smoke-derived volatile phenols by Cabernet Sauvignon grapes and their subsequent fate during winemaking. Molecules, 25(16): 3720. https://doi.org/10.3390/molecules25163720
***
Coatings based on cellulose nanofibres, chitosan and beta-cyclodextrin blocked guaiacol and syringol, or captured m-cresol, depending on the formulation. The publication doesn’t state the source of the chitosan used.
Tran, T.T., Jung, J., Garcia, L., Deshields, J.B., Cerrato, D.C., Penner, M.H., Tomasino, E., Levin, A.D., Zhao, Y., 2023. Impact of functional spray coatings on smoke volatile phenol compounds and Pinot noir grape growth. Journal of Food Science, 88(1): 367-380. https://doi.org/10.1111/1750-3841.16435
Frequently asked questions
What is smoke taint? Smoke taint is the technical term for smoky off-flavours in wine, caused by volatile phenols absorbed by the grape after exposure to wildfire smoke. The best-known compounds are guaiacol, cresols and syringol. They give the wine a smoky, ashy, sometimes medicinal flavour, which can render an entire harvest unsellable.
How exactly does smoke taint get into the wine?
The grape absorbs volatile phenols directly through the skin. Part of that binds immediately to sugars in the berry, forming glycosides. In that bound form, the compound is barely detectable by smell or taste. During fermentation, bottle ageing and even during tasting itself, some of those phenols are released again, which explains why a wine can smell noticeably smokier months after harvest than it did at first.
Do leaves also absorb smoke, and does that add extra smokiness to the grape?
Leaves do indeed absorb smoke phenols, but a 2026 study in Food Chemistry found no evidence that those compounds are subsequently transported through the plant to the grape. Earlier research that appeared to show this used plastic bags as a barrier, and volatile phenols simply pass through soft plastic. With a better-sealing material, carbon cloth, the grapes stayed largely clean.
Does removing leaves help against smoke damage?
No, and the data actually point the other way. On vines with fewer leaves, certain smoke-related glucosides were 30 to 45 per cent higher shortly after exposure, and still 12 to 43 per cent higher at harvest. Leaves appear to capture some smoke from the air themselves, so fewer leaves means less of a buffer for the grape.
Can smoke taint be removed from wine after harvest?
Techniques such as reverse osmosis and activated-carbon filtration exist and are used by producers to strip smoke phenols from must or wine. This piece focuses on the research into how smoke reaches the grape, not on those removal techniques, so I can’t make firm claims on that front based on the sources cited here.
How do you recognise smoke taint in a glass of wine?
Beyond a smoky or ashy aroma, it’s the finish that stands out most: dry, sometimes faintly medicinal, with a bitter edge that lingers longer than the fruit itself. That’s because salivary enzymes only split the last bound phenols during tasting, which is why the smoke note often only fully emerges retronasally, after swallowing.
This article first appeared in Dutch on Winecastr.com: Rooksmaak in wijn: de route van bosbrand naar druif. The English version was previously published on The Wine Shift’s Substack. Translated with the help of AI, checked and edited by the author.
Last updated: 7 September 2026