Smoke Taint in Wine: Definition, Causes and Effects
Smoke taint is a wine fault caused by the absorption of smoke-derived chemical compounds into grapes during the growing season. It can produce undesirable smoky, ashy, burnt or medicinal aromas and flavours in the finished wine.
The condition occurs primarily when vineyards experience smoke exposure from wildfires, bushfires or controlled vegetation burns. Direct contact with flames is not necessary. Grapes may absorb smoke-related compounds even when the vineyard itself suffers no physical damage.
Smoke taint affects wine quality rather than necessarily indicating a health hazard. Its severity varies according to the type and duration of smoke exposure, grape variety, growing conditions and winemaking methods.
What Causes Smoke Taint?
The principal chemical substances associated with smoke taint belong to a group called volatile phenols.
These organic compounds enter the atmosphere when fire breaks down lignin and other components of woody vegetation.
Important smoke-related phenols include:
- Guaiacol: Associated with smoky, woody and medicinal aromas.
- 4-Methylguaiacol: Contributes smoky, spicy and burnt characteristics.
- Syringol: A compound associated with wood smoke.
- Methylsyringol: Another indicator of smoke exposure.
- Cresols: A group of compounds that may produce smoky, medicinal or tar-like odours.
These substances can enter grape berries following smoke exposure. Some compounds may also enter through other parts of the vine, although researchers continue to investigate the relative importance of different absorption pathways.
Once inside the grapes, volatile phenols can undergo chemical transformations that influence how smoke taint develops.
How Does Smoke Taint Form?
The development of smoke taint involves several stages.
Absorption of Smoke Compounds
Smoke carries volatile phenols through the air. When it reaches a vineyard, grape berries can absorb some of these compounds through their outer surfaces.
Smoke exposure does not necessarily produce visible damage. Affected grapes may retain their normal appearance, colour and texture.
Formation of Phenolic Glycosides
Inside the grape, volatile phenols can bind to naturally occurring sugars through a process called glycosylation.
This creates substances known as phenolic glycosides.
Unlike free volatile phenols, these bound compounds have little or no direct smoky aroma.
Consequently, grapes containing smoke-related substances may not exhibit an obvious smoky smell or taste.
Release During Winemaking
Fermentation, ageing and other chemical processes can release some volatile phenols from their sugar-bound forms.
As the compounds become available, they may contribute undesirable smoky and ashy characteristics to the wine.
Some glycosides can also release volatile phenols during consumption through interactions with enzymes in saliva.
This helps explain why smoke taint sometimes becomes more noticeable in the mouth or after swallowing.
The intensity of these effects depends on the concentrations and combinations of compounds present.
What Does Smoke Taint Taste and Smell Like?
Smoke taint can affect both the aroma and flavour of wine.
Common sensory characteristics include:
- Ash or cold cigarette ash
- Burnt wood
- Campfire smoke
- Medicinal or disinfectant-like aromas
- Smoked meat or burnt rubber
- Lingering smoky or bitter aftertastes
In severe cases, smoke-related flavours can overpower the natural fruit characteristics of the wine.
Some affected wines also exhibit a drying sensation in the mouth.
The intensity varies considerably. Mild cases may remain difficult to identify, while heavily affected wines can become unpleasant to drink.
Not every smoky aroma constitutes smoke taint. Toasted oak barrels, certain grape varieties and some fermentation processes can produce desirable smoky characteristics.
Smoke taint specifically refers to unwanted sensory effects associated with smoke exposure.
Which Grapes Are Most Susceptible?
All wine grape varieties can potentially develop smoke-related contamination.
However, susceptibility differs according to several factors:
Grape variety: Different varieties may absorb, transform and retain smoke-derived compounds at different rates.
Stage of development: Smoke exposure during ripening presents an important risk. Research also indicates that grapes can absorb smoke compounds earlier in their development.
Exposure duration: Longer or repeated smoke exposure can increase the accumulation of undesirable compounds.
Smoke composition: The type of burning vegetation and conditions of combustion influence the chemicals present in smoke.
Weather conditions: Wind, temperature and atmospheric conditions affect the movement and concentration of smoke.
Visible smoke near a vineyard does not necessarily mean its grapes will develop noticeable smoke taint.
Are Red Wines More Susceptible Than White Wines?
Smoke-related compounds can affect red, white and rosé wines.
However, traditional red winemaking usually involves extended contact between grape juice and skins during fermentation.
This process extracts colour, tannins and flavour compounds. It can also increase the extraction of smoke-related substances.
White wine production generally involves separating grape juice from skins before fermentation. This may reduce the amount of smoke-related material transferred into the wine.
Rosé production typically involves shorter skin contact than red winemaking and may offer similar advantages.
Nevertheless, white and rosé wines can still develop smoke taint after sufficiently severe exposure.
Is Smoke-Tainted Wine Dangerous to Drink?
Smoke taint is generally considered a wine quality defect rather than a direct indication that the wine is unsafe for consumption.
The volatile phenols responsible for its characteristic flavours can also occur naturally in other foods and beverages. Some are present in smoked foods, toasted wood products and oak-aged wines.
The detection of these compounds does not, by itself, demonstrate that a wine presents a toxicological hazard.
However, wildfire smoke is chemically complex. It can contain substances beyond those responsible for smoke taint, including potentially harmful combustion products.
The presence or severity of smoke-related flavours cannot establish whether all relevant contaminants are present at safe concentrations.
Consequently, it is important to distinguish between two questions:
- Sensory quality: Does the wine contain undesirable smoky or ashy flavours?
- Food safety: Does the wine contain potentially harmful contaminants at concerning concentrations?
These are separate issues and may require different forms of laboratory analysis.
A wine’s smoky taste alone cannot provide a reliable assessment of its overall safety.
As with any alcoholic beverage, alcohol consumption itself also carries health risks unrelated to smoke taint.
How Is Smoke Taint Detected?
Winemakers and specialised laboratories use chemical analysis and sensory evaluation to assess smoke exposure.
Chemical Analysis
Laboratories measure concentrations of selected volatile phenols and their sugar-bound derivatives.
Common analytical markers include guaiacol, methylguaiacol, syringol and various phenolic glycosides.
Methods such as gas chromatography and liquid chromatography help identify and quantify these substances.
However, some smoke-related compounds also occur naturally in grapes and wine. Their presence alone does not necessarily prove significant smoke exposure.
Results therefore require comparison with appropriate background concentrations.
Sensory Evaluation
Trained tasting panels evaluate wines for characteristic smoky, ashy and medicinal flavours.
Small-scale fermentations can also help producers assess potentially affected grapes before committing to full-scale winemaking.
Combining chemical and sensory analysis generally provides a more useful assessment than relying on either method alone.
Can Smoke Taint Be Removed?
Completely eliminating smoke taint remains difficult.
Certain winemaking techniques can reduce the extraction or concentration of undesirable compounds, but treatment results vary.
Common approaches include:
Reduced skin contact: Limiting contact between juice and grape skins can decrease the extraction of certain smoke-related compounds.
Gentle pressing: Careful processing may help minimise the transfer of unwanted substances into grape juice.
Activated carbon treatment: Specialised activated carbon products can remove some smoke-related compounds. However, they may also remove desirable wine aromas.
Membrane filtration: Techniques such as reverse osmosis may reduce certain volatile phenols.
Blending: Combining affected wine with unaffected wine can reduce the intensity of undesirable flavours, although it does not remove the compounds.
A major challenge involves the sugar-bound phenols that remain in the wine. These compounds can contribute to smoky flavours even after treatment.
No currently established method guarantees complete removal of all smoke-related characteristics without potentially affecting wine quality.
Can Smoke Taint Develop During Bottle Ageing?
Smoke-related characteristics can become more noticeable after fermentation and during wine storage.
Some phenolic glycosides gradually release volatile phenols through chemical reactions, including acid hydrolysis.
Consequently, a wine with relatively mild smoke-related characteristics may develop stronger unwanted flavours over time.
However, the process varies between wines. Smoke taint does not necessarily increase continuously or predictably during ageing.
Does Smoke Taint Affect Future Harvests?
Smoke contamination primarily concerns grapes exposed during the affected growing season.
There is no established evidence that smoke-related contamination in one harvest automatically transfers into the following year’s grapes.
However, severe wildfires can cause other long-term vineyard problems. These include damaged vines, reduced productivity, soil degradation and destruction of irrigation infrastructure.
Such effects are separate from the chemical processes responsible for smoke taint.
Summary
Smoke taint is a wine fault associated with the absorption of smoke-derived volatile phenols by grapes.
These substances can bind to grape sugars and remain relatively inconspicuous until fermentation, ageing or consumption releases their characteristic flavours.
The resulting wine may develop smoky, ashy, medicinal or burnt characteristics that reduce its sensory quality.
Smoke taint does not automatically indicate a food-safety hazard, although flavour alone cannot establish whether smoke-exposed wine is safe.
Laboratory analysis, careful vineyard management and suitable winemaking techniques can help producers assess and reduce its effects. Nevertheless, complete removal remains challenging.
Sources:
- Australian Wine Research Institute (AWRI). Smoke Taint: Research, Analysis and Management. An authoritative resource covering smoke compounds, grape contamination, sensory effects and treatments.
- Krstic, M. P., Johnson, D. L. & Herderich, M. J. (2015). Review of Smoke Taint in Wine. Australian Journal of Grape and Wine Research, 21, 537–553. A peer-reviewed review of the chemistry and sensory effects.
- UC Davis, Department of Viticulture and Enology. Wildfire Impact on California Grapes and Wine. Research-based guidance on contamination, testing and mitigation.