The Australian Wine Research Institute

When vineyards and grapes are exposed to smoke this can result in wines with undesirable sensory characters, such as smoky, burnt, ashy or medicinal, usually described as ‘smoke tainted’. Consumers have been shown to respond negatively to smoke tainted wines. The compounds in smoke primarily responsible for the taint are the free volatile phenols that are produced when wood is burnt. These can be absorbed directly by grapes and can bind to grape sugars to give glycosides that have no smoky aroma. During fermentation (and also over time in barrel or bottle) these glycosides can break apart, releasing the volatile phenols into the must or wine, and allowing the smoky flavour to be perceived. These glycosides can also release the volatile phenols in the mouth during the drinking of wine, which may contribute to the perception of smoke taint.

What factors affect the risk of smoke taint?

The key factors that determine whether smoke-exposed grapes become tainted are the grapevine growth stage, grape variety, smoke composition and the length of smoke exposure. More details about vineyard risk factors and the latest research on smoke taint can be found in the following resources:

• Smoke taint – entry into grapes and vineyard risk factors
• Recent smoke research and what it means for industry (article published December 2023)

What are options for managing smoke-exposed fruit?

There are a number of steps that can be taken in the vineyard and winery to minimise the sensory impacts of smoke exposure. These include hand harvesting, excluding leaves, keeping fruit cool, separating press fractions, fining and reverse osmosis treatment. More details are available in the following fact sheets and resources.

• Smoke taint – practical management options for grapegrowers and winemakers (AWRI fact sheet)
• Tackling smoke taint head on: winery remediation options for smoke-affected juice and wine (AWRI webinar 23 July 2020)
• Treating smoke-affected grape juice with activated carbon (AWRI fact sheet)
• Treating smoke-affected wine with activated carbon (AWRI fact sheet)
• Treating smoke-affected wine with nanofiltration (AWRI fact sheet)
• Treating smoke-affected wine with glycosidase enzymes (AWRI fact sheet)
• Treating smoke-affected wine with untoasted oak chips (AWRI fact sheet)
• Remediation of smoke-affected wine by dilution (AWRI fact sheet)
• What can be done to identify and reduce smoke effect in grape and wine production (DAFWA fact sheet)

Assessing smoke marker compounds in grapes and wines 

AWRI recommends assessing the risk of smoke taint by analytical testing of grapes sampled approximately three weeks before harvest, to allow time for transport, analysis and receipt of results in time to support harvest decisions.

Grape samples should be submitted for analysis of smoke marker compounds (both volatile phenols and non-volatile glycosides). Tips for sampling, packaging and transport of grapes for smoke analysis are available in the fact sheet: Grape sampling, processing and transport following vineyard smoke exposure. Smoke analysis is available from a number of laboratories in Australia, listed on Wine Australia’s Fire and smoke assessment page. Details of the smoke analysis options available from Affinity Labs (AWRI’s commercial arm) to customers located within Australia are here: Smoke taint analysis – fact sheet for Australian customers.

Customers located outside of Australia can only submit wine samples (not grapes) for smoke analysis, due to biosecurity requirements. Information on submitting samples to Affinity Labs from outside Australia is here: Smoke taint analysis – fact sheet for international customers.

Smoke taint analysis results and interpretation

Smoke analysis results will include the volatile compounds guaiacol, methylguaiacol, ortho-, meta- and para-cresol, syringol and methylsyringol, as well as the glycosides syringol gentiobioside, methylsyringol gentiobioside, phenol rutinoside, cresol rutinoside, guaiacol rutinoside and methylguaiacol rutinoside. More information on what the analytical results mean, as well as the sensory impact on wine, can be found in these articles: Interpreting AWRI smoke panel analysis results and Update on the AWRI’s smoke ‘background levels database’ and this fact sheet: Grape smoke panel analysis results and sensory impact.

To assist with interpretation of analytical results, the AWRI has established a background database of volatile phenols and glycosides collected from grape and wine samples that have not been exposed to smoke. This background data can be compared to the results of potentially exposed fruit to determine the likelihood of smoke exposure. The background data for Australian grapes Concentration of smoke marker compounds in non-smoke-exposed grapes and wine in Australia was published in 2022 as an open access journal article in the Australian Journal of Grape and Wine Research. All results from testing by Affinity Labs include graphical representations of the results in relation to the background levels database, to assist with interpretation. Australian companies can contact the AWRI helpdesk on (08) 83136600 or helpdesk@awri.com.au  for further assistance with interpretation of results.

Information useful for understanding smoke taint results for grapes in the USA can be found in this UC Davis article. For free volatile phenols, analytical results from other laboratories can generally be compared to the AWRI’s volatile phenol background data. For glycoside data, however, analytical results produced using a hydrolysis/GCMS methods are not comparable to results from Affinity Labs’ LCMS method, as demonstrated during a cross-validation of analytical data between Vintessential Laboratories and Affinity Labs. As such, it is not possible to compare glycoside results between laboratories that use the two different methods or to compare results from a hydrolysis/GCMS method to the AWRI’s background database for glycosides. For wines that have been analysed after oak treatment, results cannot reliably be compared to background data due to extraction of oak volatile compounds from the oak.

Further information is available on analytical methods for smoke taint and the published papers that describe them.

Sensory impacts of smoke

Both the volatile phenols and glycosides are known to have a sensory impact on wine. The AWRI fact sheet Sensory impact of smoke exposure provides sensory thresholds for smoke compounds and additional information about the sensory effects of smoke compounds in wine. A study investigating consumer acceptance of wine blends with differing proportions of smoke-affected wine was completed in early 2020, with results summarised here: Case study: consumer acceptance of smoke-affected wines (AWRI fact sheet).

Smoke exposure and likelihood of smoke taint

Chemical analysis of volatile phenols and glycosides in fruit that might have been exposed to smoke can be compared to a background database of grape and wine samples that have not been exposed to smoke to determine the likelihood of smoke exposure.

Research conducted during and after the 2020 vintage focused on linking results from grape analysis to the likelihood of perceptible smoke characters in wine. This work has been published in an open access peer-reviewed article (Parker et al. 2023). Concentrations of volatile phenols and phenolic glycosides (µg/kg) in grapes (Chardonnay, Pinot Noir and Shiraz) that resulted in wines with significant smoke flavour (high risk) and concentrations above which only some wines were significantly smoky (moderate risk) are detailed in Table 5 of that paper (reproduced below). It should be noted that this research did not apply any remediation treatments to address the smoke impact. Other studies have shown that applying remediation techniques can reduce the impact of smoke in some wines.

		Chardonnay		Pinot Noir		Shiraz
Analyte in grapes	Units	Moderate risk	High risk	Moderate risk	High risk	Moderate risk	High risk
Volatiles
4-Methylguaiacol	µg/kg	4.0	5.7	nd	nd	1.0	nd
Guaiacol	µg/kg	14.3	16.0	4.0	4.0	7.0	12.0
o-Cresol	µg/kg	10.3	10.3	3.0	5.0	2.0	3.0
m-Cresol	µg/kg	6.0	10.0	nd	nd	nd	nd
p-Cresol	µg/kg	2.0	7.3	nd	nd	nd	nd
Syringol	µg/kg	nd	nd	nd	nd	nd	nd
4-Methylsyringol	µg/kg	nd	nd	nd	nd	nd	nd
Glycosides
Syringol gentiobioside	µg/kg	101.2	135.7	22.2	53.0	28.6	176.0
Methylsyringol gentiobioside	µg/kg	15.9	25.4	2.0	5.0	5.3	18.0
Phenol rutinoside	µg/kg	5.0	7.0	4.4	10.0	1.8	16.0
Cresol rutinoside	µg/kg	11.1	11.0	5.9	13.0	5.4	14.0
Guaiacol rutinoside	µg/kg	9.2	13.7	3.5	3.8	9.2	23.0
Methylguaiacol rutinoside	µg/kg	25.0	30.6	6.1	10.0	22.3	23.0

nd- denotes not determined as concentrations were below limit of quantification.

Table reproduced from “Modelling Smoke Flavour in Wine from Chemical Composition of Smoke-Exposed Grapes and Wine” by Parker et al. 2023 licenced under CC BYY 4.0

Conducting a small-scale ferment of potentially affected grapes allows wineries to conduct sensory assessment of the small-scale wines and could provide additional useful information to help determine the potential risk of smoke taint developing in wine. The Small-lot fermentation method and Small-lot fermentation video provide detailed information on how to conduct a small-lot fermentation for this purpose. The Smoke sensory evaluation procedure and Smoke sensory evaluation video provide information on how to conduct a sensory assessment on small-lot fermentations using rigorous sensory methodology.

Smoke sensory evaluation

Affinity Labs has a specialised smoke sensory panel that can assess the intensity of smoke-related characters in wine. Visit the smoke evaluation page for more information. The AWRI can also support winegrowing regions to establish local smoke sensory panels. Refer to the Smoke sensory evaluation procedure and Smoke sensory evaluation video for information on how to conduct a sensory assessment of potentially smoke-affected wines, including small-lot fermentations. Also refer to this animated video about the importance of sensory evaluation when assessing smoke taint.

Managing smoke-affected vineyards

If analysis of grapes shows high levels of smoke markers, growers may choose not to harvest affected blocks for winemaking. Once the decision not to pick has been made, there are a number of factors that should be considered in managing the blocks, to maximise their potential for the following season. It’s important to note that there is no risk of carry-over of smoke taint from one season to the next. The following resources provide advice on management practices for vineyards where grapes are not harvested for winemaking, due to smoke impacts:

• Managing smoke-affected vineyards where fruit is not harvested for winemaking (AWRI fact sheet)
• Options and considerations for dealing with unharvested fruit in smoke-affected vineyards (AWRI webinar recording 27 February 2020)

What resources are available on prescribed burns and stubble burning?

• Stubble burning – a possible source of smoke taint in grapes
• Minimising the impact of prescribed burns on wine-grape production
• Broadacre burn-off smoke management guideline
• PIRSA’s guidelines for reducing smoke taint from stubble burning

Fire damage to vineyards

If vines are actually burnt during a bushfire, these resources provide advice on managing damaged vines.

• How to manage burnt or fire damaged vines (DPI Vic fact sheet)
• Grapevine recovery after fire (AWRI fact sheet)
• Grapevine recovery from fire damage (DPI Vic fact sheet)
• Rapid visual assessment and mapping of fire-damaged vineyards (AWRI webinar 23 April 2020)
• Principles for re-establishing fire-damaged vineyards: training fire-damaged vines and replants (AWRI webinar 21 May 2020)
• Principles for re-establishing fire-damaged vineyards: winter pruning and preparation (AWRI webinar 14 May 2020)
• What should you consider when purchasing grapevine planting material? (AWRI webinar 7 May 2020)
• Bud dissection as a tool to evaluate the impacts of fire on grapevines and inform pruning decisions (AWRI webinar 30 April 2020)
• Options and considerations for dealing with unharvested fruit in smoke-affected vineyards (AWRI webinar 27 February 2020)
• Information pack – managing fire-damaged grapevines
• Assessing and managing fire-damaged grapevines (AWRI webinar 7 January 2020)
• Bushfire recovery with Greg Horner of Mt Bera Vineyards (Wine Australia podcast 22 January 2020)
• Wine Australia case study – Bushfire recovery