Technical Review No. 270, January 2025
Mango Parker – Senior Research Scientist, mango.parker@awri.com.au
Eleanor Bilogrevic – Scientist
WenWen Jiang – Senior Scientist
Eric Wilkes – General Manager Affinity Labs
Leigh Francis – Honorary Fellow
Markus Herderich – Director of Research
Introduction
When there was widespread smoke across Australia’s viticultural regions in the 2019-2020 growing season, winemakers and growers from across the country contacted the AWRI helpdesk for advice and assistance. Altogether, thousands of queries about smoke taint were received in 2020, the majority about assessing grapes to determine the risk of producing smoke-affected wine (AWRI 2020). Smoke exposure can be robustly identified when the concentrations of volatile phenols and phenolic glycosides are above those found in non-smoke exposed grapes and wines (Coulter et al. 2022). At the time, there was very little data available to determine how much smoke exposure is required to have a noticeable impact on wine quality, particularly for mildly smoke-affected grapes or grapes exposed to smoke prior to veraison. Many producers chose to go ahead and produce wines from mildly smoke-affected grapes, and were able to release commercially acceptable wines that had no noticeable smoke flavour when young. However, the helpdesk continued to receive more than 200 queries about smoke taint in 2020-2021, mainly from winemakers concerned about smoky flavours developing in the bottle (AWRI 2021).
Decisions about when to process smoke-exposed grapes into wine and when to discard them have major implications for industry. If the threshold for rejection of grapes is too high, more smoke-exposed grapes will progress to production, which could lead to wines in the market that are perceived by consumers as unpleasantly smoky, potentially causing reputational damage to wine brands. If the threshold is too low, grapes or wines will be discarded unnecessarily, disrupting supply chains and placing financial burdens on wineries and growers. Based on the results from 2020, a middle-ground approach has been adopted, whereby a wine is now being classified as ‘significantly smoky’ if the smoke flavour is higher than all clean controls using Dunnett’s comparison. This approach was previously shown to relate well to consumer rejection data (Bilogrevic et al. 2023).
As an addition to our research on predicting smoke taint in wine from grape analysis (Parker et al. 2023), a recently published paper (Parker et al. 2025) summarises data from an ageing study involving a large number of wines produced from grapes exposed to environmental smoke during the 2019-2020 growing season. This study provides for the first time, a guide for producers assessing smoke-affected grapes, based on wines produced under controlled standard winemaking conditions, stored for three years after bottling, and assessed by formal sensory methodology.
What was done?
Forty-nine wines were made from Chardonnay, Pinot Noir and Shiraz grapes exposed to various wildfire smoke events during the 2019-2020 growing season, together with 14 control wines made from non-smoke-exposed grapes. The wines were produced using standard small-lot (50 kg) winemaking protocols, without any oak contact. No special efforts were made to remediate the impact of the smoke, so reds were fermented on skins as per normal protocol. The wines were bottled under screw cap and stored for three years.
The chemical composition and smoke flavour intensity were measured four times over three years ageing in bottle, to understand how the concentrations of volatile phenols and phenolic glycosides, and smoke flavour intensity evolves over time. The goal was to summarise the concentrations of volatile phenols and glycosides in the wines considered discernibly smoky, and the concentrations of volatile phenols and glycosides in the grapes that produced those wines.
What did the results show?
In line with reports from industry, not all of the smoke-exposed grapes produced wines that were noticeably smoky. In the wines from the ageing study, concentrations of volatile phenols and glycosides did not change significantly over 39 months in the bottle, with the exception of syringol, which increased in both smoke-affected and control wines. While these findings do not support the commonly held belief that smoke-related glycosides hydrolyse over time and release volatile phenols, the results are in line with previous studies on wines aged for up to six years that were produced from grapes deliberately exposed to smoke while on the vine (Ristic et al. 2017), and shorter term stability studies on smoke-related phenolic glycosides (Whitmore et al. 2021).
Of most interest to producers is whether the wines had a noticeable smoke flavour. Wines were categorised as ‘smoky’ if smoke flavour was rated significantly higher than all non-smoke-exposed control wines of that variety and study. The significant smoke flavour ratings were consistent over the three years for the majority of the wines (73%). Of the 49 wines made from smoke-exposed grapes, twenty-one wines (43%) were not significantly smokier than controls throughout the duration of the study. Fifteen wines (31%) were rated significantly smoke-affected compared to the controls at all time points. Thirteen wines (27%) were found to change classification during the study. Nine of these were mildly smoke-affected wines, where smoke flavour became apparent in older wines that had not been apparent in the young wines. This is likely to be due to masking by other attributes such as fresh fruit flavours that are stronger in young wines, and drop away as the wines age, revealing the underlying smoke flavour. Three wines were significantly smoky at six weeks post-bottling, dropped out of significance at either nine months or 21 months post-bottling and were significantly smoky again at 39 months post-bottling. In these wine the smoke flavour was consistently rated higher than that of the corresponding controls but due to the conservative statistical approach, they were not always found to be significantly different from the controls. One Pinot Noir wine was rated significantly smoky at 6 weeks and 9 months post bottling, but not at later time points.
The wines produced from smoke-exposed grapes did not all have noticeable smoke flavour. The wines were divided into two categories, those wines with significant smoke flavour, and those with smoke flavour not significantly higher than non-smoke-exposed control wines. The concentrations of smoke markers in grapes and wine have been summarised for these two categories in the tables below, focusing on compounds important to smoke flavour, and the reliable smoke exposure marker, syringol gentiobioside (SyGG).
Table 1. Wine concentrations of volatile phenol and glycoside concentrations in significantly smoky wines and those not found to have significant smoky flavour, based on the combined results of sensory assessments conducted up to 39 months after bottling.
| Guaiacol (µg/L) | o-Cresol (µg/L) | m-Cresol (µg/L) | p-Cresol (µg/L) | GuRG (µg/L) | CrRG (µg/L) | SyGG (µg/L) | ||
| Chardonnay -not significant smoke flavour | Range | <1.0-5 | <1.0-5 | <1.0-4 | <1.0-6 | <1.0 -15 | <1.0 -17 | <1.0-195 |
| n=57 | Median | 1.0 | <1.0 | <1.0 | <1.0 | 3.0 | 4.0 | 17.0 |
| Chardonnay -significant smoke flavour | Range | 2.0-19 | <1.0-13 | <1.0-16 | <1.0-11 | <1.0 -44 | <1.0-58 | 17-743 |
| n=23 | Median | 6.0 | 4.0 | 4.0 | 2.0 | 9.0 | 6.0 | 76 |
| Pinot Noir -not significant smoke flavour | Range | <1.0-21 | <1.0-14 | <1.0-10 | <1.0-5.0 | <1.0 -22 | <1.0-29 | <1.0-96 |
| n=43 | Median | 5.0 | 3.0 | 3.0 | 1.0 | 2.0 | 4.0 | 4.0 |
| Pinot Noir -significant smoke flavour | Range | 8.0-59 | 3.0-42 | 4.0-29 | 3.0-17 | 3.0-79 | 3.0-128 | 8.0-520 |
| n=33 | Median | 32 | 15 | 15 | 7.0 | 21 | 19 | 72 |
| Shiraz -not significant smoke flavour | Range | 10-54 | <1.0-8.0 | <1.0-6.0 | <1.0-3.0 | 5.0-86 | 2.0-43 | 2.0-188 |
| n=54 | Median | 20 | 2.0 | 1.0 | <1.0 | 18 | 7.0 | 24 |
| Shiraz -significant smoke flavour | Range | 29-145 | 2.0-39 | 2.0-27 | 1.0-8.0 | 18-208 | 5.0-49 | 30-842 |
| n=30 | Median | 62 | 8.0 | 6.0 | 4.0 | 53 | 16 | 80 |
GuRG=guaiacol rutinoside, CrRG=cresol rutinoside, SyGG=syringol gentiobioside
Table 2. Summary for each variety of the concentrations of volatile phenols and glycosides in grapes that produced wine smoke flavour significantly higher than non-smoke-affected control wines, and concentrations in grapes that produced wine with smoke flavour not significantly higher than control wines.
| Guaiacol (µg/kg) | o-Cresol (µg/kg) | m-Cresol (µg/kg) | p-Cresol (µg/kg) | GuRG (µg/kg) | CrRG (µg/kg) | SyGG (µg/kg) | ||
| Chardonnay -not significant smoke flavour | Range | <1.0 -9.0 | <1.0 -7.0 | <1.0 -7.0 | <1.0 -7.0 | <1.0 -8.0 | <1.0 -9.0 | <1.0 -101 |
| n=13 | Median | 3.0 | 3.0 | 1.0 | <1.0 | 2.0 | 3.0 | 34 |
| Chardonnay -significant smoke flavour | Range | 1.0-33 | <1.0 -11 | <1.0 -11 | <1.0 -11 | 2.0-18 | 3.0-27 | 32-868 |
| n=7 | Median | 14 | 10 | 6.0 | 2.0 | 11 | 11 | 136 |
| Pinot Noir -not significant smoke flavour | Range | <1.0 -3.0 | <1.0 -5.0 | <1.0 -1.0 | <1.0 | <1.0 -4.0 | <1.0 -7.0 | 1.0-31 |
| n=8 | Median | <1.0 | 2.0 | <1.0 | <1.0 | 2.0 | 3.0 | 3.0 |
| Pinot Noir -significant smoke flavour | Range | 2.0-26 | 3.0-15 | <1.0 -8.0 | <1.0 -3.0 | 3.0-19 | 6.0-49 | 22-456 |
| n=11 | Median | 10 | 7.0 | 2.0 | 1.0 | 6.0 | 13 | 86 |
| Shiraz -not significant smoke flavour | Range | 2.0-10 | <1.0 -3.0 | <1.0 | <1.0 | 2.0-23 | 1.0-12 | 3.0-164 |
| n=12 | Median | 5 | 1.0 | <1.0 | <1.0 | 5.0 | 3.0 | 15 |
| Shiraz -significant smoke flavour | Range | 4.0-59 | <1.0 -17 | <1.0 -3 | <1.0 -2 | 6.0-74 | 5.0-16 | 29-977 |
| n=10 | Median | 12 | 4.0 | 2.0 | <1.0 | 19 | 13 | 63 |
GuRG=guaiacol rutinoside, CrRG=cresol rutinoside, SyGG=syringol gentiobioside
Arguably, the most critical point to assess risk of smoke taint is when analysing grapes in the lead-up to harvest. This study provides for the first time, a guide for producers assessing smoke-affected grapes, based on wines produced under controlled standard winemaking conditions, stored for three years after bottling, and assessed by formal sensory methodology. These concentrations have been published for all smoke markers used when assessing grapes (Parker et al. 2025), Table 2 in this article summarises the key analytes which drive smoke flavour perception, and the reliable smoke marker compound syringol gentiobioside (SyGG).
What does this mean for wine producers?
The results of this study allow producers to compare results from testing smoke-exposed grapes and wines. Values above the concentrations found in non-smoke exposed grapes or wine are reliable indicators of smoke exposure (Coulter et al. 2022). The next step is to compare values to table 1 and 2 above. If values are above those in seen in grapes that produced wines that did not have significant smoke flavour, the resulting wine is at risk of being perceived as smoky, if produced according to standard winemaking protocols. If values are within the range seen for samples with both significant and non-significant smoke flavour, then there is a reasonable chance that the wine will have discernible smoke flavour, but the smoke flavour also may not be perceivable, due to masking by other flavours. In this study, the wines were produced with standard 50 kg winemaking protocol and no special effort to remediate the impact of the smoke. Better outcomes may be achieved by adjusting skin contact, fining with activated carbon, or other remediation measures (Mirabelli-Montan et al. 2021). A range of remediation options are summarised in the AWRI fact sheet ‘Smoke taint – practical options for grapegrowers and winemakers’ (AWRI 2025).
Conclusions
This study has established the concentrations of smoke exposure markers in grapes or wine which are likely to result in a noticeably smoky sensory character in aged wine for three major cultivars grown in Australia (Shiraz, Pinot Noir and Chardonnay). Growers and wine producers are now in a better position to assess the risk of producing smoky wines – even after low to moderate smoke exposure of grapes – based on analysis of grapes for volatile phenols and phenolic glycosides. These data are key to minimising production of unsaleable smoke tainted wine, while avoiding unnecessary grape and wine value losses from mis-classified samples.
Acknowledgements
The text and tables in this article have been adapted from an article published in the Journal of Agricultural and Food Chemistry (Parker et al. 2025).
This work was supported by Wine Australia, with levies from Australia’s grapegrowers and winemakers and matching funds from the Australian Government. Additional funding and in-kind contributions from PIRSA, AWRI, the South Australian, Victorian and NSW State Governments, Wine Victoria and NSW Wine are gratefully acknowledged. AWRI is a member of the Wine Innovation Cluster in Adelaide.
The authors thank their AWRI colleagues for technical assistance, particularly Desireé Likos, Adrian Coulter, Geoff Cowey, Matt Holdstock, Dr Patricia Williamson, Dr Damian Espinase Nandorfy, Sheridan Barter, Dr Lieke van der Hulst, Dr Mark Krstic, Dr Julie Culbert, Virginia Phillips, the flavour team, sensory panellists and WIC Winemaking Services. Affinity Labs (previously AWRI Commercial Services) are acknowledged for assistance with chemical analysis. Peter Leske, Ricky James and wine industry partners across South Australia, Victoria and New South Wales provided essential support for sampling, and Dr John Blackman and Professor Leigh Schmidtke of Charles Sturt University assisted with grape sourcing. This study used NCRIS-enabled ‘Metabolomics Australia’ infrastructure. Metabolomics South Australia is funded through Bioplatforms Australia Pty Ltd (BPA), and investment from the Government of South Australia and The Australian Wine Research Institute.
References
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