Investigations conducted during 2003 and 2004 into the nature and amelioration of taints in grapes and wine, caused by smoke resulting from bushfires

Peter Godden, Ella Robinson, Leigh Francis, Kate Lattey, Geoff Cowey and David Boehm.
The Australian Wine Research Institute (AWRI), PO Box 197, Glen Osmond, South Australia 5064, Australia

During the 2003 vintage, Industry Services staff spent a very large amount of time dealing with the issue of 'smoky' taint in grapes and wine resulting from the bushfires that occurred in Victoria and southern New South Wales in January and February 2003. Some additional work was also conducted in 2004.

The investigations, while by no means definitive in nature, indicated that exposure of grapes to bushfire smoke as early as veraison may cause levels of taint in the resulting wine which substantially reduces its commercial value. It is apparent that the taint compounds are present within the grape skin, and thus their extraction is difficult to avoid during winemaking, especially red-winemaking where extended skin contact is necessary. For white wines, winemaking treatments that minimise contact between juice and skin may be beneficial in reducing the intensity of any taint.

The Institute had previously been asked to consider if smoke resulting from controlled burning of bushland might result in a taint occurring in grapes in nearby vineyards, and had provided advice that there was a possibility that such a taint could arise. The results of these investigations provide conclusive evidence that tainting of grapes and wine by bushfire smoke can occur, and potentially have a major economic impact. Many affected white juices, wines and especially sparkling base wines, were deemed to be 'unfit for purpose' and were consequently severely downgraded in terms of value.

As Australian viticulture continues to spread into locations that might be considered as more bushfire-prone than many established grape growing areas, there is a possibility that smoke taint might become a sporadic but more common occurrence in the future. It is evident that few vineyards were actually damaged by the 2003 fires, but damage caused by smoke taint was widespread. It is therefore apparent that, in this situation, insurance cover for smoke damage would have been of greater benefit than for fire damage. However, while it appears that few growers had insurance cover for smoke damage, many do maintain insurance against contamination, and in the Institute's view guaiacol in grapes and wines resulting from the bushfire smoke, is a contaminant.

In spite of the fact that these investigations have greatly increased understanding of the nature of this problem, solutions remain elusive. However, the Institute has analysed a number of commercial samples that were purported to originate from reverse osmosis treatment of red wines, which was being applied with a view to reducing the intensity of the taint, and the concentration of guaiacol in the wines. The results demonstrated an apparent reduction in guaiacol concentration of approximately one third, in the two wines tested. Sensory analysis was conduced on pre and post-treatment samples of one of the wines, with the Institute's sensory panel rating samples that contained lower guaiacol concentrations as lower in smoke taint. It is possible that the process may also remove compounds other than guaiacol that may contribute to the perception of the taint. However, there were no significant differences between the panel's ratings of preference for the samples pre or post treatment. While the results of this trial are encouraging, the Institute advises persons who are considering the use of this technology commercially to conduct their own trials, conducting rigorous sensory evaluation on samples pre and post-treatment, and to have the samples independently analysed for guaiacol concentration.

The AWRI does offer an analytical service for measurement of key compounds responsible for smoke taints attributed to bushfire smoke (guaiacol and 4-methylguaiacol) with sensitivity to levels less than the sensory threshold, approximated at 6 µg/L. If you suspect your fruit has been affected by smoke taint, please contact Randell Taylor, Trace Analysis Laboratory Supervisor or our Customer Service on 08 8303 6600 or email Randell Taylor or the Analytical Service. Please refer to the AWRI website for more information including pricing and response time.

Please note that:

• For advice or sample containers contact the Analytical Service prior to submission of samples.
• Quarantine requirements regarding the importation of grapevine material from phylloxera infested areas to South Australia are available through Plant Health Operations, Primary Industries and Resources SA (PIRSA), contact Bruce Baker 1300 666 010.
• The Analytical Service will be closed between 23 December and 2 January 2007 and we will not be able to receive samples in this period.

A full copy of Industry Services' report can be found here (106kb PDF).