Workshop and review: Influence of smoke taint on wine grapes
Abstract
Workshop and review: influence of smoke taint on wine grapes.
Summary
Smoke from bushfires and prescribed burns of forests have over the years negatively impacted on the grape and wine quality in various regions in Australia and overseas. Large bushfires in early 2003 in north east Victoria caused considerable downgrading of fruit quality and initiated a program of R&D to investigate the issue and attempt to alleviate the effects of smoke taint. Bushfires have again impacted on north east Victoria, in 2006-07 growers were unable to salvage much of the crop leading to an estimated loss of value of wine of approximately $75-90m.
In response to industry concerns, the Department of Primary Industry was able to obtain funding from the Victorian Government for further R&D into the issue during and just after the bushfire period in 2006-07. In addition to the R&D program in north east Victoria, DPI organised and conducted a series of industry meetings utilising the resources of an R&D group from Western Australia who had also been dealing with smoke taint issues in that state. Around 130 people attended the four grower meetings held throughout Victoria, at Knoxfield, Milawa, Oxley and Nagambie, where they were presented with the most up to date information on smoke taint. The concentration of indicators of smoke taint in the grape (guaiacol and 4-methylguaiacol) was greater in the King Valley compared with the Alpine Valleys region and other regions in the state (e.g. Yarra Valley, Strathbogie Ranges, west Gippsland and Mornington Peninsula). Localities in the King Valley that were closer to the fires, and in locations where smoke naturally accumulated in higher concentrations, had higher levels of smoke taint compound in the fruit and wine.
Results from grape sampling suggested that uptake of smoke taint compounds by grapes was greatest during the immediate post-veraison period (as was suggested from WA R&D activities from smoke applied during the veraison to harvest period only) yet other sites did not show such a pattern. An early white grape, Chardonnay, and a later ripening red grape, Shiraz, showed similar patterns of uptake, but the rate of uptake of smoke taint compounds differed markedly between localities. The spatial patterns of variation in smoke taint compounds in grapes on individual vineyard blocks showed that those zones closest to the fires and the prevailing wind direction of the smoke had the highest values and there was potential for selective harvesting to separate relatively high and low smoke affected parcels of fruit.
The analysis of vineyard block variation has enabled optimum sample sizes to be calculated to get accurate estimates of mean smoke taint indicator compound values across a block.
Substantial variations in the uptake of smoke taint compounds into the grapes were observed between varieties with Sangiovese > Cabernet Sauvignon > Chardonnay > Shiraz > Merlot. The conversion of grapes into wine demonstrated variations in extraction rate of smoke taint compounds between varieties. Both wine and juice aroma and taste assessments correlated well with the measurements of principle indicators of smoke taint, guaiacol and 4-methylguaiacol, in both grape juice and wine. A commercial winery provided data on various options for minimising and/or mitigating smoke taint character in wines. Chilled grapes, early press fractions, hand harvested grapes, and charcoal fining of wine all contribute to minimising the development of smoke taint in the wine. Suggestions for further R&D to address the smoke taint issue were identified.
The aim is to continue on with this research and industry liaison effort throughout 2007/08, to continue to assist the Victorian and Australian Wine Industry in providing more insights into the management and mitigation of bushfire smoke impacts. This will involve close planning and collaboration between key researchers and industry personnel across Australia.