Background
Smoke from bushfires negatively impacts on the quality of grapes and wine by causing undesirable smoky flavours and aromas.
The impact of smoke from wildfires (compared to prescribed burns) is generally greater due to a combination of intensity, duration, topography and proximity to the fire.
What is known…
•Guaiacol and 4-methylguaiacol are two of the compounds associated with the smoke effect in fruit and wines.
•Fruit from grapevines has shown the highest sensitivity to smoke-effect at seven days after the onset of ripening1 .
•Repeated and longer exposure to smoke results in increased levels of guaiacol and 4- methylguaiacol through a cumulative effect1,2 .
•Levels of “smoke” compounds can increase in wine over time due to these compounds becoming released from bound forms.
•Some techniques can reduce the “smoke effect”. They include hand harvesting of fruit (to reduce contamination from leaves), chilling grapes after harvest, altering strength and duration of grape pressing time and reverse osmosis treatment of the wine2 .
•No carry over effect from one growing season to another.
Currently unknown…
A large collaborative approach is currently being undertaken across Australia to solve the issue of smoke effect on grapes and wine.
This includes research on controlled experiments in field, glasshouse and laboratory as well as samples of grapes taken from vineyards affected by prescribed burns and wildfire situations.
Specifically, research focuses on:
•Investigation of compounds contributing to smoke effect – Department of Agriculture and Food WA (DAFWA) and University of Adelaide.
•Identification of guaiacol glycosides and other precursors or smoke compounds in grapes and wine, and their expression in the wine - University of Adelaide.
•Extractability of smoke compounds into wine in relation to management processes (such as hand harvesting, duration of skin contact and pressing of grapes after fermentation) - AWRI.
•Location of smoke compounds in grapes and vines and their mode of smoke entry into grapevines and fruit – DPI Victoria.
•Effect of stage of development and variety on susceptibility of grapevines to smoke taint – DAFWA, Curtin University of Technology, the University of Adelaide and DPI Victoria.
Information gathered from current research will assist the development of an impact assessment tool for growers and land managers to use in setting and achieving controlled burning objectives.
Summary
As we move into a hotter drier climate, smoke from bushfires and prescribed burns will become more prevalent. The combined efforts of research agencies, land managers and the grape and wine industry across Australia are essential to enable the future management of smoke taint by the grape and wine industry in Australia and overseas.
Acknowledgements
We would like to acknowledge the hard work of all the research and funding bodies working towards understanding the impacts of smoke on grape and wine quality.
Photos:
Courtesy of Stephen Lowe (King Valley Vignerons).
