The effects of fire and smoke are an increasing problem for global wine regions under a warming climate, with many wine companies rating smoke taint as their greatest environmental and economic risk. Although research over ten years has contributed greatly to our understanding of smoke taint, the Australian wine sector had a very limited number of unselective, generally ineffective options for remediation. A project to address such gaps was funded in Round 2 of the Australian Government Department of Agriculture Water and the Environment Rural R&D for Profit program and ran from July 2016 to February 2020. Outcomes are detailed in the overall project report from Wine Australia to the Commonwealth and in constituent project reports from La Trobe University (LTU 1601) and the Australian Wine Research Institute (AWR 1603).
The exposure of vineyards and grapes to smoke from bushfires and/or controlled burn events may result in ‘smoke-tainted’ wine, which can cause serious economic losses to industry. Between 2003 and 2015, major fire events in Australia resulted in over $400 million worth of grapes being lost or downgraded due to smoke taint. As bushfire frequency and severity are only expected to increase under climate change scenarios, it is important that the Australian wine industry develops novel tools to manage smoke-affected grapes and wine.
The key objectives of the project were to:
1. Develop an improved early warning system for smoke exposure in vineyards
2. Understand how smoke dose and composition link to levels of smoke taint compounds in grapes and wine and to sensory outcomes in wine
3. Investigate practical options to prevent or limit smoke taint compounds being absorbed by grapes in the vineyard
4. Improve analytical methods of assessing the risk of smoke taint in both grapes and wine
5. Evaluate remedial management options for dealing with smoke-affected grapes and wine in the winery.
A network of seven remotely accessible smoke detectors was set up across wine regions of Victoria and was operational from the controlled burning period of autumn 2017 onwards. The network proved to be effective for monitoring widespread smoke events during the growing season. In addition, roving detectors were used to take smoke dose measurements at and around controlled burns in Victoria and during bushfires in three states from 2018-2020, along with smoke composition data and grape uptake of smoke taint compounds. Wines were produced from smoke-exposed grapes to assist with developing thresholds for smoke taint.
Together, this data allowed the establishment of some key relationships between smoke measurements and levels of smoke taint compounds in grapes and wine. Development of smoke taint is site-specific and depends on the proximity of a vineyard to a burn or bushfire, the intensity of the fire, the age of the smoke and the prevailing weather conditions. Smoke haze from old smoke from controlled burns was not shown to be sufficient to cause smoke taint.
Since smoke taint compounds occur naturally in grapes at low concentrations, it is important to know background concentrations when assessing whether grapes have been exposed to smoke. Extensive sampling across the country allowed for the expansion of baseline concentration data of smoke taint compounds in both grapes and wine to be extended to 12 of the main winegrape varieties grown in Australia.
A total of 21 different barrier-type materials were tested for their ability to protect grapes from smoke taint compounds in the vineyard. Treatments typically did not provide any significant protection and often increased the uptake of smoke taint compounds by grapes. Only one product — chitosan — a biopolymer extracted from fungi and shellfish, was effective as a protective coating on grapes. Adsorption of smoke taint compounds onto the berry skin was found to be rapid and generally complete within a day of smoke exposure.
This project also evaluated a range of remedial treatments for dealing with smoke-affected grapes and wine. Fifteen commercially available activated carbons were tested, along with five commercially available enzyme treatments. Chemical and sensory evaluation showed that carbon treatment was able to reduce smoke taint in wine, especially when added to grape juice prior to fermentation. Results were dependent on the type of carbon product used, the matrix (juice versus wine; red versus white wine) and the dose applied, and desirable aroma and flavour compounds were often also removed. Enzymes only removed certain classes of smoke compounds but may be effective for certain wine styles when combined with carbon treatment.
Blending was shown to be an effective option for remediation of smoke-affected wine. A blend of 25% or less of smoke-affected Pinot Noir with unaffected wine was sufficient to reduce sensory perception of smoke taint to the same as the control wines. Consumer tasting studies showed that wine preferences are highly variable. Some people are either not sensitive to smoke or enjoy the sensory characteristics it provides and for others, even a small proportion of smoke-affected wine in a blend can significantly affect liking.
Recommendations arising from the project are that:
• Future projects place heavy emphasis on sensory testing to link all data collected from smoke events to smoke taint, to define smoke thresholds to predict the risk of smoke taint and to define sensory thresholds for a range of varieties and wine styles
• A smoke taint risk assessment tool be developed for the wine industry. This would involve establishment of a national network of smoke detectors, which provides real-time measurement of smoke compounds in the air, is readily accessible to industry and can convert smoke exposure levels into smoke taint risk
• Field testing of chitosan be carried out to develop it as a product which could be practically and economically applied as a spray to protect crops in the event of smoke
• Evaluation of commercially available enzymes, activated carbons and other emerging mitigation technologies be continued for use by winemakers.
The significant benefits for the wine sector which arose from this project have already been realised, particularly in the context of the 2019/20 bushfires. The research teams provided extensive on-the-ground support and information to the sector during and after the fire events in SA, NSW and Victoria this season and following the Tasmanian bushfires of 2018/19. Uptake of findings, especially regarding testing of grapes for exposure to smoke and treatment of smoke-affected wine with activated carbon or by dilution, has been significant. Wine made for this project is being used in regional training workshops, to aid winemakers with the detection and mitigation of smoke taint. Grapes and wine sourced during the 2019/20 season are a valuable resource for future studies.
The success of this project was made possible through many collaborations with researchers at Agriculture Victoria, La Trobe University, the Australian Wine Research Institute, University of South Australia, University of Adelaide, University of Melbourne, Metabolomics Australia, the University of Nottingham and the Cooperative Research Centre for Polymers. Grape growers and wine industry partners across wine regions of Australia were key to provision of access to vineyards for smoke monitoring and collection of grape samples and commercial winemaking, as were wine industry suppliers in Australia and overseas. The project also relied heavily on partnership with public land management agencies throughout Victoria, including the Country Fire Authority Victoria, VicForests and the Department of Environment, Land, Water and Planning (DELWP).
This project was funded by the Australian Government Department of Agriculture Water and the Environment Rural R&D for Profit program with co-investment from Wine Australia, La Trobe University, the Australian Wine Research Institute and the Department of Jobs, Precincts and Regions in Victoria.