This project was initiated by Wine Australia following the catastrophic bushfires of 2019-20 across Victoria and NSW, which provided a unique opportunity to collect grapes and make reference wines for this and future projects on smoke taint. A collection of 91 wines and a large set of smoke, grape and wine data were generated, which added to previous work linking smoke dose and composition, grape phenol levels, wine phenol levels and sensory outcomes for taint. Previous correlation was confirmed, showing that smoke dose can provide an indicator of smoke taint risk. A winemaking trial showed the influence of skin contact time on levels of smoke taint compounds in finished red and white wines. Pre-veraison analysis of some taint compounds can be used as a predictor of taint at harvest and research also showed how the levels of specific phenolic marker compounds in smoke change with smoke movement and distance from fire.
The summer of 2019-20 saw an unprecedented scale and intensity of bushfires across Australia, with severe impact on the grape and wine sector. This project aimed to capitalise on the important smoke, grape, wine and other air quality data resources from the catastrophic bushfires in Victoria and NSW in 2020, to aid in our understanding of smoke taint.
Through highly coordinated collaboration between industry (Chrismont Wines) and La Trobe University, 91 vintages of wines were made from fruit subjected to different levels of bushfire smoke. Wines were made in the King Valley using a standardised commercial winemaking process with minimal intervention, to ensure that wine composition can be characterised accurately against smoke taint in future sensory studies.
Cumulative smoke doses calculated from 13 smoke detectors placed in smoke zones from bushfires in December and January in Victoria were used to select the regions to access wines for this study. Where necessary, supplementary data was obtained from state air quality sensors used for public health. Results showed an excellent spread of cumulative smoke dose, which meant a consistent spread of phenols in the grapes and final wines across the eight key varieties in the study.
Of priority were smoke levels that would produce wines in the ‘grey zone’ for assessment of smoke taint, as it is this zone which provides the most uncertain outcomes for grapes and wine. Improving these thresholds for industry will support downstream decision-making and the development of an early warning system for smoke taint risk. This is the key task of a parallel project which is making use of all data from this project as well as data from bushfires and controlled burns which have occurred in Australia since 2016.
This project achieved its objective to correlate smoke, grape and wine data from 91 vintages of wines made from fruit subjected to different smoke levels. Analysis showed that smoke dose correlates well with smoke, grape and wine phenol composition. This augments previous studies which showed that the smoke dose to which the grapes are exposed is a reliable indicator of smoke taint in wine. Additionally, the project showed how the levels of specific phenolic marker compounds in smoke change with smoke movement and distance from fire.
Results also showed how traditional ‘no skin’ fermentation for whites and fermentation on skins for reds affects the levels of smoke taint compounds in wine. A Shiraz winemaking trial showed that increasing the amount of time on skins elevates the levels of smoke phenols in wine, which has a sensory impact when the wine is consumed.
Preliminary tasting of the wines produced in this project showed that the desired outcome of producing a reference set of wines for future studies in Australia was achieved. These wines are now in an optimum state to be rated by industry in professional sensory studies for smoke taint. The collaboration with industry has been the key success factor behind the outcomes to date and the completion of successful sensory studies should, for the first time globally, see a new smoke warning system and new risk thresholds established for smoke taint.
This project was funded by Wine Australia as part of emergency support provided in response to the catastrophic bushfires which occurred in south eastern Australia in 2019-20.