With the devastating bushfires of 2019–20 still firmly etched in memory, and the return of El Niño, grapegrowers will understandably be nervous heading into a hot, dry, bushfire-prone summer.
However, a comprehensive research program undertaken in the wake of the 2019–20 bushfires provides growers with a measure of reassurance.
Bushfire recovery funding from state government programs was leveraged to support R&I activities by a number of research organisations including the Australian Wine Research Institute (AWRI), La Trobe University, Charles Sturt University (CSU) and The University of Adelaide. Results from this work not only improve the sector’s response to major smoke events but also maintain Australia’s position as a global leader in smoke taint research.
The focus of research at the AWRI was on early season smoke exposure and baseline levels of smoke markers in winegrapes. In addition, the opportunity to make wine from grapes with various smoke exposures contributed to knowledge on how much is too much for sensory perception in wine.
“We can now answer the question about what concentrations of smoke markers are a concern – at least for the varieties we studied, which are Shiraz, Pinot Noir and Chardonnay,” said chief investigator Mango Parker, senior research scientist at the AWRI.
“This means that more accurate decisions can be made about smoke-exposed grapes; and fewer grapes will be unnecessarily rejected.
“Importantly, it also means that less smoky wine will be unintentionally produced.”
This new knowledge helps put Australian producers in a strong position to manage future smoke events and base their decision-making on the latest evidence.
Following the bushfires of 2019–20, growers and winemakers were trying to decide what to do with grapes that had been exposed to smoke from bushfires across the country. The AWRI’s commercial laboratory alone received 4,800 grape samples for smoke analysis, which includes both volatile phenols and phenolic glycosides.
“Everyone was asking about what concentrations of smoke markers in grapes could be tolerated to produce acceptable wine,” recalls Mango. “Previous research was focused on highly smoke-affected grapes and wine, but there was a gap in the knowledge about the concentrations of smoke markers that would produce a commercially acceptable wine, or an unacceptably smoky wine.”
The research team collected a total of 65 Shiraz, Chardonnay and Pinot Noir grape samples from vineyards exposed to bushfire smoke, as well as unaffected vineyards, in New South Wales, South Australia and Victoria. The smoke-affected fruit had been impacted by various smoke events, ranging from mild to heavily smoke-exposed. Unoaked wines were then produced under controlled conditions.
Smoke aroma and flavour were assessed by a trained panel, and the sensory results were compared to grape and wine composition.
The research team found that many of the wines had significantly higher smoky flavour than clean controls. However, some smoke-exposed wines did not have significant smoky flavour.
“As a result, a high-risk zone has been defined above which all wines were significantly smoky, and a moderate risk zone where some wines were significantly smoky and others were not,” said Mango.
There is an opportunity to remediate those in the moderate or "grey" zone using winemaking techniques such as minimising skin contact.
The research team also found that average consumer acceptance decreased with increased smoky flavours in wine from smoke-exposed grapes.
“Some consumers disliked wines with even low levels of smoky flavours; which was in line with the smallest differences detectable by the trained panel. This told us that some consumers are as sensitive as experts to the smoky flavours from smoke-exposed grapes, and dislike them,” said Mango.
Want to learn more about managing smoke-exposed fruit? The AWRI and Wine Australia have a comprehensive collection of resources available for growers and winemakers.