Research adds to smoke exposure “grey zone” understanding

A recently completed research project has added greater understanding of the “grey zone” of smoke exposure.

The project was part of a co-ordinated program of work that was carried out across multiple sites. It tested the hypothesis that markers of smoke exposure measured in grapes would provide an indication of smoke compounds in finished wine. 

“Following the 2020 bushfire event it was important to establish the levels of smoke exposure at which it may still be possible to make acceptable wines – i.e. the ‘grey zone’ of smoke exposure,” said project lead Leigh Schmidtke, Professor of Oenology at Charles Sturt University’s Gulbali Institute.

The research confirmed that grape markers are a useful measure of smoke exposure, and indicate to some extent the levels of smoke-derived compounds in wine made from grapes with low to moderate levels of smoke exposure.

“We found a positive correlation between the levels of smoke taint markers, especially the total glycoside concentration, and their counterparts in finished wines.

“This demonstrates that at low to moderate levels of smoke exposure, as measured by phenol glycosides in grapes, good correlations for the corresponding wine markers exist,” said Leigh.

The project also confirmed previous findings: that by applying modified winemaking techniques to reduce skin contact and extraction, it was possible to reduce the concentration of smoke exposure marker compounds in the final wine.

“For example, limiting juice extraction techniques, i.e. reduced pressing yields in white grapes, or limiting time on skins in the production of rosé, may reduce the level of smoke-derived compounds in the wine. This suggests that there is a level of markers in the grapes that are inherently associated with grape skins.”

Leigh said this technique was especially helpful for Chardonnay wines when press fractions were reduced. “Although Chardonnay has a relatively low fruit intensity, the results showed that with judicious winemaking aimed at reducing skin contact and pressing yields, it may be possible to produce acceptable wines, provided that the smoke exposure level was low to moderate at most.”

However, rosé wines lacked sufficient fruitfulness to enable a satisfactory winemaking outcome and had overt smoky characters, compared to their table wine counterparts. This was especially evident in wines made from Pinot Noir grapes. Leigh said that acceptable Pinot Noir wines were challenging to make “regardless of the wine making approaches and level of grape glycosides and hence smoke exposure.”

This result reflects the general finding that obvious fruit characters (e.g. red and dark fruit) tend to have a masking effect on the smoke aroma and flavour in wines made from grapes produced from low-moderate levels of smoke exposure. 

“This means that in addition to the levels of grape glycosidic markers, winemakers need to understand how grape composition – apart from smoke derived compounds and wine making decisions – impact the level and intensity of fruit flavours in wine.” 

Shiraz grapes with low to moderate levels of smoke exposure may still have the potential produce wines without perceptible smoke characters.

Importantly, Leigh said acceptable wines were made from grapes that imparted sufficient fruit flavours to balance smoke derived compounds.