Jacques-Olivier Pesme, University of British Columbia, Wine Research Center & University of Adelaide
Let me share some comments about the effects of smoke taint, based from a research conducted at the University of British Columbia (UBC), located in a region where forest fires occurred regularly during the summer season.
Smoke-taint is a wine defect that may occur when ripening grape crops absorb volatile phenols (VPs), compounds associated with the negative sensory attributes of smoke-taint, due to exposure of grapes to wildfire smoke.
Researchers and vintners around the world are increasing focus on understanding smoke taint and investigating ways to evaluate its risks. One of the key aspect of the research is to develop methods to identify regionally specific molecules involved in smoke residues. Wherever they are located, this allows producers to predict the degree of smoke taint in wine from the chemical composition of smoke exposed berries, thus enabling them to minimize economic and quality impacts of smoke exposure.
This research is conducted by Wesley Zandberg from UBC with some extensive collaboration with the University of Adelaide (Australia) and UC Davies (USA).
Here is what we know from the research
1. The presence of ash on the berries does not guarantee you will have smoke-taint. Nor does the absence of ash mean you will not have smoke taint.
2. Washing the berries after smoke-exposure (via overhead irrigation) will not decrease the risk of smoke-taint.
3. Testing for smoke-taint marker compounds can be done immediately after smoke exposure, rather than waiting until close to commercial maturity.
4. There is no evidence of carry-over effects in the vine from year-to-year (i.e., you can't taste last year’s taint in the grapes).
5. Evidence from the research suggests that smoke taint presents itself in a regional fashion: both the levels of volatile phenols and the way in which they are biochemically transformed/ stored within grapes appears to vary from region to region.
6. Current research does not provide any clear evidence that one varietal is more susceptible than another. There is anecdotal evidence that Cabernet Franc and Pinot Noir are preferentially impacted, but such claims have not been rigorously substantiated.
7. There are a variety of viticultural techniques (e.g., canopy trimming, early harvest) and vinification practices (e.g., reverse osmosis, specific fining agents) that have been investigated to mitigate smoke-taint, but they have not been widely implemented and their efficacies in the scientific literature (and anecdotally) are, at this point, still inconsistent
8. Evidence from experience and literature shows that smoke taint in wine arises from very close exposure of vines to wildfire at very specific stages in berry development.
9. Reverse osmosis to reduce the intensity of the perceptible smoke-taint
10. Mounting evidence that the intensity of perceptible smoke-taint frequently increases in bottle, even after reverse osmosis.
For further information, see W. Zandberg ‘Development and evaluation of a vineyard-based strategy to mitigate smoke-taint in wine grapes’, Journal of Agriculture and Food Chemistry, 2019
[Source cover picture : https://www.adelaidehillswine.com.au/fireappeal/ ]