Improving our response to smoke taint

Wine Australia has partnered with several organisations over the last 10 years on smoke taint R&D. We now have a good understanding of the problem, which will help to develop some solutions.

In a nut shell, smoke tainted wines have high levels of volatile phenols and this makes them taste like smoked meat, disinfectant, leather, char, salami or an ashtray.

These compounds come from smoke and they are absorbed directly by grapes exposed to smoke. Some of these compounds get ‘detoxified’ by the grapevine into glycosylated precursors but can convert back, they act as a pool of compounds waiting to be released. The conversion back occurs in wine, which means that smokiness gets worse with time. It also occurs in our mouth thanks to our resident microbial population, that’s why smoke tainted wines can be described like ‘licking an ashtray’ – we are quite literally making the wines more smoky by putting them in our mouth.

Smoke exposure is most damaging from about a week after veraison through to harvest.

Its impact can be reduced by minimising extraction from skins by hand harvesting, keeping fruit cool and whole bunch pressing, or using oak to add complexity and mask some of the smokiness. The volatile phenols that make the wine taste smoky can be removed through reverse osmosis, but their precursors cannot so the problem comes back over time.

If your vineyard has been exposed to smoke after veraison, what can you do to assess the impact?

Doing a sensory assessment of the aroma of the juice alone won’t tell you much if anything about the precursors. We do know that these precursors are released during fermentation, so a small-lot fermentation a few weeks before harvest will allow you to assess how smoky the wines are likely to be. The details of this method, developed by the AWRI, are available here.

Australian Wine Research Institute (AWRI) Victorian Node Manager Dr Mark Krstic also suggests that the sector send grape samples for specific chemical analysis. ‘We are still promoting the need to conduct a mini-ferment in parallel, but also suggest sending a grape sample in for analysis’, he said. ‘That way you can have a wine sample for sensory analysis and a grape analytical result to make a more comprehensive assessment of the likelihood of being affected by smoke.

Since the Sampson Flat fire in the Adelaide Hills early last year, research led by the Victorian Department of Economic Development, Jobs Transport and Resources, in collaboration with the AWRI, has made progress in better understanding how smoke taint compounds are taken up by the vine.

The major entry pathway appears to be absorption directly into berries via the waxy cuticles. ‘This study revealed that smoke compounds may not be absorbed through leaves via stomates and then translocated to fruit as once thought’, Dr Krstic said.

‘This has really important implications in thinking about potential vineyard mitigation strategies that might be trialled in the future, such as spraying potential protectants onto grapes prior to a smoke exposure event.’

Updated smoke taint factsheets will be available in early 2016 and over the next two years the AWRI will expand the number of varieties on which it has background data from non-smoked years.

‘We already have data on Riesling, Chardonnay, Pinot Noir, Cabernet Sauvignon and Shiraz and will focus on adding Sauvignon Blanc, Pinot Grigio/Gris, Semillon, Grenache and Merlot to the list’, Dr Krstic said. ‘This is critical for making objective risk assessments.’

For further information about smoke taint support, please contact the AWRI helpdesk on (08) 8313 6600 or helpdesk@awri.com.au.