Smoke taint in wine at-a-glance
Smoke taint is considered relatively rare and will not automatically affect wineries and vineyards near to a fire. Wind direction and how long smoke lingers in an area are key factors.
Unharvested grapes that have been through the colour change or ripening process – known as veraison – are most at risk, but it can be hard to spot problems before fermentation.
Smoke taint aromas in wine include:
- plastic or chemical smell
- medicinal aromas
- wet cigar or ash aromas
It is not harmful to health in the wine itself, according to current research, although smoke can of course pose air quality risks for vineyard workers.
Some observers have questioned whether large wildfires are the ‘new normal’ for California, as firefighters battled to save lives and property by containing several blazes across the state, including the Kincade fire in northern Sonoma County.
While the safety of people, communities and property are naturally paramount, outbreaks of large wildfires in recent years have seen the potential issues posed by smoke taint become a bigger topic within California wine.
UC Davis said in 2018 that it was researching better ways to mitigate the effects of smoke taint, following the devastating wildfires of 2017.
That is not to say, of course, that recent California wine vintages have been ruined by smoke taint. It is a big place and while a few producers have reported issues for the 2017 wines, many have not had any problems.
Nor is California the only at-risk wine region.
What are the risk factors?
‘While the physical loss of vines is an obvious consequence of a fire, smoke taint can also be an issue and can have a negative effect on the wine,’ said Michael Hill Smith MW, responding to a Decanter reader’s question in 2016 about Australian wildfires.
‘Compounds in the smoke can be absorbed through the grape skin, particularly if the fire occurs close to harvest,’ said Hill Smith, now co-chair of the Decanter World Wine Awards.
A key factor is therefore whether or not grapes have been harvested, as well as the length of time that vines are exposed to smoke.
California’s Wine Institute said that 90% of grapes had been harvested prior to the fires of 2017, for example, while Sonoma County Vintners said last week that a ‘vast majority of grapes’ had been picked before the Kincade Fire started.
Smoke taint risks are also lower if grapes have not yet started ripening process – including colour change – known as veraison.
Burning wood releases volatile phenols that can be absorbed by grapes and which then bind to molecules in the grape in a process known as glycosylation.
Problems can then occur later in the cellar.
‘Although the compounds do not contribute to grape aroma in the glycosylated form, the free volatile phenols can be released throughout winemaking and wine ageing to produce undesirable “smoke tainted” wines,’ said a team of mostly-UC Davis researchers in a new study published this month.
Writing in the American Journal of Enology and Viticulture, they sought to measure the release of 31 different ‘phenolic glycosides’ during the winemaking process, finding that the first half of fermentation appeared to be the most critical period.
Tasting smoke taint in wine
The Australian Wine Research Institute (AWRI) found more than 50 compounds linked to smoke taint in wine in a 2009 study.
It quoted winemakers describing overly smoked aroma in the wines, or that some contaminated wines were like ‘licking an ashtray’.
Other key aromas linked to smoke taint issues include medicinal / sticking plaster, chemical and wet cigar flavours.
A winemaker can ferment a small batch of grapes to see whether smoke has contaminated them. If grapes do show signs of smoke taint, winemakers may choose not to pick that section of vineyard.
Grape samples can also be submitted for chemical analysis, according to AWRI.
Several studies have sought to identify the main compounds responsible, with ‘guiacol’ named as a lead protaganist by researchers in a 2019 article in the South African Journal of Enology and Viticulture.
However, it needed accomplices – namely other phenols – to cause smoke taint aromas, they said.
See also: Why Touriga Nacional is a rising star