Fight against smoke taint boosted

King Valley vineyard affected by smoke taint

At a glance

• New Centre for Expertise in Smoke Taint Research has been established in Mildura.
• Smoke taint in wine to become an increasingly serious issue due to the increased threat of bushfires due to climate variability.
• Web-based risk assessment tool being developed to help guide prescribed burns.
• New method found to detect smoke taint prior to harvest.
• Investigations now determining shelf life of smoke tainted wines.

The devastating effects of smoke taint on Victoria’s wine industry are set to be minimised thanks to new developments at DPI, including $4 million in funding for the Centre for Expertise in Smoke Taint Research.

This new venture, based at Mildura, will aid research already underway, including work identifying the chemicals associated with smoke taint to help growers decide whether wine grapes are worth harvesting and processing for wine making.

The centre will also boost research into the best times of year for prescribed burning to reduce the impact of smoke on vines.

DPI group leader Dr Davinder Singh said the centre came out of an election promise of the Victorian Government, after the wine industry lost over $300 million as a result of bushfires in 2007 and 2009.

Fire approaches during the Victorian bushfires, 2007

Destruction of wine grapes, reduced wine production and reduced market shelf space all contributed to losses.

“The wine made from the grapes exposed to bushfire smoke had a really nasty aroma and taste. For example, bacon, leather, barbeque and disinfectant — basically any bad smell you can think of,” Dr Singh said.

Ultimately, the affected wine could not be sold. Dr Singh said the problem of smoke taint was not a one-off.

“This problem is not going away. With climate variability this problem will probably be exacerbated because we’re going to have 45 per cent more days where our chance of bushfires is very high.”

He said the Royal Commission into Victoria’s 2009 bushfires recommended a tripling in the area of prescribed burning to reduce the risk of devastating bushfires.

Increasing prescribed burns, however, could also increase smoke taint.

In response to the recommendations, DPI is determining a timeline for land managers of when they can burn without negatively impacting on wine grapes.

Taste test: smoke taint can affect the taste of wine but it is not always detectable

Dr Singh said currently there is little information available about when grapevines are more sensitive to smoke.

He said one publication had looked at Merlot grapes, citing the development after the onset of ripening to harvest as the critical time.

“We don’t know whether all varieties do the same thing, so we’re trying to find that out.”

As well as creating a web-based risk assessment tool, the project team are also developing an analytical method to detect the chemicals that constitute smoke taint.

“We’re trying to find what’s in the smoke, what gets into the grapes and what goes into the wine,” Dr Singh said.

He said finding the relevant chemicals in smoke was extremely difficult because when plant material burns, hundreds of different chemicals are released.

“What we are trying to do is to find the major ones and see whether these are taken up by the wine grapes and how that might translate into smoke taint in the wine.”

“All of these chemicals have a threshold value — below that you can’t smell or taste it.”

He said the difficulty lay in the fact that different people had different thresholds.

Dr Singh has spent the last two years working on developing an analytical method to detect those chemicals.

“At that time we could detect these chemicals only in the free form, but didn’t have a method to detect the chemicals in the sugar-bound form.”

The sugar-bound form refers to the chemicals before processing.

This means that at times grape growers are not able to detect smoke taint until they have picked and processed the grapes into wine.

Researchers collected Chardonnay, Merlot, Shiraz, Sangiovese and Cabernet Sauvignon fruit following bushfires in 2006–2007 in the King Valley region and from experimental field trials in Western Australia (Department of Food and Agriculture), making wine from a number of the samples.

Typically, grape growers and winemakers have relied on two smoke taint related markers, guaiacol and 4-methyloguiaicol measurements, to determine smoke exposure of grapes.

But these measurements do not always correlate to the extent of taint in the finished wine.

Researchers compared and validated several analytical methods, but ultimately found that where smoke-affected grapes contain low levels of the two key markers, methods that quantified their sugar-bound forms (prior to processing) provided the best indication of the extent of smoke taint.

The findings confirmed that guaiacol and 4-methyloguiaicol indicated smoke taint, with much higher levels recorded in smoke affected fruit.

The levels of these chemicals increased over time during bottle storage.

Researchers also found that certain grape varieties had different levels of taint, suggesting different sensitivity to smoke uptake, or possibly mechanisms to exclude it, metabolise it or store it as bound chemicals.

DPI is now working on experiments to determine the shelf life of smoke tainted wines and also what options there are for growers to market wine with small levels of smoke taint in short time frames before taste became an issue.

The results of the research to date have been published as two articles in a special issue of Australian Journal of Grape and Wine Research 2011.

Further Information - watch one of our Farmview Videos (Series 1 Episode 5) on understanding smoke taint