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Researchers working towards smoke taint answers

GRAPEGROWERS in the northern Adelaide Hills are only just beginning to understand the full impact of the Sampson Flat bushfire, five months on.

By Clare Peddie

While many can finally breathe a sigh of relief, others face the prospect of pouring their hard work down the drain.

Smoke leaves an invisible trace that remains hidden in the grapes, bound up with sugars, until it is released during fermentation and storage.

University of Adelaide Associate Professor Kerry Wilkinson says it is “a very complicated process” that had scientists baffled at first.

“From all of the research that’s been done over the past 10 years, we have a much better understanding of what the problem is,” she said.

At a public talk held last night in the Research Tuesday series, Associate Professor Wilkinson described the work done to date.

Techniques for detecting and measuring smoke taint precursor compounds in grapes, juice and wine are now available at the Australian Wine Research Institute.

They give growers and winemakers a red, amber or green light to help them decide whether to proceed with fermentation.

The Institute also recommends small-scale ferments of potentially affected grapes, in an attempt to better understand the actual impact on the final wine.

But recent research at the University has revealed some grape varieties only reveal their smoky off-flavours and aromas at fermentation when they are fully ripe.

Wine tasters have identified aromas including ‘burnt’, ‘smoked meat’, ‘leather’, ‘disinfectant’, ‘charred’, ‘ashtray’ and ‘salami’.

Methods of reducing smoke taint at the vineyard include leaf removal, high-volume cold-water wash, hand harvesting and avoidance of leaf matter in the grape load.

Scientists have also tried different winemaking yeasts, oak and tannin additives, fining agents and processes such as reverse osmosis to remove the offending substances.

But the ultimate goal is to permanently bind or lock up the smoke-taint chemical and render it inactive.

Experiments with purpose-built smoke tents show just how sensitive the grapes can be.

“Depending on the experiment we are doing, we might expose the grapevines to the smoke for anywhere between 30 minutes to one hour,” Associate Professor Wilkinson said.

“It’s fairly dense smoke but that’s sufficient to taint a wine. You then harvest the grapes two to three months later and make wine from it.”

Grapes are most sensitive as they ripen, in the days and weeks leading up to harvest.

The Sampson Flat bushfire took place towards the end of the growing season, at a crucial time.

But it is difficult to predict how individual growers will be affected, Associate Professor Wilkinson said.

“There will be pockets, areas in the Adelaide Hills where the smoke hung around,” she said.

“There might be valleys, where the smoke got caught up in the valley and there wasn’t any airflow or wind to take it away, so the smoke hung around the vineyard for longer.

“Then there will be other areas that weren’t affected, or the smoke might have blown through but it was only partial exposure, where there’s no impact at all.”

Adelaide Hills Wine Region chairman Tom Keelan said the wine making process had to run its course before growers would know if their fruit was clear of smoke taint.

“It’s really isolated to that northern pocket of the Adelaide Hills, the rest of the Adelaide Hills had probably the best vintage of the last 10 years,” he said.

“That’s where it’s such a bitter pill for these growers to swallow, they were sitting on a potential goldmine in terms of fruit quality and yield. To have it affected by such a tragedy as a bushfire highlights the fact that as an industry and as a region we need to learn more about it. That’s why this seminar is so important.”

He is busy crunching the numbers from a survey of growers, in order to “ascertain the economic footprint” and go to the State Government for assistance with low-interest or no interest, long-term loans for those worst affected.

One Hills grower, who did not wish to be named, reported losses of $500,000 after the Sampson Flat fire.

Mr Keelan said it was reasonable to expect losses to the region in the “tens of millions of dollars” from wasted grapes, but there was a “ripple effect” through the industry, including losses to premium wine sales.

The South Australian wine industry as a whole produces $1.87 billion worth of wine every year.

University of Adelaide Wine Economics Research Centre executive director Professor Kym Anderson said bushfires were sporadic so the cost to the industry would depend on the circumstances.

“There’s no average cost,” he said.

“But you’d be running into tens of millions for a major event.”

AWRI industry development and support group manager Con Simos said the first official recognition of smoke causing taint in wine was back in 2003 with the Eastern Victorian (Alpine) Fires, which burnt more than 1.3 million hectares. With climate change bringing more bushfire weather, the issue is permanently “on the radar”.

“Yes we’ve done a lot of testing,” he said.

“We have worked very, very closely with industry this year on smoke. It’s an issue that’s not going to go away … We’re going to see potentially more and more conditions that are going to favour these sorts of events.”


This story was originally published in The Australian.

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