A promising new technology could help grapegrowers recover from smoke taint in the wake of fires.
University of Adelaide researchers say this could be the solution for a problem that has led to ruined and smoke-affected fruit, and in some cases, the loss of whole vineyards.
In a study published in Australian Journal of Grape and Wine Research, lead researcher and author Kerry Wilkinson, from the School of Agriculture, Food and Wine, said there was promising results from the use of activated carbon fabric bags in preventing the uptake of smoke by grapes.
"These prevented more than 95 per cent of the aromatic compounds responsible for unpleasant smoky, ashy flavours associated with smoke taint from getting into grapes during exposure to smoke," she said.
"Smoke taint occurs because volatile compounds present in smoke are absorbed by grapes when smoke from bushfires drifts into vineyards and lingers for prolonged periods of time.
"It can greatly alter the composition and sensory properties of wine, leading to unpleasant smoky, medicinal and burnt rubber aromas and flavours - and a drying, ashy aftertaste."
In 2020, bushfires resulted in an estimated 4pc of Australian wine grapes being lost because of smoke taint - while in the United States, some of the largest wildfires in California's history led to grape yields being down by nearly 14pc.
The study was initiated by Peter Michael, founder of the Peter Michael winery in Sonoma County, California, and involved the application of smoke to bunches of Mataro grapes, some of which were first enclosed in bags made from different activated carbon fabrics (felt, light cloth and heavy cloth).
Sensory analysis was performed on resulting wines and found those made from grapes that were enclosed in AC fabric couldn't be differentiated from control wine - made from grapes which hadn't been exposed to smoke.
Professor Wilkinson said there were drawbacks to the application of this strategy on a widespread basis.
"There are several shortcomings that we still need to overcome: first, the AC fabrics studied were prone to tearing and had to be handled carefully to avoid damage," she said.
"Also, labour cost (of) applying AC fabric bags to individual grape bunches on a commercial scale is prohibitively expensive and probably viable only for ultra-premium grapes at this stage."
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But she said these results demonstrated a proof-of-concept, and they hope to develop a more functional, cost-effective application for use in commercial vineyards.
One plausible option suggested might be more durable AC-based netting that could be applied to the grapevine fruit zone.
This would be far more cost-effective and offer dual protection from birds - but Prof Wilkinson said any impact on photosynthesis, fruit composition and disease pressure resulting from shading and diminished air-flow would need to be studied.
The potential for AC fibre residues to remain in either the vineyard or in finished wine also needed to be evaluated.
"Nevertheless, use of AC fabric offers the most promising vineyard-based strategy so far for overcoming the issue of smoke taint," Prof Wilkinson said.
"It could address a problem that has become a blight for producers globally. Initial uptake of smoke volatiles by grapes would be preferable to other strategies that ameliorate smoke-tainted grapes or wine and which are associated with potential loss of desirable wine constituents."
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