When smoke gets in your vines

University of Adelaide researchers have found a promising new technology for overcoming smoke taint in grapes – a serious issue for grape and wine producers worldwide in the wake of recent devastating fires that have led to ruined and smoke-affected fruit and in some cases the loss of entire vineyards.

“We investigated the use of activated carbon (AC) fabric bags to prevent 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,” said lead researcher and author Professor Kerry Wilkinson from the School of Agriculture, Food and Wine.

“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 4 per cent of Australian wine grapes being lost because of smoke taint - while in the US, some of the largest wildfires in California’s history saw grape yields down by nearly 14 percent.

“These results demonstrate proof-of-concept, and we now hope to develop a more functional, cost-effective application for use in commercial vineyards.”Professor Kerry Wilkinson

The study was initiated by Sir 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, and explained: “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. 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.” But she added: “These results demonstrate proof-of-concept, and we now hope to develop a more functional, cost-effective application for use in commercial vineyards.”

One plausible option 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 Professor 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,” said Professor Wilkinson.

“It could address a problem that has become a blight for producers globally. Preventing 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.”

The study was published in the Australian Journal of Grape and Wine Research