Up in smoke: Wildfire season and the risk of smoke taint

by | Nov 28, 2020 | News, Article

As major wine regions around the world face the immediate effect of devastating wildfires, the threat of smoke taint is a slow burn. But how do you mitigate the risk, and what are the most effective solutions on offer?

The Cape’s dreaded fire season officially starts on 1 December, and this season, the Western Cape Environmental Affairs Department has predicted wildfire risk to be higher than previous years. This is because the Department was unable to do all the necessary fire breaks and regular preparation work in risky areas during the lockdown.

Every year, local firefighters deal with around 17 000 incidents, of which approximately 9 000 are wildfires.

Earlier this year, wildfires once again, wreaked havoc in Australia and California. Californian vineyards and vintners faced challenges even before the start of what has turned out to be a record-breaking wildfire season, as the Covid-19 pandemic stalled tourism and cut off a key sales channel with the closure of restaurants around the country.

Cast your mind back to January 2019 when a fire in the Hemel-en-Aarde Valley outside Hermanus destroyed approximately 10 ha of vineyards and caused extensive damage at Hamilton Russel Vineyards. In December 2019, a bushfire devastated Lismore Estate, the South African winery owned by Samantha O’Keefe – destroying the winery, her home and a large part of the vineyards in Greyton.

Those who’ve experienced or witnessed the deadly, destructive blazes produced by the Western Cape’s dry, arid summers know how damaging they can be to property and vineyards. But there’s another concern in the back of winemakers’ minds: How will the vintage be affected by blankets of smoke that can linger in vineyards for days?

An appropriate descriptor for the flavour profile of a smoke-tainted wine is like licking a wet ashtray.

Where there’s smoke …

So what is smoke taint? The general consensus is that you’ll know it when you taste it. Unfortunately, it’s not the typical smoky characteristics associated with wines aged in toasted oak barrels. A more appropriate descriptor for the flavour profile of a smoke-tainted wine is like licking a wet ashtray.

It’s more than just residue sitting on the grapes that cause these unpleasant flavours. When wood burns, aroma compounds called volatile phenols are released. According to Dr Marianne McKay from Stellenbosch University – a leading expert on smoke taint – these compounds can permeate grape skins in the vineyard and bind with sugars to form molecules called glycosides.

“Glycosylation renders the phenols no longer volatile, meaning the smokiness cannot be detected by smell.”

Mitigating risks

In her article entitled Guidelines to reduce smoke taint in grapes and winesMarianne provides some useful, quick-fire tips for handling smoke-tainted grapes (more tips are available in the article linked).

  • A high-pressure cold water wash in the vineyard can be effective to remove ash, but only after canopy leaf plucking. Rinsing off grapes once harvested might be more practical. This won’t affect the volatiles already in the grapes, but it will help remove excess ash and smoke particles that contribute to the ‘ashtray’ taste. Grapes need to be drained and dried off afterwards.
  • Hand harvest grapes, but minimise the breaking or rupturing of skins as long as possible. It’s been found that the volatile phenols responsible for smoke taint are more concentrated in grape skins.
  • Remove leaves and other material other than grapes. It’s been shown that leaves contain higher volatile phenol concentrations than grapes.
  • Process grapes cool. Grapes processed at 10 °C have less extraction than those processed at 25 °C.
  • Limit skin contact. In the case of white grapes, Marianne recommends whole bunch pressing, and keeping press fractions separate from free-run juice. Only add enzymes after pressing to free-run juice to improve settling. A large proportion of the volatile phenols occur in a non-odorous glycosylated form that can be hydrolysed by glycosidases naturally occurring in non-purified white wine processing enzymes.

Trailblazing research

Every year research yields more insight into smoke risk. Smoke researchers in the United States are investigating the possibility that a vineyard’s proximity to the fire matters when it comes to smoke, and smoke blown in from elsewhere loses potency. “That nuance in risk marks one of the many mysteries of smoke damage that researchers are beginning to unravel,” says Washington State University’s wine science professor and smoke expert Tom Collins.

Tom and his team aim to answer some of the key uncertainties surrounding smoke damage: what exposure levels and conditions put different cultivars at risk, how to predict impacts based on air monitors, better analytic tests, and how to adapt winemaking to mitigate impact?

The Australian Wine Research Institute (AWRI), found that the risk of smoke taint is directly correlated with the stage of a grapevine’s growth and development. Their research shows that the period between veraison and harvest is when grapes are most susceptible. Even 30 minutes of heavy smoke exposure to grapes could cause smoke taint in subsequent wines.

In South Africa, Dr Marianne McKay (Stellenbosch University) and Dr Heinrich du Plessis (ARC-Nietvoorbij) have conducted extensive research on smoke taint over the past few years. Marianne’s research is focused primarily on amelioration techniques to reduce smoke taint in wines while Heinrich’s research is focused on the influence of wine yeasts and bacteria on the release of volatile phenols from their non-volatile precursors.

Solutions on offer

Enrico Bocca, export area manager in biotechnology at Enologica Vason, says the company has since 2015, developed a solution to the smoke taint problem by using activated carbon products which are highly porous carbon-rich materials used in applications such as filtration and water treatment.

Activated carbon products are known to absorb organic compounds, including undesirable contaminants such as the volatile phenols associated with smoke taint. “Activated carbon products can be used to treat smoke-affected juices or wines,” says Enrico. “Carbons might also remove positive colour, aroma and flavour compounds if not scientifically proven and selected.”

He adds when smoke taint became an issue of global interest, many other researchers became involved and found the problem wasn’t limited only to free form phenols, but also on phenols bound to sugars.

Testing samples received from CJP Chemicals (VASONGROUP’s Smoke Taint products).

“Finally we found a procedure to release those phenols and remove it,” says Enrico. The solution is based on a specific enzyme and carbon. “We have another product in the works that applies to the bound fraction without enzyme treatment.”

In a report released by the Australian Wine Research Institute (AWRI), researchers stated that Carbocromos and FPS (both Enologica Vason products) were among the best performers for the removal of volatile phenols from both juice and wine.

Both products can be purchased through Enologica Vason’s sole distributor in South Africa, CJP Wine – a division of CJP Chemicals. Contact Walbrie de Klerk on 021 534 0727 or 073 916 5730. Email walbriedk@cjpchemicals.co.za

Fining agents have also been shown to be effective for remediation of some volatile fractions of smoke taint in wine. For this reason, measuring the total and free levels of smoke taint markers in wine can provide information for the amount of smoke taint which still exists in a bound form in the smoke affected wine.

Enartis South Africa’s manager Lida Malandra says the company offers several fining agents which can be utilised to remove volatile smoke taint. Speaking on the range, Lida says “Fenol Free is an activated carbon with specificity for phenol removal with low colour removal capacity.”

She says EnartisStab Micro M is a pre-activated chitosan blend which can also remove smoke taint markers such as Guaiacol.

Enartis offer protocols for both WHITE and RED wine affected by smoke taint, and even hosted a webinar on the issue.

Enartis has a range of solutions for smoke taint. Visit www.enarits.com or call Lida Malandra on 021 870 1181

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