Modified Polymers Can Remove Wildfire Smoke Taint From Wine, at the Cost of a Little Flavor

Wildfires are an increasing threat to vineyards around the world. From California to central Chile, recent fires have scorched countless wine growers’ fields.

The surviving crops may be the lucky ones, but even they aren’t left unscathed; wine made from these grapes is often said to be imbued with the bitter flavor of smoke – an undesirable quality in a market that, more than most, is dictated by taste.

So, given that the frequency of such wildfires is only set to increase as global temperatures continue to climb, what can vignerons do to preserve the precious tasting notes of their produce? Well, they could use molecularly imprinted polymers (MIPs), says Kerry Wilkinson, a professor of oenology at the University of Adelaide.

Trapping the smoke

MIPs are synthetic polymers made using molecular imprinting techniques, which create cavities in the polymer shaped to match a particular molecule.

Wilkinson and her colleagues wondered whether bespoke MIPs could bind with and remove the volatile phenols behind the smoky taints found in wildfire-wines.

Their research was published in the Journal of Agricultural and Food Chemistry.

“Our use of MIPs to remediate smoke taint either during or after fermentation is novel – we are not aware of MIPs having been used this way before,” Wilkinson told Technology Networks.

“The benefits of MIPs over other adsorbent materials are their purported selectivity – i.e., in theory, they better target the constituents you are looking to remove because the MIP has been tailored specifically for that molecule – in our case, volatile phenols.”

Her team added beads made of MIPs – either contained in muslin or floating freely in the liquid – to several smoky Pinot Noir, Semillon and Merlot wine samples, some of which were mid-way through fermentation, others of which were fully fermented.

The team then used a mixture of chemical analysis and taste testing to judge whether the acrid aroma had been successfully removed.

“We used gas chromatography-mass spectrometry and high-performance liquid chromatography-tandem mass spectrometry to measure volatile phenols in free and glycosylated forms, respectively,” said Wilkinson.

This testing revealed that the MIPs had extracted 35–57% of the guaiacol, 4-methylguaiacol, cresols and phenol present in the wine samples. The beads added to the fermented wine tended to remove more volatile phenols – an outcome also noted by the panel of wine-tasting experts.

Unfortunately, the micro-beads also removed some of the wine’s desired flavors and color in the process.

Wilkinson said her team is already researching ways to retain as many of these coveted flavor notes as possible, but they concede that any use of MIPs will always risk some sensory loss.

“There is inevitably some removal of color and/or aroma with most methods,” she said. “However, we are having some success with the combined use of spinning cone column distillation (typically used for dealcoholization to produce no/low or zero alcohol wines).”

“SCC distillation allows us to separate the (desirable) aroma volatiles – while the volatile phenols (despite being volatile – they’re less volatile than most wine aroma compounds) and their glycoconjugate remain in the ‘stripped wine’. We have then treated the stripped wine with activated carbon to remove the smoke taint compounds, before blending the treated wine with the condensate containing the aroma volatiles.”

“Depending on the level of taint in the initial wine, this seems to retain more of the aroma in the final treated wine, with minimal impact on color. We are finalizing this work for publication in coming months.”

A tainted future

If and when Wilkinson’s method is perfected, it might just become a vital tool for wine growers in the face of a warming planet.

“Unfortunately, I think it is inevitable that wine regions around the world will have to manage the impacts of increased wildfire activity and therefore, the occurrence of smoke taint,” Wilkinson told Technology Networks. “Hopefully it remains the occasional fire. But the forecasts are certainly for more frequent and more severe fires as our climate continues to warm.”

Dr. Kerry Wilkinson was speaking to Leo Bear-McGuinness, Science Writer for Technology Networks.

About the interviewee

Kerry Wilkinson is a professor of oenology at the University of Adelaide. Her primary research interests concern the flavor chemistry of grapes and wine. She has studied the impact of bushfire smoke on grapes and wine, the improved utility of oak wood for wine maturation and the influence of production method on the composition and sensory profiles of sparkling wine. Other areas of interest include the chemical and sensory analysis of foods and beverages and their appeal to consumers. She completed her PhD in wine science and analytical chemistry at Flinders University and the Australian Wine Research Institute.

Reference: Huo Y, Ristic R, Puglis C, et al. Amelioration of Smoke Taint in Wine via Addition of Molecularly Imprinted Polymers during or after Fermentation. J Agric Food Chem. 2024. doi: 10.1021/acs.jafc.4c03912