Harnessing Nature: Bacteria to Combat Smoke Taint in Wine Grapes

Recent research shines a light on the remarkable potential of natural bacteria found in grape plants to mitigate the unpleasant ashy aftertaste that can permeate wine grapes after exposure to wildfire smoke.

Scientists have identified a gene from the bacterium Gordonia alkanivorans that plays a crucial role in dismantling one of the principal smoky compounds responsible for smoke taint — the undesirable flavor reminiscent of burnt wood, as detailed in a study published on October 1 in PLOS One. These microbes reside on the surface of grape leaves and on the porous skin of the fruits themselves. This discovery could pave the way for winemakers to utilize these bacteria to degrade harmful chemical compounds before they develop into the campfire-like flavor known as smoke taint.

The urgency behind this research is underscored by the wine industry’s struggles with increasingly damaging and frequent wildfire seasons. In 2020 alone, winemakers in California and Oregon faced losses exceeding $3 billion due to damages and unusable grapes. “More often than not, fires impact vineyards somewhere in the western United States or British Columbia,” states Tom Collins, a grape and wine chemist at Washington State University in Richland. “Given the increasing frequency, it’s imperative that we develop effective solutions.”

Wildfire smoke carries volatile phenols, chemical compounds that can infiltrate the grape’s waxy outer layer. Smoke taint detection is complicated by the fact that grapes can attach sugars to these foreign molecules, temporarily masking the smoky flavors. However, these unpleasant tastes often resurfaces post-fermentation, as the process breaks down the sugary matrices.

In their study, Collins and his team gathered samples of leaves from Chardonnay and Cabernet Sauvignon grapevines to analyze the bacterial communities present and their interactions with smoke taint compounds. Bacteria were cultivated in petri dishes, each given a unique energy source — glucose, guaiacol (a key volatile phenol linked to smoke taint), or no food at all. The team observed vibrant orange colonies forming in the guaiacol-only conditions, leading to the genetic identification of two strains of G. alkanivorans capable of degrading guaiacol.

The research team tracked the degradation process over time, finding that after 96 hours, guaiacol levels in the tested dishes had plummeted to near undetectable levels. When fed similar smoky compounds, however, these bacteria did not proliferate, implying that they are selective, requiring diverse bacterial strains to confront the various compounds contributing to smoke taint.

The gene linked to guaiacol degradation was isolated, and its deletion from one strain resulted in a failure to metabolize the compound, underscoring its pivotal role in the process.

Existing techniques for mitigating smoke taint often remove far more than intended. For instance, using activated charcoal to filter affected wines can eliminate not just smoky flavors but also desirable characteristics such as color. “This microbial method could offer a more targeted approach without compromising the wine’s overall quality,” adds Cole Cerrato, a smoke taint researcher from Oregon State University, who was not part of the study.

Nonetheless, guaiacol represents only a fraction of the volatile phenols that contribute to smoke taint. Collins emphasizes the need for further exploration into the grape plant microbiome to discover additional microbial solutions for combating smoke-related flavor issues intertwined with modern winemaking.