Volatile Phenols in Smoke-Exposed Pinot noir Wines - Biomarkers and Model Prediction

Background and goals Wildfires have become a significant concern for the wine industry in the United States. When grapes or grapevines are exposed to bushfire smoke, the grapes can absorb smoke compounds, resulting in smoky, medicinal, and ashy wines. Extensive research has been published on smoke taint and smoke exposure, and volatile phenols—such as guaiacol; 4-methylguaiacol; m-, o-, and p-cresol; and their precursors—have been investigated to assess grape smoke exposure. This study investigated these biomarkers to develop a more integrated model.

Methods and key findings The free and bound forms of phenolic compounds in non-oak-aged wines were analyzed by solid-phase microextraction and gas chromatography-mass spectrometry with stable isotope-labeled internal standards. We analyzed 377 smoke-exposed Pinot noir wines collected in 2020 from Oregon and 86 non-smoke-exposed Pinot noir wines from multiple vintages. Statistical analysis was used to identify biomarkers and correlations between the smoke exposed and non-smoke-exposed wines. Smoke exposure was correlated with guaiacol; 4-methylguaiacol; and m-, o-, and p-cresol. Heatmaps and Pearson’s correlation analysis demonstrated a strong correlation between some phenol compounds. Principal component analysis and common factor analysis suggested that free-form cresols could be significant factors.

Conclusions and significance From the statistical analysis, a similarity index was constructed by using Mahalanobis distance to rank the likelihood of smoke-exposed wines relative to non-smoke-exposed wines in a 10-dimensional phenol space based on free and total phenol concentration. Further study associating this index with actual sensory evaluation could help to assess smoke risk.