# Discrimination of Smoke-Exposed Pinot Noir Wines by Volatile Phenols and Volatile Phenol-Glycosides
###### Abstract  
This study investigated the correlation between five primary volatile phenols (VPs) and their glycosides in smoke-exposed and non-smoke-exposed Pinot noir wines to assess and identify potential markers for smoke taint. The results showed that all putative VP-glycosides in smoke-exposed wines were higher than in non-smoke-exposed wines, with a fold change ranging from 2.11 to 31.88 for the top fifteen differentiations. VP-glycosides showed strong positive correlations among themselves, with correlation coefficients of 0.94 for hexose-guaiacol vs. pentose (P)-hexose (H)-cresol and 0.92 for syringl-\(\beta\)-D-glucopyranoside vs. H-P-4-methylguaiacol. VP-glycosides also showed relatively high correlations with free and strong acid-hydrolyzed VPs. The correlation coefficient between H-P-guaiacol and free-form guaiacol is 0.71, and between H-P-guaiacol and total guaiacol is 0.78. The strong correlation suggests that these compounds are interconnected and regulated by the severity of smoke exposure. Multivariate analysis effectively differentiated smoke-exposed wines from non-smoke-exposed ones. However, more research is needed to fill the gaps in understanding smoke-derived compounds.  
P 2025 3 Jun 2025 3 Jun 2025 21 June 2025 24 June 20  
Some VPs, including guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, syringol, \(\circ\)-, \(p\)-, and \(m\)-cresols, eugenol, vanillin, _cis-_ and _trans_-oak lactone, fur furludienphonols, etc., have been established to some extent as indicators of the smoke effect [6; 8; 9; 10; 11]. Although extensive research has been conducted to identify the volatile phenols contributing to smoke taint, the results are inconclusive because there are no universally accepted chemical markers or threshold levels for smoke taint. Additionally, the severity of smoke damage to wine grapes depends on several factors, including smoke intensity, fuel type, wind patterns, exposure time, grape variety, and microbial fermentation [8; 12; 13; 14; 15; 16; 17]. Some grape varieties absorb more of the offending taint compounds than others, while others are more tolerant [15]. Specifically, Syrah seems to favor a slightly smoky character. As a result, smoke taint is highly unpredictable, making it extremely challenging to determine which grapes to use and mitigate the risk of smoke taint [16].  
Furthermore, volatile phenols can bind to sugar molecules to form stable glycosides [14; 18; 19; 20]. Phenol glucosides, consistently found at elevated concentrations in smoke-affected wine, can function as smoke-tain precursors. They can be hydrolyzed to free VPs during winemaking and aging [21; 22; 23]. Thus, bounded-form precursors have also been evaluated as the potential smoke taint to improve the evaluation of smoke taint risk [5; 6; 24; 25]. So far, all the glycosides identified in grapes or wine have the sugar directly bound to the aglycone as a \(\beta\)-D-glucose [26]. The second and third can be added to the \(\beta\)-D-glucose moiety to form disaccharide and trisaccharide glycosides. The tentatively identified phenolic glycosides, such as \(\beta\)-D-glucosyl-\(\beta\)-D-glucosides (gentiobiosides), \(\beta\)-D-glucopyranosides (monoglucosides), and disaccharides, have been found in smoke-affected grapes and wines at significantly elevated levels [16; 18; 27; 28; 29].  
In 2020, a historic windstorm accompanied by hot, dry conditions triggered simultaneous \"mega-fires\" across Oregon, devastating wineries and other areas. The flavor chemistry laboratory at Oregon State University analyzed hundreds of wine samples for five primary volatile phenols (VPs), including guaiacol, 4-methylguaiacol, \(\circ\)-, \(p\)-, and \(m\)-cresols, to assess the potential for smoke taint, thereby enabling wineries to make informed decisions about harvest and wine production. This study aimed to characterize VP-glycos in selected samples and correlate them with free and bound forms of VPs to help evaluate and identify potential markers for assessing smoke exposure.