“Smoke taint” refers to the aroma that wine takes on when grapes in a vineyard are exposed to smoke from wildfires during ripening, a frequent occurrence in Australia and recently the western US. Wines afflicted with smoke taint are often described as “campfire” or “ash tray”-like and are typically not accepted by consumers. Because of this, a fast and accurate screening method for smoke taint is necessary for winemakers who are faced with remediation, blending, or discarding decisions when grapes are being harvested during or after a wildfire. Guaiacol and 4-methylguaiacol are two compounds typically analyzed as markers of smoke taint, as they are most abundant compared to other smoke-derived odorants like 4-ethylguaiacol, 4-ethylphenol, and eugenol.<br/>By combining solid phase microextraction (SPME) sampling prior to analysis by triple quadrupole gas chromatography-mass spectrometry (GCMS), sensitivity of volatiles increases while matrix effects decrease. In SPME, a sorbent fiber is exposed to the headspace of a sample allowing volatiles to ad/absorb to the fiber and then injected into the system where desorption occurs immediately prior to analysis. This technique is ideal for the analysis of ppb-level odorants, such as smoke taint compounds, because of the sensitivity it can achieve while minimizing sample preparation.<br/>In this work, a multiple-reaction monitoring (MRM) method with SPME preconcentration was developed for quantification of guaiacol and 4-methylguaiacol in smoke taint-afflicted wines. Method validation was performed on wines containing low-ppb levels of analytes. Sub-ppb detection limits were achieved for both compounds with the use of a deuterated internal standard.

Quantification of “smoke taint” compounds in grapes and wine by SPME-GCMS

ACS Spring 2022

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