Identification of smoke odorants by gas chromatography/olfactometry and assessment of smoke odorants in grapes and wine

Smoke taint has become a significant concern for the wine industry, particularly in Southern Oregon and California, partly due to climate change. Smoke taint is an off-aroma describing the wine with smoky, medicinal, and ashy characters, and this unpleasant taint is caused by grapes or grapevine exposed to bushfire smoke before. Wine made from smoke-tainted grapes is often characterized by smoky, burnt, burnt rubber, ashy, smoked salmon, smoked meats, salami, leather, disinfectant/hospital, medicinal, dusty, and earthy aromas. Guaiacol, 4-methylguaiacol, and syringol have smoky odors with low sensory thresholds, and these compounds are likely to contribute to the overall smoke flavor.

When guaiacol and other smoke-related compounds are absorbed by the grapevine, the grapevine will convert them to the corresponding glycosides or other bound forms. These glycosides as well as the bound form precursors do not exhibit aroma themselves, but can be converted back to the odorants during winemaking and wine aging process. Grape maturity, grape varieties, and bottle aging can all influence the intensity of smoke taint in wines.

Smoke taint precursors, including glycosides, can persist in the wine and directly affect flavor perception during consumption. Guaiacol β-D-glucoside and m-cresol β-D-glucoside in model wine were found to give rise to a smoky or ashy flavor in-mouth, due to the release of respective free volatiles in-mouth. It has been confirmed that the enzymes present in human saliva can release the volatile smoke compounds from their glycoconjugates even under low pH and elevated ethanol conditions. Smoke taints in grapes and their conversion during winemaking, and wine aging are very complex, the mechanisms of transformation need to be thoroughly investigated to mitigate the issue.

Although guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, eugenol, and furfural are related to bushfire smoke, but not all of them are directly generated from smoke, some of them can naturally exist in grapes or extracted from the wine barrel. These compounds are essential contributors to wine flavor at low concentrations.
Our initial experiments were designed to extract the smoky chemicals from wine. Complementary analytical methods have been evaluated. The results showed that smoky odorants can be obtained from wine using different methods. Further investigations were under progress to identify the smoky odorants.