Kristen Kennison

Smoke-derived taint in wine: The release of smoke-derived volatile phenols during fermentation of Merlot juice following grapevine exposure to smoke

The release of smoke-derived volatile phenols during the fermentation of Merlot grapes, following grapevine exposure to smoke, has been investigated. The concentrations of guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, and eugenol were determined by gas chromatography-mass spectrometry and found to increase throughout the winemaking process. Only trace levels (< or = 1 microg/L) of guaiacol and 4-methylguaiacol could be detected in free run juice derived from the fruit of smoked vines; the highest levels, 388 microg/L and 93 microg/L, respectively, were observed in the finished wine. Control wine (derived from fruit of unsmoked vines) contained 4 microg/L guaiacol, with the volatile phenols either not detected or detected at only trace levels (< or = 1 microg/L) throughout fermentation. The role of enzyme and acid catalyzed hydrolysis reactions in releasing smoke-derived volatile compounds was also investigated. The volatile phenols were released from smoked free run juice by strong acid hydrolysis (pH 1.0) and enzyme (beta-glucosidase) hydrolysis, but not mild acid hydrolysis (juice pH 3.2-3.7). Guaiacol was again the most abundant smoke-derived phenol, present at 431 microg/L and 325 microg/L in strong acid and enzyme hydrolysates, respectively. Only trace levels of each phenol could be detected in each control hydrolysate. This study demonstrates the potential for under-estimation of smoke taint in fruit and juice samples; the implications for the assessment of smoke taint and quantification of volatile phenols are discussed.

Identification of a β-D-glucopyranoside precursor to guaiacol in grape juice following grapevine exposure to smoke

The presence of the beta-D-glucopyranoside of guaiacol (glucoside) in juice of grapes following grapevine exposure to smoke was investigated. The glucoside was synthesized as a reference compound and an HPLC-MS/MS method was developed for its detection in juice. The glucoside was found in the juice extracts of grapes exposed to bushfire smoke, as well as grapes experimentally exposed to smoke. Compared to the control (unsmoked) juice sample, the experimentally smoked juice contained a significant amount of the glucoside, indicating glucosylation of guaiacol occurred following grapevine smoke exposure. The reference compound, and the glucoside found in the smoked juice samples were less susceptible to acid treatment but virtually disappeared after enzyme treatment with beta-glucosidase. The susceptibility of the glucoside to enzyme hydrolysis could be one reason for the release of guaiacol from smoke affected grapes during fermentation.