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 (<= 1 mu g/L) of guaiacol and 4-methylguaiacol could be detected in free run juice derived from the fruit of smoked vines; the highest levels, 388,mu g/L and 93 mu g/L, respectively, were observed in the finished wine. Control wine (derived from fruit of unsmoked vines) contained 4 mu g/L guaiacol, with the volatile phenols either not detected or detected at only trace levels (<= 1 mu g/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 mu g/L and 325 mu g/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 underestimation of smoke taint in fruit and juice samples; the implications for the assessment of smoke taint and quantification of volatile phenols are discussed.