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.

Although smoke exposure has been associated with the development of smoke taint in grapes and subsequently in wine, to date there have been no studies that have demonstrated a direct link. In this study, postharvest smoke exposure of grapes was utilized to demonstrate that smoke significantly influences the chemical composition and sensory characteristics of wine and causes an apparent 'smoke taint'. Verdelho grapes were exposed to straw-derived smoke for 1 h and then fermented according to two different winemaking treatments. Control wines were made by fermenting unsmoked grapes. Sensory studies established a perceivable difference between smoked and unsmoked wines; smoked wines were described as exhibiting 'smoky', 'dirty', 'earthy', 'burnt' and 'smoked meat' characteristics. Quantitative analysis, by means of gas chromatography-mass spectrometry, identified guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, eugenol, and furfural in each of the wines made from smoked grapes. However, these compounds were not detected in the unsmoked wines, and their origin is therefore attributed to the application of smoke. Increased ethanol concentrations and browning were also observed in wines made from grapes exposed to smoke.

Background and Aims: Grapevine smoke exposure has been reported to produce smoke aromas in wine, resulting in 'smoke taint'. This study describes the application of smoke to field-grown grapevines between veraison and harvest to investigate the effect of timing and duration of smoke exposure on wine composition and sensory attributes. Methods and Results:Smoke was applied to grapevines as either a single smoke exposure to different vines at veraison or at 3, 7, 10, 15, 18 or 21 days post-veraison or repeated smoke exposures to the same vines at veraison and then at 3, 7, 10, 15, 18 and 21 days post-veraison. Gas chromatography-mass spectrometry analysis of guaiacol, 4-methylguaiacol, 4-ethylguaiacol and 4-ethylphenol showed elevated levels in all wines produced from fruit from smoked grapevines. Repeated smoke exposures had a cumulative effect on the concentration of these compounds. A trained sensory panel identified the aromas of 'burnt rubber', 'smoked meat', 'leather' and 'disinfectant' in all wines derived from smokeexposed grapevines but not in control wines. Conclusions: Smoke application to field-grown grapevines between veraison and harvest can influence the accumulation of volatile phenols and intensity of smoke aromas in resultant wines. A peak period of vine sensitivity to smoke at 7 days post-veraison is identified. Repeated smoke exposures have a cumulative effect. Significance of the Study: This is the first study to report the deliberate and controlled smoke application to field-grown grapevines demonstrating the timing and duration of smoke exposure to significantly affect wine chemical and sensory characters. AbbreviationsBET best estimate threshold; FAN free amino nitrogen; GC-MS gas chromatography-mass spectrometry; PCA principal component analysis; TSS total soluble solids.

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Background and Aims: Smoke exposure of grapevines and development of smoke taint in wine are issues of increasing incidence and severity. There is limited understanding of the effect of phenological stage at the time of smoke exposure on taint development. The aim of this study was to demonstrate the variation in smoke uptake and taint development between and within seasons. Methods and Results:Smoke was applied to field-grown Merlot grapevines at 12 stages of vine development over three growing seasons. Key periods of vine sensitivity to smoke taint in wine were (i) from shoots at 10 cm to full bloom (low levels of smoke taint); (ii) from berries at pea size to the onset of veraison (variable levels of smoke taint); and (iii) between 7 days post-veraison and harvest (high levels of smoke taint). Conclusions:The severity of taint in wine varied depending on the phenological timing of grapevine smoke exposure. Taint was elevated when exposure occurred between 7 days post-veraison and harvest. The carry-over of smoke constituents the following season was not detectable in wine but yields were reduced. Significance of the Study: This is the first study to demonstrate the timing of smoke exposure to critically affect wine chemical and sensory characters. These effects were consistent and reproducible over three seasons.

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