Browsing by Author "McKay, M."

Now showing 1 - 4 of 4
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    Determination of volatile phenol in cabernet sauvignon wines, made from smoke-affected grapes, by using HS-SPME GC-MS
    (South African Society for Enology and Viticulture, 2015-10) De Vries, C. J.; Mokwena, L. M.; Buica, A. S.; McKay, M.
    The increased incidence of vegetation fires near vineyards in the Western Cape, South Africa has led to growing concern over the appearance of smoke taint in the affected grapes. This study focused on the effect of smoke exposure on the volatile phenol (VP) composition of wines made from affected grapes over two vintages (2012 and 2013). Cabernet Sauvignon grapes were exposed, 10 days post-véraison, to a single, hour-long treatment with smoke derived from burning a mixture of vegetation (including fynbos) under controlled conditions in enclosures. Enclosures were sealed for 24 h after exposure, and then removed. Grapes were allowed to ripen and wines were then produced. Wines were analysed by headspace gas chromatography mass spectrometry (HS-SPME GC-MS) for selected volatiles. The results of the investigation show that the exposure of grapes to smoke during ripening leads to the accumulation of VPs that were detected in wines. The detected VPs were guaiacol, phenol and the cresols. Smoke exposure of grapes during ripening may have a negative impact on wine quality due to the accumulation of these compounds.
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    The impact of smoke from vegetation fires on sensory characteristics of cabernet sauvignon wines made from affected grapes
    (South African Society for Enology and Viticulture, 2016-01) De Vries, C. J.; Buica, A. S.; Brand, J.; McKay, M.
    The increased incidence of vegetation fires near vineyards in the Western Cape, South Africa has led to growing concern over smoke taint in wine made from affected grapes. This study focused on the sensory properties of wines made from grapes that have been exposed to bushfire smoke. Cabernet Sauvignon grapes (ten days’ post-véraison) were exposed to a single, hour-long treatment with smoke from burning fynbos under controlled conditions. The grapes were allowed to ripen and wines were then produced. Descriptive analysis of the wines was done for aroma and taste attributes. The results of the investigation show that the exposure of grapes to smoke during ripening led to sensory differences between wines made from different treatments, and that wines made from smoke-exposed grapes were perceived as having ‘burnt’, ‘smoky’ aromas and an ‘ashy’ aftertaste. Despite levels of free volatile phenols (VPs) being below or close to odour threshold levels for individual phenols, their combination led to a perception of the socalled ‘burnt rubber’ taint perceived in some South African red wines.
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    Potentially smoke tainted red wines: volatile phenols and aroma attributes
    (South African Society for Enology and Viticulture, 2019) McKay, M.; Bauer, Florian; Panzeri, V.; Mokwena, L.; Buica, A. S.
    Malodourous compounds, including volatile phenols (VPs) are frequently found at concentrations below their odour thresholds in wine, and may therefore be considered to present no threat to wine quality. Most investigations into smoke taint quantify compounds by chemical/analytical means, or investigate sensory effects of supra- and peri-threshold contamination in model wine. In this project, twelve wines submitted by the South African industry as ‘faulty’ and/or smoke tainted were screened for VPs using GC-MS, and characterized using Descriptive Analysis (DA) by a sensory panel highly trained in smoke taint evaluation. Results were compared statistically to elucidate relationships between chemical and sensory characteristics. It was demonstrated, using the combined dataset, that concentration and composition of VPs in the wines correlated well with certain sensory attributes. Guaiacol was present in most samples at peri- or supra-threshold levels, but did not cause taint unless in combination with other phenols, when it was associated with ‘smoky’, ‘ashy’ and ‘herbaceous’ attributes. Wines with very low levels of VPs showed more sweet-associated aroma characteristics. Wines with supra-threshold levels of VPs showed negative attributes (‘chemical/plastic’, ‘tar/BR’ and ‘medicinal/Elastoplast™’). In some cases, sensory effects (‘earthy/dusty/potato skin’, ‘mouldy/musty’ and ‘cooked veg’) could not be attributed to peri- or supra-threshold concentrations, but seemed to be due to combinations of volatile phenols at subthreshold levels. Associations between negative attributes and historical bushfire events prior to harvest were found for a number of the wines. This study emphasizes the importance of understanding effects of VPs on wine aroma, and escalating awareness and sensitivity to these issues in the wine industry.
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    Profiling potentially smoke tainted red wines : volatile phenols and aroma attributes
    (South African Society for Enology and Viticulture, 2019) McKay, M.; Bauer, F. F.; Panzeri, V.; Mokwena, L.; Buica, A.
    Malodourous compounds, including volatile phenols (VPs) are frequently found at concentrations below their odour thresholds in wine, and may therefore be considered to present no threat to wine quality. Most investigations into smoke taint quantify compounds by chemical/analytical means, or investigate sensory effects of supra- and peri-threshold contamination in model wine. In this project, twelve wines (submitted by the South African industry as potentially smoke tainted) were screened for VPs using GC-MS, and characterized using descriptive analysis (DA) by a sensory panel highly trained in smoke taint evaluation.  Results were compared statistically to elucidate relationships between chemical and sensory characteristics.  It was demonstrated, using the combined dataset that concentration and composition of VPs in the wines correlated well with certain sensory attributes. Guaiacol was present in most samples at peri- or suprathresholdlevels, but was not correlated with taint unless in combination with other phenols, in which case it was associated with ‘smoky’, ‘ashy’ and ‘herbaceous’ attributes. Wines with supra-threshold levels of VPs showed negative attributes (‘chemical / plastic’, ‘tar / BR’ and ‘medicinal / Elastoplast™’). In some cases, sensory effects (‘earthy / dusty / potato skin’, ‘mouldy / musty’ and ‘cooked vegetables (veg.)’) could not be attributed to supra-threshold VP contamination, and therefore seemed to be due to combinations of VPs at subthreshold levels. Associations between negative attributes and historical bushfire events prior to harvest were found for a number of the wines. This study emphasizes the importance of understanding effects of VPs on wine aroma, and escalating awareness and sensitivity to these issues in the wine industry.