Browsing by Author "Langa, Nongcebo Portia"
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- ItemAmelioration of smoke taint in wine using commercially available and legally permissible additives(Stellenbosch : Stellenbosch University, 2019-04) Langa, Nongcebo Portia; McKay, Marianne; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.ENGLISH ABSTRACT: The changes experienced in climate in many parts of the world have led to an increase in incidences of wildfire, and it has been predicted that these events will become more prevalent over time. All fires release volatile compounds into the atmosphere, and if they occur near vineyards where grapes are ripening, smoke taint may be detected in wines made from these grapes. Smoke taint is a critical issue for wine producing regions of the world as smoky and unpleasant flavours and aromas are perceived in affected wines, and this may have serious economic implications for producers. A number of researchers have tried to understand smoke taint, and their research has shown that volatile phenols (VP) are chemical compounds responsible. Additional research has revealed that although guaiacol, 4-ethylguaiacol, and 4-methylguiacol were originally identified as chemical markers of smoke taint, other VPs such cresols, eugenol, and phenol derivatives also play a role in causing smoky and ashy flavours. Strategies to eliminate the problem have ranged from washing the grapes and harvesting by hand, to minimising skin contact and choosing yeast and bacteria for minimal impact, and marketing wines for early release. These techniques work but do not eliminate an important underlying issue: glycoconjugates. Glycoconjugates or glycosides (VPs bound to sugars) are compounds that act as precursors of smoke taint produced as a detoxification by-product by vines. Glycosides can be hydrolysed by acid and enzymes, which means wines have the potential to increase available VPs in the wine, despite great care being taken to minimise VPs. This study expands on previous strategies that have been used to ameliorate smoke taint by using commercially available and legally permissible products in South Africa and exploring their effectivity at different dosage levels. Grapes in this study were harvested and deliberately smoked in crates using a bee-smoker, which produced smoke generated from fynbos (indigenous vegetation) and pine needles. Activated charcoal, oak extract, polymer powder were used in the first part of this study to try and ameliorate the taint during winemaking. GC-MS analysis of treated wines and controls revealed that only activated charcoal at elevated levels decreased VPs chemically. Sensory analysis of treated wines and controls by a trained panel using Descriptive Analysis showed that oak extract did increase levels of eugenol and consequently increased the ‘woody’ attribute, thus somewhat masking the smoke aroma. None of the treatments were able to remove the smoke aroma and flavour satisfactorily, primarily because of ashy flavour on the palate, likely due to in-mouth enzymes hydrolysing VP-glycosides. Building on the data and knowledge accumulated during the first part of the study, the second part of the study attempted to reduce levels of volatile phenol glycosides by using β-glucosidases before treatment application for removing free volatiles (“release-and-remove”). The treatments used after the enzyme hydrolysis were activated charcoal, polymer powder, yeast hulls, and mannoproteins. Chemically, GC-MS showed that there were sharp increases of VPs after the addition of enzymes, and some success in subsequent removal of the free volatiles. Further work is needed to determine the optimum levels of treatment. The data in this study showed potential for β-glucosidases to be used in the winemaking process, not only to release VPs (for later removal) but to increase the expression of fruity aromas in the wine. Enzymes may help to release other compounds that contribute to wine flavour, thus masking some of the smoke taint. This study contributes to the improved understanding of methods that can be used for the removal or treatment of smoke taint, but the need for further work was highlighted. The use of β-glucosidases followed by multiple finings could be an option for producers after a fire incident has occurred near a vineyard during ripening of grapes.