Winetech Technical Yearbook 2022

OCTOBER

Yeasts, smoke taint and Chenin blanc wines THIS PROJECT INVESTIGATED YEAST SELECTION’S EFFECTS ON THE VOLATILE PHENOLS ASSOCIATED WITH WINES MADE FROM SMOKE-EXPOSED CHENIN BLANC JUICE.

BY HEINRICH DU PLESSIS, JUSTIN HOFF, LUCKY MOKWENA, MARIETA VAN DER RIJST & NEIL JOLLY

I

SHUTTERSTOCK

INTRODUCTION Several wine-producing countries, including Australia, Chile, Greece, France, Italy, Portugal, Spain, South Africa and the United States of America, have been affected by fire or smoke damage to vineyards. 1 Some of these fires are so devastating that entire vineyards and regions are destroyed. To date, Australia and USA suffered substantial losses in revenue due to fire and smoke damage to vineyards and wines. 2,3 Wines produced from smoke-exposed grapes can have unpleasant, burnt, medicinal, smoky and ashy characteristics, collectively known as “smoke taint”. 1,4 The compounds usually associated with this taint are known as volatile phenols. Guaiacol, 4-ethyl guaiacol, 4-methylguaiacol

and 4-ethylphenol are the main volatile phenols used as chemical ‘markers’ for smoke-tainted wine. 5 These volatile phenols and their precursors accumulate in grapes and leaves after smoke exposure and are then released into the wines during winemaking. The yeasts responsible for transforming grape must into wine through alcoholic fermentation contribute to flavour and quality through producing and modifying metabolites, including volatile phenols. Commercial yeasts have differing abilities to affect the volatile phenols in wine. Consequently, this study investigated the levels of volatile phenols in Chenin blanc wines fermented with a range of different yeasts to determine if some are better suited for producing wines from smoke-affected grapes by reducing the quantity of smoky phenols or by masking it. This article summarises the scientific article, “Impact of yeast selection on volatile phenol levels of wines produced from smoked-exposed juice”, published in the Fermentation journal. 6

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WINETECH TECHNICAL YEARBOOK 2022