WINETECH Technical Yearbook 2019

to sugars). Both free volatile phenols, as well as their glycoconjugates, can contribute to the negative sensory experience a wine drinker has when drinking wine from smoke- exposed grapes. The reason for this is because enzymes from bacteria in a person’s mouth can release the sugars from the glycosylated phenols, rendering the phenols volatile (Mayr, et al ., 2014) and able to impart smoke flavour. It is therefore possible to detect very little or no smoke taint in the aroma of a wine, yet on the palate the wine can be perceived as ashy. Individuals also differ in terms of sensitivity towards tasting smoke taint. EXPERIMENTAL LAYOUT In the study researchers exposed Sauvignon blanc, Chardonnay and Merlot grapevines to smoke for one hour, approximately 10 days after veraison, using purpose-built smoke tents (Van der Hulst et al ., 2019). Three treatments in total were conducted: a control treatment with no kaolin and no smoke, a smoke treatment, and a treatment of kaolin addition 24 hours before smoke treatment. Samples were collected at one day and seven days after smoke treatment, as well as at maturity, which were 15, 12 and 30 days after smoke exposure for Sauvignon blanc, Chardonnay and Merlot respectively. Volatile phenol concentrations were determined by GC-MS and phenol-glycoconjugate concentrations were determined by LC-MS/ MS. Reflectance measurements, using a “Jaz”

This study demonstrated the different effects of the same amount of smoke on different

KARIEN O’KENNEDY: Winetech KEYWORDS: Volatile phenol glycoconjugates, smoke-exposed grapes. APRIL 2019 ACCUMULATION OF VOLATILE PHENOL GLYCOCONJUGATES IN GRAPES AFTER BUSHFIRES

grape varieties. INTRODUCTION

It is well-documented that wines made from grapes that were exposed to smoke from bushfires can contain smoky and ashy characteristics (Ristic, et al ., 2017). These characteristics are derived from volatile phenols, such as guaiacols, cresols and syringols, which are taken up by the grapevine during a smoke event and stored in the fruit, mainly as glycoconjugates (bound