The impact of wine yeast strains on the aromatic profiles of Sauvignon blanc wines derived from characterized viticultural treatments

[摘要] ENGLISH ABSTRACT: Grape must is a complex medium, and during wine production numerous biochemical pathwaysand metabolic reactions are taking place simultaneously to produce a specific taste and aroma.Microorganisms, specifically yeast, play a key role in the formation of metabolites formed duringalcoholic fermentation. Sauvignon blanc, a well studied grape cultivar, is known to have aversatile range of aroma profiles ranging from 'green to 'tropical. It has been broadly statedthat a 'green Sauvignon blanc can be created in the vineyard and a 'tropical Sauvignon blanccan be created by selecting a specific yeast strain, and that the balance between 'green and'tropical characters is essential for the final aroma profile. Except for grape-derived varietalaromatic compounds such as methoxypyrazines (green), volatile thiols (tropical) andmonoterpenes (floral), yeast derived volatile compounds including esters, higher alcohols, fattyacids and carbonyl compounds will also contribute to the final wine aroma.The main aim of this study was to assess how viticultural treatment-derived differences ingrape must, can impact on aroma production when this grape must is fermented with differentcommercial wine yeast strains. The viticulture treatment focused on light intensity modulatedthrough canopy treatment. Volatile aroma differences were compared for canopy and yeasttreatments, specifically focusing on the fermentation derived bouquet (esters, higher alcohols,volatile fatty acids, carbonyl compounds and monoterpenes).Results showed significant differences between initial must compositions, includingtitratable acidity, malic acid and yeast assimilable nitrogen. The volatile aroma compounds were also significantly impacted although no noticeable effect on the overall fermentation kinetics was observed.Depending on the yeast strain differences in volatile compounds varied. A clear vintageeffect is noticeable between volatile compounds affected by the treatments. Data generated in2012 shows clear differences between ethyl- and acetate esters and could clearly be groupedaccording to yeast strain through multivariate analysis.Sensory evaluation results could clearly be distinguished according to canopy treatmentand to a lesser degree according to yeast strain used. This indicates that although yeast has amore prominent impact on the fermentative bouquet that develops during alcoholic fermentationthe overriding aroma is primarily derived from grape-derived metabolites which can bemanipulated by canopy treatments. None the less the difference in fermentation bouquet doesadd to the complexity of the wine especially in the case of fermentation derived 'tropicalaromas including guava and passion fruit. In some cases where shaded grapes had higherester concentrations, the resultant wine also had higher aroma quality.This study has contributed to a better understanding of the complex relationships betweencanopy manipulation and yeast selection on aroma formation. The analysis of volatile aroma alone however is not enough to understand the final perception of wine taste and further indepthstudies of the viticultural and oenological factors is needed.In particular, this project has focused on a single vineyard over only two vintages. Thegeneral validity of the conclusions derived from this study therefore will require additional datasets.

[发布机构] Stellenbosch University