The compositional basis of the aroma of Riesling and unwooded Chardonnay wine.

Abstract

The aim of this research project was to explore, in detail, the relationship between volatile composition and wine aroma for two white wine varieties, namely Riesling and unwooded Chardonnay, so that the most influential volatile aroma compounds to the aroma of these two varieties could be identified. Twenty Australian commercial wines of each variety were analysed by quantitative sensory descriptive analysis and targeted for the chemical analysis of more than 45 volatile compounds. The compositional and sensory data sets were related using multivariate methods (e.g. PCA and PLS), and aroma volatiles were identified that related to the specific sensory properties of each variety. Most of the Riesling and several of the unwooded Chardonnay sensory properties were well predicted by the compositional data and several compounds were identified as important to the aroma of each variety. The unwooded Chardonnay wines were higher in concentration of various fermentation- derived compounds than were the Riesling wines, and these volatiles played an important role in the sensory properties of this variety. The Riesling wines were higher in concentration of grape-derived compounds including the monoterpenes, norisoprenoids, and dimethyl sulfide. These compounds, and also many of the fermentation-derived compounds, were identified as important contributors to the aroma of the Riesling wines. The results from this study have greatly advanced our understanding of the complex interactions between volatile compounds and the role that they play in the specific aroma nuances of white wines. The prediction of sensory properties of the Riesling and unwooded Chardonnay wines was investigated using rapid instrumental techniques, namely mass spectrometry based electronic nose (MS Enose) and visible and near infrared (VIS-NIR) spectroscopy. A combination of MS Enose and VIS-NIR gave the best predictive results compared to either method alone. Promising results were achieved for many of the sensory properties indicating that this technique shows good potential for application. The so-called 'wine lactone' (3a,4,5,7a- etrahydro-3,6-dimethylbenzofuran-2(3H)-one) is known to be an important white wine odorant. The formation of wine lactone was investigated from two potential precursors, namely (E)-2,6-dimethyl-6-hydroxyocta-2,7- dienoic acid and the glucose ester of this acid, in model wine at room emperature and 45⁰C. The hydrolytic results show that the rate of formation of wine lactone is too slow for either the acid or the glucose ester to be major precursors to wine lactone in young white wine. Therefore, different precursors are most likely responsible for the formation of wine lactone in young white wine.