for assistance in carrying out the study; Michelle Beresford for help with the sensory analysis; Richard Gardner for comments and suggestions during the study; and Denis Dubourdieu for support of the project.
In this study three different approaches were employed to identify key odorants in Sauvignon blanc wines. First, the concentrations of the odorants were compared to their respective aroma detection thresholds. The resulting odor activity values (OAV) were transformed into a normalized and weighted measure that allows the aroma profiles of different wines to be compared and the contribution of a single aroma in a complex mixture to be evaluated. Based on their OAV, 3-mercaptohexanol and 3-mercaptohexyl acetate were the two most important aroma compounds in many Marlborough Sauvignon blanc wines. Due to limitations with the OAV approach, the study was extended to include aroma extract dilution analysis (AEDA), which revealed that β-damascenone, together with the varietal thiols, esters, and higher alcohols, are key odorants in Sauvignon blanc wines. The final approach undertaken was aroma reconstitution and omission tests using a deodorized wine base and the creation of a model Marlborough Sauvignon blanc. Single compounds and groups of compounds were omitted from the model to study their impact on the sensory properties of the model wine. Reconstitution and omission confirmed that varietal thiols, esters, terpenes, and β-damascenone are all important contributors to Sauvignon blanc aroma. The methoxypyrazines showed an important but relatively low impact in all three of the approaches undertaken in this study.
Two volatile thiols, 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA), are key aroma impact compounds in many young white wines, especially of the variety Sauvignon blanc (SB). Although great effort has been invested to identify their precursors in recent years, the origin of the majority of 3MH and 3MHA generated during wine fermentation still cannot be explained. Here we demonstrate that supplying an external source of hydrogen sulfide to grape juice hugely increases its thiol-forming potential. We further describe the discovery of (E)-2-hexen-1-ol as an additional new thiol precursor and demonstrate that it possesses, together with (E)-2-hexenal, an immense thiol-forming potential during fermentation. Both C6-compounds are extremely rapidly metabolized by yeast during the first hours after inoculation, even under commercial conditions, and can be interconverted during this phase depending on their initial concentration in the grape juice. Spiking grape juice with additional acetaldehyde greatly enhanced the (E)-2-hexen-1-ol to (E)-2-hexenal conversion rate. Delaying the metabolization of the two unsaturated C6-thiol precursors by yeast, at the same time as increasing hydrogen sulfide production early in fermentation, opens up a great opportunity to tap into this enormous potential 3MH and 3MHA source in grape juice and extends the possibility of thiol production to other non-grape-based alcoholic beverages as well.
The analytical scope of static headspace–gas chromatography–ion mobility spectrometry (SHS–GC–IMS) was applied to wine aroma analysis for the first time. The method parameters were first fine-tuned to achieve optimal analytical results, before the method stability was demonstrated, in terms of repeatability and reproducibility. Succinct qualitative identification of compounds was also realized, with the identification of several volatiles that have seldom been described previously in Sauvignon Blanc wine, such as methyl acetate, ethyl formate, and amyl acetate. Using the SHS–GC–IMS data in an untargeted approach, computer modeling of large datasets was applied to link aroma chemistry via prediction models to wine sensory quality gradings. Six machine learning models were compared, and artificial neural network (ANN) returned the most promising performance with a prediction accuracy of 95.4%. Despite its inherent complexity, the ANN model offered intriguing insights on the influential volatiles that correlated well with higher and lower sensory gradings. These findings could, in the future, guide winemakers in establishing wine quality, particularly during blending operations prior to bottling.
Background and Aims Marlborough is the largest wine‐growing region in New Zealand and Sauvignon Blanc varieties represent over 60% of the vineyard area. The main compounds responsible for the most intense aromas in Sauvignon Blanc wines have been assumed to be methoxypyrazines and varietal thiols; however, the aromatic potential of Sauvignon Blanc wines should not be limited to these compounds. Methods and Results Commercially pressed juices from seven Marlborough subregions were fermented using replicated research‐scale winemaking over two harvests. Fifty‐five compounds were quantified in the resulting wines, including varietal thiols, methoxypyrazines, reduced sulfur compounds, esters, terpenes, C6 and higher alcohols, fatty acids, C13‐norisoprenoids, cinnamates, and aminobenzoates. At least 21 compounds were identified that were present at a concentration above their perception threshold or can enhance the aroma impact of other compounds. Many aroma compounds showed a similar concentration across the subregions and the two seasons, while the concentration of the prominent varietal thiol 3‐mercaptohexanol was higher in the second year. Conclusion Considerable diversity exists in the concentration of aroma compounds in Sauvignon Blanc wines across the Marlborough subregions. The ‘green’ characters ascribed to wines from certain subregions may be linked to a lower concentration of fruity esters as much as to differences in methoxypyrazines, C6 alcohols and certain varietal thiols. Significance of the Study The profiles of aroma compounds in Marlborough Sauvignon Blanc wines have been more clearly defined and the extent of subregional differences has been evaluated for various classes of aroma compounds.
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