Abstract
During the alcoholic fermentation of grape sugars, wine yeast produces a range of secondary metabolites that play a critical role in the aroma profile of wines. One of the most impactful yeast-modified compound families, particularly in white wines, are the ‘fruity’ polyfunctional thiols, which include 3-mercaptohexan-1-ol (3-MH) and 4-mercapto-4-methylpentan-2-one (4-MMP). While the formation and stylistic contribution of these thiols have been extensively researched in white wines, little is known about the conditions leading to their formation in red wines. In this study, we explored the ability of yeast strains to modulate the release of these aroma compounds during the fermentation of two red musts. In laboratory-scale Pinot Noir fermentations, the formation of 3-MH strongly correlated with yeast β-lyase activity, particularly with the presence of certain genotypes of the flavour-releasing gene IRC7. Subsequent production of Grenache wine at the pilot scale, with detailed compositional and sensory analysis, was undertaken to confirm laboratory-scale observations. A commercial wine strain used for expressing ‘fruity’ thiols in Sauvignon Blanc was shown to produce wines that exhibited more intense red fruit aromas. These results reveal an opportunity for winemakers to shape red wine aroma and flavour by using yeasts that might typically be considered for white wine production.
Highlights
The polyfunctional thiols 4-mercapto-4-methylpentan-2-one (4-MMP), 3-mercaptohexan1-ol (3-MH), and 3-mercaptohexyl acetate (3-MHA) impart ‘passionfruit’, ‘grapefruit’,‘guava’, and ‘box tree’ aromas in white wines [1–3]
While the different precursors and pathways leading to the formation of these polyfunctional thiols, as well as their contributions to wine aroma and flavour, have been extensively studied in the context of wines made from white cultivars, little is known about their impact in red and rosé wines
Analysis of the genomic sequence of 179 wine yeasts showed that around 80% of strains with at least one copy of IRC7L have one or more deleterious
Summary
‘guava’, and ‘box tree’ aromas in white wines [1–3]. These compounds have very low perception thresholds, in the low nanogram-per-litre range, and are important contributors to the flavour of Sauvignon Blanc, Chardonnay and Scheurebe wines [4,5]. While the different precursors and pathways leading to the formation of these polyfunctional thiols, as well as their contributions to wine aroma and flavour, have been extensively studied in the context of wines made from white cultivars, little is known about their impact in red and rosé wines. 3-MHA in commercial Pinot Noir and rosé wines comparable to those found in Chardonnay. A survey of 105 Australian commercial red wines found concentrations of 3-MH well above its perception threshold (60 ng L−1 ) in a wide range of single variety red wines [9]
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