Abstract
The influence of two yeast strains and the addition of copper sulphate on the aroma of Riesling wines was monitored. Two commercially available yeast strains, Zymaflore VL3 and X-Pure, were applied. General composition, volatile thiols, norisoprenoids, free terpenes, aroma fermentation, sulphur compounds and copper content were determined, and the sensory attributes were assessed by 22 tasters in a balanced incomplete block design (BIBD). The VL3 yeast produced a higher concentration of thiols than the X-Pure yeast. Wines treated with copper sulphate showed a higher concentration of 3MH than the wines produced without copper sulphate addition for both yeast strains. Yeast strain and copper sulphate addition both influenced the amount of β-damascenone in Riesling wines significantly, but they showed no significant influence on the level of terpenes. Five out of eight rated sensory attributes showed significant differences. Yeast strain and copper sulphate addition were decisive factors for the sensory profile of experimental wines.
Highlights
Riesling is a very important grapevine variety with very large areas of it planted in Germany, Australia, North America (California) and France (Alsace)
Fermentation aroma has an impact on Riesling wines in general, but has higher impact on young Riesling wines
The increase in 3MH in Riesling wines after the addition of copper sulphate during the maturation on fine lees has been reported for the first time in this study
Summary
Riesling is a very important grapevine variety with very large areas of it planted in Germany, Australia, North America (California) and France (Alsace). Riesling is a semiaromatic variety and contains a few important classes of aromatic substances: Norisoprenoids, terpenes and volatile thiols. Alpha-terpeniol, nerol and geraniol are important terpenes in Riesling wines; they possess floral and fruity aromas, their precursors are glycosidic derivatives and their levels in wine are influenced by many factors. The volatile thiols of Sauvignon blanc and a few other varieties are very well known and they are present in Riesling wines. The most studied volatile thiols are 4-mercapto-4methylpentan-2-one (4-MMP), 3-mercaptohexanl-ol (3-MH) and 3-mercaptohexyl acetate (3MHA). They possess different types of odours: broom, box-tree and grapefruit respectively. Fermentation aroma has an impact on Riesling wines in general, but has higher impact on young Riesling wines
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