Influence of Sulfur Dioxide Additions at Harvest on Polyphenols, C₆-Compounds, and Varietal Thiols in Sauvignon blanc

Abstract

The varietal thiols 3-mercaptohexanol (3MH), derived from odorless precursors in the grape juice, and 3-mercaptohexyl acetate (3MHA), arising from 3MH during fermentation, are prominent compounds responsible for tropical fruit aromas in Sauvignon blanc wines. Machine-harvested grapes were sourced from three different locations in Marlborough, New Zealand. Different concentrations of sulfur dioxide (0, 30, 60, 120, and 300 mg/kg) were added to the grapes and juice in the field, followed by transport to the University of Auckland, pressing, and fermentation in triplicate 750 mL bottles using EC1118 yeast at 15°C. Juices transported without SO₂ or with a low SO₂ addition were more oxidized and contained lower concentrations of most polyphenols. The juices fermented at a similar rate, with a delay in the onset of fermentation of up to a day with the 120 mg/kg SO₂ juices, but around 12 days for the 300 mg/kg SO₂ additions. In the more oxidized juices, there were higher concentrations of C₆-alcohols in the finished wines but lower concentrations of the corresponding acetate esters. With each set the highest concentrations of 3MH and 3MHA were found in wines produced from the juices with a 120 mg/kg addition of SO₂ at harvest. Conversely, wines made from juices that were transported with low SO₂ additions had much lower concentrations of the varietal thiols.