Winetech Technical Yearbook 2022

MARCH

Elemental sulphur residues at harvest – BOOSTING BOTH THE GOOD AND THE BAD

A RECENT STUDY CONDUCTED BY NEW ZEALAND RESEARCHERS INVESTIGATED THE EFFECTS OF THE ADDITION OF ANTIOXIDANTS (A COMBINATION OF ASCORBIC ACID AND SULPHUR DIOXIDE) AND ELEMENTAL SULPHUR DURING GRAPE PROCESSING ON THE SENSORY AND CHEMICAL COMPOSITION OF THE RESULTING WINES.

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BY CARIEN COETZEE

The reduction of elemental sulphur to H 2 S takes place in the presence of antioxidants. 1 In juices that lack antioxidant protection, H 2 S is expected to be rapidly removed by reaction with oxidised o- quinones. 3 This is important given the ability of H 2 S to combine with certain C6 alkene compounds present in the juice to form 3-mercaptohexanol (3MH) and 3-mercaptohexyl acetate (3MHA) during the early stages of fermentation. 4 MATERIALS AND METHODS Sauvignon blanc, Pinot gris and Chardonnay grapes were collected from different sites in New Zealand during the 2018 harvest. Grapes were obtained from three different sites for each variety. The following additions were made after destemming and crushing: • No addition. • 100 mg/L ascorbic acid + 50 mg/L SO 2 . • 100 mg/L ascorbic acid + 50 mg/L SO 2 + 100 mg/L elemental sulphur. The grapes were pressed, juice cold settled, racked into 1.5 L glass bottles and inoculated with Anchor VIN7 yeast whereafter fermentation took place at 15°C. Sensory evaluation was performed using descriptive analysis by a trained sensory panel. RESULTS Results differed significantly not only between the different treatments, but also between the varieties, as well as between

INTRODUCTION Elemental sulphur is an effective, durable and economical fungicide for the management of powdery mildew in vineyards. But sulphur residues present on the grapes at harvest can have adverse effects and concentrations exceeding 10 µg/g in musts are associated with increased hydrogen sulphide (H 2 S) formation during fermentation. 1 Growers and winemakers are therefore cautious when applying elemental sulphur closer to the harvest date for fear of increased residual elemental sulphur being transferred into the juice. However, studies have shown that H 2 S during fermentation could significantly contribute to the fruity volatile thiol formation resulting in increased intensity of desirable attributes in the finished wines. 2

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WINETECH TECHNICAL YEARBOOK 2022