WINETECH Technical Yearbook 2021

eSH eSH

eSH eSH When the one-year wine storage data was compared to the previously reported six- week period, the bound H 2 S concentration levels were further increased in all the wine samples with added copper. This bound H 2 S does not contribute to reductive or “boiled egg” off-odours in wines. In the wine samples spiked with H 2 S, but without added copper, free and bound H 2 S were present at very low levels. This is most probably due to the wine matrix (e.g., quinones) binding to H 2 S, which also occurs under the regular winemaking conditions (Nikolantonaki & Waterhouse, 2012). The results indicate that copper takes a longer time to effectively react with MeSH and remove the “cabbage” off-odour from the wine. Our six-week wine storage data showed that copper fining did not result in a big decrease in free MeSH. The action of removing free MeSH with copper only occurred after six weeks and was confirmed after one year of wine storage. The sensory analysis confirmed a decrease in “cabbage” off-odour in wine spiked with C + H2S + MeSH + Cu C + H2S + MeSH + Cu C + H2S + MeSH + Cu C + H2S + MeSH + Cu • After each time point, a sensory analysis with a trained panel and a chemical analysis of the bottled wines were performed. RESULTS Reductive odours

Control Control C + Cu C + MeSH C + MeSH + Cu C + Cu C + MeSH C + MeSH + Cu • For this experiment, Chenin blanc 2019 from Worcester (South Africa), naturally high in varietal thiol levels was used as a base wine. • The wine was sparged with nitrogen to reduce dissolved oxygen (to <1%) and free SO 2 was adjusted to 38-40 mg/L (the wine had a pH of 3.4 and an alcohol content of 12.73 vol %). • Various combinations of H 2 S, MeSH and copper (in the form of copper-sulphate solution) were added to the base wine, resulting in eight different treatments. The concentrations of reductive com- pounds used in this experiment were at the high range of the spectrum normally found in wines (Siebert et al ., 2010): 40 µg H 2 S/L and 20 µg MeSH/L. The wines were treated with 0.3 mg/L copper. • Wines were bottled in a reductive (anoxic) environment, under crown caps, and stored for 24 hours, six weeks and one year at 15°C. Treatments Treatments C + Cu C + MeSH C + MeSH + Cu C + Cu C + MeSH C + MeSH + Cu C + H2S C + H2S + Cu C + H2S C + H2S + Cu Treatments Treatments Control the “passion fruit” aroma (when compared to non-treated control wine). This article reports on the chemical and sensorial long- term effects of copper fining on reductive Chenin blanc wines after one year of wine storage. MATERIALS AND METHODS

2300 2500 2700 2900 3100 3300 3500 3700 3900 2300 2500 2700 2900 3100 3300 3500 3700 3900

2300 2500 2700 2900 3100 3300 3500 3700 3900 2300 2500 2700 2900 3100 3300 3500 3700 3900

3MH concentration (ng/l) 3MH concentration (ng/l)

3MH concentration (ng/l) 3MH concentration (ng/l)

C + H2S C + H2S + Cu C + H2S C + H2S + Cu

C + H2S + MeSH C + H2S + MeSH

Control Control

C + Cu C + MeSH C + MeSH + Cu C + Cu C + MeSH C + MeSH + Cu

C + H2S C + H2S + Cu C + H2S + MeSH C + H2S C + H2S + Cu C + H2S + MeSH

C + H2S + MeSH + Cu C + H2S + MeSH + Cu

Treatments Treatments

3MH – after 1 year (Graph 1)

20 20 25 25 30 30 35 35 40 40 45 45

20 25 30 35 40 45 20 25 30 35 40 45

Perception intensity rating Perception intensity rating

Control Control

C + Cu C + MeSH C + MeSH + Cu C + Cu C + MeSH C + MeSH + Cu

C + H2S C + H2S + Cu C + H2S + MeSH C + H2S C + H2S + Cu C + H2S + MeSH

C + H2S + MeSH + Cu C + H2S + MeSH + Cu

Treatments Treatments

Control Perception intensity rating Perception intensity rating

C + H2S + MeSH C + H2S + MeSH

“Guava” aroma after 1 year (Graph 2)

WINETECH TECHNICAL YEARBOOK 2021 | 104