Long-term sensorial and compositional effects of copper fining on the wine containing ‘reductive’ and ‘tropical’ volatile sulfur compounds

The aim of this study was to investigate long-term sensorial and compositional effects of copper addition to the white wine naturally high in varietal thiol levels, with added volatile sulfur compounds [hydrogen sulfide (H2S) and methanethiol (MeSH)]. The novelty of this study lies in the inclusion of sensory analysis at each time point by using Check-All-That-Apply and Descriptive Analysis methods to evaluate the sensory interaction between ‘reductive’ thiols and tropical thiols after copper fining. The Chenin Blanc wine was used as control (base) wine to which combinations of 40 µg/L H2S and 20 µg/L of MeSH were added, followed by an addition of 0,3 mg/L of copper to selected samples. The wine samples were stored for 24 hours, 6 weeks and 1 year. At each time point chemical analysis of varietal thiols, volatile sulfur compounds and copper levels were performed. The chemical results after 1 year of wine storage, showed a significant increase in the levels of varietal thiol 3-sulfanylhexanol (3-SH) and a decrease of 3-sulfanylhexyl acetate (3-SHA) concentration levels. However, a significant loss of 3-SH occurred in all the copper treated wines after 1 year of storage. On the other hand, the decrease of 3-SHA levels over time was less influenced by copper treatment, but rather due to acid hydrolyses and a subsequent increase in 3-SH (Makhotkina & Kilmartin, 2012). The presence of copper seem to further increase levels of bound- H2S in wine samples, which after 1 year of storage amounted to more than 25 µg/L. Chemical analysis of MeSH showed the significant increase in free and bound MeSH after 1 year of storage in wine samples spiked with MeSH. However, the addition of copper to the MeSH-spiked samples resulted in significant decrease of free and bound MeSH. The most significant sensory impact of the addition of H2S and MeSH to control wine was the suppression effect on “fruitiness” of wine after 24 hours which after 6-weeks and 1-year wine storage period decreased, potentially due to wine matrix absorption of H2S and MeSH (Nikolantonaki & Waterhouse, 2012). Sensory results after 1 year of wine storage showed that “guava”, a “tropical” attribute, was not suppressed with the addition of H2S and MeSH and low doses of “reductive” aromas deriving from H2S and MeSH in wine might even contributed to its sensory perception. Copper additions mainly decreased the perception of “guava” after 1 year. In contrast, the “passionfruit”, also a “tropical” attribute, was slightly suppressed when H2S and MeSH were present. The perception of the ester-derived attributes namely “peach” and “banana” increased in the samples containing copper after 1 year of storage, suggesting that a decrease of the 3-SH varietal thiol due to copper addition may enhance the perception of ester-derived aromas in wine.

Authors: Matija Lesković – *South African Grape and Wine Research Institute/Department Viticulture and Oenology, University of Stellenbosch, Private Bag X1, Matieland (Stellenbosch) 7602, South Africa,Marlize BEKKER † Jeanne BRAND * Allie KULCSAR † Wessel DU TOIT * *South African Grape and Wine Research Institute/Department Viticulture and Oenology, University of Stellenbosch, Private Bag X1, Matieland (Stellenbosch) 7602, South Africa † The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, South Australia, 5064.

Email: matija@sun.ac.za

Keywords: varietal thiols, volatile sulfur compounds, wine copper fining, ‘reductive’ and ‘tropical’ volatile sulfur compounds, copper fining and wine storage, wine sensory analysis

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