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Factors affecting the perception of thiols in SA white wines

by | Oct 28, 2020 | Oenology

Project Number
WW WdT 17-02

Project title
Factors affecting the perception of thiols in SA white wines

Project leader
du Toit, W

Institution
Stellenbosch University. Department of Viticulture and Oenology

Team members
Brand, J

 

Objectives and Rationale

Varietal thiols such as 3MH and 3MHA can contribute positive aromas to white wine, but certain reductive sulphur compounds can negatively influence the wine’s aroma.  More research is required on the sensory interactions between these compounds and the effects of copper fining on them.  The main aim of this project was to investigate factors that influence the perception of certain volatile sulphur compounds in white wine.

 

Methods

Different combinations of thiols and reductive sulphur compounds were assessed in model wine over time as well as in real wines using descriptive analyses and a novel time-based sensory technique, Temporal Rate-All-That-Apply. The effects of copper on these compounds were also followed using a combination of different sensory techniques and GCMS.

 

Key Results

Large differences in individual 3MH levels and, to a lesser extent, 3MHA levels are required to induce a significant change in thiol-derived aroma descriptors.

H2S additions led to decreases in the intensity of certain varietal thiol descriptors, with Cu additions significantly reducing this effect. Cu additions did not lower the intensity of thiol-derived descriptors in white wine in the short and medium term, but small decreases were seen after 12 months of bottle ageing.

Differences between samples over time and interactions between compounds (3MH, 3MHA and ethanethiol) and descriptors evaluated with the new TRATA method were found.

 

Key Conclusion of Discussion

Small differences in varietal thiol levels in white wines do not lead to significant sensorial changes. The negative sensory effects of H2S in white wines seem to be safely negated by Cu additions without stripping it of positive thiol-derived aromas in the short and medium term, but this might change after prolonged bottle ageing.

 

Take Home Message for industry

Practices/products that can influence varietal thiol levels need to induce a large difference in varietal thiol levels to justify their usage. Copper finings can be considered a viable option to rectify a reductive wine’s sensory characteristics. However, it should still be applied with care, as it might decrease varietal thiol levels in the long term. Pre-fining trials with Cu are thus recommended. Wines with an H2S aroma should also not be left on the yeast lees for too long, as this might lead to increases of larger reductive sulphur compounds, which are harder to remove with Cu than H2S.

FINAL REPORT

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