Evaluation of three alternative strategies for the long-term remediation of reductive off-odours in wines

Abstract

Sulfur-like off-odours are a problem caused by the presence of free forms of volatile sulphur compounds (VSCs). H2S is the most frequently found above its odour threshold (1-10 µg/L), followed by methanethiol (MeSH). Recent evidences showed that the usual treatments to eliminate VSCs from wine e.g.: addition of Cu salts or micro-oxygenation only delay the occurrence of reductive off-odours. (Vela et al., 2017, 2018) The present work aims to assess the effectiveness of three alternative remediation strategies on the removal of VSCs:

1.- intensive oxygenation in the presence of a 3-mercaptopropyl-functionalized adsorbent (MPS);

2.- purging out with N2 the wine stored in reductive conditions; and,

3.- incubation with lees. The treatment with MPS consisted in the addition of 1 mM (of -SH groups) of the functionalized adsorbent to two different wines.

They were further saturated with air and, after three days, were centrifuged and analysed. The purge with N2 was applied to two different wines, which had been previously stored during 2 weeks at 50ºC under anoxia. They were purged at 100 mL/min during 60 min and analysed after the treatment. For lees treatment, three different types of lees were studied: fresh active lees, fresh inactive lees and commercial inactivated dry yeast. They were added (3,3 g/L) to wines with reductive off-odour, then they were incubated for 16 weeks at 25ºC, with weekly agitation. After the incubation, the wines were centrifugated to remove the lees. VSCs and redox potential of wines were analysed by GC-SCD (Ontañón et al., 2019) before and after each essay. Additionally, after the treatments an accelerated reductive aging was carried out (incubation at 50ºC under anoxia for 2 weeks) to assess the long-term effect of the treatments. Intensive oxygenation was very effective (-85% H2S BR after treatment and accelerated aging in both cases). Purge treatment was effective only in the short time, removing completely free H2S free and -70% BR-H2S. However, it was not effective in the long-term. The use of inactivated dry yeast was ineffective. The use of active or inactive fresh lees was effective only in some cases. In conclusion, oxidation with MPS provides the most effective treatment; purging was effective only in the short-term; and treatments with lees were not conclusive. Further studies to assess side effects of oxidation with MPS on wine characteristics should be carried out.