WINETECH Technical Yearbook 2021

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0 5

Control

C + Cu C + MeSH C + MeSH + Cu

C + H2S C + H2S + Cu

C + H2S + MeSH

C + H2S + MeSH + Cu

Perceptiuon intensity rating

Peach Banana candy “Peach” and “Banana” aromas after 1 year (Graph 3)

MeSH followed by the copper treatment. However, even after one year of wine storage, the free MeSH and corresponding “cabbage” off-odour was still present in the wine and only decreased to around 50% of its initial value. Contrary to the H 2 S results, levels of bound MeSH increased in all the wine samples after one year of storage, whether the wine was copper fined or not. Varietal thiols The overal l concentrations of 3MH increased and 3MHA decreased after one year of wine storage. This change is due to the already known process of hydrolysis of 3MHA to 3MH occurring during wine

ageing. Interestingly, a decrease in 3MH levels was seen in all the samples with added copper (graph 1). That is a change from the previously reported data after six weeks of wine storage, which showed a 3MH decrease only when copper was added to the wine without reductive compounds present. Therefore, copper addition had prolonged detrimental effects on 3MH, even after one year of wine storage. On the other hand, 3MHA levels were not affected by the copper additions even after one year. However, due to the majority of 3MHA being converted to 3MH during the wine storage, the newly created fraction of 3MH could also be affected by copper fining.

Sensory results after one year showed a decrease in “guava” aroma in Chenin blanc wine treated with copper (graph 2). On the other hand, when reductive compounds H 2 S and MeSH were present in the wine, the decrease was less apparent. Interestingly, the aromas of “peach” and “banana” were elevated in the samples with added copper after one year (graph 3). Researchers have previously published results that showed when varietal thiols are present in higher concentrations, esters present in wines boost the varietal thiol aromas, while ester aroma perception is decreased (King et al ., 2011). However, when esters are present in higher levels,

the varietal thiols enhance the perception of esters (e.g., “banana” aroma derived from isoamyl acetate). This might apply here, as the decrease of varietal thiol 3MH concentration by the copper addition could give esters and other aromatic compounds enhanced sensorial perception. CONCLUSION In Part 1 of this series, we suggested that to preserve varietal thiols, the minimum required amount of copper additions should be made to remove H 2 S off-odours from wine. After one year of wine storage, we have seen that the wines that contained copper, also went through changes in

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