WINETECH Technical Yearbook 2021

intensity was decreased in the presence of EtSH. Thus, EtSH had a suppressing effect on the thiol synergism. ● The intensity of the fruit-associated attributes (guava, passion fruit and grapefruit) decreased at a faster rate over time when compared to the aroma attributes typically associated with reductive compounds, such as H 2 S and cooked veg. The perception of the reductive aroma thus remained for a longer time compared to the fruity attributes. ● Surprisingly, an increase in EtSH not only increased the intensity of the attributes usually associated with reductive compounds, but it also in­ creased the intensity of tomato leaf, an attribute usually associated with higher volatile thiol concentrations. CONCLUSION In general, the continuous evaluation of a wine sample over time provides valuable insights into how a wine sample is perceived and the changes that can take place during the evaluation. However, the method and

the data generated is complex and more work is needed to facilitate the processing of this data into usable information. The initial higher intensity scoring followed by a decrease in attribute intensity during the 120 seconds was evident for all attributes. The rate at which this decrease took place depended on the compound responsible for the attribute, as well as the concentration. These effects should be considered, for instance, the persistence of the reductive aroma (compared to that of the fruity volatile thiols) could have significant impl icat ions during wine tast ings. Convenors of wine competitions should be aware of the effect of time on the perception of the sample. In a non-continuous evaluation, such as the judging at wine competitions, the timing of the pouring of samples should be standardised and optimised and judges should perhaps be instructed to not revisit a sample unless necessary. However, the exact reason for the changing of the aroma profile over time needs further investigation.

For the producer, the complex sensory interactions between the fruity volatile thiols and reductive compounds can become important. Suppressing/enhancing effects could change the overall perception of a wine, which might not be reflected in the chemical analysis. The contribution of compounds to contrasting aromas should also be considered carefully. This effect is often seen when certain aroma compounds are present at higher concentrations, which then intensifies the perception of unwanted flavours and can thus have adverse effects. SUMMARY A recent Winetech-funded study by researchers, Sebastian Vannevel, Dr Jeanne Brand, Dr Astrid Buica and Prof Wessel du Toit from the South African Grape and Wine Research Institute (SAGWRI) and Department of Viticulture and Oenology (DVO) at Stellenbosch University developed a new sensory method to continuously assess the aromatic profile of a wine over time. This method was used to evaluate samples containing combinations of the fruity volatile thiols

and ethanethiol, a reductive compound. Results showed complex interactive effects including synergism and suppression. The contribution of one compound to attributes usually associated with a contrasting compound was also demonstrated. The new method also highlighted the changes that take place during sensory assessment and how the perception of wine changes over a 120-second interval. REFERENCES Goniak, O.J. & Noble, A.C., 1987. Sensory study of selected volatile sulfur compounds in white wine. American Journal of Viticulture and Enology 38(3): 223-227. Du Toit, W., 2020. Factors affecting the perception of thiols in white wines. Winetech Final Project Report No. WWWdT 17/02.

For more information, contact Carien Coetzee at carien@basicwine.co.za.

WINETECH TECHNICAL YEARBOOK 2021 | 66