WINETECH Technical Yearbook 2021

intensity was again reported when the 3MH concentration was increased from level 4 to level 5. • Tomato leaf Even though increasing the 3MH concen- tration from level 1 to level 3 resulted in a gradual increase in the intensity of tomato leaf, the increase in intensity was not sub- stantial. Only from level 3 to level 4 was the tomato leaf intensity reported as being notably higher. • Passion fruit The intensity of passion fruit also increased gradually from level 1 to level 3, however, at level 4 a decrease in intensity was observed. This confirms that the intensity of attributes originating from specific aroma compounds does not always increase in agreement with the increase in concentration. • Green apple The intensity of green apple was reported as being relatively low for all samples and a slight decrease in intensity was observed At most of the 3MH concentrations, the intensity of cooked veg/onion was reported as being very low. However, the judges reported a notable increase in cooked veg/ onion when the concentration increased from level 4 to level 5. Therefore, at these from level 1 to level 5. • Cooked veg/onion

extreme concentrations, 3MH could also contribute to the reductive aroma of wine. 3MHA • Guava As with 3MH, the guava attribute was scored at the highest intensity when compared to other attributes. Here, a notable increase in intensity was observed when the 3MHA concentration increased from level 1 to level 3. Another increase was reported when the concentration increased from level 2 to level 5. • Passion fruit The intensity of the passion fruit attribute increased as the concentration of 3MHA increased, however, this increase was not always noteworthy. • Tomato leaf As with 3MH, a substantial increase in to - mato leaf intensity was only reported when 3MHA was at very high concentrations. • Blackcurrant The panellists reported an important increase in blackcurrant aroma as soon as the concentration exceeded level 4. CONCLUSION When it comes to sensorially relevant in- creases of thiol-related attributes, it seems that concentration increases need to be relatively large for aromatic changes to take

place. Even though the very low perception thresholds reported (in model wine) for these thiol compounds demonstrate the potency of these aroma compounds, in a real wine medium smaller increases might not have the desired effect. This should be considered before changing winemaking processes according to scientific data alone. Preferably, the effect of viticultural and oenological treatments reported in research studies should not only include chemical results, but it should also report the sensory significance. The complex interactive effects that occur between aroma compounds in wines, which are not dearomatised, should also be considered. Sensorial differences observed as compound concentrations changes could rely on the presence of supporting compounds or groups of compounds. These are extremely complex interactions and will be unique for each unique wine. SUMMARY Thiols are powerful aroma compounds sensorially described as guava, passion fruit and tomato leaf. These compounds have very low sensory perception thresholds in a model wine solution, however, in a real wine medium, the sensory impact is complex and influenced by interactive effects with other wine constituents.

Research studies often show the effects of viticultural and oenological treatments on the concentration of thiols in wine. Whether these concentration changes have a significant impact on the sensory perception of the wine is not always known. A recent Winetech-funded study by researchers, Matija Lesković, Dr. Jeanne Brand 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, investigated the effect of increased thiol concentrations on the sensory significance of a wine. Results showed that the concentrations of 3MH and 3MHA need to increase considerably for sensory changes to be sensorially perceived. REFERENCES Coetzee, C. & Du Toit, W.J., 2012. A com­ prehensive review on Sauvignon blanc aroma with a focus on certain positive volatile thiols. Food Research International 45(1). Du Toit, W., 2020. Factors affecting the perception of thiols in white wines. Winetech Final Projects Report, No. WWWdT 17/02.

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

WINETECH TECHNICAL YEARBOOK 2021 | 60