WINETECH Technical Yearbook 2020

Thiols in red wine (PART 4): The matrix

lected and consisted of 13 samples in total (three different Cabernet Sauvignon (plus a blind duplicate), three Pinotage, three Merlot and three Shiraz), all commercially available (figure 1). To create the de-aro - matised base, the wines were evaporated under vacuum to avoid oxidation. Spiking with thiols was carried out 24 hours before organoleptic evaluation. The wines were evaluated blind by 15 experienced judges using Projective Mapping (PM) as sensory method (for more details see Part 1). RESULTS The results can be analysed from two separate points of view, the first one by looking at the attributes generated by the panel, the second one looking at the spatial configuration of the samples on the 2D plane. Considering the top 10 most used descrip- tors generated, eight were common to both combinations of thiols for all cultivars and ‘berry jam’ clearly took the crown. Some unique characteristics can also be observed: while the 4MMP x 3MH mixture is described as ‘fruity’ and ‘cooked vegeta - bles’, 4MMP x 3MHA displayed ‘caramel’ and ‘blackcurrant’ as typical features. An interesting observation comes from fo- cusing on ‘blackcurrant’. It was expected for this attribute to play a central role: it is often associated with 4MMP and here it could be clearly seen for both sets. The intriguing aspect is how the perception

changes: in the 4MMP x 3MH combina- tion, the ‘blackcurrant’ word is cited 32 times versus the 52 for the 4MMP x 3MHA set. An assumption made often in sensory science when looking at the frequency of cited attributes, is that the more a term is used, the more intense it must be. In this case, it would lead us to the conclusion that 3MHA increases the perception of ‘black- currant’ much more compared to 3MH (as already seen in Part 3 for only one matrix). When observing the MFA maps (figure 2a and 2b), the configurations of the samples have no obvious pattern related to cultivars. For example, Pinotage samples group together regardless of the thiol combination. Cabernet Sauvignon samples clustered together for 3MH x 4MMP, but not for 3MHA x 4MMP. Two of the Merlot samples are closed to each other, but not in the same combination across the two maps. Shiraz samples are scattered in both cases. TAKE-HOME MESSAGE The journey that took us into the fascinating world of thiols in red wine is now coming to an end. So what have we learnt so far? In Part 1 we talked about the bigger picture, the complexity of defining thiols-associated aromas, the interactions between thiols and about the approach followed by our group of researchers in expanding the knowledge on the subject.

SEPTEMBER 2020

VALERIA PANZERI, GONZALO GARRIDO-BANUELOS & ASTRID BUICA: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch KEYWORDS: Pinotage, thiols, interaction, matrix

It is all about the (wine) matrix. The work presented in this article forms part of a series of experiments on the interaction between thiols and red wine matrices as

compounds in the matrix that appear to play an important sensory role. PROBLEM STATEMENT The identification and quantification of this large amount of unrevealed molecules still elude us and it might be some time before we manage to do so. As a consequence, we have set out to shed some light on the matrix by rather looking at its impact on the sensory properties of wine when thiols

described in Part 1. BACKGROUND

The keyword for this latest aspect of thiols in red wine which we are going to talk about is surely ‘matrix’. By definition, in biology: “matrix is the fine material used to bind together the coarser particles of a composite substance”; in terms of this project: the essence of a wine. Of course the great majority of it is composed of water (about 86%) and ethanol (about 12%) but, despite the great progress made in wine chemistry, there is still a very large number of unexplored and unidentified

come into play. APPROACH

The experiment evaluated the thiol inter- actions 4MMP x 3MH and 4MMP x 3MHA at high concentrations (based on reported literature values) in de-aromatised wine from five different matrices. Wines were se -

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