WINETECH Technical Yearbook 2020

Thiols in red wine (PART 3): Thiols interaction in a Pinotage base wine

And this brings us to the last term, ‘masking effect’, most probably the easiest of the three to explain. Various food properties can be suppressed by others and, as consequence, not be picked up. At times, this masking effect is sought after; for example the addition of sugar to tonic water to hide the bitterness of quinine or, in some white wines, the sourness is masked by a relative high residual sugar concentration. PROBLEM STATEMENT Given the complexity of wine and the numerous chemical compounds at play, it can be understandable why so many questions still need answers in the field of aroma and taste interactions. From an experimental point of view, it is logistically impossible to evaluate at once all probable combinations of the three chosen thiols 3MH, 3MHA and 4MMP. Therefore, Experiment 2 explores the interaction of two thiols at the time in Pinotage red wine, and specifically examines the synergistic and masking effects caused by them. APPROACH De-aromatised Pinotage wine was used as base for this part of the project which assessed the sensory impact of interaction between two thiols at a time as illustrated in figure 1. The spiking of the compounds was done 24 hours before evaluation to allow for integration of the samples. A panel of trained judges executed the task and a

total of 12 wines (x2 repeats) were tasted in a single session. Projective mapping was chosen as sensory method which allowed to evaluate the wines according to similarities and dissimilarities, as well as profiling each individual sample. The results were illustrated using 3D scatter plots also known as surface plots. RESULTS The information extracted from the results can be presented from different angles. First, the data generated are twofold: descriptive and spatial. The frequency of attributes cited by the panel constitute the descriptive data and the positioning of the samples on the 2D space is the spatial. Each of them is analysed using specific statistical tools. From the results, we can see the relationship between the samples, the attributes, and the samples and attributes combined. For example, 4MMP x 3MH interaction leads to separations of the samples driven by increasing 3MH concentrations. The associated descriptors from low levels of 3MH to high, changed from ‘fruit jam’ and ‘oaky’ to ‘herbaceous’ and ‘coffee’. In the case of the interaction between 4MMP and 3MHA, the separation of the samples is driven by 4MMP increasing concentrations. Associated descriptors from low to high 4MMP ranged from ‘blackberry’ and ‘green’ at the lowest level, to ‘raspberry’, ‘oaky’, ‘yeasty’ and ‘nutty’ at the highest.

AUGUST 2020

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

When does 1 + 1 = 3? The work presented in this article forms part of series of experiments on the interaction between thiols and red wine matrices as described in Part 1. BACKGROUND In sensory science there are terms that describe the relationship between aroma compounds in a food product. They are often used and are indeed very important, but might need to be clearly defined before we get to the core of the article. The concepts are ‘interaction’, ‘synergy’ and ‘masking’ effects. Let us consider them one by one. When two or more compounds have an effect on each other, but neither dominates the other, this is known as an interaction. For example, it has been proven that adding ethanol to a regular wine will reduce the

amount of volatile compounds in the head space of a glass; on the contrary, by adding water, the amount of aroma volatiles in- creases. The components of the wine matrix interact with the ethanol (or water) added and this creates a specific outcome/result. In the case of a synergy (or synergistic ef- fect), the effect of combining two or more substances is greater than the sum of the separate end results. A relatively easy exam- ple, reported in sensory science text books, is the intrinsic property of salt (NaCl). Once added in small amounts to sugar, it enhances sweetness. Sodium chloride in low levels has a sweet taste, which is masked once the level is higher. Sugar, as we all know, is sweet; but the combination of the two creates a greater sensation than the individual ones.

WINETECH TECHNICAL YEARBOOK 2020 89