WINETECH Technical Yearbook 2020

This work is part of a comprehensive study conducted at the Department of Viticulture and Oenology and aimed at shedding light on the thiol composition of Chenin blanc and various red cultivars using chemical

done in collaboration between the Chemical Analytical Laboratory at the Department of Viticulture and Oenology (DVO) and the Central Analytical Facility at Stellenbosch University (SU) proved the presence of thi- ols in South African single varietal Pinotage, Cabernet Sauvignon, Merlot and Shiraz There is still a lot we do not understand about the influence of thiols on the perception of red wine aroma and the contribution the non-volatile component (matrix) plays. With the exception of 4MMP, which has been identified as one of the contributors to the ‘blackcurrant’ aroma in Cabernet Sauvignon, there are no studies demonstrating the impact of 3MH and 3MHA in red wine. APPROACH As the chemistry already demonstrated that these compounds are present in South African red wines, the purpose of this study was to elucidate the sensory role that 4MMP, 3MH and 3MHA play. Due to the complexity of the investigation, the approach was multi- layered. We were interested in the attributes associated with these thiols, the extent that their concentration influences their perception, and the effect of the cultivar. Projective Mapping (PM) was chosen as the most suitable method for the task. This method allowed us to evaluate multiple wines (Mafata et al ., 2018). PROBLEM STATEMENT

and sensory tools. BACKGROUND

Wine quality is an abstract concept, as well as a controversial one, because it evades objective definition. What we know for sure is that, among other factors, it is directly correlated to the aroma, taste and mouth- feel of the wine. Traditionally the aromas of wine are divided into three groups. According to their origin, primary or varietal aromas derive from the grape itself, secondary are formed during fermentation and tertiary during maturation and ageing. Recent developments in analytical chem- istry offered the possibility to investigate and validate the impact of thiols, a class of compounds thought to play a significant role in wine aroma. The three most relevant representatives of this class are 4-mercap- to-4-methylpentan-2-one (4MMP), 3-mer- captohexan-1-ol (3MH) and 3-mercapto- hexyl acetate (3MHA). In white wine they contribute to the perception of ‘passion fruit’, ‘grapefruit’ and ‘guava’ aromas. Thiols are also known to occur in Merlot, Shiraz, Grenache and Malbec. Reports from France indicated the presence of thiols in Bordeaux blends (Rigou et al. , 2014). Recently, work

Thiols in red wine (PART 1): Background and relevance

JUNE 2020

VALERIA PANZERI, GONZALO GARRIDO-BANUELOS & ASTRID BUICA: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch KEYWORDS: Red wine, thiols, Projective Mapping

WINETECH TECHNICAL YEARBOOK 2020 83