Browsing by Author "Qwebani, Sinazo"

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    Sensory profiling, quality evaluation, and chemical profiling of South African de-alcoholised still wines
    (Stellenbosch : Stellenbosch University, 2023-03) Qwebani, Sinazo; Nieuwoudt, Helene; Brand, Jeanne; Pentz, Chris; Muller, Magdalena; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: A relatively new category of wines with <0.5% v/v ethanol produced through physical removal of ethanol is in demand by many health-conscious consumers. However, this physical intervention has an impact on the wines’ sensory profiles. Accordingly, there is an interest in understanding this category’s sensory aspects and chemical composition. The aim of this study was to investigate the sensory profiles and quality of South African (SA) de-alcoholised still wines, and to do chemical profiling, with focus on volatile aroma compounds, of the wines. The sensory profiles of a set of commercial de-alcoholised still wines (n=16) were generated by the free listing (FL) method. Wine industry professionals (n=52) from seven different wine cellars participated were asked to freely list the sensory descriptors they associated with the wines upon tasting. For quality evaluation, the same panel was required to score the wines’ perceived quality using a 20-point scale. The sensory modalities evaluated for quality were appearance (max=3), nose (max=7), and palate (max=10) added up to a score of 20. In addition, to obtain a chemical profile, chemical compounds of a wine set (n=14) were quantified. However, data processing was required for the text generated from the free listing sensory evaluation method. For instance, free listing generated 11627 words which were standardised to 3846 descriptions after removal of non-sensory descriptions, repetitions of descriptions and comparisons. Thereafter, lemmatisation was done where descriptors were reduced to their roots and grouped into descriptor categories. The established sensory profile consisted of positive, neutral, and negative descriptor categories. The results of the study reveal that negative sensory descriptors were cited many times compared to positive characteristics: “off-odours”, “lack of aroma”, “lacks flavour”, and “watery”. However, it is important to note that there were positive descriptors: “good aroma” and “good palate”. Even though, “fruit” a neutral descriptor was the most cited which might have contributed positively to the sensory quality of these wines. In overall these results lack cultivar specific descriptions and thus wine authenticity which indicates that the complex aroma and flavour profile of full-strength white, rosé and red wines can be lowered drastically due to the process of de-alcoholisation. These sensory descriptors were then correlated with quality scores attained using the 20-point scale scoring system in which some of the wines received very low scores. As a result, the average of the overall scores was 13 out 20 which is explained as “borderline faulty”, “unbalanced wine”. In addition, the concentrations of the wines under study had 4 folds less of esters, 17 folds less of higher alcohols, and 3 folds less of fatty acids when compared to published ideal wines values, depicting poor wine quality. This pioneering study has established the sensory, quality, and chemical profile of this wine for the improvement of this category. As a result, major concerns both in sensory quality and the chemical profile of this new category have been successfully identified and insights into the way forward have been recommended to the wine industry and future studies.