Physical-chemical characterization of Moscatel de Setúbal fortified wines from different vintages

Abstract

Moscatel de Setúbal is a Portuguese fortified wine with Protected Designation of Origin (PDO Setúbal), made from Moscatel de Setúbal grape variety (Muscat of Alexandria) [1]. The particular winemaking process of this white wine comprises fortification with wine spirit or vinous alcohol after a short period of alcoholic fermentation, followed by a prolonged maceration stage (commonly 5 months) with the skins and grape seeds. After that, traditionally the mixture of free-running wine and press wine is aged in used wooden oak barrels, for a minimum of 18 months [1]. Although highly recognized for its quality, only scarce scientific knowledge is available on this wine. This study aimed to characterize Moscatel de Setúbal wines from different vintages, in terms of general physical-chemical composition, phenolic composition and chromatic characteristics. For that, twenty-seven Moscatel de Setúbal fortified wines from different vintages (1985 and from 1995 to 2020), collected in May 2023, from the corresponding barrels where they are ageing, were analysed regarding chromatic characteristics [Absorbance at 420 nm, CIELab (L*, a*, b*, C, h)], turbidity [2] tanning power [3], and phenolic composition (total phenols [4], monomeric flavanols and proanthocyanidins according to the degree of polymerization [5] [6]). All analytical determinations were performed in triplicate and the data results were subjected to one-way analysis of variance (ANOVA). Whenever a significant effect (p<0.05) of the year of production was observed, the Fisher’s minimum significant difference test was used to compare the wines. For the parameters for which there was a significant effect of the vintage year, principal component analysis (PCA) was performed. As expected, it was found that the longer the barrel ageing time, the more intense the colour of these wines. Higher values of total phenols content were observed in the older wines and, simultaneously, the tanning power was higher in wines with longer ageing period. In the older wines, the oligomeric proanthocyanidins and flavanol monomers were found in higher proportion than the polymeric proanthocyanidins. Therefore, two profiles of wines were identified: a first one in which flavanol monomers predominate (vintages from 1985 and 1995 to 2001, except 1997), and a second one with predominance of polymeric proanthocyanidins (vintages from 1997 and 2003 to 2020). The results obtained confirm that the ageing step influences the chromatic characteristics and phenolic profile of this fortified wine. Finally, this study enlarges the very limited knowledge on Moscatel the Setúbal fortified wines.

References

[1] Portaria No. 118/2014 de 3 de Junho de 2014. Diário da República n.º 106/2014, Série I de 2014-06-03, 3047-3050.

[2] OIV, 2021. International Code of Oenological Practices. International Organisation of Vine and Wine, Paris, France.

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