Effect of the estufagem process on the chemical constituents of Madeira wines

Madeira wine is a product of well-established reputation, whose aroma and flavour is the result of unique combinations. Particularly, its maturation may include estufagem, wherein wine is usually heated at 45 °C for three months. During this period, several chemical changes may occur, so it is essential to assess its impact on the wine. In this sense, the main objective of the thesis was to evaluate the effect estufagem on the chemical constituents of Madeira wine, specifically on those molecules potentially important in the development of its typical features. Firstly, analytical methodologies capable of determining the target compounds, combining precision and reproducibility to execution effectiveness, were developed. Then various monovarietal Madeira wines were analysed during estufagem under standard and overheating conditions in order to assess its effect. The following compounds were evaluated: furans, amino acids, biogenic amines, polyphenols, organic acids and volatile compounds. In addition, the total polyphenolic composition, the antioxidant potential and the colour of these wines were also evaluated. The results show that most constituents change due to the heating process. Particularly, the heating promotes the development of 5-hydroxymethylfurfural (HMF) in sweet wines submitted to estufagem at higher temperatures. Moreover, estufagem provides the decrease of most amino acids, suggesting their involvement in the formation of the bouquet of these wines. Regarding the total polyphenol content and antioxidant potential of these wines they do not seem to be greatly affected by the heating step, however most monomeric polyphenols decrease during this process. The thermal processing of Madeira wines favours the development of the volatile composition, especially of volatiles usually reported as typical aromas of Madeira wines. Finally, it was demonstrated that the thermal degradation of sugars, especially of fructose, promotes the emergence of volatile compounds identified in baked wines.

Impact of forced-aging process on Madeira Wine flavor

The aim of this study was to determine the optimal temperature and baking time to obtain a Madeira wine considered typical by an expert panel. For this purpose simultaneous descriptive analyses of typical Madeira wines were performed, and seven descriptors were selected: “dried fruit”, “nutty”, “musty”, “baked”, “oak”, “mushroom”, and “brown sugar”. Up to 10 odor-active zones were the most frequently cited by the members of the GC-olfactometry panel as corresponding to the panel’s descriptors. The odor importance of each of the zones reported by the GC-O analysis was ranked by AEDA. Three odor zones were identified as common to both Malvasia and Sercial wines and had retention indices (RI) of 1993 (“brown sugar” and “toasted”), 2151 (“brown sugar”), and 2174 (“nutty”, “driedfruits”);sotolonwasidentifiedasresponsibleforthislastaroma.Severalmoleculeswereselected to be quantified on baked wines on the basis of AEDA results and expected Maillard volatiles, such as sotolon, furfural, 5-methylfurfural, 5-ethoximethylfurfural, methional, and phenylacetaldehyde. It was observed that typicity scores were positively correlated with the concentrations of sotolon and sugar and baking time and negatively with the fermentation length.