Contribución al estudio de los factores que afectan la astringencia del vino tinto.

Identificador:  TDX:441

Handle: https://hdl.handle.net/20.500.11797/TDX441

Autores:  Llaudy Fernández, M. del Carme

Resumen:
The PhD thesis 'Contributions to the study of the factors that affect the red wine astringency ' approaches the study of wine astringency and some factors that determine it.On one hand, a new and reproducible methodology is described that allows measuring wine astringency, using a protein of easy availability: the ovalbumin, and tannic acid as standards. Based on this methodology was studied the influence of some not phenolic components of the wine as pH, ethanol concentration, glycerol concentration and the use of the Arabic gum, as example of polysaccharide, on the astringency. The results show that inside the usual intervals of pH, concentration of ethanol and of glycerol, the likely astringency variations would be moderate. On the contrary, the addition of Arabic gum to the wine produces an important decrease of the astringency. Besides, we compare the ovalbumin and the whole salivary proteins reactivity with tannic acid (tannin used as standards), different proanthocyanidins, and different degrees of polymerization and commercial wines of different origins. Both models of proteins present a high statistical correlation, which would indicate a similar behaviour when reacting with tannic acid and the proanthocyanidins, in spite of different affinities. The study of the wines gave statistically similar results in more than 80 % of case, concluding that utilization of ovalbumin as precipitation agent seems to be a good solution for the objective determination of the astringency in wines.On the other hand, two experiments are described where the new methodology is applied: - The study of the influence of the ripening stage and maceration time (1-23 days) on the contribution of each cluster grape components to phenolic composition and astringency in wine simulated macerations. In general terms, proanthocyanidin extraction from skins, stems and especially from seeds increased with maceration time. The ripening stage also had a major influence on tannin extraction and astringency. The tannin contribution from skins and stems increased with ripening but the contribution from the seeds decreased. The contribution to astringency from all cluster components was clearly higher when the grapes were unripened. The mean degree of polymerization of the tannins from skin and seed components was unaffected by ripening and maceration length.- The study of the micro-oxygenation used to complement aging in order to improve the quality of very astringent and herbaceous red wines. When this technique is applied prior to oak aging, the wine has slightly less intense red color and significantly higher levels of combined and free anthocyanins and ethyl bridged anthocyanin-flavanol pigments, too higher mean degree of proanthocyanidin polymerization and a drastically lower astringency. These wines also present a clearer impact of wood aromas.