Resumo

CANAS, Sara; LEANDRO, M. Conceição  e  SPRANGER, M.I.. The precipitation of colouring matter in red wines. Contribution to the study of the deposits composition . Ciência Téc. Vitiv. [online]. 2000, vol.15, n.1, pp.27-40. ISSN 0254-0223.

The colour instability of some red wines, particularly those from the Delimited Region of Vinhos Verdes, has caused a great depreciation of these products, with heavy economics and social effects. In fact, in recent years an excessive precipitation of colouring matter has been observed at the bottom of the storage tanks and even in bottled wines. This precipitation occurs along with the natural evolution of red wine during the storage period, and origins a considerable modification of its colour, that is one of the most important aspects for the evaluation of its quality. In this work is presented the study of some characteristics of the deposits of Vinhos Verdes Vinhão, Espadeiro and Borraçal, as well as the characteristics of the deposits of a Tinta Miúda wine with stem and without stem, that seems to be closely related with colouring matter stability. Their knowledge is of considerable interest to better understand the compounds and the mechanisms involved in that precipitation. Thus, it can contribute to find any solution to this problem. The deposits are constituted by a soluble fraction and an insoluble fraction. The former is mainly formed by tartrates, while monomeric anthocyanins only represent a small part of it. The latter is possibly constituted by micro-organisms, mucilages or the remaining solid part of the grape, as well as polymers or condensed pigments that are responsible for its red coloration. Among the anthocyanins there are a preferential precipitation of the cinnamic esters, mainly the cumaric ones. The non esterified anthocyanins have also an important precipitation, especially delphinidin-3-glucoside, cyanidin-3-glucoside and petunidin-3-glucoside, probably due to their higher polarity. The results also suggest that the preferential precipitation of some monomeric anthocyanins may be due to the tartaric precipitation, but the type of wine (the grape cultivar) is the most determining factor.

Palavras-chave : Red wines; Precipitation; Colouring matter; Tartrate; Anthocyanins.

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