Multiannual Study of the Polyphenolic Potential of Tannat Grapes in Southern Uruguay

Abstract

This study was conducted to characterize the polyphenolic potential of Tannat grapes and to evaluate the usefulness of these indices as indicators of maturity, oenological quality, and as reference values to optimize the management of the vinification. The tests were conducted during four years (2001-2004) in variety Tannat vineyards located in southern Uruguay. The analyses were performed from veraison to harvest of the grapes. The berry weight and the basic composition of the grapes (sugar, total acidity and pH) were determined. The polyphenolic potential indexes were analysed according to Glories and Augustin (1993), modified by González-Neves (2005). Total and extractable anthocyanins potentials increased during ripening; however, the maximum concentrations of these compounds were obtained some days before the maximum of the sugars concentration in the majority of the situations. The extractability of anthocyanins had a varied evolution, depending on the vineyards and the vintages, with a decreasing trend during most of the period evaluated. The concentrations of tannins in the seeds decreased, but the concentrations of tannins in the skins increased during ripening. At harvest, significant differences were observed in the contents of polyphenols in the skins and seeds of grapes from different vineyards and years considered.. The polyphenolic indexes of the grapes do not allow to define the optimum moment of harvest, but they provide important information for the oenological assessment of the grapes, and for the conditions for the winemaking.