Phenolic ripeness assessment of grape skin by texture analysis

The elaboration of high quality red wines requires the assessment of grape phenolic maturity by the determination of phenolic compound concentration and their extractability during winemaking process. The main aim of this work was to ascertain whether simple texture parameters, like the grape skin hardness and thickness, account for phenolic maturity of berry skin. Furthermore, the function of these grape mechanical properties in the differentiation of 13 grapevine varieties from Galicia (northwest of Spain) was studied during both 2005 and 2006 vintages. An Universal Testing Machine TAxT2i Texture Analyzer was used to carry out the texture test. Total anthocyanin concentration varied from 191 to 2660 mg kg−1 fresh berry weight, while extractable anthocyanin concentration ranged from 116 to 1453 mg kg−1 fresh berry weight, respectively, found in Merenzao and Loureira Tinta varieties. A significant regression was found between anthocyanin extractability, berry skin break force and thickness. Berry skin break force and energy represent meaningful variables for varietal characterization and differentiation. The toughest berry skin corresponded to the Sousón variety, while Mouratón cultivar indeed was the weakest berry skin.