Assessment of physicochemical differences in Nebbiolo grape berries from different production areas sorted by flotation

In vineyards, the existence of in-field grape variability attributable to environmental factors can induce differences in the ripening process and, therefore, in the physicochemical characteristics of the grape berries. This variability is often higher among different growing locations. Automatic, densimetric berry-sorting machines have recently been developed and proposed for use in wineries to reduce this variability, thereby making the grape quality uniform in terms of density. Densimetric sorting requires the selection of a density value according to objective quality parameters of the berries. The aim of this work was to determine the relationships among different objective quality parameters of Nebbiolo grapes harvested on the same date, such as mechanical properties, phenolic composition and extractability indices; to determine the berry density estimated by flotation in different salt solutions of densities ranging from 1069 to 1125 kg m-3; and to investigate the influence of the growing location on these relationships. The results revealed that the most promising physicochemical parameters for determining the appropriate density are the total anthocyanin and flavonoid concentrations in the skins, the total flavonoid and oligomer proanthocyanidin contents in the seeds, as well as skin hardness and thickness. Nevertheless, density selection must be performed for each individual vineyard or homogeneous group of vineyards belonging to the same production zone because the correlation of the berry density with these parameters also depends on the vineyard effect. The results of densimetric sorting of berries are attractive because this emerging technology can be pursued to separate grapes with different quality parameters.