Cabernet Franc grapes belonging to six different classes of sugar level content (from 176.5 to 258.5 g/L) at harvest were studied. Their physical proprieties and mechanical behavior were measured using compression and puncture tests. The evolution of anthocyanins extractability was determined. Significant differences were found in grape textural properties and anthocyanins content due to the sugar level content in the different samples of berries tested. It appears that the sweetest berries are characterized by a higher extraction yield of anthocyanins (up to +3.55%) with respect to those with more low sugar content. Furthermore, significant relationships exist between the extractability of anthocyanins and the mechanical and physical attributes of the grape berries. The best correlations were obtained with physical parameters such as the berry weight and the surface : volume ratio (r = −0.99 and 0.97, respectively) and with double compression test parameters such as hardness, chewiness and springiness (r = −0.90, −0.91 and 0.92, respectively).
The purpose and the originality of this work were to determine the real impact of the heterogeneity of grapes at harvest. Among the berries with different sugar contents, were assessed the real differences in anthocyanin contents and extractability at harvest. The results acquired, also in function of different distribution percentage of the berries after floatation, suggest that each class of berries may influence in unlike way the final quality of wine. Therefore, automatic densimetric berry-sorting machines recently developed and proposed for use in wineries could be indeed useful to select the grapes after the harvest.