Assessment of the pedicel detaching and crashing forces of grape berries to determine the right mechanical harvesting time

Abstract

During the mechanical harvesting the shakers cause the detachment of the grape berries from the grape stalk but also the breaking of the grape berries peel with the consequent production of must that influences the quality of the harvested grapes. This one is higher in the varieties having grape berries more resistant to the crushing and, at the same time, an easier detachment of the pedicel. The aim of this work is to evaluate, for three different varieties of grape (Chardonnay, Catarratto comune and Nero d’Avola), the crushing strength of the berry, that represents the cause of the production of must during the mechanical harvesting, and the resistance of the berry-pedicel system that influences the detachment of the berries during the harvesting. The tests were carried out both by day and by night in order to evaluate the physical-mechanical response of the grape berry to different temperatures and were repeated in different periods, the last corresponding to the harvesting. The results show that the time of harvesting can be certainly brought forward for the three varieties in order to obtain an higher quantity of integral berries, then a better quality of the final product. Moreover, the must index by night was higher than the must index by day. Comparing the three different varieties it comes out that the variety Catarratto comune has the highest crushing strength values both by day and by night, while the variety Nero d’Avola has the highest values of detaching force by day and the Catarratto comune by night.