Evolution of mechanical variables of winegrapes for icewine production during on-vine drying

The evolution of some mechanical properties of the berry skin and pedicel during on-vine drying of wine-grapes was studied, in order to assess the suitability of two alpine cultivars, Becuét and Fumin, for the production of icewines. This overripening process on the vine, which lasts until complete freezing of the grapes, results in marked changes in the mechanical characteristics of the grapes. During grape dehydration, the skin thickness increased in both cultivars (Becuét +73 μm, Fumin +85 μm). The skin hardness also increased, particularly in the Becuét berries, in which the break skin force and break skin energy values increased of 0.148 N and 0.823 mJ, respectively. In contrast, the peduncle detachment force decreased during the drying process; in Becuét grapes, this occurred after only 15 days. While the two cultivars have different mechanical properties, both proved to be suitable for the production of icewines ("Vini del ghiaccio"); the changes that occur during on-vine drying do not preclude the resistance of the berries to shattering and of the berry skin to splitting.