Evolution of grape berries during ripening: investigations into the links between their mechanical properties and the extractability of their skin anthocyanins

Aims : The aim of this work was to study the evolution of grape berries during ripening and investigate the possible relationship between the extractability of anthocyanins from grapes and their rheological properties. Methods and results : Cabernet Franc grapes belonging to three different vineyards were harvested weekly from 10 September to 8 October 2007. Their mechanical behavior was measured by compression and puncture tests and the evolution of anthocyanin extractability was monitored during ripening. Significant differences were found in grape textural attributes and anthocyanin content due to the ripening stage and type of vineyard. A multivariate regression model was built to explain the evolution of anthocyanin extractability, by using the mechanical attributes of grape berries as variables. Conclusion : Our results show that differences in the easiness of anthocyanin extraction from grapes could be linked to differences in the mechanical behavior of berries and that the extraction yield of anthocyanins from grapes could be predicted by their rheological properties. To confirm this first hypothesis, further studies with a larger number of vintages and vineyards would be necessary to link the mechanical properties of grape berries, established at macroscopic scale, to the susceptibility of anthocyanin extraction from grape skin. Significance and impact of the study : The need to understand the evolution of the mechanical behavior of winegrapes during ripening and its impact on the release of anthocyanins is important for wine quality control. Understanding the evolution of the material properties of grapes is essential for developing better approaches to improve grape quality and could help winemakers to choose the best time of harvest and the process best adapted to the wine quality desired.