Metabolic modifications occurring during maturation in Ribolla Gialla grapes, and implication of vineyard site, cluster thinning, and harvest time on the composition and the sensory evaluation of sparkling wines

Ribolla Gialla (Vitis vinifera L.) is an indigenous white grape variety cultivated in northeastern Italy, in Slovenia and on the Ionian Islands in Greece, where it is known as Rebula and Robola, respectively, and can be considered as one of the most promising for producing high-quality monovarietal sparkling wines. However, due to its neutral aromatic potential, the manipulation of wine quality thus mainly depends on the application of viticultural or oenological practices. For instance, cluster thinning is a commonly adopted viticultural technique for selective removal of excessive clusters and allows calibrated vine productivity with increased accumulation of metabolites in the fruit. Modulating of wine grapes yield will therefore activate the intrinsic changes in basic berry composition (including soluble solids, organic acids, pH phenolics and anthocyanins), resulting from thinning treatment, while also changing the rate of grape ripening. Consequently, monitoring the ripening of the grapes is important mainly to determine the ideal harvest time. As this study shows, different harvest times have a significant impact on chemical composition of wines, which can lead to different sensory characteristics. The objective of this research work was therefore to produce a comprehensive study of discussed viticultural measures in the production of monovarietal Ribolla Gialla sparkling wine from two different locations. The position of vineyard site should not be neglected, as it is an integral part of the terroir, that can be defined as an ecosystem, in a given place, including factors like climatic conditions, cultivar and rootstock, geography and topography, as well as soil characteristics like mineral nutrition and water supply. For this purpose, the multi-targeted approach was adopted, using different analytical techniques (GC-MS, UPLC-MS, and FTIR) to investigate the aromatic characteristics of the sparkling wines obtained, including their volatile organic composition, lipid compounds, and the metabolites of aromatic amino acids, which play a key role in the organoleptic and sensory properties of wine. The findings of this study could provide a sort of guideline, intended for winegrowers and professional experts, designed to facilitate the decision about the level of production, or to help out determine the optimal harvest time, by taking into account changing climatic conditions.