EXPLORING THE IMPACT OF PRESSING: FROM GRAPE COMPOSITION TO SPARKLING WINE PRODUCTION.

Pressing has a relevant impact on the characteristics of the must and, consequently, the wine produced with it. Therefore, the appropriate management of pressing leads to balanced chemical characteristics, in particular in terms of organic acid, potassium and pH, as well as the adequate extraction of aromas and their precursors, and phenols. This aspect is especially important for the production of sparkling wine which requires a base wine with specific features, such as high acidity, and low pH and phenols. The general objective of the PhD thesis was to address the knowledge gap existing with regard to grape, must, and base and sparkling wine composition based on the pressing conditions applied. Grape juice was obtained under laboratory-scale with the aims to select the pressing method for the (i) proper monitoring the grape ripening and (ii) the simulation of the grape pressing under industrial-scale. Chardonnay and Pinot blanc grape samples were collected across vintages 2022 and 2023; they were characterized for quality parameters (total and extractable flavonoids, and extractability). Four different pressing methods (manual pressing, vacuum pressing, small screw press and juicer) were applied to produce juice. Characterization of grape samples showed relevance variability of phenol extractability with significant differences between vintages, reaching up to 64.1% and 43.8% for 2022 and 2023, respectively. The small screw press showed consistently lower phenol extraction, suggesting it can be a suitable pressing method for monitoring grape maturity and appropriately choosing harvest date based on phenolic-related indexes alongside sugars, pH, and titratable acidity. The differences among the adopted pressing methods were further proved by Raman spectroscopy and the built predictive models showed good accuracy. The results highlight the need to carefully select the pressing method for monitoring the grape ripening. The pressing under industrial-scale was monitored in order to evaluate the impact of pressing on the composition of industrial musts collecting at different yields. Higher extraction yields led to decreased readily assimilable nitrogen and titratable acidity. On the contrary, pH, turbidity, color index, total phenolic index, and antioxidant capacity increased for higher extraction yields. 1° (30%) and 2° (50%) must fractions, addressed to sparkling wine production, showed significant differences for phenolic-related indexes for two consecutive vintages. These results indicate the importance of taking into account the concentration of phenols for improving the grape fractioning and to possibly adapt the pressing conditions to vintage-specific characteristics. The differences among fractions were consistent even considering the chemical parameters coupled with chemometrics. This data analysis showed high accuracy in classifying 1° and 2° must fractions as well as pressing machines. Experimental base and sparkling wines were produced with 1° and 2° fraction musts in order to clarify the relation between must and wine composition. The results indicated the characteristics of base wine, dependent from the pressing conditions adopted, were crucial especially for the phenolics content of sparkling wines. Therefore, the achievement of adequately-balanced base wine can be effectively managed through appropriate pressing conditions considering the grape characteristics and variety as well as vintage-specific factors.