INSIGHT THE IMPACT OF GRAPE PRESSING ON MUST COMPOSITION
The pre-fermentative steps play a relevant role for the characteristics of white wine . In particular, the grape pressing can affect the chemical composition and sensory profile and its optimized management leads to the desired extraction of aromas and their precursors, and phenols resulting in a balanced wine [2-4]. These aspects are important especially for must addressed to the sparkling wine as appropriate extraction of phenols is expected being dependent to grape composition, as well. To the best of our knowledge, a gap exists regarding grape composition – pressing conditions – must composition. To fulfill this gap and support the wine industry, this research aimed to clarify the impact of grape pressing based on both grape and must composition.
Chardonnay (7 samples) and Pinot blanc (2 samples) grapes were collected in vintage 2022 from different vineyards in Franciacorta area (Lombardy, Italy). These grapes were used to produce musts under an industrial scale following the pressing conditions adopted by wineries. Must samples were obtained at different extraction yields (e.g. running juice, 20, 30 [first fraction], 40, 50 [second fraction], 60 and 70 [third fraction] % must yields). The chemical parameters, turbidity units (NTU), color index (ABS 420 nm), total phenol index (TPI), polyphenol oxidase (PPO) activity and antioxidant capacity (AC) were assessed in both grape and must samples.
A decreasing trend of readily assimilable nitrogen and titratable acidity was found in must samples with higher extraction yields, while the opposite was observed for pH, NTU, color index, TPI and AC with a different extend dependent from the grape varieties and pressing conditions. Considering the first fraction must, a high variability in phenol extraction was found, from 16% to about 35%. Such a difference could be attributable to the different pressing conditions adopted as comparable levels of TPI were detected in grapes used (1.7-2.2 g/L, RDS=10%). The PPO activity seemed to be unaffected by the increased must extraction yield. Grape variety was influential on phenol content for the same must yield being higher for Pinot blanc probably due to its thinner skin in comparison to Chardonnay.
This study suggests the phenol-related indexes should be considered in addition to the chemical parameters for the accurate management of the pressing step; it also has been clarifying the relation existing between the composition of grape and must.
Issue: OENO Macrowine 2023
Contact the author*
White grape, Must extraction, Sparkling wine, Phenols