Exploring the impact of grape pressing on must and wine composition

Pressing has a relevant impact on the characteristics of the must and subsequently on white wines produced. Therefore, the adequate management of pressing can lead to the desired extraction of phenols and other grape compounds (i.e. organic acids), aromas and their precursors, allowing the production of balanced wines. This aspect is especially important to sparkling wine where the acidity and pH, and the content of phenols affect its longevity and the expected sensory character. To the best of our knowledge, a gap exists in the scientific literature regarding the correlation within the composition of grape, must, and wine that should be clarified. To fill this gap and support the wine industry, this research aimed to clarify the impact of grape pressing based on grape, must, and wine composition. Chardonnay grapes (7 samples) were collected in vintage 2022 from different vineyards in Franciacorta area (Lombardy, Italy) in which total and extractable flavonoids (FLVs) were determined. These grapes were pressed under industrial conditions, following the procedures applied by the wineries, and samples were collected at different extraction yields (e.g. running juice, 20, 30 [1° fraction], 40, 50 [2° fraction], 60 and 70 fraction] % must yields). Experimental base wines were produced from 1° and 2° fractions following a minimal intervention approach. These base wines were submitted to the in-bottle fermentation and aging on yeast lees was performed. The general chemical parameters, color index (ABS 420 nm), total phenol index (TPI) were assessed for must, base wine and sparkling wines. Moreover, turbidity units (NTU), FLVs, polyphenol oxidase (PPO) activity, and antioxidant capacity (AC) were determined in must samples. A moderate variability in the total FLVs was detected in the grape samples analyzed. In particular, one grape sample showed a content of total FLVs approximately twice compared to the other samples. Nonetheless, comparable extractability was estimated suggesting a similar behavior under pressing in the same conditions of these grape batches. During the pressing, a decrease of titratable acidity was found in must samples with increasing extraction yields, while the opposite was observed for pH, NTU, color index, TPI, TFVs and AC. The PPO activity seemed to be unaffected by the increased must extraction yield. Considering the 1° fraction musts, a relevant variability in phenol extraction was detected up to about 18%, while for the 2° fraction musts it was up to 28%. Wines produced from 1° fraction, had higher titratable acidity and dry extracts, while those from 2° fraction showed higher pH. The sparkling wines did show little differences for titratable acidity, pH and color index after 6 months of aging on yeast lees. The tasting revealed that the floral, fruity and nuts notes were highly scored in most of the sparkling wines from 1° fraction musts in comparison to those from 2° fraction musts. However, longer aging on yeast lees is necessary to better understand the evolution of sparkling wines. The results obtained from this study suggests that the phenol-related indexes should be also considered during the must production. These parameters are of importance in particular for sparkling wine as its freshness can be preserved and its oxidability can be limited.