Influence of Pressure and Cake Crumbling on Must Compounds Extraction during Automated Grape Pressing

Grape pressing represents a critical technological stage in winemaking, profoundly influencing the chemical composition and sensory characteristics of the final must and wine. This study investigated the impact of two key operational parameters of automated pneumatic membrane presses – applied pressure and pomace cake crumbling (shuffling) – on the extraction of fundamental compounds from Macabeo grape must. The objective was to quantify how these variables modulate the release of sugars, acids (malic, tartaric), calcium, phenolic compounds (catechins, total polyphenols), and turbidity. Utilizing an experimental design involving synchronized must sampling during controlled pressing cycles and subsequent chemical analysis (refractometry, pH-metry, nephelometry, enzymatic and spectrophotometric methods), the effects were evaluated via ANOVA. Results demonstrated that while raw material variability impacts baseline concentrations, pressure and shuffling exert distinct and statistically significant effects. Increased pressure significantly influenced the extraction of compounds predominantly located in the berry's more resistant parts (skins and seeds), such as tartaric acid, calcium, total polyphenols, and catechins. Conversely, the shuffling operation was crucial for malic acid extraction (located in the inner pulp), modulating must turbidity (due to pomace filter disruption), and significantly contributing to calcium and total polyphenol extraction by enhancing the effectiveness of applied pressure. Sugar extraction was largely independent of these parameters after the initial phases. These findings confirm that targeted management of pressure and shuffling allows winemakers to selectively control must composition, thereby guiding the style and quality of the final wine.