Fermentation-Generated Wet Foams: Working-Volume Scaling, Temporal Evolution and Nominal-Freeboard Burden

Foam generated during wine-must fermentation can reduce the vessel space available for processing liquid. Its practical impact depends on the amount of foam, its persistence, and its position relative to the initial liquid level. This study quantified these features in five must batches: Sauvignon Blanc, Vidiano, Xinomavro rosé, Syrah rosé, and a 50:50 Syrah/Cabernet Sauvignon co-vinification. Two types of experiments used transparent open-topped 1 L vessels. The first tested four initial liquid volumes (500, 600, 700, and 800 mL), with three independently fermented vessels per batch–volume combination (60 vessels), at approximately 12 °C for white musts and 14 °C for rosé musts. The second followed three vessels per batch containing 700 mL at a common temperature of 12.0 ± 0.3 °C, with 12 sampling times from day 0 (D0) to day 16 (D16). Photographic measurements estimated apparent foam volume and recorded the underlying bulk-liquid level. Peak foam volume increased by 11.51–14.16 mL per additional 100 mL of must; peak foam-to-initial-liquid ratios were 11.75–13.29% across batch means. Foam reached sampled maxima on days 10–11 and remained visible at D16. Area under the foam-volume curve ranged from 798.60 ± 1.89 to 954.85 ± 8.89 mL·day. At 800 mL initial fill, peak apparent foam corresponded to 46.83–53.17% of the initial 200 mL headspace. Paired data at 700 mL showed that the lower foam boundary moved downward during foam development and partly recovered as foam declined; total foam-layer burden is therefore distinct from net protrusion above the initial liquid level. These batch- and vessel-specific results support preliminary assessment of fermentation foam and freeboard, but do not establish general varietal rankings or industrial safe-fill limits.