Term (also pumping over, circulating) for the mixing of the fermenting grape must with the grape skins (the mash), which is especially common in red wine production. During the mash fermentation in the vinification of a red wine, the solid components (berries, skins and rape) rise to the surface of the fermentation container due to the carbon dioxide pressure and form the so-called pomace cap. To maintain contact between this and the must, the must is pumped off the bottom and poured over the pomace. This forces the extraction of the colour and tannins from the grape skins, which then enter the must to a greater extent. Alternatively, the marc cap is submerged mechanically or manually (French: pigeage). At the beginning of fermentation during the first few days, this process takes place several times a day and must then be completed at the best possible time. This also depends on the colour intensity of the berry skins, which varies depending on the grape variety. The resulting oxygen supply favours oxidative processes.