Term (also pumping over, circulating) for the mixing of the fermenting grape must with the grape skins (mash), which is particularly common in red wine production. During mash fermentation, the solid components (berries, skins, rape) rise to the surface of the fermentation tank due to the carbon dioxide pressure and form the cap. To maintain contact between the cap and the must, the must is pumped from the bottom and poured over the cap. This forces the extraction of colour and tannins from the grape skins, which are then increasingly released into the must.
Alternatively, the cap is submerged mechanically or manually...
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Andreas Essl
Autor, Modena