Definition - What does Pomace mean?
Pomace refers to the leftover solids from grapes after they have been pressed for juice for white wines, or the after juice has finished its fermentation for red wines. It includes the skins, seeds and stems.
These are unwanted materials and they are sometimes made into a compost pile to fertilize the vineyards in a later stage.
WineFrog explains Pomace
While pomace may be a byproduct of winemaking, for some wineries, it still has a use. After white grapes are pressed, the remnants of skin, stems and seeds are rich in sugar, amino acids, nitrogen and other elements.
For red wine making, the pomace remains after the run-off from the fermentation vat has been removed. The cap is left behind to be shoveled out and moved to a press where more wine can be extracted. It contains less sugar, but it still has a variety of interesting components; organic acids, sugars that cannot be fermented, tannins, anthocyanin and phenolic compounds. The seeds which are left behind are still solid and still contain nutritious oils. Sometimes, the latter is sent to press for top-quality oil for cooking.
White and red grape skins from pomace also contain cream of tarter. This is an important ingredient for baking, and some wineries will sell their pomace so these extras can be separated and later sold to restaurants or the public.