The crusty layer, up to two feet or more deep, of grape skins, pulp, stems, and seeds that rises and floats on top of the juice during a red wine’s FERMENTATION. The cap must be kept in contact with the juice by one of several methods. It may be frequently PUNCHED DOWN into the juice, or the juice can be PUMPED OVER, that is, drawn up from the bottom of the tank and then showered over the cap. As a result of being punched down or pumped over, the ALCOHOL in the fermenting juice can extract COLOR, AROMA, flavor, and TANNIN from the cap. In addition, if the cap is not broken up and kept wet with the juice, it dries out and becomes a haven for bacteria that will ultimately mar the wine.