After harvesting and pressing, the must is left to ferment in stainless steel tanks. Traditionally, and until recently, this was done in oak or chestnut barrels, called kupels, in Basque. Fermentation lasts 20–25 days and then the txacolí is left to lie on its lees. The CO2 prevents oxidation and dissolves the sediments and gives the wine its sparkling characteristic. The wines is not racked so it does not lose its sparkle and is clarified by natural sedimentation by gravity in the tank or barrel. Traditionally, the wine is tasted on the feast of San Antonio on 17 January, which is known as Txacolí Day (Txacoli Eguna, in Basque).