Fermentation in oak occurs by placing the must or crushed grapes directly into oak barrels whose heads have been removed. Dry ice maybe added to control the temperature of fermentation. The barrels may then be seal and rolled back and forth to ensure the cap stays moist. Fermentation in oak is labor intensive but adds imparting the oak characteristics to the wine as well as allowing micro-oxygenation to achieve a rounder, more lush mouthfeel.