Withering, rolling, fermenting, and burning are the four essential phases in the fermentation process for black tea (or drying). The plucked leaves are first fanned out to dry. The withered leaves are then rolled to release the compounds that are necessary for the final color and flavor of the leaf. The curled leaves are stretched out again to collect oxygen (oxidize), turning them from green to coppery crimson. Finally, the oxidized leaves are burnt to stop the fermentation process, turning the leaf black and imparting the distinctive tea aroma.