Step 4. Oxidation: After rolling, the leaves are laid out to rest for several hours, allowing oxidation to take place. Oxidation is the process in which the oxygen in the air interacts with the now-exposed enzymes in the leaf, turning it a reddish-brown color and changing the chemical composition. This step also has the greatest impact in the creation of the many wonderful and complex flavors in tea. The length of this process depends on the style of tea being produced and the ambient conditions at the time. [Photo provided to China Daily]