Tea leaves used for black teas are allowed to oxidize fully before being heated and dried. Black teas from India are oxidized for shorter periods of time than those from China. They also tend to be a little more astringent. Black teas from China tend to be darker and a bit smokier.
China Black Tea:
Withering: After being picked, tea leaves are taken to a factory to wither, a process that softens and removes some of the moisture in the leaves. Traditionally the leaves may be spread onto bamboo racks or onto the ground and turned over the course of five to six hours. Mechanical withering involves using fans to circulate heated air around the leaves. This method is a bit shorter.
Rolling: The leaves are rolled to help expose the flavorful and aromatic oils within as well as aid in oxidation. This is typically done by machine.
Oxidizing: The withered and rolled leaves are then laid out and covered with damp cloths for eight to twelve hours to allow them to fully oxidize.
Drying: The tea is then dried to halt oxidation and eliminate moisture from the leaves.
Sifting: Finally, the leaves are sifted to remove broken bits and sorted into varying sizes.
India Black Teas:
Withering: After being picked, tea leaves are placed in a temperature and humidity controlled environment with air circulating around the leaves. The process will take about 14 – 17 hours.
Rolling: Withered leaves are placed into vats and pressed into a mass then rolled under varying degrees of pressure. To ensure the most attractive and best tasting finished tea, the Indian rolling process is very precise.
Oxidizing: The tea is laid onto trays and, depending upon humidity and the type of finished tea, allowed to oxidize for as little as 15 minutes or as long as four hours.
Drying: The tea is then dried for 20 – 30 minutes to halt oxidation and eliminate moisture from the leaves.
Sorting: Finally, the leaves are sorted into varying sizes. As Indian teas are graded by size, this is an important last step.