Tea leaves used for green tea are heated shortly after being picked to stop them from oxidizing. Green teas from China are typically allowed to wither briefly before being heated to stop the oxidation of the tea leaves. Green teas from Japan are typically heated with steam right after picking without withering. This stops the oxidation process more quickly than most green teas from China. This steaming gives Japanese green teas a more vegetative taste.
China Green Teas:
Picking: Generally only the youngest, most tender leaves are plucked – the first one or two leaves and the unopened leaf bud. The leaves begin to oxidize as soon as they are picked.
Withering: The leaves are then taken to a factory to wither, a process that removes some of the moisture in the leaves. The leaves may be spread onto bamboo racks or clothes. This is the traditional method. However, they may also be tumbled in machines as fans blow air to aid the withering. Withering can last up to a few hours, but may take less time depending on the method used and the weather conditions.
Heating: The withered leaves are then heated to prevent them from oxidizing further. The traditional method is to place small batches of leaves into heated, round-bottomed pans and continually stir them. Alternately, the tea may be heated in rotating machines.
Rolling: The leaves are rolled to help expose the flavorful and aromatic oils within as well as give them their finished shape. If the leaves are heated the traditional way (in pans and stirred by hand), then rolling is done at the same time. Leaves may be rolled into rounded shapes by hand and then further heated so they keep that shape (as with Pinhead Gunpowder). Or, they may be pressed into the pan to flatten them as they heat (as with Dragonwell Lung Ching). Various machines may also be employed to roll the leaves and provide the finished shapes.
Drying: The tea is then fully dried, which allows the flavorful components of the natural oils to remain on the leaves. It also ensures the leaves will keep over time without any chance of mold growth.
Sifting: Finally, the leaves are sifted to remove broken bits and sorted into varying sizes.
Japan Green Teas:
Picking: Machines are used to trim the tea leaves and buds from the plant then blow the cuttings into a collection bag.
Steaming: The tea leaves are then heated with steam to halt the oxidation process.
Cooling: The steamed leaves are tumbled or blown through mesh tubes to cool them and rid them of excess moisture.
Drying: The leaves are dried in four stages with rolling, shaping, sifting and sorting taking place between the stages. During the first and second stages, the leaves are tumbled in heated cylinders. In the third stage, they are heated on a conveyor belt. The final drying stage may vary according to the type of finished green tea.
Rolling: In between the first and second drying stages, the leaves are rolled by machine to release their flavorful, aromatic oils.
Shaping: In between the second and third drying stages, the leaves are shaped by machine.
Sifting: In between the third and fourth drying stages, the leaves are sifted to eliminate stems and dust. They are then sorted by size.