About Tea
Oxidation levels and production
Green tea (Chinese: Lü CHA; Japanese: RYOKU CHA)
Unoxidized.
The damp leaves are quickly steamed (Japan) or quickly heated (China) on heated metal pans. This breaks down the enzymes (all biochemical processes are stopped in the plant cells) the leaves are shaped and then dried. In China, high-quality green tea leaves are sorted by hand.
Fermentation level: 0%
Typical tea: Zhu Cha (“Gunpowder” from Zhejiang province)
White tea (Chinese: BAI CHA)
Light oxidation.
The harvested leaves are generally put out to dry in the sun on large, rounded bamboo plates. The withering process, little by little, turns into a drying process during which the leaves are aerated through jiggling by hand, and some sap from the cells oxidizes slightly. The leaves are finally dried in a drum dryer to prevent any further oxidation. The dried tea is patiently sorted by hand from straw baskets to remove stalks and impurities.
Fermentation level: 10 – 20%
Typical tea: Bai Mu Dan (China, Fujian province)
Yellow tea (Chinese: HUANG CHA)
Light-late oxidation (incorrectly placed in the category of green, lightly-fermented teas)
The fresh leaves are quickly heated to denature their enzymes (preventing undesirable oxidation processes) and are shaped by hand or machine while still damp. Then, they are placed in a heating vessel and kept at a constant temperature and humidity, which leads to very gradual late oxidation. This process can take several days. Finally, the leaves are dried and sorted..
Fermentation level: 10 – 20%
Typical tea: Meng Ding Huang Ya (China, Sichuan province)
Semi-fermented tea (Chinese: QING CHA, Oolongs; Western languages: Green-blue, Semi-Green)
Partially oxidized.
The fresh leaves are placed in horizontally turning baskets and slowly wither and dry with a continuous, forced inflow of warm air. During this process, some types (Tie Guan Yin, Taiwan Tungting) are placed on cloth wrappers in which they are compressed on special rotating tables such that they roll up into little balls. Afterwards, they are again put into the rotating baskets. This process is repeated several times (up to seven). While turning in the baskets, the leaves’ cell walls are ruptured and the cell sap is oxidized. This process is stopped by the final drying in the drum dryers. For other types (Shui Xian, Wu Long), the compression process is skipped, which gives long leaves with a spiral shape. Again, most are sorted and cleaned by hand.
Fermentation level: 15 – 70%
Typical tea: Tie Guan Yin (China, Fujian province)
Black tea (Chinese: HONG CHA meaning red tea)
Fully fermented.
The damp leaves are placed on a bed, under which warm air is blown, where they wither for 6 to 24 hours. After this, they are placed on rotation baths – rollers, where their cell structures are disrupted. A deep, enzymatic oxidation of the freed polyphenols starts to take place. The leaves are then spread out on so-called fermentation tables in a room with high temperature and humidity for 2 to 3 hours. Here, they are completely oxidized. In the end, they are rapidly and thoroughly dried on belt dryers at high temperature. For Indian Darjeeling, complete oxidation is broken by drying.
Fermentation level: 80 – 90%
Typical tea: Dian Hong (China, Yunnan province)
Pu-er teas (Chinese: PU’ER, HEI CHA which means black)
Double fermented.
The damp leaves are spread out under the sun, where they wither. As they wither, they are turned and dried. This manipulation disrupts their cell structure and starts the oxidation process. The dry leaves are steamed and spread out in layers in the fermentation room where they are covered with a cloth and kept at high humidity. The additional fermentation process begins, which then lasts several days. At the end, they are thoroughly dried at high temperature on belt dryers.
These teas are often pressed into various forms, in which case the leaves are steamed before being formed, and additional fermentation occurs while they dry.
Fermentation level: 100%
Typical tea: Pu-Er in bulk, Tuo Cha (China, Yunnan province)