Tea leaves are fermented by first being withered and then having their cell juices released, initiating oxidation.
Here's a breakdown of the tea fermentation process (more accurately called oxidation):
Steps in Tea Fermentation (Oxidation):
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Withering: Freshly harvested tea leaves are spread out in well-ventilated areas, often on withering troughs. This reduces the moisture content of the leaves, making them more pliable for subsequent processing. The leaves begin to wilt.
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Leaf Disruption (Rolling/Bruising): The withered leaves are then rolled or crushed using machines. This process breaks down the cell walls of the tea leaves, releasing cell juices containing enzymes and other compounds necessary for oxidation. Various methods can be used including:
- Orthodox Rolling: Uses machines to twist and curl the leaves.
- Cut, Tear, Curl (CTC): Machines chop the leaves into small pieces.
- Rotorvane: Uses an auger-like device to macerate the leaves.
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Oxidation: Once the cell walls are broken, the released enzymes react with oxygen in the air. This is where the "fermentation" actually occurs (it's technically oxidation, not fermentation in the strict microbiological sense). The leaves are spread out in a cool, humid environment to allow oxidation to proceed. The tea leaves gradually change color, from green to copper-red. The length of the oxidation process determines the type of tea (e.g., black tea is fully oxidized, oolong tea is partially oxidized, and green tea is not oxidized).
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Firing (Drying): After the desired level of oxidation is achieved, the tea leaves are dried using hot air. This stops the oxidation process and reduces the moisture content to about 3%, preventing spoilage and preserving the tea's flavor.
Key Factors Influencing Fermentation (Oxidation):
- Temperature: Affects enzyme activity.
- Humidity: Prevents the leaves from drying out too quickly.
- Time: Determines the extent of oxidation and the type of tea produced.
In summary, "fermentation" in tea production refers to the oxidation process that develops the tea's characteristic color, flavor, and aroma. It involves withering, leaf disruption to release cell contents, controlled oxidation, and finally, drying to halt the process.
