Tea Processing and Classification Based on Fermentation Levels (Non-Fermented and Fully-Fermented)
Tea leaves can be classified into two main categories based on the production and processing procedures as well as the quality characteristics of the tea after processing: (1) based on the degree of fermentation and oxidation during tea processing: non-fermented tea, partially fermented tea, and fully fermented tea; (2) based on the appearance, color, and soup color of the finished tea: green tea, yellow tea, white tea, oolong tea, black tea, and dark tea. (1) Tea processing with different levels of fermentation. During the processing procedure, the tea leaves will undergo withering and water loss, followed by twisting and crushing, causing damage to the leaf structure, and further oxidizing the chemical components inside the tea leaves, mainly including polyphenols such as catechins. The polyphenols will undergo oxidation through the action of polyphenol oxidase and peroxidase enzymes, resulting in varying degrees of oxidation depending on the processing methods. Tea can be divided into non-fermented tea, partially fermented tea, and fully fermented tea.
1. Non-fermented tea: The general processing method for non-fermented tea is to directly kill the fresh tea leaves, destroy the enzyme activity inside the tea leaves, and inhibit the oxidative activity of the enzymes. Green tea is the most common non-fermented tea, with the main production area in northern Taiwan, such as Biluochun and Longjing, with a mainly strip-shaped appearance, and a small amount of leaf-shaped appearance. Green tea is picked on the same day and slightly withered, then directly undergoes short-term killing at high temperature to suppress enzyme activity, prevent tea oxidation, and maintain the fresh green color.
2. Fully Fermented Tea: After the tea leaves are properly withered and lose moisture, they are rolled and kneaded to break the tea leaf tissue and release the enzymes inside. The humidity is adjusted to an appropriate level to allow the enzymes and tea content to undergo an oxidation reaction, and after sufficient reaction time, the tea leaves are fully fermented and oxidized. Black tea is the main type of fully fermented tea, and Nantou in central Taiwan is the main production area, with large-leaf varieties as the main production type and a small amount produced from small-leaf varieties. Black tea can be divided into two types based on the final appearance of the tea leaves, strips and broken pieces. After the tea leaves are picked, they are appropriately withered and either cut and crushed or not before being rolled and kneaded to break up and unblock the tea leaves. During the repeated rolling and kneading process, the tea leaves undergo fermentation and oxidation. Subsequently, in a high relative humidity environment, oxidation is allowed to continue until the unique aroma and color of black tea are formed. Finally, the enzyme activity is stopped at high temperature, and the tea leaves are dried to produce the final product.