A Detailed Explanation of Black Tea Manufacturing: The Complete Process and Key Steps

Chinese black tea includes congou black tea, broken black tea and souchong black tea. Their manufacturing methods are largely similar, all involving the four processes of withering, rolling, fermentation and drying. The quality characteristics of all kinds of black tea are a red liquor and red leaves, and the formation of their colour, aroma and taste involves similar chemical change processes, differing only in the conditions and degree of the changes. The following uses congou black tea as an example to briefly introduce the manufacturing process of black tea.

(1) Withering

Withering refers to the process in which fresh leaves lose water over a period of time, causing the somewhat hard and brittle stems and leaves to become limp and wilted. It is the first step in the primary processing of black tea. Through withering, moisture can be properly evaporated, the leaves become soft and their flexibility increases, making them easier to shape. In addition, this process also causes the grassy smell to disappear and the fresh tea aroma to begin to emerge, making it an important processing stage in the formation of black tea aroma. There are two withering methods: natural withering and trough withering. Natural withering involves spreading the tea leaves thinly indoors or outdoors in a place where the sunlight is not too strong, and leaving them for a certain period of time. Trough withering involves placing the fresh leaves in an aerated trough and passing hot air through it to accelerate the withering process; this is currently the commonly used withering method.

(2) Rolling

The purpose of rolling black tea is the same as for green tea: the tea leaves are shaped during rolling and their colour, aroma and taste are enhanced. At the same time, because the leaf cells are broken, it is easier for the necessary oxidation to take place under the action of enzymes, which facilitates the smooth progress of fermentation.

(3) Fermentation

Fermentation is the unique stage of black tea production. Through fermentation, the leaf colour changes from green to red, forming the quality characteristics of red leaves and red liquor in black tea. The mechanism is that, under the action of rolling, the tissue cell membrane structure of the leaves is damaged and permeability increases, allowing polyphenolic substances to come into full contact with oxidase, producing oxidative polymerisation under enzymatic action. Other chemical components also undergo profound corresponding changes, causing the green tea leaves to turn red and forming the colour, aroma and taste quality of black tea. At present, fermentation machines are commonly used to control the temperature and time for fermentation. When fermentation is moderate, the tender leaves are even red in colour, the older leaves are red with a touch of green, the grassy smell disappears, and there is a ripe fruit aroma.

(4) Drying

Drying is the process of rapidly evaporating moisture from the fermented tea material by high-temperature roasting to achieve a moisture level that preserves quality. It has three purposes: to use high temperature to rapidly deactivate enzyme activity and stop fermentation; to evaporate moisture, reduce volume, fix the shape, and maintain dryness to prevent mould; and to dissipate most of the low-boiling-point grassy odours, activate and retain high-boiling-point aromatic substances, and obtain the sweet aroma characteristic of black tea.