Black tea is fully fermented tea. Black tea enhances enzyme activity through withering, and then through rolling and fermentation, a series of changes occur centered on the enzymatic oxidation of tea polyphenols. Tea polyphenols are heavily oxidized and contain more theaflavins, thearubigins and theabrownins, which form the quality characteristics of red leaves with red soup.

During the processing of black tea, the oxidative polymerization reaction produces colored substances such as theaflavins, thearubigins, and theabrownins. These substances, together with caffeine, free amino acids, soluble sugars and other contained ingredients, affect the color and taste of black tea. At the same time, the hydrolysis of glycosidase releases terpene compounds, and the oxidative degradation of unsaturated fatty acids jointly affect the aroma type of black tea.

The method of making black tea remains the same, and the processing technology mainly includes four steps: withering, rolling, fermentation and drying. What responsibilities do these processes play in the black tea production process?

Withering is the first process in the initial production of black tea, and it is also the basic process that forms the quality of black tea.

Withering serves two purposes:
One is to evaporate part of the water, reduce the tension of the tea cells, make the leaf stems from brittle to soft, increase the toughness of the buds and leaves, and facilitate rolling into strips.

The second is that it is conducive to the change of contained substances. Due to the loss of water, the permeability of the cell membrane increases, and the contained biological enzymes are gradually activated, causing a series of chemical changes in the substances contained in the tea tips, laying the foundation for material changes to form the specific quality of black tea color and aroma.

Rolling is an important process for shaping the beautiful appearance and inner quality of Gongfu black tea and black broken tea. Gongfu black tea requires a tight and beautiful appearance and a rich inner taste, which depends on the tightness of the leaves and the degree of destruction of cell tissue.

There are three functions of rolling:
First, the leaf cell tissue is destroyed by rolling, causing the tea juice to overflow, accelerating the enzymatic oxidation of polyphenolic compounds, and laying the foundation for the formation of the unique endoplasm of black tea.

The second is to roll the leaves into tight straight strips to reduce the size and create a beautiful appearance.

Third, the tea soup overflows on the surface of the leaves and is easily soluble in water during brewing, increasing the concentration of the tea soup and forming a shiny and oily appearance.

Fermentation is a key process in forming the color, aroma and flavor characteristics of black tea. Good fermentation can produce more theaflavins and thearubigins, as well as more taste and aroma substances.

Fermentation is a continuous process, not just one process. Fermentation always exists from the time of rolling black tea to drying. Usually, a fermentation process is specially set up after rolling and before drying, so that the tea leaves can reach the most suitable level.

When black tea is fermented, the rolled tea leaves are generally placed in a fermentation frame or fermentation car, and then placed in a fermentation box or fermentation chamber for fermentation. In recent years, some new fermentation equipment have also been produced. Fermentation requires mastering the appropriate temperature, humidity, and oxygen required for tea polyphenolase to undergo oxidative polymerization.

Drying is the final step in black tea processing. Drying is done by oven drying, which is usually done in two steps. The first time is called gross fire, and the second time is called full fire. The hair and feet need to be cooled down between the fires.

Drying also serves three purposes:
One is to use high temperature to quickly inactivate enzyme activity, prevent enzymatic oxidation, and stabilize the quality of fermentation.

The second is to evaporate water, tighten the tea bar, fix the shape, and keep it dry, which is beneficial to maintaining quality.

The third is to emit most of the grassy smell with low boiling point, intensify and retain the aromatic substances with high boiling point, and obtain the unique sweet aroma of black tea.

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