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the leaf color is essential to judge the quality of black tea
The well-fermented black tea and the poorly fermented black tea have very noticeable difference in flavour. The well-made black tea produces a sweet flavour, while the poorly made black tea produces a sour or musty smell.

Observing the colour, knowing the skill

In addition, the liquor of the tea will show the effects of the fermentation. The well-fermented tea would produce a reddish liquor with yellow hue, while the poorly fermented tea would produce a brown liquor. Besides, the difference in colour was not only visible in the liquor, but it affects the brewed leaves too. As a matter of fact, there is an obvious difference in the constituents between the well-fermented tea and poorly fermented tea.

The well-made black tea contains theaflavin

It is often said that the main constituent of black tea is tannin. However, the tannin is the “general name” of a substance formed by the oxidation and conjugation of a plant’s polyphenols. Any substance can be called tannin as long as it consists of high molecules and produces a brownish colour. To some extent, the substance contain in green tea are also called as tannin in some tea book. Since the word tannin lacks clear definition creating confusion among tea folks, I try not to use this term when describing the fermentation of tea.

The main substance in a well-processed black tea is the theaflavins. There is variance of theaflavins depending on which polyphenol it is made from. It is formed by the conjugation of 2 to 3 flavonoids and is mediated by the oxidation enzyme which produces the substances that show bright yellow colour. It is known that a cup of fine black tea shows a golden ring at the wall of the tea cup. This golden ring is formed with yellow pigments, i.e., the theaflavin.

Thearubigin is the symbol of failure in fermentation

If the fermentation was not well managed, the theaflavin would conjugate each other and form a larger molecule substance. These substances do not have a specific structure and there are thousands or millions of different substances. These substances are called thearubigin. Once this substance is formed, the tea would produce an unpleasant flavour simultaneously.

The process of black tea requires very delicate handling

The fresh tea leaves contain polyphenols. During fermentation (oxidation), the polyphenols are conjugated and formed theaflavin. However with additional oxidation, the theaflavin will be converted into thearubigin.

Polyphenol >> Theaflavin >> Thearubigin

When minor errors occur during the process, the theaflavin goes too far and instantly produce thearubigin. This reaction is irreversible. Therefore, the production of black tea is very difficult and it requires a lot of experiences and know-how to control the process precisely. The process of black tea consists of withering, rolling, fermentation and drying. In fact, besides the importance of the fermentation process, manufacturers have to pay more attention to the entire process to ensure that the leaves are not over fermented.
It is very easy to tell the quality when you observe the brewed leaves. The brewed leaves of well-processed tea will be of bright orange-brown colour, while the poor quality tea is of dark brown.

The leave color is reflected from the fermentation

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