Black tea, the second largest tea category in China. During the processing of black tea, a chemical reaction centered on the enzymatic oxidation of tea polyphenols occurs, and the chemical composition in the fresh leaves changes considerably, with tea polyphenols reduced by more than 90% and new components such as theaflavins and theaflavins produced, and the aroma substances increase significantly compared to the fresh leaves. Therefore, black tea has the characteristics of black tea, red soup, red leaves and sweet and mellow aroma. Black tea is a fully fermented tea, which is refined from a series of processes such as withering, kneading (cutting), fermentation and drying, using suitable new tooth leaves of the tea tree as raw materials. Withering is an important process in the initial production of black tea, and black tea is called "oolong tea" when it is first produced. Black tea is named after the red colour of the tea broth and leaf base when the tea is brewed. Black