As the basic raw material for tea processing, the quality of fresh leaves is directly related to the quality of tea, which is the basis for the formation of tea quality. In the process of making tea, a series of chemical changes occur in the chemical components of the fresh leaves, and the physical properties of the fresh leaves have also undergone significant changes, thus forming a tea with a specific quality and style. It can be said that the quality of tea mainly depends on the quality of fresh leaves and the rationality of tea-making technology. The quality of fresh leaves is the internal basis, and the tea-making technology is the external condition. Therefore, in order to produce good-quality tea, it is necessary to understand the chemical components contained in fresh leaves and the relationship between the quality of fresh leaves and the quality of tea, in order to effectively adopt appropriate management measures and tea-making techniques to produce high-quality tea.

So far, there are more than 700 kinds of compounds that have been separated and identified in tea, which can be divided into three parts: water, inorganic components, and organic components. In addition to the three primary metabolites of sugar, lipid and protein, the organic compounds of tea also include many important secondary metabolites, such as polyphenols, alkaloids, theanine, aromatic substances, pigments, etc. Although the content of some metabolites is not high, they play a very important role in the formation of tea quality.