Fermentation Level of Tea

The Fermentation of Tea requires the simultaneous presence and involvement of three essential elements:

1. Polyphenol oxidase, is an enzyme within the tea leaves that possesses oxidative activity.
2. Tea polyphenols, are located within the vacuoles of the mesophyll tissue.
3. Oxygen, is present in the environment.

During the fermentation process of tea leaves, tea polyphenols gradually decrease due to oxidation and transform into various compounds contributing to tea's colour and flavour, such as oolong tea substances, theaflavins, and Thearubigins. Among these, most oolong tea characteristics are the primary flavour compounds of partially fermented oolong tea. The fermentation process of tea leaves is a complex chemical process involving a series of polymerization reactions of tea polyphenols. It is the transformation of tea from green tea to oolong tea and then to black tea, undergoing various chemical changes. Among them, tea polyphenols play a crucial role. They interact with other polyphenolic substances in the tea leaves, leading to the oxidation of these substances and the generation of more aroma compounds. This is one of the most important chemical changes during the fermentation process.

The fermentation process of tea leaves imparts a unique flavour by generating various aroma compounds through chemical changes, such as phenols, alcohols, esters, etc., making the taste of tea leaves richer and more complex. Specifically, during the fermentation process of tea leaves, polyphenolic substances are oxidized to produce substances such as theaflavins and aromatic alcohols, which give tea leaves floral, fruity, and herbal flavours. Additionally, amino acids in tea leaves react with other substances during fermentation, resulting in the formation of substances like theanine and tea peptides, enhancing the sweetness and freshness of tea leaves.

To facilitate the fermentation process of tea leaves, specific processing steps are typically required. This process usually occurs after tea leaves are harvested and includes withering, rolling fermentation, and roasting stages. Among these, the fermentation stage is crucial, as tea leaves need to undergo fermentation under appropriate temperature and humidity conditions to promote the activity of enzymes and chemical reactions. The choice of fermentation technique depends on the type of tea leaves and processing methods. Common fermentation techniques include static fermentation, pile fermentation, and various temperature and humidity control methods. Through these processing steps, tea leaves undergo fermentation, resulting in the development of rich aroma and flavour profiles, creating a delightful beverage experience.