The Fixation process in green tea production is not simply about using high temperatures to deactivate enzymes. During fixation, various thermal and physical changes occur, significantly impacting the formation of green tea quality. So, why is high temperature used in the fixation of green tea?
What is the purpose of fixation in green tea?
Fixation is a crucial step in the production of green tea. If this step is not performed properly, subsequent steps cannot proceed as planned. After picking from the tea Tree, the leaves undergo withering and stirring before starting the fixation process. Why do we need to fixate the tea leaves? Fixation uses high temperatures to kill the activity of Polyphenol oxidase in the tea leaves. This prevents the enzymatic oxidation of polyphenols, stopping fermentation and preserving the original components of the tea. Additionally, after fixation, the leaves lose some of their moisture, become softer, making them easier to shape, and allowing for more efficient processing in the next step.
There are three main reasons why high temperature is used in the fixation of green tea:
First: High temperatures can quickly deactivate the enzymes present in fresh leaves, preventing the enzymatic oxidation of polyphenolic compounds;
Second: High temperatures can volatilize low-boiling-point substances in the tea leaves, eliminating odors and grassy smells;
Third: High temperatures promote hydrolysis and thermal cracking, while also softening the Leaf texture, facilitating rolling.
What is the temperature for fixation in green tea?
The fixation temperature for green tea varies depending on the tenderness of the fresh leaves, their water content, and the amount of leaves processed. For example, in handcrafted tea (Longjing), the initial pan temperature is 90–100°C (for high-grade teas) or 100–140°C (for medium- and lower-grade teas). For the 6CST drum fixation machine, the drum temperature is generally above 200°C, with an outlet temperature above 85°C.
The difference in temperature between these methods is significant, but they all achieve the goal of avoiding red stems and red leaves. The high temperature referred to in high-temperature fixation mainly involves heat transfer and radiation to reach a leaf temperature sufficient to deactivate the enzymes.