Fixation, also known as “shaqing,” is one of the initial processing steps for green tea, Yellow Tea, dark (black) tea, Oolong Tea, Pu'er tea, and some black teas. The primary purpose is to destroy and deactivate the oxidase enzymes in fresh leaves through high temperatures, inhibiting the enzymatic oxidation of polyphenols. This step also evaporates some of the water content, making the leaves softer for rolling and shaping, while eliminating the grassy odor and promoting a pleasant aroma.

Which Teas Require the Process of Fixation?

1. Green Tea

Fixation is a critical process for shaping and determining the quality of green tea. Methods of fixation include pan-firing, steaming, baking, and sun-drying. Steaming was commonly used during the Tang Dynasty and remains prevalent in Japan, Russia, and India. Since the Ming dynasty, pan-firing has been widely adopted in China and is now used globally. General principles for fixation include “high temperature fixation, starting high then lowering; older leaves should be treated gently, younger leaves more rigorously; a combination of tossing and covering, with more tossing and less covering.” For steaming, the key is “high temperature and rapid.”

2. Oolong Tea

The manufacturing process for Anxi Tieguanyin involves: picking, wilting, cooling, shaking (also known as bruising), pan-firing, rolling, initial roasting, secondary roasting, re-rolling, slow baking at low heat, sorting, and sifting. Pan-firing should be done promptly once the grassy smell disappears and the aroma begins to emerge from the bruised leaves.

3. Yellow Tea

The principle and objective of fixation for yellow tea are similar to those for green tea, but yellow tea requires a specific yellow hue and flavor, so the temperature and technique have unique considerations. The pan temperature for fixation is lower than that for green tea, typically between 120°C and 150°C. Fixation involves more covering and less tossing to create a high-moisture, high-temperature environment, which degrades chlorophyll, inactivates oxidase enzymes, and promotes auto-oxidation and isomerization of polyphenols. These processes, along with the breakdown of starches into simple sugars and proteins into amino acids, contribute to the mellow taste and yellow color of yellow tea.

4. Dark (Black) Tea

Dark tea is made from coarser and older leaves, so to ensure even fixation, water is often added (at a ratio of 10:1, meaning 1 kg of water for every 10 kg of fresh leaves). Water should be distributed evenly to achieve uniform fixation.

Methods of Fixation for Tea

Pu'er tea is fixed using pan-firing or drum fixation. Larger factories and most plantation teas use drum machines for fixation, while ethnic minorities and wild-grown teas tend to be hand-fired in pans. The purpose of fixation in other teas is to halt enzymatic activity with high heat, whereas in Pu'er tea, it slows down fermentation and makes the leaves more pliable for rolling, as well as removes the grassy odor. The temperature for fixing Pu'er tea varies based on the condition of the fresh leaves, typically around 180°C inside the pan, with a higher temperature outside.

Purposes of Fixation in Tea processing

1. To quickly deactivate polyphenol oxidase in fresh leaves using high temperatures, preventing enzymatic oxidation and allowing non-enzymatic reactions to form the color, aroma, and taste characteristics of green tea, dark (black) tea, yellow tea, and Pu'er tea.

2. To remove some moisture, making the leaves softer and easier to roll and shape.

3. To eliminate the grassy scent and release an appealing tea aroma.

In summary, fixation destroys the tissues and structures of fresh leaves, transforming their properties and laying a solid foundation for the unique qualities of the final tea product. This is the goal of fixation and the fundamental basis for fixation techniques.