Once the freshly picked leaves have been spread out to become soft and have lost some moisture, they can proceed to the fixation stage.

The ‘fixation' stage is not exclusive to Pu'er Tea production; it is also part of the initial processing steps in Green Tea, Yellow Tea, Oolong Tea, etc.

However, Pu'er tea has a very particular approach to the ‘fixation' process, which is critical in determining whether the raw Pu'er tea material meets the standards and has aging potential.

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The “Line Between Life and Death” for Pu'er Tea

If you've ever visited a Pu'er tea factory, you'll undoubtedly remember the tilted iron pots. Traditional Pu'er tea production uses pot stirring for manual fixation of fresh leaves, a method still widely used today, especially for more valuable materials that require precise control during the fixation process.

Fresh tea leaves contain various enzymes. If high temperatures are not used to inhibit their activity, these enzymes will react with chlorophyll and polyphenols in the leaves through enzymatic oxidation.

For example, the high-temperature fixation process in green tea involves destroying the activity of enzymes in the fresh leaves to prevent the chlorophyll and other compounds from undergoing enzymatic oxidation, preserving the green color and avoiding premature fermentation.

Typically, enzymes are most active at 35-45°C and can still function at 60-82°C, albeit less efficiently. However, when the temperature exceeds 82°C and reaches 100°C, these enzymes are completely “deactivated.” In green tea fixation, temperatures above 100°C destroy enzyme activity, ensuring the green color remains vivid when drinking the tea.

For Pu'er tea, one of its core values lies in its aging potential. As such, it must retain a certain level of “biological activity,” so protecting the active substances in Pu'er tea during the fixation process is crucial.

Therefore, the Leaf surface temperature during pot stirring fixation should not exceed 80°C. This is the “line between life and death” for Pu'er tea fixation. Exceeding this temperature too much can cause irreversible damage to the enzyme's protein structure, robbing the leaves of their future aging potential.

Another purpose of the fixation process is to eliminate low-boiling-point aromatic compounds that can give the tea an unpleasant flavor, such as geraniol and trans-2-hexenal, which impart an undesirable grassy odor.

During fixation, the moisture in the fresh leaves evaporates further, making the leaves softer and more pliable, facilitating the next step of rolling.

With advancements in production technology, mechanical drum fixation or mechanical pot fixation is sometimes used in Pu'er tea production instead of manual methods. These methods are faster and more efficient, being several times quicker than pot stirring by hand.

However, the main drawback is that the temperature can easily become too high, causing the leaf surface temperature to exceed 80°C. Therefore, temperature control during mechanical fixation becomes even more important.

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Problems Caused by Improper Fixation

Mastery of the fixation process in Pu'er tea requires long-term experience. The duration of fixation must be adjusted according to the characteristics of different grades of raw materials. Stirring too quickly can make it difficult to reach the necessary temperature, while allowing certain parts of the material to remain in contact with the extremely hot bottom of the pot for too long can result in uneven heating. High-temperature, long-duration fixation can also destroy the tea's activity.

Improper handling of the fixation process can cause irreversible damage to the processed material. We often see high-quality teas that have suffered various issues due to improper fixation techniques.

Firstly, insufficient fixation. Some people try to avoid over-fixation by shortening the fixation time or causing uneven heating during stirring, leading to thin leaves becoming cooked too quickly while coarser stems remain underdone. This can cause enzymatic oxidation in subsequent processing stages, resulting in red leaves and stems.

Or it may leave an unpleasant grassy aroma. Over-fixation, with excessively high temperatures, not only destroys the active substances in the tea but can also cause the leaves to scorch, producing a burnt smell or aromas typically associated with green tea, like bean or chestnut fragrance.

Prolonged fixation at low temperatures or yellowing. If the pot temperature during fixation is too low, below the range where enzymes become inactive, it won't achieve the goal of inhibiting enzymatic reactions. Increasing fixation time at this low temperature can accelerate enzymatic reactions, causing continued “fermentation” in later stages and the formation of theaflavins, leading to red stems and yellow leaves.

Such tea might have a bright yellow liquor and floral aroma when young, but it no longer possesses the true value of aging potential for Pu'er tea.

Additionally, some people attempt to reduce the bitterness and astringency of new tea by allowing the fixed leaves to “yellow,” meaning they stack the leaves without rolling them, allowing them to oxidize to some extent in humid and warm conditions. This causes the internal components of the tea to rapidly transform, resulting in yellowed leaves and occasional reddish changes. The newly made tea lacks bitterness and exhibits a pronounced honey-like aroma, but it loses its potential for aging and no longer qualifies as traditional Pu'er tea.

Originally published in Pu'er Magazine

April 2025 Issue

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