Tea rolling is the process that follows the fixation (kill-green) step, where external force is applied to shape the tea leaves and break down the cellular structure of the fresh leaves. This process allows the internal components of the tea leaves to adhere to their surface. Rolling involves two main actions: rolling, which shapes the leaves into strips; and pressing, which breaks down the cells and releases tea juices, increasing the stickiness and aiding in the formation of the tea's appearance.
The Purpose of Rolling Tea Leaves
1. Shaping the Appearance
The method and intensity of rolling can create different shapes for the tea leaves. Light rolling results in what is commonly referred to as a “striped” appearance, including flattening the tea leaves (as in Dragon Well tea) or rolling them into needle-like shapes (as in Eyebrow tea or Jade Dew). There is also an even lighter rolling technique where the tea leaves are gently handled, leaving them largely unchanged (as in Lu'an Melon Seed tea).
In the case of Oolong teas, heavier rolling generally produces spherical shapes through a process called “rolling and baking” inside a cloth bag. For heavily withered and fully oxidized black teas, the rolling is more intense without using a cloth bag. This can either result in broken leaf Black Tea (C.T.C.) or finely rolled strips (as in Keemun black tea).
2. Promoting the Entry of Tea Juice into the Infusion
The effect of rolling on fresh leaves varies by tea type. For green tea, since enzyme activity is destroyed by high-temperature fixation, there are no significant chemical changes during rolling. The impact of rolling on the leaves is primarily physical rather than chemical. Rolling focuses on breaking down the cell structure of the leaves, making it easier for the internal components to permeate the surface. This ensures that they are more readily released into the infusion during drinking and evaluation.
3. Promoting Further Changes in Internal Components
Rolling black tea not only shapes the leaves and damages the cells but is crucial for initiating fermentation. From a biochemical perspective, rolling essentially starts the fermentation process because it damages the leaf cells under pressure, leading to a series of biochemical reactions centered around the enzymatic oxidation of polyphenols. Thus, rolling techniques have a significant impact on the quality of black tea.
The Role of Heavy Rolling in Pu'er Tea
1. Difference in Leaf Selection
Pu'er tea uses different tea leaves compared to green tea. Green tea typically uses leaves dominated by buds, which are small and delicate, making them suitable for a “light rolling” approach. However, Pu'er tea uses large-leaf varietals from broad-leaved trees, which rarely have tender buds and instead feature thick and large leaves. The rolling method used for green tea would not be applicable. In fact, describing the rolling of Pu'er tea as “heavy rolling” might be more accurately described as “heavy kneading.”
2. Difference in Temperature During Rolling
Green tea rolling is completed at high temperatures in an iron pot. In contrast, Pu'er tea rolling is done outside of the iron pot, on bamboo mats, wide wooden boards, or rolling machines, all at room temperature.
3. Difference in Process Arrangement
For green tea, rolling is the final step in processing, giving the tea its final form both internally and externally. For Pu'er tea, however, rolling is a preparatory step before fermentation, placing it among the early stages of production. It is far from being the finished product.
4. Additional Purpose of Heavy Kneading
One of the most important purposes of heavy kneading in Pu'er tea is to break down the protective layer on the surface of the leaves. By drying naturally afterward, various microorganisms in the air can infiltrate the leaves, achieving the first natural inoculation in a natural state. This is also the primary stage of oxidation for Pu'er tea before fermentation. This step is strictly avoided in green Tea processing, as damaging the surface membrane would lead to rapid oxidation and a change in quality.
Therefore, “heavy kneading” is a critical step in Pu'er tea production, laying the foundation for subsequent fermentation. Many Pu'er tea producers do not complete this step in one go but perform multiple kneadings – traditionally referred to as “re-kneading.” This re-kneading serves to supplement the initial natural inoculation, ensuring a more thorough primary oxidation.