In the previous article (Wilt: The Prelude to Transformation from Fresh Leaves to Tea), Lu Li provided an in-depth introduction to wilting. Next comes kneading, which involves the actions of “kneading” and “twisting” to roll the wilted leaves into a specific shape, reducing their surface area.
Purpose of Kneading in Pu'er Tea
Most of the six major types of Chinese tea undergo a kneading process, but the shapes they are formed into vary. Examples include snail-shaped Biluochun, needle-shaped Nanjing Yuhua, flat-shaped West Lake Longjing, curled Anxi Tieguanyin, and pointed Taiping Houkui, among others.
Yunnan large-leaf sun-dried green tea (the precursor to Pu'er tea) is categorized as a strip tea, characterized by its pursuit of being “tight, round, and straight,” while avoiding being “loose, flat, and broken.” When kneading by hand, it's important to maintain consistent movement direction for the leaves to avoid counter-twisting.
For many types of tea, the primary purpose of kneading is to shape the leaves, enhancing their economic value. Therefore, the kneading time is short and the pressure light. However, this is not the case with Pu'er tea, because kneading serves another critical function: breaking down leaf cells.
During kneading, significant pressure is applied to the leaves, disrupting their surface cells and causing the rupture of vacuoles within the leaves. The sap rich in internal substances flows out and, through repeated kneading and rolling, gradually adheres to the tea strips.
Once the tea leaves are dried, these juices solidify on the leaf surfaces. During brewing, the soluble components dissolve into the tea Infusion, becoming the source of most of the tea's aroma and flavor.
Kneading has a significant impact on the appearance and luster of Pu'er tea. The greater the pressure applied during kneading, the higher the degree of cell disruption, resulting in a more intense flavor and lower infusion rate. The term “cell disruption rate” specifically quantifies the extent of kneading, with different types of tea requiring different rates of cell disruption.
Generally, green tea has a cell disruption rate of 40% to 45%, while Yunnan large-leaf sun-dried green tea ranges from 38% to 45%. “Dian Hong” black tea requires a rate above 72%, and Yunnan CTC (Crush, Tear, and Curl) black tea exceeds 90%.
Additionally, the kneading process in Pu'er tea serves another function: inoculation. After kneading, the damaged cell walls lose their protective membranes, allowing microorganisms from the air to enter the tea leaves, completing “natural inoculation” and laying the foundation for aerobic Fermentation.
Key Points of Using Kneading Machines
Similar to other processes, kneading can be done manually or mechanically. Since sun-dried green tea is a straight strip tea with a simple process, kneading machines are well-suited for the task. Furthermore, manual kneading is time-consuming and labor-intensive, making mechanical kneading increasingly popular in tea production areas.
Currently, various types of kneading machines are used in tea production areas, each with different models and performance characteristics. They are categorized by size, such as 25, 50, 60, 70, and 90 models, and by kinetic energy, including single-motion (where only the upper kneading bucket rotates) and double-motion (where both the upper kneading bucket and the lower kneading plate rotate in opposite directions). There are also single-arm and double-arm models.
However, due to the relatively late emergence of the Pu'er tea industry and inadequate supporting facilities, some tea farmers use second-hand kneading machines designed for Dian Green and Dian Red teas (which require higher cell disruption rates). This results in excessive kneading that is unsuitable for sun-dried green tea.
The method of distinguishing them is straightforward: kneading machines dedicated to sun-dried green tea have fewer ridges on the kneading plate and smaller ridge inclination angles (more gradual, applying lighter pressure). Suitable kneading bucket sizes should not exceed 60 centimeters, with smaller 25-type models sufficient for household use.
The kneading of sun-dried green tea emphasizes “tight, round, and straight” strips. Based on the grade of fresh leaves, the amount of leaves added, the taste characteristics of the raw materials, and the desired final product texture, several techniques can be flexibly chosen.
The first key point is cold versus hot kneading. After wilting, the tea leaves become warm and soft. Kneading them while still warm is known as hot kneading; waiting until they cool before kneading is cold kneading. The choice should follow the principle of “cold kneading for tender leaves and hot kneading for older leaves.”
This is because tender leaves have strong resilience, thin cuticle layers, fewer fibers, and more water-soluble Pectin. Cold kneading prevents the formation of a “yellow cooked” flavor that can result from heat generated during the kneading process.
On the other hand, older leaves have harder textures, more fibers, and less pectin. Kneading them while they are still warm and at a higher temperature makes the strips easier to tighten and reduces the amount of broken tea, improving the quality ratio.
The second key point is to ensure an appropriate amount of leaves for kneading. Different models of kneading machines have varying diameters, and if too few leaves are added, the kneading pressure effect is not noticeable, making it difficult to tightly shape the strips.
If too many leaves are added, the leaves' ability to turn over is hindered, leading to poor initial rolling (“stripping”) effects. As a result, there will be more broken pieces at the bottom and more flat strips at the top, with a loose appearance and more broken and flat leaves. To address this, after selecting the right model, fill the kneading bucket naturally with the wilted leaves.
The third key point is to control the kneading duration. The choice depends on the grade and tenderness of the fresh leaves, the diameter of the kneading bucket, and the tightness of the strips on the kneading plate.
Using a commonly used 60-centimeter diameter kneading bucket as an example, first to second-grade fresh leaves should be kneaded for 12 to 15 minutes; third-grade fresh leaves for 15 to 20 minutes, and fourth to fifth-grade fresh leaves for 20 to 25 minutes. For kneading buckets larger than 60 centimeters in diameter, add approximately five minutes to each category, and reduce five minutes for those smaller than 60 centimeters.
The fourth key point is the application of pressure during kneading. The increase and decrease in pressure, as well as the duration of pressure application, directly affect the cell disruption rate, which in turn impacts the color, aroma, and taste of the finished tea, as well as the tightness, flatness, and fragmentation of the tea strips. Pressure should be applied flexibly based on actual conditions, generally using a “light-heavy-light” technique.
The fifth key point is to use re-kneading cautiously. Re-kneading refers to kneading the tea again after unclumping and sieving. Re-kneaded sun-dried green tea lacks sharp tips, has more blunt ends, appears broken, and contains more sub-standard tea (broken, flaky, and powdered tea), resulting in a lower quality ratio.
Therefore, as long as the fresh leaves are graded relatively clearly and consistently in terms of tenderness, re-kneading should be avoided. If there are inconsistencies in the tightness of the strips and a high number of loose, flat leaves on the surface, the sieve size can be increased, using a No. 2 sieve for unclumping. The coarse and loose surface tea can then