Kneading is a very important step in the production process of Pu'er tea, following the initial steaming. Kneading involves the actions of “kneading” and “twisting,” transforming the steamed leaves, which are close to their natural state, into a specific shape through either “hand” or “mechanical” methods. The purpose of this process is to break the cell walls and release the tea juices, allowing for the polymerization of tea polyphenols, catechins, and other active components, preparing the tea for later Fermentation. Additionally, it helps to curl the loose leaves into strips, facilitating an even release of the tea's contents during brewing. The strength of the kneading, duration, and degree of cell wall rupture are closely related to the taste, aroma, and aging potential of the Pu'er tea.
The Characteristics of Kneading in Pu'er Tea
Among the six major types of Chinese teas, all except traditional white tea undergo a kneading process. However, in many types of tea, the kneading process is primarily for shaping, often using a “light kneading” approach, which is essentially completed without pressure and with very short kneading times. The goal is to achieve a high rate of leaf formation, low breakage, and maintain the original color of the tea. After kneading, the dried tea meets traditional aesthetic standards. In contrast, the kneading of Pu'er tea employs a heavy kneading method and is typically done over multiple sessions. This is because Pu'er tea uses large-leafed tea trees from Yunnan, whose fresh leaves include buds, leaves, and stalks, and are mostly thick and large. Using a light kneading method would not fully extract the inner contents of the leaves.
Secondly, the use of “heavy kneading” in Pu'er tea serves another crucial purpose: to break the “protective layer” on the surface of the leaves. Then, by naturally air-drying the leaves, various microorganisms in the air can “invade,” completing the first “natural inoculation” of the tea under natural conditions. This is also the primary oxidation stage for Pu'er tea before fermentation. Therefore, the “heavy kneading” in the sun-drying process of Pu'er tea can also be referred to as “heavy kneading.” It is a critical step that lays the foundation for subsequent fermentation. Many producers of Pu'er tea do not complete the kneading in one go but perform multiple rounds of kneading—traditionally called “re-kneading.” This “re-kneading” strengthens the initial “natural inoculation,” ensuring more thorough primary oxidation of the Pu'er tea.
Kneading can be divided into “hot kneading” and “cold kneading.” Cold kneading refers to kneading the steamed leaves after they have cooled down; hot kneading is performed while the leaves are still warm. Specifically, the principle followed is “cold knead young leaves, hot knead older leaves.” Young leaves contain less cellulose, have greater flexibility, and a thinner cuticle layer, with more water-soluble Pectin. During kneading, they easily form strips. Cold kneading prevents the yellowing caused by frictional heat, maintaining the characteristic “apricot-yellow brightness” of the infusion and the tender green color of the leaf base in raw Pu'er tea. For coarser, older tea leaves, which are harder and contain more cellulose and less pectin, hot kneading takes advantage of the softening effect of heat to tighten the strips and reduce the amount of broken tea. Before the advent of machine kneading, Pu'er tea was mainly kneaded by hand.
The Purpose of Kneading in Pu'er Tea
1. In terms of appearance: Kneading makes the steamed tea leaves curl and become supple, resulting in an attractive strip shape in the final product.
2. Regarding subsequent oxidation: Kneading damages the cellular structure of the tea leaves, releasing tea juices. This allows the polyphenols, polysaccharides, Caffeine, and other chemical components within the tea to come into contact with oxygen in the air, triggering oxidation reactions.
Thus, the kneading process in Pu'er tea not only influences the appearance of the strips but also plays a key role in the subsequent oxidation process.