Image source: Kaiyuan Qixihao.
As a tea that becomes richer and more fragrant with age, Pu-erh tea requires storage over time; during this storage process, influenced by both external and intrinsic factors, Pu-erh tea undergoes a series of changes.
The principle of Pu-erh tea maturation is very clear. Currently, there are four mechanisms driving these changes, primarily through the combined action of auto-oxidation, microbial activity, enzymatic catalysis, and moist heat—what is commonly referred to as post-fermentation. During the post-fermentation process, the changes occurring in Pu-erh tea can be divided into two main categories: changes in physical properties and changes in chemical composition.
Changes in physical properties include a series of alterations such as loss of dry matter, heat, trace gases, pH value, tensile elasticity and hygroscopicity, ash content, and color.
For example, the change in heat.
During the storage of Pu-erh tea, appropriate heat is a key factor in its maturation; however, the indoor temperature does not equal the core temperature of the tea package.
Two phenomena are relatively common: first, when maocha has high moisture content and is piled in a warehouse, the tea packages will heat up as temperatures rise during late spring and early summer; second, in a storage room at a room temperature of 25°C, the core temperature of the tea often exceeds the room temperature by 5°C to 7°C. These phenomena all demonstrate that slow oxidation occurs during the storage of Pu-erh tea, releasing carbon dioxide and other volatile substances while simultaneously generating heat.
The greater the amount of heat generated, the more intense the quality changes in Pu-erh tea. Based on these principles, we can use the fluctuations in core temperature as a technical indicator for storage process operations to control the changes occurring during the storage of Pu-erh tea.
However, it should be noted that the level of core temperature does not fully represent the magnitude of heat generation in Pu-erh tea. This is because factors such as the size and tightness of the tea packaging, the volume of the storage room, the rate of heat dissipation, and the heat lost due to the evaporation of moisture in the Pu-erh tea all affect the core temperature. The level of core temperature merely represents the excess heat remaining after subtracting the value of heat loss from the heat released by the Pu-erh tea.
The “change” in Pu-erh tea is the essential path toward it becoming “richer and more fragrant with age.” Of course, this is predicated on having high-quality raw materials, correct processing techniques, and scientific storage; otherwise, no matter how much it “changes,” it will never transform into “good” Pu-erh tea.
(Speaker: Zhou Yunchuan, Chief Researcher of the Yunnan Black Tea Leaf Science Research Institute, National Senior Tea Taster,
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Author: Lam Sam (LamSam), the Old Tea Head
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