“From Leaf to Flavour: How Processing Creates Tea”
There is no such thing as a tree that tastes like jasmine, nor one that tastes like peach, or carries a citrus note. If you pick a leaf and taste it as it is, what you get is bitterness with a slight sweetness. The floral and fruity notes we recognise in tea are not present in the leaf itself; they are formed later, through process.
Tree age, cultivar, soil, and location provide the internal material of the leaf. They form the base for later reactions, but they do not in themselves become flavour. If these compounds are not properly brought out and guided through appropriate processing, they do not turn into something we can recognise. What a tea eventually becomes depends on what happens in between. From fresh leaf to finished tea, the early stages of processing include wei diao (withering), zuo qing (bruising / partial oxidation), sha qing (fixation), and rou nian (rolling). These steps build the structural foundation of flavour. They activate and organise the internal system of the leaf, but they do not directly produce a fully recognisable flavour. At this stage, the tea holds the necessary information, but it has not yet been expressed.
The first step is wei diao (withering), which exists in almost all types of tea. Its role is not only to reduce moisture, but to initiate the internal system of the leaf. Light, especially ultraviolet light, acts on the leaf and alters cellular conditions, activating a range of enzymes. These enzymes are required for later reactions, and if they are not sufficiently activated at this stage, subsequent processes cannot proceed effectively. This is why teas that have not undergone proper sun withering often show weaker aroma. During withering, moisture migrates through the leaf. Water from the veins moves toward the leaf surface, carrying dissolved substances with it. Polysaccharides begin to break down into simpler sugars such as glucose and fructose, while free amino acids increase, including glutamic acid and theanine. These compounds serve as the material for later transformations.
Once withering is complete, different processing paths lead to different tea types. If the leaf is quickly heated and dried, it becomes green tea; if it is slowly dried, it becomes white tea.
The next stage is zuo qing (bruising). Through controlled movement and mechanical action, the edges of the leaf are slightly damaged, exposing internal compounds. At the same time, the leaf responds to this damage by transporting material toward the affected areas. Within this process, enzymes interact with exposed compounds, producing a range of intermediate substances. Many of the foundations of floral and fruity notes are formed here. This stage requires control over time, intensity, and environmental conditions. After processing, the leaf develops a red edge, which reflects the level of reaction that has taken place. When handled appropriately, the aromatic structure becomes clear and layered, and the internal flow remains coherent. If the process is too heavy or too light, the conditions required for later flavour development are affected.
Following this comes sha qing (fixation). Heat is applied to reduce or halt enzyme activity, bringing the previous reactions to a stop, while at the same time redistributing moisture within the leaf. If this step is uneven, the internal state of the leaf becomes unbalanced; if it is incomplete, enzymatic reactions continue, and the tea continues to evolve beyond the intended point.
The next step is rou nian (rolling). Mechanical pressure breaks the cells and brings internal compounds, particularly sugars and pectins, to the surface of the leaf. These substances later participate in further reactions, especially during roasting, and contribute to the formation of additional flavour.
After the early stages are complete, the tea is dried and becomes mao cha (unfinished tea). At this point, the structural conditions for flavour are in place and the necessary compounds are present, but the flavour has not yet fully emerged. It exists in a state that is not yet clearly defined or fully expressed.
In the later stages, including roasting, blending, and brewing, these existing materials are brought forward and made perceptible. If the earlier stages have not been properly carried out, later processing cannot compensate for it. If the structure has been established, these later steps determine how it is expressed.
Traditional classifications divide tea into categories based on processing methods and oxidation levels. From the perspective of processing, however, these categories are not strictly parallel, and their boundaries have become increasingly fluid. In practice, different tea types may adopt similar techniques; some green and white teas incorporate elements similar to zuo qing to enhance aroma, while certain methods resemble those used to adjust sweetness and texture in other styles.
Tea-growing regions provide the foundational material within the leaf, but the process determines how that material is extracted, transformed, and expressed. The final flavour is formed gradually through this sequence of steps.
