Tea processing is the method in which the leaves and flushes from the Camellia sinensis plant that are transformed into the dried leaves for brewing tea. The types of tea are distinguished by the processing they undergo. In its most general form, tea processing involves oxidizing the leaves, stopping the oxidation, forming the tea and 茶葉 drying it. Of these steps, the degree of oxidation plays a significant role of determining the final flavor of the tea, with curing and leaf breakage contributing to a lesser amount flavor.
The main steps of tea processing are:
Picking: Tea leaves and flushes, which includes a terminal bud and 2 young leaves, are plucked from Camellia sinensis bushes twice a year during early spring and early summer or late spring.
Wilting: The tea leaves will begin to wilt soon after picking, with a gradual onset of enzymatic oxidation. Wilting is used to remove excess water from the leaves and allows a very light amount of oxidation.
Bruising: In order to promote and quicken oxidation, the leaves may be bruised by tumbling in baskets or by being kneaded or rolled-over by heavy wheels. This also releases some of the leaf juices, which may aid in oxidation and change the taste profile of the tea.
Oxidation: For teas that require oxidation, the leaves are left on their own in a closed room where they turn progressively darker. In this process the chlorophyl in the leaves is enzymatically broken down, and its tannins are released or transformed. This process is referred to as fermentation in the tea industry, although no true fermentation happens since the process is not driven by microorganisms. The tea producer may choose when the oxidation should be stopped. For light oolong teas this may be anywhere from 5-40% oxidation, in darker oolong teas 60-70%, and in black teas 100% oxidation.
Heating: Heating is done to stop the tea leaf oxidation at a desired level. This process is accomplished by moderately heating tea leaves, thus deactivating their oxidative enzymes, without destroying the flavor of the tea. Traditionally, the tea leaves are panned in a wok or steamed, but with advancements in technology, heating is sometimes done by baking or “panning” in a rolling drum. In CTC black teas, heating is done simultaneously with drying.
Shaping: The damp tea leaves are then rolled to be formed into wrinkle strips. This is typically done by placing the damp leaves in large cloth bags, which are then kneaded by hand or machine to form the strips. This rolling action also causes some of the sap and juices inside the leaves to ooze out, which further enchances the taste of the tea. The strips of tea can then be formed into other shapes, such as being rolled into spirals, kneaded and rolled into pellets, or tied into balls and other elaborate shapes.
Drying: Drying is done to “finish” the tea for sale. This can be done in a myriad of ways including panning, sunning, air drying, or baking. However, baking is usually the most common. Great care must be taken to not over-cook the leaves.