The Camellia sinensis plant is an evergreen bush that thrives in tropical and subtropical climates. This plant prefers acidic soil and a significant amount of rainfall for the best growing conditions. Tea plants are categorized into three different groups based on their size. Assam leaves are the largest, followed by Cambodian, which are medium-sized and China-type leaves, which are the smallest. Most plants for tea harvesting are kept to waist height in order to make it easier to pluck the young, fresh leaves at the top of the plant.
Tea leaves are harvested from the tea plant and then transported to a nearby tea factory for production. During the harvest, leaves are only plucked from the top one to two inches of the tea plant. Tea leaves are generally hand-plucked from the tea garden or tea plantation and placed into large wicker baskets. Once a basket is full, it is brought to a tea master where leaves are inspected and weighed to ensure quality. Broken leaves are typically discarded as are ones that show signs of sun or water damage. Tea leaves are examined based on size, type, and appearance. Each individual tea leaf is also inspected and sorted into white, green, black, pu-erh, and oolong categories for the next processing step.
As mentioned, all true teas are derived using the same leaves—the difference in color, aroma and flavor arises from the ways in which they are processed following harvest. Leaves can be withered, dried, oxidized, fired and shaped depending on the desired tea type. For example, leaves for green and white teas are not oxidized at all—leaves are simply dried in the sun, pan-fired or steamed and then shaped into pellets or small twigs. Green tea leaves can also be ground to create matcha green tea powder. On the other hand, robust, darker teas such as oolong tea and black tea are created through an oxidation process. During this stage, leaves are withered and rolled in order to encourage enzymes within the leaves to react with oxygen. This process results in darker tea leaves and more potent flavors than those characterized by delicate true teas such as green tea and white tea. The oxidation process is comprised of two methods, the orthodox method, which is most common and the CTC method.
For the standard method for most types of tea, tea leaves are subjected to a 4-step process with each step producing the flavor profiles associated with darker true teas.
a. Withering - Tea leaves are transported from the fields to the tea factory within hours after plucking and sorting. Leaves for black or oolong teas are withered in order to reduce moisture content so that leaves can be rolled without flaking. The water content of leaves is removed by laying leaves on a flat mesh surface or a bamboo tray and dried with cool air, for anywhere from 8 to 18 hours.
b. Rolling - Once the leaves are withered, they are rolled in order to promote oxidation. In traditional production methods, leaves are hand rolled although, in modern times, many manufacturers use rolling machines to expedite the process. As the withered leaves are rolled, internal cell structures are broken down, releasing essential oils that react with oxygen to develop flavor and aroma.
c. Oxidation - After the leaves are rolled, they undergo a process of oxidation, also known as fermentation, which determines the strength and flavor of the tea. The interaction between enzymes and oxygen breaks down chlorophyll and releases tannins, which causes leaves to turn darker. The process of oxidation is controlled by tea producers who maintain a warm, moist environment.
d. Drying - To stop the oxidation process, tea leaves are subjected to methods of drying. Depending on tradition and tea producer preference, tea leaves can be dried by pan-firing, sun drying, or baking. The leaves are subjected to hot temperatures over 100 F to stop the oxidation process and reduce the moisture content.