There are many stages of processing that fresh tea leaves must undergo before becoming the dried leaves and buds that us tea drinkers have come to cherish. The processing of the leaves also determines the type of tea that the fresh leaves will become. These types are either the familiar Black or Green teas as well as Oolong, White, Yellow, Puerh, or Matcha. However, it should be noted that for all teas there are many unique processing techniques carried out before the fresh leaves are even harvested. One such technique is the shading of the tea plants for sometimes weeks before harvest.
Picking and Withering
The fresh tea leaves are ready to be picked once the new growth of the tea plant has a bud and a few new leaves. The bud and first few leaves are the most prominently picked leaves for tea production. These are the tender leaves. These young leaves have are more potent with the nutrients and chemicals that are desired and necessary for making quality tea and achieving the best tastes. The lower, more brittle, leaves of the tea plant lack the desired nutrients and produce less desired flavor. These leaves are left untouched to support the plant with energy for its future new growth.
On small lot farms the tea leaves and buds are typically picked by hand. On large plantations picking is less strict and done mostly by machine. Machine picked tea leaves are most commonly used in mass marketed teas, especially for that used in tea bags, and are less gentle and specific in their harvesting of tea leaves. This results in a less uniformed flavor in the finished tea product. However, small lot farms, especially in Japan, are implementing the use of sophisticated tea leaf picking machines which are constantly being refined in order to eliminate the undesired effects of machine picking in general.
After the leaves have been picked the tea leaves begin their withering phase. Withering simply refers to the loss of water and wilting of a leaf after it is picked from a plant. While the leaf withers the chemicals in the leaves start to react with the air, resulting in passive oxidation. This is most noticeable with the browning of a Banana. However, after bruising a leaf you will begin to see a darker spot where the leaf was bruised. This is oxidation. Oxidation changes the chemicals in the leaves, resulting in changes in flavor in the finished tea liquor. Because of this, the harvesting and processing of tea leaves focuses on halting and stopping the oxidation process in some teas, while intentionally oxidizing leaves for other teas. This is why we have teas known as “oxidized tea,” Black tea, and “unoxidized tea,” Green tea. This is also why we have such a spectrum of flavors to enjoy when it comes to tea!
Withering techniques include sunning the leaves on bamboo mats or with temperature and moisture controlled air.
Once enough of the moisture in the leaves has been extracted, the leaves are ready for either shaping or rolling–depending on the desired finished tea type. During these processes is where oxidation is either encouraged or prevented. For Green teas the oxidation of the leave leaves will be prevented or limited. For Black teas and Oolongs, oxidation will be encouraged until the desired levels are reached. Oxidation is encouraged by rolling and bruising the leaves so that the chemicals throughout the tea are exposed to the oxygen in the air. Oxidation is responsible for converting Catechins, which are Polyphenols in tea, into Theaflavins and Thearubigins, other types of Polyphenol. Theaflavins give tea sharp and bright flavors with a yellow color, while Thearubigins give it depth and its red color. Chlorophylls are also subjects of change in the oxidation process. Here, Chlorophylls break down and contribute to the black or brown colors of dry tea leaves that have been oxidized.
All of these reactions affect the overall taste and appearance of the finished tea product, showing us just how important the Oxidation process is for finished tea. This is why Oxidation is started, stopped, or prevented for different types of desired tea. When oxidation is prevented, the Catechins in the tea do not convert to the Polyphenols that offer the darker colors and robust flavors. Instead, the leaves keep their green color and, and the flavors of the tea have more fresh, vegetal characteristics. Oxidation is stopped or prevented by the method of Fixing the leaves. This method can be understood as heating the leaves in order to dry them. This is commonly done by Pan Firing, Baking, Heat Tumbling, or by Steaming.
Leaf drying is the last step before the tea is sifted and ready for brewing. Most drying methods do not change the flavor of the tea, but charcoal roasting is a method of drying that does. This offers the tea a more roasted, burnt flavor. This roasting is typical in darker teas, such as Oolongs, and it is particularly desirable on cold days.