Green teas are often referred to as non-fermented or unfermented teas. The chief feature in manufacturing of green tea as distinguished from black is that the leaves do not undergo any process of fermentation, while the slow operation of natural withering is replaced by a more rapid one for steaming or sun drying. The objective of this is to inactivate the enzyme and thereby preventing the process of fermentation. The traditional method of processing green teas involves withering (though not always), heating, rolling and drying. After plucking, the fresh leaves are spread out on bamboo trays and exposed to sunlight or warm air for one to two hours. Then the leaves are heated to prevent oxidation and preserve freshness. Finally, the leaves are rolled into various shapes and then dried. The rolling also helps regulate the release of natural oils and flavor during steeping.
In China, green teas are often pan-fired in very large woks and then rolled by hand into various styles, twisted, flat, curly or balled. In Japan, the plucked leaves are quickly steamed on a bamboo tray over water or in a steaming machine, making them easier to shape. The leaves are then rolled by hand or machine before being dried. Though traditionally green tea was produced manually, the process has been fully mechanised in Japan .In Japan, steaming is normally done. Before the steaming process begins, the tea leaves are sorted and cleaned. The steaming time determines the type of tea that is produced. Sencha tea is normally steamed for 30-90 seconds. Another type of Sencha called Fukamushi is steamed for 90-150 seconds to produce a flaky light yellowish green tea. Steaming is conducted in a bamboo tray over water or by a revolving or belt-conveyor type machine. After mechanical steaming, the leaves go into a cooling machine that blows the water from the leaves.
In Japan, a number of rolling and drying steps take place. A special machine is used to accomplish the first rolling and drying steps simultaneously and takes about 48 minutes. The tea leaves are dried to improve their strength so they can be pressed during the next drying process. Moisture from both the surface and from the inside of the tea leaves is removed using this machine.
This machine consists of a spindle with finger-shaped extensions that stir the leaves while heated air (at 34-36°C) is blown into the machine. Though the rolling temperature is automatically controlled by the computer, it is still important for the operator to touch the tea by hand to make sure it feels right. In China, high-end leaves are hand-rolled into various shapes, including curly, twisted, pointed, round, and more. Rolling the tea creates a distinctive look, as well as, regulates the release of natural substances and flavor when it is steeped in the cup. The finest handmade teas are made during the spring season in China and Japan.
In Japan, green tea is dried for about 30 minutes after the final rolling step for storage. The tea is spread on a caterpillar-type device and dried slowly to about 5% moisture content or less. At this stage the half-processed tea, called Aracha, is sent to the tea merchants or wholesalers for final processing. Aracha is not uniform in size and still contains stems and dust.
After the tea is shipped to the wholesalers in Japan, it undergoes several other steps to produce the final product. A special machine grades and cuts the tea by particle size, shape, and cleanliness, depending on the final qualities desired. The machine uses mechanical sieves or sifters fitted with meshes of appropriate size, as well as cutting devices to achieve a quality tea. Another drying step followed is to produce the aromatic flavor, followed by blending as per customer's specifications, packing and finally shipping to retail shops. In most countries (India, Indonesia, Korea, Nepal, Sri Lanka, Taiwan, and Vietnam), rolling or shaping, sorting of green tea leaves is done through machinery.
The quality of green tea depends first on using good tea leaves. The natural quality of the leaf, including color and aroma, must then be preserved during the manufacturing process to produce a good green tea. In Japan, this involves controlling the temperature to 93.2-96.8° F (34-36° C) during rolling, drying, and storage. Since tea leaves can generate their own heat, cool air is blown into the bottom of the container to keep the leaves at the proper temperature during storage.