Tea leaves have a unique combination of constituents, including essential oils, flavonoids, tannins, and caffeine. These, along with climate and growing conditions, influence a tea's flavor. But a particular tea's flavor is also dependent on the way the leaves are processed.
The first step, withering (or wilting), begins immediately after the leaves are harvested. Withering causes leaves to lose one-quarter to one-half their weight and become soft and pliable. Typically, the leaves are spread on large racks and left to dry for 10 to 24 hours. Some growers speed up the process by using large fans to gently circulate the air, some wither in cooler temperatures, while some wither tea leaves in the sun. After withering, the real task of processing begins.
Whether a tea becomes black, green, oolong, or white depends on when the leaves are crushed or broken after withering and how long the leaves are allowed to oxidize, or ferment, before they are dried. The longer the leaves are exposed to air, the more they will ferment. During fermentation the leaves darken because the chlorophyll they contain breaks down, and the tannins are released.
In general, black tea is fully fermented, oolong is partially fermented, green tea is not fermented or only minimally fermented, and white tea is entirely unfermented.
Each tea producer uses its own proprietary process to create its own unique varieties, but there are some general principles used in the making of each type of tea.
Black tea takes the most time to make and is the most processed form of tea. First the withered leaves are rolled and bruised (the more traditional method) or cut, torn, and curled (the CTC method) to rupture the cells in the leaves and release some of the essential oils. As these oils come in contact with air, the leaves begin to oxidize (oils and chemicals in the leaf react with the oxygen in the air -- the same thing happens when metal rusts or a cut apple turns brown). This process is also known as fermentation. Oxidizing causes the leaves to turn brown and gives a richer flavor and a darker color to the brew.
Black tea leaves are allowed to oxidize for about three to four hours. The leaves are then dried, or fired, by passing them on trays through a hot air chamber. This firing stops the oxidation process and preserves the leaves. The leaves are now dark, or black -- which is why this type of tea is called black tea -- and are sorted, graded, and readied for packaging.
Tea leaves destined to become oolong oxidize for a shorter period of time than those for black -- only about one to two hours -- though growers vary the oxidation time to produce unique flavors. Oolong leaves are typically rolled and sold loose as full leaves rather than cut for tea bags. Oolong is considered the "champagne of tea" and can vary from bright amber to pale yellow in color and from light and floral or fruity to smoky in flavor.
Immediately after withering, leaves designated for green tea are heated to prevent oxidation. The Japanese use steam, while the Chinese prefer pan-frying. After heating, the leaves are cooled and rolled into various shapes. These leaves remain green, and they make a pale brew with a very light, sometimes astringent, grassy flavor.
White tea is made from the unopened leaf buds, which have a white fuzzy undercoat. Some tea companies shield the buds from sunlight while they are growing to prevent chlorophyll from forming. White tea buds are usually not withered. Rather, they are dried immediately after harvesting to prevent any oxidation. White tea requires a lot more individual attention, from picking to processing, than any other tea variety. Though production is increasing, white tea is rare and is usually more expensive than the more common varieties. It brews into an almost colorless liquid with a delicate flavor and aroma.
Of course, all teas are not created equal. On the next page, learn about the qualities of tea.