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Types of Tea and the Role of Oxidation

tea-blog-jas-keemun-mao-fenga0a.jpgAll tea comes from the leaves of the Camellia sinensis plant. A tea style is defined by the way it is processed. The styles of tea are produced by altering the shape and chemistry of the leaf. Once this alteration is complete, all teas are finished by drying the leaves. The following information focuses on the step between picking and drying.

What is oxidation

The primary impact of the way a leaf is processed, and the main indicator of how the tea will be classified, is oxidation. Oxidation is the natural process by which enzymes in the tea leaf are exposed to, and interact with, the oxygen in the area after the cellular structure of the leaf has been broken. This can happen quickly, through rolling, cutting or crushing, or more slowly through the natural decomposition of the leaf. You see the same process in a piece of fruit. Left to sit, the fruit will slowly turn brown. Cut or bruise the fruit and it will brown much more quickly.

The oxidation process is stopped by drying the leaf down to 5-6% moisture content (or less) which prevents the remaining enzymes from interacting with the oxygen in the air.

NOTE: Oxidation is commonly, but incorrectly (in my opinion), referred to by some in the tea industry as fermentation. This is likely a mistaken comparison to the more familiar fermentation process involved in converting grapes into wine.

The four basic styles of tea

Listed in order from least oxidized to most oxidized, the four basic styles of tea are White, Green, Oolong, and Black. There is also yellow and pu-erh.

White Tea

Technically defined as a tea that is relatively unprocessed, and has been kept from oxidizing as much as possible. The name is derived from the fuzzy white "hairs" that appear on the unopened or recently opened buds of new growth on the tea plant. Because they are typically comprised of the newest leaves, which the plant has been pouring its energy into, they also tend to have the highest antioxidant content. In practice, some white teas, like the Chinese White Peony, undergo a multi-step process of steaming and drying that does result in some uneven oxidation which can be seen in the varying shades of green in the open leaf and even some brown around the outside edges of individual leaves. White teas produce very pale green or yellow liquor and are the most delicate in flavor and aroma. There are several grades of white teas, with Silver Needle being the highest and comprised solely of tender silvery “hair” covered leaf buds (two tender, partially formed leaves closed around a third inner leaf).

Green Tea

Typically subjected to a multi-step process of steaming, pan-firing, and/or rolling before being dried to freeze the oxidation process. Little oxidation occurs in most green teas. They are differentiated from white teas primarily by the extra steps of manipulating or processing the leaf before drying. The liquor of a green tea is typically a green or yellow color, and flavors range from grassy to sweet with mild astringency.

Oolong Tea

Also subjected to a multi-step process of steaming, pan-firing or rolling but also set out and allowed to "wither" which gives the leaves time to oxidize. Oolongs usually range between 20% and 80% oxidized. This range results in a dramatic variety of colors (from green to nearly black) and an equally dramatic variety of flavors and aromas. Oolongs typically are bolder in flavor than green or white teas and offer less astringency than either the stronger black or lighter green teas. Because of their smooth yet rich flavor profiles, oolongs are ideal for those new to tea drinking.

Black Tea

Called “red tea” in many Asian countries due to the color of the tea liquor. The leaves undergo similar processing to green and oolong teas but are allowed to oxidize more completely. The brewed liquor of a black tea ranges between dark brown and deep red. Black teas offer the strongest flavors and, in some cases, the greatest astringency. Black teas are the only style of tea regularly drunk with milk and sugar (though some drinkers of darker oolongs may disagree) and are the most popular bases for iced tea.

Pu-erh Tea

The leaves undergo similar processing to green teas but then are allowed to go through an entirely unique process of fermentation over an extended period of time (sometimes many years). Pu-erh teas are often pressed into dense cakes or other decorative shapes. They are known for their unusual status as the only aged, fermented teas and are prized for their earthy, musty aroma and rich, smooth taste.