The process of oxidation is very important in tea. This is essentially the part that differentiates each of the teas. The industry also refers to this process as fermentation. The white teas and green teas go through the least amount of natural oxidation while oolongs and black teas are partially oxidized and fully oxidized respectively.
The process of oxidation is when the chlorophyll in the leaves is broken down at the enzyme level and tannins are released. The tea producer decides the amount of oxidation depending on what tea is being produced. For the green and white teas only a small amount of natural oxidation occurs while the oolong and black teas are placed in climate controlled rooms. Oolongs range from light (5-40% oxidation) to dark (60-70% oxidation); blacks are 100% oxidation. Through oxidation, the leaves turn progressively darker as the process is furthered. Oxidation is essential. It allows for the color of the liquor, the briskness and strength of flavor.
Oxidation is not only controlled, there are times that the process occurs naturally. When teas are recently picked, they go through a process of withering or wilting. This process is used to pull moisture from the leaves and it allows for a slight amount of oxidation.
Next, the leaves go through the process of bruising in order to initiate, promote or quicken oxidation. The leaves are either tossed or shaken in a bamboo tray, tumbled in a basket or being kneaded or rolled over by heavy wheels. This process breaks down both the inside and outside structures of the leaves. It also allows for the comingling of oxidation enzyme and leaf juices which help with the taste of tea. This is just the beginning process for greens and whites.
In order to stop oxidation, the teas go through fixation or kill-green. This process is performed by heating the tea leaves thus deactivating their oxidative enzymes.
What a process, no? It’s big and complex and natural, too! What do you guys think? What’s your favorite tea?