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Tea Oxidization (Oolong Teas)

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Have you ever had this experience while you’re buying teas at a tea shop?

Q: How many percents did the tea oxidized?

Possible answers from tea sellers or tea masters:

It’s lightly oxidized about 15%.

It’s a little bit higher, more than 20% oxidized. 

Here’s the point, no matter how many percents it was oxidized,

what we intend to understand is:

How to distinguish 15%~20% oxidization?

Or lower/higher oxidization? 

How to define the percentage is the major difficulty in the tea making process.

Why is the color of the tea liquor so green?

Why is the color of the tea liquor honey yellow?

Why is the color of the tea liquor so red?

Experienced tea lovers will know the answers in the meantime they saw the color of the tea liquor. 

The TRES gave a definition for the degree of fermentation (oxidization) in the 1970’s. The amount of catechins in the tea reduced during the tea process is the percentage of oxidization which can only be measured by certain equipment called HPLC. For example, the freshly picked tea catechin (or tea polyphenol) content is 85%, but 65% left in the finished tea. The 20% amount of tea catechins reduced is applied to the degree of fermentation. In general, the tea producers/masters will tell a rough figure of percentage, but probably, it is needed to be measured with HPLC equipment. 

In terms of the degree of fermentation, the TRES has revised the definition for the degree to use light, medium and heavy fermentation rather than the percentage. This mainly happens in the category of green oolongs. Baozhong Tea (the lightest oxidized oolong) has been experimented for many times, the total amount of catechins in the finished tea was always higher than those in the freshly picked tea, causing unexplained. The main reasons for this result are 1. After the tea was picked, the first metabolism stopped except for the respiration and the decomposition, but the second metabolism was still going on which led to a small number of catechins synthesized. 2. During the process of fermentation, a part of oxidized catechins will deoxygenize in order to oxidize the aroma precursor and then to generate the aroma. The number of catechins in this phase cannot be detected precisely during the process of the experiments (because only before and after fermentation can be measured.). 

The percentage of oxidization gives the concept of the degree (light, medium and heavy) that tea leaves being oxidized. Therefore Baozhong Tea and high mountain teas are roughly considered to be lightly fermented, while Dong Ding Tea and Tieguanyin Tea are medium fermented; Baihao Oolong and Red Oolong are heavy fermented. 

Partial fermentation means that the catechins developed into many degrees of oxidization and has many possibilities with tremendous knowledge in between; however, it cannot be precisely defined with the percentage which means that it used to be a very reasonable explanation but cannot be verified by experiments at the meantime.   

The oxidization phase in the tea making process plays an important role in the whole procedure. Well oxidized tea contributes good substances and discharges the bad ones. However, tea garden management is always the initial critical factor to produce fine teas while the oxidization phase is the crucial one. Well educated and experienced tea masters always produce fine tea quality as expected. Tea drinkers will realize the differences right after drinking their teas. Always trust your body reactions and taste buds is more important than believe the tasting notes from others.

The end.

Translated and edited by Adm./Fong Mong Tea Corp, all rights reserved.