Blog 166: The Chemistry behind Oolong Tea-making

All oolong tea products are considered as “half-fermented”. In oolong tea’s tea-making, tea leaves’ physical characteristics and fragrance transformation are controlled within a certain range. Every step of the tea-making only begins when the previous step meets the requirement.



Every tea product’s taste and fragrance profile are the result of the chemical reaction during the tea-making. For example, black tea’s taste profile is largely polyphenols and other oxides. To better understand oolong tea’s taste profile, we need to take a closer look at the chemistry side of the tea-making.

First of all, in tea-making, there’s no chemicals added to fresh leaves. All reactions are natural. This is why tea is still an agriculture product.

Oolong tea’s tea-making and quality characters decide the kind of fresh leaves are required. Generally speaking, we prefer fresh leaves that are “hard and crisp”, and with a “thick cuticle”. Fresh leaves with these features can better endure the tea-making.

During the shaking/摇青/Yao Qing step, there are 2 features that are crucial in the formation of oolong tea’s color and taste. The first one is called “green leaf with red edge/红边镶绿叶”, and the second is called “glossy sand green/砂绿油润”.

The major substances behind these 2 features are:


Green Leaf with Red Edge/红边镶绿叶

Green leaf: (compared to the edge) theaflavin, thearubigins, more theabrownin and less chlorophyll.

Red edge: (compared to the leaf center) more chlorophyll remained, less theaflavin, thearubigins, and theabrownin.


Glossy Sand Green/砂绿油润

(compared to black tea) more chlorophyll and the degradation product of pheophytin; few theaflavin, thearubigins, and theabrownin.

In our tea-making, we prefer slightly darker fresh leaves with higher chlorophyll content.

When we sample an oolong tea, the color and the mouthfeel are 2 important criteria. Commonly, a bright orangish yellow tea soup color and a thick, refreshing mouthfeel.

A standard color oolong tea soup contains mainly theaflavin and a small amount of thearubigins, slightly oxidized catechin acids and flavonoids.


If tea leaves are over-fermented, polyphenols such as thearubigins and theabrownin would over-accumulate. As a result, tea soup would look too dark. On the other hand, if leaves are under-fermented, tea soup would look too green.

Standard fresh leaves with proper tea-making taste balanced. If fresh leaves are too old or over-fermented, tea soup would taste too plain because polyphenols are excessively transformed during the tea-making. If fresh leaves are under-fermented, tea soup would taste too bitter and dull.

We hope you enjoyed today’s blog. As always, if you have questions or suggestions, please leave a comment, tweet us @valleybrooktea or email the author directly at zhang@valleybrooktea.com. Please also follow us on Instagram @valleybrooktea and join our mail list to get our daily tea updates and our latest promotions!

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