Dong Ding Oolong Tea and Withering ─ Part 1 [What is Withering]

It is sometimes said that tea is a fermented food.

Removing moisture from tea or bruising the leaves through rolling causes the cells to break down, allowing enzymes and polyphenols to interact, which in turn alters the flavor (this is why tea processing is referred to as "fermentation").

However, if you think about it calmly, that is merely oxidation. Since no biological reaction is involved (though things get complicated if you claim the tea is still "alive"), one might wonder if it’s just enzymatic activity rather than fermentation.

The main topic here is how that flavor difference, brought about by enzymatic reactions, manifests in tea. I would like to explore how Dong Ding Oolong, one of the most famous Taiwanese teas, acquires its characteristic aroma by looking at the technique of "withering" and geographical factors.

What is Withering?

Japanese: A tea manufacturing process in which plucked tea leaves are withered to reduce moisture and promote slight fermentation via enzymes.

English: The controlled process of reducing moisture in freshly plucked tea leaves, making them flaccid and pliable, and allowing biochemical changes that enhance aroma and flavor.

This is how it is defined in dictionaries. The term "slight fermentation" keeps appearing, but in English, it feels more like a "biochemical change." Language is difficult.

Tea leaves contain "polyphenols," such as catechins, and "enzymes," which trigger changes in certain substances; these seem to be kept in separate compartments. It is the techniques of withering and rolling that bring together these two elements that do not usually interact.

How does withering trigger enzymatic reactions?

Freshly plucked tea leaves are succulent. It is said that by drying them, moisture gradually escapes from inside the cell membranes, weakening their functionality. Think of it like a sealed water tank that suddenly loses its water—it collapses and dents. This causes polyphenols inside the cell membranes to leak out. However, unlike rolling, it does not destroy cells externally, so the reaction is very slow, sometimes even called a "static reaction."

The fact that even this gradual reaction results in changes to the final flavor depending on how and at what temperature the leaves are dried is what makes tea so fascinating.

How is Dong Ding Oolong made?

Now to the main point. How does the enchanting Dong Ding Oolong, which continues to captivate us, acquire such an aroma? I would like to focus specifically on the withering process. There are many other interesting aspects, but let's start with the theme of region × withering.

I will continue from here next time.