Tea Oxidation - How to Tell?

by Sigurd
(Sweden)

Reading about tea oxidation on your web page, I wonder what actually happens during oxidation, both chemically and taste wise.

Maybe you know?

I see you write "Depending on the variety, it can range from 10% to 70% oxidized."

But how can one know when the leaves have been oxidized by 35%?

Answer:

Sigurd, the oxidation percentages of oolong teas are quoted from producers, rather than the results of scientific studies. So you are right, we are not talking about exact science here.

The effect of oxidation is to oxidize a group of constituents called catechins, which make up the bulk of tea antioxidants.

When catechins oxidize, they form more complex compounds called thearubigins and theaflavins.

More oxidized teas not only contain different kinds of compound, the total quantity is also lower. So trying to measure oxidation scientifically is tricky, although not impossible.

One of the compounds (I can't remember which), is red color. So the effects of oxidation is to turn the color of tea from green to red.

Consequently, in China, oolong tea is called "half green half red", and fully oxidized tea is called red tea.

Oxidation makes the flavors more aromatic at light oxidation. At heavier oxidation, a more masculine flavors emerge.

Heavily oxidized teas are often roasted longer to increase the "fire" flavor. This reduces the floral aroma but increases the mouth-feeling and lengthens the aftertaste. A prime example is the Wuyi Rock tea.

I suspect tea makers use color and aroma as a guide to gauge the degree of oxidation.

I hope this helps.

Julian