Chemical reaction during tea fermentation

Among all the teas with various degree of fermentation, the ones with higher degree of fermentation have better storage stability.

In consequence, black tea has the best storage stability, followed by Oolong tea, Pouchung tea and white tea.

The most important reaction in tea fermentation is the oxidative chemical reaction included by the polyphenol oxidase on the polyphenols in tea leaves. This subsequently causes the formation of different colors, aromas, and tastes in tea with various degrees of fermentation.

The reactions result in the formation of two groups of coloring compounds – the yellow group (theaflavins) and the red group (thearubigins). During fermentation tea phenol reduced over 90%.

In partially fermented tea, the fermentation process generally involves a withering or all shaking step to induce oxidation in the tea leaf, followed by blanching to terminate the process.

In the manufacture of fully fermented tea, the tea leaves are withered, rolled and fermented thoroughly, followed by drying or complete the process.

The rolling and crushing of the leaves frees essential oils and cellular constituents that promote the enzymatic activity of polyphenoloxidase.

Under traditional chilling techniques a typical 2-3 hrs fermentation may yield a reddish color tea with strong astringent qualities, while 4 to 5 hr fermentation in black teas provide a bright colored tea with a very low quantity of extractives from a similar fermentation.

While green tea retains the thin and refreshing flavors of the leaves, the fermented black tea gives a stronger and thicker flavor.
Chemical reaction during tea fermentation