Rolling of tea leaves

Once tea leaves are withered to the desired status, the leaves are fed into rollers and are lightly, without pressure, conditioned in order to attain a uniform distribution of polyphenol oxidase enzymes.

These enzymes are present in epidermis tissue cells, spatially separated from their substrates. This is followed by a true rolling step in which the tea leaf tissue is completely macerated by conventional crank rollers under pressure.

Once done by hand but now performed mainly by machine, rolling transforms the flat leaves into mesmerizing twists, coils, balls or spears.

The rolling process physically crushed the leaves, opening sand exposing the leaf matrix and cellular compartment providing a more homogenous mixture for oxidative reactions and amore extractable matrix for brewing.

Rolling times vary between ten minutes and one hour. Young leaves are rolled under lighter pressure and for shorter duration compared to older leaves, in order to prevent the leaf breakage and yellowing that results from hydrolysis of chlorophyll and autoxidation of polyphenols.

In general, lightly rolled teas have mellower and gentler flavors, while leaves rolled with greater pressure break up into smaller pieces and form brews that are more brisk and intense.
Rolling of tea leaves 

Fermentation of tea

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.
Fermentation of tea