High temperature drying (or roasting) is used to stop fermentation. This is the only way to prevent molding and decay of tea under the influence of its own juice.
The roasting process is very delicate, because not sufficiently dried tea is perishable in packs, but overdried tea is charring and attains an unpleasant burnt taste. An ideal drying result is dry tea, containing not more than 2-5% water.
In the past, traditionally tea was roasted in the large roasting pans, grilles or pans on an open fire. From the nineteenth-century the closed ovens with air supply have been widely used. Standard roasting temperature is around 90 C, but in modern equipment the roasting temperature can reach several hundred degrees. In such cases the roasting time is shortened to 15-20 minutes.
An important condition for proper tea making is the rapid cooling of tea raw material, taken out of the oven (like any organic substance, tea can begin to smolder and „burn down” even after taking out pf the oven). So, the leaves are being dried in big ovens, in a hot air stream, at the high temperatures. Tea leaf’s juice, released in the process of curling, and aromatic essential oils, strongly “stick” to the leaf surface and retain their qualities for a quite a long time, extracting just under the effect of the boiling water at the moment of brewing.