FERMENTATION It is the practice in south Indian CTC factories to pass the CTC, 'dhool' through a large revolving drum for 60 - 90 minutes with conditioned air. Rotation of the fermentation drum facilitates granulation of the tea particles and increases the bulk density which is desirable for South India CTC teas. In drum fermentation, the whole process is dynamic and the leaves are constantly rotating. Every bit of tea that is being fermented is constantly layered and exposed to the fresh air or conditioned air. Rubbing of leaf against leaf takes place and the juices present in the micro cells of leaf are evenly coated on the exterior of the tea leaf. Drum fermentation produces blacker teas as compared to floor fermentation. These teas are usually brisker due to better aeration.

Since most of the biochemical reactions occurring during fermentation are oxidative in nature, mass transfer of oxygen to the tea particle is a critical parameter in the design of any fermentor. The fermenting drums are equipped with spiral flights on the interior for lifting and showering the solids through the air stream and to accelerate the forward flow in the drum.

Good ventilation and access to fresh air are paramount to proper fermentation. In most of the factories, the air required for fermentation is drawn from the rolling room. This results in recycling of spent air for fermentation which is not advisable. It is suggested to have a co-current air flow arrangement in the fermenting drum; the blower type is preferable to the suction type of fan. co - current air is required to supply more oxygen during the initial stages of enzymic fermentation when it is needed at maximum levels. This air should be fresh, cool and saturated with moisture.

Another new and promising aid to fermentation is ultraviolet radiation. Ultraviolet rays have two functions. (1) it kills external bacteria and other micro organisms (2) it triggers the activity of polyphenol oxidase and thereby hastens the biochemical reactions. Bright infusions are obtained by passing conveyor racks which contain fermented dhool through a UV chamber. It is practically impossible to fix UV bulbs inside the fermenting drum. However, UV lamps could be easily installed in continuous fermenting machines(CFM). CFM gives closer control of the entire fermentation process resulting in tea with improved quality. Leaf spread and run through time are infinitely variable within a selected range to ensure optimum fermentation under different climatic conditions.

A post fermentation ball breaker is essential. This, while ensuring minimum ball formation will also increase in the percentage of dust grades.

DRYING The objectives of drying are to :
	Arrest fermentation
	Remove moisture and produce tea with good keeping qualities

Drying is the most expensive process in the manufacture of tea. The capital investment on the driers is also the highest among the different processing machines.

Before going to the different types of drying systems it is essential to know the basis of drying. Drying a solid matter indicates removal of water from the solid materials by evaporation. During the early stages of drying, the solid is so wet that a continuous film of water exists over the entire surface. The water removed during in this period is mainly superficial water. During this period the rate of drying under a given set of air conditions is constant and independent of the moisture content. This period is known as the constant rate of drying and the temperature of the solid during this period approaches the wet bulb temperature of the air. The magnitude of the constant rate depends on the area exposed to the drying medium, the difference in temperature between the gas stream and the wet surface of the solid and the air velocity.