Tanganda has four processing factories: Ratelshoek, Jersey, Zona and Tingamira, with a combined capacity of up to 10,000 tonnes of made tea per annum. Tingamira is the “Flagship” factory with up to date processing machinery.
Processing is split into five sections. Withering, maceration, fermenting, drying and sorting, followed by packing into paper sacks and palletisation.
Withering: Leaf is collected in the fields and transported to the factories using a trailer/basket system (Developed by Tanganda). The leaf is deposited onto withering trough mesh beds and spread to a depth of 250mm (25kgs m2). These trough beds have air plenum chambers connected to fans blowing ambient air up through the leaf (some troughs are enclosed and air flow can be reversed). On cold wet days, warm air facilities are available at a temperature of no more than 30?Celsius.
There are two aspects of this process, chemical and physical. The optimum duration for withering is 16 to 20 hours, after which the moisture in the leaf is reduced by 25 to 30 percent. Correct withering is extremely important to enhance colour, strength and brightness of the finished product.
Maceration (Cell Distortion): Withered green leaf from the troughs is transported via the overhead rail system to a cleaning sifter fitted with magnets to remove metal objects and any other extraneous matter which can damage maceration machines. These sifters are also important to control the feed rate of withered leaf.
The initial cut is either through a Green Leaf Cutter (GLC) or a Rotorvane (large mincing machine) which conditions the leaf before being passed through a series of Cut Tear and Curl Machines (CTC). The choice of a GLC and, or a Rotorvane, depends largely on the standard of green leaf, similarly the number of CTC machines.
CTC machines have two opposing stainless steel rollers (1070mm long by 300mm diameter), with a speed ratio of 10:1 (1000 RPM: 100RPM). These rollers are machined with parallel and spiral grooves and the cut is controlled by the mesh - the rollers must not touch each other. The time taken to pass from the sifter to the final CTC is approximately eight minutes.
Fermentation: The term fermentation can be misleading in regards to tea processing. The process is actually oxygenation which creates heat and it is well established that the most important factor affecting liquor quality is to control the temperature to around 24 degrees Celsius throughout the operation. Correct maceration plays an extremely important part, as if this is not complete, not all chemical compounds can be released to form the special taste of tea.
Fermenting machines generally consist of perforated belts passing over air plennum chambers at a controlled variable speed. The cut leaf is spread on the belt to a depth of about 150mm with conditioned air blowing up through the leaf. This system was mainly developed by Tanganda.
Heat transfer from air to leaf is not efficient and it is, therefore, necessary to agitate or turn the leaf at least three times by means of incorporating agitators along the belt and installing a mid fermentation CTC or ball breaker, the necessity of doing this is to force out juices that have migrated back into the balling that takes place during the maceration process. These particles/balls have not been in contact with air to form theaflavins to improve brightness/briskness in the infusions.
The fermenting process can take 45 to 90 minutes depending on the type of leaf and temperatures.
Drying: From fermentation, leaf is conveyed into Fluidised Bed Driers (FBDs) and subjected to a temperature of 140 degrees celsius, which immediately stops fermentation by killing the enzymes. The FBD has three stages of fluidisation and temperatures,140?C, 120?C and 85?C with a retention time of about 15 minutes from when leaf enters to being discharged as black tea of various size particles. The ratio from being green leaf from the field to black tea is 4.3:1 (with good leaf). Air being discharged from the FBD is virtually saturated and contains small particles of tea fibre which is collected through a cyclone system before the air returns to the atmosphere.
Sorting: From the FBD, the black tea is conveyed to Drier Mouth Sorters where the main bulk of stalk/fibre is extracted. Then the cleaned tea is conveyed onto sorters with different screen sizes which grade the tea to various international classifications and densities and depending on plucking standards, approximately 20 percent of this tea becomes secondary grades. The graded tea is conveyed into holding bins and is then packed into 50kg foil lined paper sacks or bags, for sale either to the export markets or Tanganda's packing facility in Mutare.
Plucked tea arrives at the factory
Green Leaf Sifter
Appraisal of tea qualities
The appraisal of tea quality is an art - if not a science - learnt over many years of comparative tasting. Each factory conducts tasting sessions every day to evaluate each day's production and to make the necessary and continuous adjustments to improve quality.
Palletised tea for export