Black tea production
There are three different methods of producing black tea:
Orthodox production
CTC production
LTP production
The orthodox production method
The orthodox production method consists of five stages
withering, rolling, fermentation, drying and sorting.
1 The freshly picked green leaves are spread out to dry on ventilated trays. During this process, approx. 30% moisture is extracted from the leaves, making them soft and pliable for further processing.
2 The leaves are then rolled by applying mechanical pressure to break up the cells and extract the cell sap. After 30 minutes, the leaves, still damp from the sap, are sieved to separate the finer leaves. These are spread out immediately for fermentation, while the remaining coarse leaves are rolled for a further 30 minutes under higher pressure. If necessary, this process is repeated several times. A short rolling time produces larger leaf grades, while longer rolling breaks the leaves up more resulting in smaller grades. During the rolling process, the cell sap runs out and reacts with oxygen, thus triggering the fermentation process. At the same time, the essential oils responsible for the aroma are released.
3 After rolling, the tea is spread out in layers approx. 10 cm high for one to three hours in a cool, damp atmosphere to finish off the fermentation process. During this process, the substances contained in the cell sap oxidise. In this production phase, the green leaf gradually turns a copper colour. The colour and typical odour tell the person supervising the process how far the fermentation has progressed. Various chemical reactions cause the leaf to heat up during fermentation. It is critical for the quality of the tea that the fermentation process be interrupted at its peak, when the temperature is at its highest.
4 Next, the tea is dried with hot air at a temperature of approx. 85º-88ºC in order to interrupt the oxidation process. The residual moisture is thereby extracted from the leaves, the extracted sap dries on the leaf and the copper-coloured leaf turns dark brown to black.
5 Finally, the dried tea is sieved to separate the different leaf grades. The orthodox production method provides teas of all leaf grades: leaf, broken, fannings and dust. Leaf grades only refer to the leaf size, however: they are not an indication of the quality of the tea.
The CTC production method
Both the CTC and LTP methods are mainly used for the finer end of the scale, i.e. fanning and dust grades. These teas are usually destined for teabag production.
CTC stands for crushing, tearing and curling. The withered leaf is often cut to a uniform size by machine. Then the leaves are fed into the CTC machine where they are crushed, torn and curled in a single operation by metal rollers. The extracted cell sap is collected and added to the leaves again. The crushed leaves are then fermented, dried and sorted. The CTC method is mainly used in Indian regions.
The LTP method
The third method of producing black tea is the LTP method,
named after the inventor of the relevant machine, the
Lawrie Tea Processor. In this method, the withered leaves
are often levelled before being processed in the LTP machine.
Here they are virtually torn to pieces by blades rotating
at high speed. This is followed by the usual fermentation,
drying and sorting procedures.
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