Tea manufacturing Process
Once the fresh leaf is brought in to the factory, the leaf undergoes a process that transforms the fresh leaf into black tea, or ‘made tea’. On average, 22 to 25kgs of made tea is manufactured from every 100kgs of fresh leaf tea. This process is one which has been honed and perfected for more than a century and demands a great deal of expertise and experience to ensure that the quality of the tea is not compromised at any stage of the manufacturing process.
Withering is the most critical process in black tea manufacture. The primary aims of withering are to reduce the moisture content of the leaf and to soften it, so it becomes pliable and will withstand the subsequent process of ‘rolling’, without breaking up into flakes. Additionally, controlled moisture extraction from fresh leaf is required to activate a series of bio-chemical reactions. These enzymatic changes are ultimately responsible for the production of various bio-chemicals desired for achieving quality parameters in made tea.
Withering duration is dependent on temperature and humidity and could range from 18 to 24 hours, with season and region also being a factor. A careless wither such as an uneven spread will not result in good tea even from the best type of leaf. A good wither will prevent the leaf from breaking up, but will impart a twist. Liquors from fresh leaf are bitter, but in well-withered leaf, sweetness develops.
The purpose of rolling is to achieve the final curved appearance and to break the leaf cell walls so as to release essential oils to start a chemical reaction of fermentation. The rolling process is what releases the colour, strength, aroma and the taste of the liquid we ultimately pour into our cups.
In this process the green colour of the leaf is replaced by a brown coppery coloured texture. The application of pressure during rolling is important for squeezing out the sap and the rolling cycle consists of pressure being applied and then released. During the process the leaf juices spread themselves over the leaf, where they dry and remain in a soluble state. When the leaf cells are ruptured following the rolling of the withered leaf, the enzymes in the leaf come in to contact with oxygen in the air which initiates chemical reactions that are necessary for the production of black tea.
Roll breaking has two primary objectives. To remove twisted leaf off the rolled shoots that clogs and impedes circulation, and facilitate further twisting action on the large leaf. Additionally, it also cools the leaf which would have risen in temperature during the process of rolling. The roll-breaker is simply a sloping table which shakes backwards and forwards at high speed. The fineness of the mesh allows only the small tea particles through, which falls in a fine sprinkle in to a container below. The rest is shaken down to the end of the table, and is taken back to the rollers, where the process is replicated. This cycle is generally repeated at least four times.
The finer particles collected after roll breaking, are fermented to bring about the changes necessary to make a tea liquor palatable. This process can only take place when the cells of the tea leaf are properly ruptured. Here, in the coolness and the darkness of the fermentation room, an oxidizing enzyme produces brown products from the remaining water in the tannin. During this process, the green leaf is converted to black tea. Although this is referred to as fermentation it became recognised around 1901 as an oxidization process initiated by the tea enzymes. The characteristic coppery colour and fermented tea aroma is a gauge to completion of the fermenting process. This is a fine art of the factory tea maker.
Firing & baking
The fermented leaf is next passed through a dryer to stop any further chemical reactions taking place. Passing hot forced air over the tea leaves deactivates fermenting enzymes. Many organo-chemical processes are accelerated during this period, as are the enzymatic reactions before they are inactivated due to heat. Firing also reduces the moisture levels of the tea to 2 – 3%. This is critical as incomplete inactivation can accelerate deterioration of the tea during storage.
Sorting & grading
The last operation in this long process of manufacture is the sorting and grading of the fired tea. Its importance cannot be overstated as it is here that the value of the final product is often determined. The separation of tea particles into ‘grades’ (different shapes and sizes) is required so as to conform to trade standards. This process can be long and tedious, particularly if a large number of grades are made. This is particularly so in low grown areas which can have as many as 12 to 15 grades. Dried tea is sorted into different grades by passing them over a series of vibrating screens of different mesh sizes..
The various grades of tea only denote a certain size and appearance of leaf; it has no reference to quality. Broken grades normally give darker liquor and a stronger tea. Leaf grades on the hand, are lighter coloured and less strong. The quality of tea is unrelated to a grade.
The graded teas are finally weighed and packed into plywood chests, multi-walled bags or corrugated cardboard cartons – all inner lined with aluminium foil. Each chest, bag or carton is stencilled with details such the plantation name, grade of tea, weight, invoice number and so on. This is the final process in the manufacture of black tea and the tea in the chests is what constitutes ‘made tea’.