Tea Processing Line

Overview

A tea processing line turns freshly plucked green leaf into shelf-stable black tea by chaining five operations: withering, rolling or cutting, fermentation, drying, and grading. The line accepts 700–2,800 kg of fresh leaf per hour and yields 150–600 kg of made tea, since roughly three to four kilograms of green leaf reduce to one kilogram of finished tea once water is driven off. Stations are linked by belt and bucket conveyors so leaf moves under continuous flow rather than being carried in baskets between separate machines.

Two recipes share the same backbone. The orthodox route twists whole leaf in a Rolling Machine to keep particle size and produce the larger graded teas prized for flavour and appearance. The cut-tear-curl route feeds leaf through a CTC Rotorvane and then a CTC Roller Bank to make small granular particles that brew fast and colour strongly, the style used in most tea bags. Many factories install both paths and switch the rolling section to match the order while sharing withering, drying, and grading.

Withering

Plucked leaf arrives at 78–80% moisture and is too turgid to roll without shredding. The Withering Trough spreads leaf 20–30 cm deep on a Withering Mesh Bed and pushes air up through it for 12–18 hours. A Withering Fan moves the air, and in cold or damp weather a Air Heater using a finned coil and electric Heating Element banks lifts inlet air to 30–38 °C. Operators trim fresh-air and recirculation ratios with louvre dampers while a humidity probe tracks the plenum. Physical withering removes water until the leaf is limp and pliable at 68–74% moisture; chemical withering during the same hold develops the amino acids and aroma precursors that later define the cup.

Rolling, rotorvane and CTC

Withered leaf must have its cells ruptured so that polyphenols and oxidising enzymes mix. In the orthodox machine a Rolling Jacket gyrates over a battened Rolling Table, driven by an Eccentric Drive, while a Pressure Cap sets the load on the leaf charge. A typical batch rolls for 30–45 minutes, twisting the leaf into the wiry shape that survives into the dry product.

The CTC route works continuously. The rotorvane macerates leaf with a Rotorvane Auger turning inside a barrel fitted with resistor vanes, producing a uniform feed. That feed passes through the roller bank, where each CTC Roller Pair runs its two engraved rollers at about a 1:10 speed difference so the surfaces cut, tear, and curl the leaf into fine granules. Three roller pairs in series, set to progressively finer cuts, give the final particle size.

Fermentation

Ruptured leaf is laid on the Fermentation Bed, a slow perforated Oxidation Conveyor that holds it for 60–120 minutes. This stage is oxidation rather than microbial fermentation: enzymes convert colourless catechins into the theaflavins and thearubigins that give black tea its colour and briskness. The reaction is sensitive, so a Humidifier Unit keeps the air at 90–95% RH to stop the leaf drying out, and a Temperature Control Unit holds it at 22–26 °C. Too warm and the leaf stews and turns dull; too cool and oxidation stalls. The conveyor speed sets the dwell, and the leaf is judged ready by its coppery colour and aroma before it goes to the drier.

Drying

Drying fixes the tea by deactivating the enzymes and dropping moisture from around 70% to 2.5–3.5%, which arrests oxidation and makes the tea stable for storage. The Fluid-Bed Drier passes leaf on perforated trays through hot air supplied by a Drier Burner firing at 110–130 °C inlet temperature. A Drier Fan fluidises the bed so every particle dries evenly, and a Dust Cyclone recovers fine dust from the exhaust. Drying takes 18–25 minutes. Overheating scorches the leaf and burns off aroma, so the burner modulates against an outlet temperature and a moisture target.

Sifting and grading

Dry tea leaves the drier as a mixed stream of particle sizes mingled with stalk and fibre. The Sifting and Grading Unit unit shakes the tea across stacked Sorter Screen decks driven by a Vibrator Drive, separating it into broken, fannings, and dust grades that fall down the grading chutes. A Fibre Extractor uses a charged roller to lift light stalk and fibre out of the made tea so the graded product is clean. Five to seven grades are typical, each routed to its own bin for blending and packing.

Drive, control and frame

A Drive and Transmission of induction motors and reduction gearboxes powers each station, with line shafts and belts distributing motion to the conveyors. The Control Panel runs a PLC that sequences the line, holds the recipe, and trims conveyor and roller speeds through variable frequency drives, with an HMI for the operator. All stations bolt to a Structural Frame of steel columns and beams with grated walkways. Wetted parts in the rolling, fermentation, and drying stations are stainless steel or food-grade polyurethane to meet hygiene rules, while the structural frame and ducting are painted carbon steel.