The steps and equipment for refining tea leaves


Refined tea leaves

There are five purposes for refining tea leaves: firstly, to tidy up the appearance and use various screening equipment to process the tea leaves, so that they are of appropriate length and consistent size, achieving the requirements of neat and beautiful appearance; The second is to classify the grades according to the tenderness and quality differences of the raw materials, achieving the requirements of uniform quality and distinguishing between good and bad; The third is to remove impurities and foreign objects mixed in the tea leaves, and improve the purity; The fourth is moderate drying to enhance aroma and facilitate storage; The fifth is to combine the finished products and adjust the quality to unify the specifications. In short, adjust product quality according to standards or customer needs.

Refined tea leaves (1)

Pre refined processing of raw tea

(1) Acceptance, grading, and organization of raw tea

Due to coming from different regions, seasons, and grades, the quality of raw tea varies greatly, and there is a significant difference in quality specifications compared to commercial tea. In order to simplify the processing of raw tea, save labor, reduce costs, and improve product quality, strict control is exercised over the acceptance, grading, stacking, and blending of raw tea purchased from the factory, thus fully realizing the highest economic value of raw tea. When purchasing raw tea into the factory, it is necessary to conduct timely acceptance, quality evaluation of the appearance and internal quality of raw tea, moisture acceptance, and grading. Store raw tea from different origins in separate piles, and store raw tea from different seasons separately; Remove the deteriorated tea and stack it separately for processing; If the moisture content of raw tea exceeds 9%, immediately reheat and dry it.

(2)  Develop evaluation criteria for raw tea

To ensure that the quality of finished tea of all levels of color throughout the year is basically consistent before and after leaving the factory, the following 5 tasks should be done before the production of raw tea:

  • One is to be familiar with and master the quality and specification requirements of the standard tea samples for processing raw tea, strictly follow the specification requirements for blending, and ensure the quality of the finished tea.
  • The second is to grasp the quality characteristics of different regions’ raw tea, appropriately mix raw tea from different regions, complement each other’s strengths and weaknesses, and fully tap into the economic value of raw tea.
  • The third is to master the quality characteristics of hairy tea in different seasons, and mix them in a certain proportion according to the different qualities of spring, summer, and autumn tea, so that the quality of finished tea before and after the year is basically consistent.
  • The fourth is to arrange production reasonably based on the customer’s requirements for product grade and delivery date, raw material entry situation, and processing technology and equipment.
  • The fifth is to develop a grading system based on the raw material situation to ensure the economic benefits of the raw materials are fully utilized.

Refined tea leaves (2)

The main machinery for refining tea leaves

(1)  Screening machinery

After sieving through different types of screening machines, the tea strips of different types such as long, short, and fine in the raw tea are separated, and then sorted into various sieve numbers of tea with similar sizes and thicknesses that meet certain specifications. There are two main types of machinery: flat circular screening machines and vibrating screening machines.

1. Flat circular screening machine

This is a screening machine that separates the length and size of strip tea from circular tea, used to distinguish the length and size of tea leaves.

The flat circular sieve machine uses an eccentric mechanism to drive the rotation of the sieve bed, allowing the screened tea leaves to slide on the inclined sieve screen of 630 ‘. Tea leaves with sizes smaller than the sieve hole size fall through the sieve hole, while tea leaves larger than the sieve hole size slide along the sieve surface from high to low and concentrate at the tea outlet for tea. The size specifications of the screen mesh can be replaced with different sizes according to different job requirements. The flat circular screening machine can be divided into multi-layer screening and single-layer screening according to the arrangement of the screen mesh. Currently, multi-layer screening is commonly used in tea processing.

The flat round screening machine separates tea into certain specifications through screening, lifting screening, and foot cutting processes. Remove the round tea head, shake off the tendon stem, and the reciprocating shaking sieve machine has a certain inclination angle between the sieve surface and the horizontal plane; The screening bed is driven by the crankshaft and connecting rod, and oscillates back and forth under the elastic force of the spring steel plate.

Due to the alternating acceleration of the sieve bed, tea leaves have slight up and down jumps on the sieve bed, allowing the tea leaves on the sieve to stand upright. Small tea leaves pass vertically through the sieve holes and fall under the sieve, while larger ones move towards the outlet on the sieve surface, thus separating the thickness and shaking of the tea leaves. The shaking screen machine is applied in different processes and has different functions. In production, it is usually referred to as shaking screen, tight door, shaking rib, and punching foot.

2. Shake screen machine

The reciprocating shaking sieve machine is used to distinguish between the thickness of strip tea and the roundness of round tea.

(2) Tea cutting machine

The cutting and crushing operation mainly involves disassembling the sieved hairy tea and the shaken sieved long tea, cutting them into coarse to fine and short lengths, and processing them into standardized tea strips.

1. The gear cutting machine is composed of roller gear shaft, gear plate, tea hopper and other parts. When the toothed cutter is working, the tea leaves entering the tea hopper fall into the toothed shaft through the tea inlet door. Due to the relative motion between the rotating toothed shaft and the fixed toothed blade, large or long pieces of tea are cut to complete the tea cutting process.

2. There are two types of roller tea cutting machines: single roller and double roller, both consisting of rollers, cutting blades, tea hopper, tea inlet baffle, tea outlet slide, cutting blade safety device, and frame. The surface of the tea cutting machine roller is covered with rectangular pits of the same size. During operation, the tea leaves that fall through the tea inlet funnel are guided into two roller pits with the same speed and opposite directions by the tea inlet baffle. As the roller rotates, they are taken to the cutting blade 0.5-1.5 millimeters away from the roller and cut horizontally. The tea leaves are then exported out by the tea outlet slide.

(3)  Tea air sorter

Wind selection operation is to separate different qualities of tea leaves based on their different weights, volumes, shapes, and landing points in the wind field, in order to achieve clear grades of tea leaves at all levels, uniform softness and hardness, without feeding, and meeting certain specifications. Wind selection has two functions: grading and cleaning. Grading wind selection consists of two steps: coarse selection and fine selection. Different qualities of tea are separated and graded according to the weight and quality of each level of tea. Cleaning is the process of using wind power to remove tea powder, yellow flakes, impurities, as well as sand, stones, metals, and light dust from the tea leaves before the finished tea is evenly stacked.

Tea air selection machines can be divided into two types based on the form of wind input: supply air type and suction air type. Air supply type air sorting machine, the fan is located at the front end of the equipment and blows wind into the tea box under positive pressure. The tea leaves move at a relatively uniform speed under positive pressure and are in a laminar flow state; The disadvantage is that tea dust and other particles fly outside the machine during homework. The suction type air separator fan is located at the tail end of the equipment to suck air into the tea box, and the tea leaves move under negative pressure. The sealing requirement of the tea box is high to ensure uniform wind force. The advantage is that tea dust does not fly outwards during homework, which can maintain a relatively clean and hygienic processing environment.

The air separator is mainly composed of a fan, air duct, feeding device, and air box. During work, the tea leaves to be selected are evenly fed into the inlet of the air box by the feeding device. Under the action of wind, the weight of the tea leaves and the impurities inside are different, resulting in different weights of tea leaves and impurities at different distances, achieving the purpose of tea grading and material collection.

(4) Picking and selecting

The purpose of picking is to eliminate impurities and maintain pure quality, removing non tea impurities such as stems, tendons, and seeds from regular tea leaves, and enhancing the appearance of tea leaves. Machine picking is the main method of picking, supplemented by manual labor. Tea stem picking machines can be divided into three types based on their working principles: step type, electrostatic type, and photoelectric type.

1.Ladder style tea stem picking machine

It uses the physical property of the difference in length between tea leaves and stems to pick tea stems. The machine consists of three main parts: a frame, a transmission mechanism, and a picking bed. When the stem picking machine is working, the transmission mechanism drives the connecting rod, causing the spring flat steel to vibrate in a directional manner, thereby causing the entire picking bed to vibrate. The multi slot boards on the bed are arranged in a stepped pattern, with the front lower and the back higher. Due to the continuous forward and backward vibration of the picking bed, the tea leaves are arranged in rows longitudinally on the picking bed and move forward along the inclined multi slot plate. When passing through the gap between the front and rear multi slot plates, the shorter and bent tea leaves, just before touching the picking shaft, have just approached the gap and their center of gravity has exceeded the edge of the multi slot plate, flipping into the groove and entering the next layer of multi slot plate for further picking; A longer and straight tea stem, due to its center of gravity being relatively backward, can maintain a forward tilt before touching the stem picking axis, and be transported over the groove by the stem picking axis to separate the tea leaves from the stem.

2. Electrostatic tea stem picking machine

There are two types of electrostatic stem pickers: high-voltage electrostatic stem pickers and friction electrostatic stem pickers. They are mainly used to pick out fine and discolored stems from tea leaves. The high-voltage electrostatic tea stem picking machine utilizes the difference in moisture content between tea leaves and stems. Under the action of an electrostatic field, the induced electricity and electrode attraction are not consistent, and tea stems with high moisture content are adsorbed, thereby separating them from tea leaves with low moisture content. Mainly suitable for tea types with no significant difference in length between tea leaves and stems.

3. Friction electrostatic stem picking machine

When the operation is composed of plastic rollers, wool rollers, feeding devices, transmission devices, picking plates, etc., the plastic rollers and wool rollers (sheets) are parallel and closely adjacent. The rotation and friction of the plastic rollers generate static electricity, and an electrostatic field is generated around the plastic rollers. When the tea leaves are moved into the electric field, the tea stems with high moisture content have a large amount of induced electricity and are easily adsorbed by the plastic rollers, achieving the purpose of separating the tea leaves from the tea stems. The magnitude of friction between plastic rollers and wool rollers (sheets) is a regulator that obtains electric fields of different strengths to adapt to different types of tea leaves to be picked.

4. Photoelectric tea stem picking machine

The photoelectric tea stem picking machine consists of a tea queuing device, a light box, a control circuit, and a frame. When the photoelectric tea stem picking machine is in operation, the tea leaves are uniformly and stably fed into the light box by the queuing device. Due to the different colors of the tea leaves and stems in the light box, different light pulse signals are generated under the illumination of the light inside the light box. The light pulses are converted into electrical pulse signals, which are amplified and identified before controlling the action of the solenoid valve. When the tea stems are transported to the solenoid valve, the solenoid valve opens the compressed air nozzle to blow out the tea stems, achieving the purpose of separating the tea leaves from the stems.

(5)  Tea drying machine

In the refining and processing of tea, according to different drying purposes, it is divided into reheating drying and supplementary drying processes.

1. Due to insufficient dryness, tea leaves that have been reheated generally need to be dried by a dryer in order to make the tea body compact and crisp, and to facilitate screening, shredding, air selection, and picking. In the refining process, the methods of raw and cooked tea are adopted according to the different moisture contents of the tea leaves. For raw tea with a moisture content exceeding 10%, it is necessary to first reheat and adopt the method of cooking and taking. After rough selection, green tea should be stir fried and dried in a pot, and then polished and colored. Its purpose is to facilitate the selection, screening, and grading of finished products in the production section.

2. Before evenly stacking and packing the tea leaves, the semi-finished tea products of each sieve size should be graded, and then pan fried and colored, which is called reheating. At present, there are frying pan machines, rolling frying machines, and drying machines for processing and drying raw tea.