Microwave fixation is an advanced technique used in tea processing to preserve the quality and flavor of the leaves. Here's a detailed explanation of the process, its benefits, and operational guidelines.
**1. Microwave Fixation:**
**(a) Principle of Microwave Heating:**
Microwave heating works by using electromagnetic waves as a source of energy. When microwaves interact with the molecules in the tea leaves, they cause molecular polarization, orientation, friction, and collisions. This interaction allows the material to absorb microwave energy, generating heat internally. Unlike traditional methods that rely on external heat transfer, microwave heating warms the leaves from the inside out, ensuring uniform and efficient thermal treatment.
**(b) Advantages of Microwave Fixation:**
1. During microwave fixation, the surface temperature of the tea leaves remains relatively low, reducing the need for cooling. This minimizes the loss of chlorophyll and aroma, resulting in a vibrant green color and a more mellow fragrance.
2. The fresh leaves are exposed to the microwave chamber for a short duration, eliminating the need for heat conduction through air or steam. This helps retain the nutrients in the tea, contributing to a richer texture and better quality.
3. Microwave fixation has a natural sterilization effect, which reduces the risk of secondary contamination during the production process. This ensures a safer and more hygienic final product.
4. The simultaneous internal and external heating prevents issues like uneven drying, charring, or burning. It also effectively reduces the bitterness and astringency commonly found in summer and autumn teas, enhancing their commercial value.
5. The rapid evaporation of moisture during microwave fixation creates a porous structure in the leaves, improving their rehydration properties. This makes it easier for the tea to release its flavors and nutrients when brewed.
**(c) Operation Essentials of Microwave Cleaning Machine:**
1. Turn on the power and ensure the machine is running smoothly.
2. Adjust the rotation speed for optimal performance.
3. Confirm that the fan is operating normally to aid in heat dissipation.
4. Place a wet towel on the belt to maintain proper humidity and ensure the machine is ready for operation.
5. Apply high pressure, evenly distribute the leaves, open the exhaust valve, and activate the fan.
6. After the process is complete, continue spreading wet towels, close the high-pressure system, and allow the machine to cool for 10 minutes before turning off the power.
**(d) Precautions:**
1. Do not operate the equipment under empty load conditions, and avoid placing any metal objects inside the heating chamber.
2. Never open the power box or heating chamber doors while the machine is in operation.
3. Regularly lubricate the moving parts of the machine to ensure smooth functioning.
4. In case of a sudden power outage, switch all controls to the "off" position to prevent damage.
**2. Full-Mechanical Production Process for Flat Tea:**
The full-mechanical process includes the following steps: Spreading – Fixing – Multi-Purpose Machine – Rolling – Grading – Packaging – Storage.
After harvesting, the fresh leaves lose about 30% of their moisture. The fixing machine is preheated, and the seals are checked. The leaves are evenly spread at the feeding port and transported via conveyor belt. The fixation process lasts for two minutes, achieving the desired degree of wilting. After 20 minutes of fixation, the leaves are transferred to the multi-purpose machine. The pot is heated to 100°C, and after the oil vapor evaporates, 0.3 kg of leaves are added per tank. The machine is operated at 50 rpm for one minute, then slowed to 30 rpm. A light pressure bar is applied, and the leaves are monitored for changes in color and texture. After two minutes, the leaves are decompressed for one minute, pressed again for one minute, and then cooled for half a minute or gently pressed for two minutes. Finally, the leaves are removed and sent to the rolling machine.
Rolling (Titian) also has a drying effect. The time and temperature settings are adjusted according to the requirements. The rolled tea is placed on the sieve tray, evenly distributed and secured. The machine is closed, the fan is turned on, and the heating function is activated. Once the set time is reached, the machine automatically stops. The tea is then removed, the heating is turned off, and the fan continues to run for 10 minutes. After this, the tea is graded, packaged, and stored.
**3. Semi-Mechanical Production of Flat Tea:**
Unlike the full-mechanical process, the semi-mechanical method involves manually removing the leaves from the multi-purpose machine after pressure. The pan is heated to 80°C using an electric fryer. The leaves are then manually ground and further processed to achieve 90% dryness before being sent to the Titian machine.
**4. Maojian Tea Manufacturing Process:**
The process for Maojian tea includes: Fixing – Rubbing – Unblocking – Shaping – Sorting – Titian – Packaging – Storage.
After the initial fixation, the leaves are fed into the kneading machine. Before starting, the machine is cleaned, and the switch is turned on. The machine is run idle to check for normal operation. Then, 10 kg of leaves are loaded, and the rubbing process takes 10–20 minutes. The pressure should be gradually increased, following the principle of light, light, light, and light. After rubbing, the leaves are ejected. They are then passed through the deblocker, ensuring even distribution. The leaves are sent to the shaping machine, where the temperature is maintained between 80–100°C, and 2.5 kg of leaves are added per tank. After about four minutes, the leaves are panned. Once cooled, they are placed in a 80°C tank for two minutes. When 90% dry, the leaves are panned, sieved, and sent to the Titian machine, where the same process as the full-mechanical method is followed.
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