A method for preparing yeast red tea by using double bio-enzyme fermentation

Abstract

The application discloses a kind of yeast black tea products and process method for preparing by double biological enzyme fermentation, which includes the process steps of picking and removing impurities of fresh leaves, light heat wilting, light heat steam biological fermentation, enzyme oxygenation kneading, deagglomeration double enzyme biological fermentation, hot air aroma extraction initial baking and vacuum freeze drying etc.The yeast black tea with higher fermentation enzymolysis power can be prepared by process optimization, which has strip shape, red leaves, sweet aroma, the activity of tea polyphenol oxidase (ppo) is kept at 1.5-2 U / G, and can drive other plant leaves to carry out mixed fermentation enzymolysis reaction, to make high-quality composite black tea, which has wide application prospect in the field of fermentation composite black tea.

Description

Technical Field

[0001] This invention relates to the field of tea processing technology, and in particular to a method for preparing yeast black tea using dual-enzyme fermentation. Background Technology

[0002] In recent years, the development of compound black tea has been rapid, mainly including kudzu leaf black tea, ginkgo black tea, and chrysanthemum leaf black tea. Current processes for these compound black teas involve fermenting tea leaves with other plants, utilizing the fermentation enzymes in the tea leaves to promote the fermentation of the other leaves, thus producing compound black tea. However, due to various constraints such as season, origin, factory conditions, and the mismatch between the growth periods of tea leaves and other plants, large-scale production is difficult. Another process uses finished red amaranth to blend with other plants to produce compound black tea, but because the polyphenol oxidase (PPO) activity in finished red amaranth is very low, it is difficult to drive the fermentation of other plants and produce a high-quality compound black tea with good color, aroma, taste, and appearance. To solve the problem of low PPO activity in existing finished black tea, which cannot promote the fermentation of other plants, it is necessary to change the existing yeast black tea processing technology and develop a completely new process method. This method should ensure the taste of yeast black tea while maximizing the activation and preservation of PPO activity in the tea leaves, enabling long-term preservation and facilitating subsequent fermentation with other plants. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing yeast black tea using dual-enzyme fermentation, which solves the problem that the polyphenol oxidase activity is low in traditional processing technology and cannot be used for subsequent mixed fermentation.

[0004] The technical solution adopted by this invention to solve its technical problem is: a method for preparing yeast black tea using dual-enzyme fermentation, the process flow of which includes: fresh leaf picking and impurity removal → photothermal withering → photothermal steam bio-fermentation → enzyme addition and oxygenation rolling → de-clumping dual-enzyme fermentation → hot air aroma enhancement and initial drying → vacuum freeze-drying → yeast black tea. The specific operation method is as follows:

[0005] 1) Fresh leaf picking and impurity removal: Pick tea leaves in spring, summer and autumn, picking one bud and 3-4 leaves of relatively coarse old buds and leaves and paired leaves. The picked fresh leaves are fed into a quantitative impurity removal feeding conveyor for quantitative impurity removal.

[0006] The quantitative impurity removal feeding conveyor includes a feed hopper, a weighing device, an impurity removal device, and a screen-type impurity removal conveyor belt. The impurity removal device includes an electromagnetic roller and a suction hood. The settings are as follows: the screen-type impurity removal conveyor belt is an 8-10 mesh stainless steel conveyor belt; the weight for each withering is 80-90 kg; the electromagnetic roller speed is 20-24 rpm; and the suction hood's air volume is 180-200 cubic meters per minute. The electromagnetic roller and suction hood remove dust, fibers, hair, broken leaves, and metal debris from the fresh tea leaves. The 8-10 mesh screen-type impurity removal conveyor belt further removes mud, small insects, insect eggs, and other debris during transport, ensuring the cleaned tea leaves are properly withered.

[0007] Specifically, the feed hopper is a stainless steel "trumpet-shaped" structure with a rectangular opening measuring 60cm in length and 35cm in width. The hopper is 45cm high and positioned at the front end of the screen-removing conveyor belt to weigh the fresh tea leaves before placing them onto the belt. The weighing device is an R546H type electronic sensor weigher, installed inside the feed hopper to achieve quantitative withering in the withering trough, thus improving withering quality. The impurity removal device includes an electromagnetic roller and a suction hood, installed at the discharge end of the screen-removing conveyor belt to remove dust, fibers, hair, broken leaves, and metal debris from the fresh tea leaves during discharge. Specifically, the screen conveyor belt is a 2.5-3m long, 55-60cm wide, 8-10 mesh stainless steel screen conveyor belt. It is connected to the feed trough of the photothermal withering layer of the withering fermentation machine at an upward inclination of 12-15 degrees. This allows the fresh tea leaves to be screened during transport to remove mud, small insects, insect eggs, and other debris, ensuring the cleaned tea leaves undergo photothermal withering. The beneficial effects of this quantitative impurity removal feeding and conveying process are: using electromagnetic rollers, suction hoods, and the inclined screen conveyor belt, dust, mud, small insects, insect eggs, fibers, hair, broken leaves, and metal debris are removed from the fresh leaves. The cleaned fresh tea leaves are then quantitatively fed into the photothermal withering layer of the withering fermentation machine for photothermal withering to produce yeast-based black tea, which helps ensure the quality and safety of the product.

[0008] 2) Photothermal Withering: After weighing and impurity removal, clean the fresh tea leaves and feed them into the photothermal withering layer of the withering fermentation machine. Turn on: the spiky leaf-shaping roller, quartz infrared electric heat lamp, hot air pipe, clockwise rotating arc-shaped spiky hot air leaf turner, and counter-clockwise rotating arc-shaped spiky hot air leaf turner. Settings: leaf thickness 15-20cm, hot air temperature 30-42℃, withering time 2.5-3.5h, spiky leaf-shaping roller speed 16-20 rpm, spiky hot air leaf turner speed 12-16 rpm, turning the leaves every 15-20 minutes for 1-1.5 minutes. The photothermal withering process is divided into three stages: First, move the fresh tea leaves to the high-temperature withering chamber, using a high temperature of 35-42℃ for 1.2-1.5h to enhance the activity of polyphenol oxidase, causing the buds and leaves to lose water and wither, resulting in a reddish leaf color. After the high-temperature photothermal withering process, the conveyor belt moves to the right, and the tea leaves are fed into the medium-temperature withering chamber. At a medium temperature of 34-36℃ for 0.8-1.1 hours, the activity of polyphenol oxidase is stabilized, promoting the enzymatic transformation of starch, protein, cellulose, and other substances in the fresh tea leaves, resulting in a sweet floral aroma. After the medium-temperature photothermal withering process, the conveyor belt continues to move to the right, and the tea leaves are fed into the low-temperature withering chamber. At a low temperature of 30-32℃ for 0.5-0.7 hours, the activity of polyphenol oxidase is weakened to prevent over-withering, excessive water loss, and leaf dryness. This photothermal withering process utilizes a thorny leaf-shaping roller and a thorny hot air leaf turner. The technical effect of these components is that the clockwise rotation of the thorny leaf-shaping roller and the counter-clockwise rotation of the hot air leaf turner not only evenly spreads the fresh tea leaves on the screen conveyor belt and intermittently turns the leaves, but also pierces the cell walls, allowing photothermal radiation to penetrate deep into the cell layers for withering. The beneficial effects of this photothermal withering process, which employs a three-stage photothermal withering method involving high temperature, medium temperature, and low temperature, are as follows: by strengthening, stabilizing, and weakening the activity of polyphenol oxidase, it promotes the enzymatic transformation of a large amount of starch, protein, cellulose, and other substances contained in fresh tea leaves, thereby revealing the sweet floral aroma and improving the quality of photothermal withering.

[0009] 3) Photothermal Steam Bio-fermentation: After photothermal withering, the tea leaves are fed into the inlet and outlet troughs of the photothermal steam bio-fermentation layer of the withering and fermentation machine. The following are activated: spiked leaf-shaping roller, steam nozzle, quartz infrared electric heat lamp, hot air pipe, and spiked hot air leaf turner. Settings: leaf thickness 30-40cm, hot air temperature 28-40℃, steam nozzle temperature 30-40℃, fermentation time 1.1-1.4h, spiked leaf-shaping roller speed 10-14 rpm, spiked hot air leaf turner speed 8-12 rpm, with leaf turning every 15-20 minutes for 1-1.5 minutes. The photothermal steam bio-fermentation process is divided into three stages: The photothermal withered tea leaves on the reciprocating conveyor belt are first moved to the left to the low-temperature photothermal bio-fermentation chamber, where they are fermented at approximately 28-32℃ for 0.3-0.4h to stimulate polyphenol oxidase activity and initiate low-temperature photothermal bio-fermentation. After completing the low-temperature photothermal fermentation process, the conveyor belt moves to the left, and the tea leaves are fed into the medium-temperature photothermal biological fermentation chamber. Under the influence of photothermal heat at approximately 33-36℃ for 0.6-0.7 hours, the activity of polyphenol oxidase is enhanced, and medium-temperature photothermal fermentation takes place. After completing the medium-temperature photothermal fermentation process, the conveyor belt continues to move to the left, and the tea leaves are fed into the high-temperature photothermal steam biological fermentation chamber. Utilizing high-temperature steam at approximately 38-40℃, the fermentation time is 0.6-0.8 hours, further enhancing the activity of polyphenol oxidase and converting it into a large amount of fermentation enzymatic hydrolysis products. After completing the three-stage photothermal steam biological fermentation process, the reciprocating conveyor belt is switched to moving to the right, and the fermented tea leaves are output from the inlet / outlet trough. This photothermal steam bio-fermentation process utilizes a spiked leaf-spreading roller, steam nozzles, and a spiked hot air leaf turner. The resulting technology not only evenly spreads the tea leaves on the conveyor belt but also continues to pierce the cell walls. The 35°C steam from the nozzles heats the tea leaves after photothermal withering, further disrupting the cell structure and allowing the photothermal heat to penetrate deep into the cell layers, stimulating polyphenol oxidase activity for efficient bio-fermentation. This short-time photothermal steam bio-fermentation process employs a three-stage process (low temperature, medium temperature, and high temperature) to achieve the following benefits: by stimulating, enhancing, and increasing the fermentation kinetics of polyphenol oxidase, it converts the tea leaves into a large amount of fermentation enzymatic hydrolysates, optimizing the quality of the yeast-fermented black tea. Simultaneously, the short-time steam fermentation prevents leaf drying, which would affect the activity of tea polyphenol oxidase (PPO), maintaining a high activity of 4-5 U / G in the fermented leaves.

[0010] The withering fermentation machine includes a photothermal withering layer and a photothermal steam bio-fermentation layer.

[0011] Specifically, the photothermal withering layer has a feeding trough located at the front of the trough and an outlet at the rear. A 20-mesh stainless steel screen conveyor belt carries the fresh tea leaves, moving from left to right via a rotating pulley for photothermal withering. To overcome the technical obstacle of photothermal withering in the coarse, old tea buds and leaves used for yeast-based black tea due to their developed palisade tissue and thick cuticle, a stainless steel spiked leaf-equalizing roller is installed in the feeding trough. Its clockwise rotation evenly spreads the fresh tea leaves onto the screen conveyor belt and pierces the cell walls, allowing photothermal light to penetrate deep into the cell layers for withering. To achieve efficient photothermal withering, four "U-shaped" supports are installed 65cm apart above the withering layer. Four quartz infrared electric heating lamps are installed at even intervals on these supports, and four hot air pipes are arranged intermittently between the lamps to create a photothermal space for withering the tea leaves on the screen conveyor belt. Above the screen conveyor belt, at 65cm intervals, two clockwise rotating thorn-shaped hot air leaf turners and two counterclockwise rotating thorn-shaped hot air leaf turners are arranged in a crisscross pattern. Their clockwise and counterclockwise rotation not only turns the tea leaves and blows hot air to increase temperature, but also continues to pierce the cell walls, allowing photothermal heat to penetrate deep into the cell layers for photothermal withering. To improve the withering quality of the yeast-treated black tea, two vertically movable partitions are installed within the photothermal withering layer, dividing it into three withering chambers: high-temperature, medium-temperature, and low-temperature, achieving segmented photothermal withering. The fresh tea leaves move gradually on the screen conveyor belt through the "high-temperature withering chamber → medium-temperature withering chamber → low-temperature withering chamber," transforming into a large number of withering enzymatic hydrolysis products, thus improving the quality of photothermal withering.

[0012] Specifically, the photothermal steam bio-fermentation layer has its feeding and discharging sections located in the same trough at the rear of the tank. A reciprocating 20-mesh stainless steel screen conveyor belt carries the tea leaves at the bottom of the trough, allowing them to pass through the feeding and discharging troughs to receive the upper layer of photothermal withered buds and leaves. The conveyor belt then moves to the left for photothermal steam bio-fermentation. After bio-fermentation, the buds and leaves are moved to the right via the reciprocating screen conveyor belt and fed into an enzyme-added oxygen-infused steam kneading machine through the tea outlet of the feeding and discharging trough for steam kneading. To enhance polyphenol oxidase activity for efficient bio-fermentation, spiky leaf rollers and steam nozzles are installed in the feed troughs. The spiky leaf rollers rotate clockwise to pierce the cell walls of the wilted buds and leaves, spreading them evenly on the screen conveyor belt. Simultaneously, the 35°C steam from the steam nozzles further disrupts the cell structure and enhances polyphenol oxidase activity for bio-fermentation through heating and humidification. Above the hot steam fermentation layer, at 65cm intervals, are four "U-shaped" supports. Four quartz infrared electric heating lamps are installed at even intervals on these supports. Four hot air pipes are arranged alternately between the quartz infrared electric heating lamps. A steam nozzle is positioned above the high-temperature photothermal steam bio-fermentation chamber, spraying 30-35°C high-temperature steam to create a photothermal steam space for the photothermal wilted buds and leaves on the screen conveyor belt to undergo photothermal steam bio-fermentation. Above the screen conveyor belt, at 60cm intervals, are installed two clockwise rotating arc-shaped spiky hot air leaf turners and two counterclockwise rotating arc-shaped spiky hot air leaf turners. Their clockwise and counterclockwise rotation not only turns the tea leaves and heats them with hot air, but also pierces the cell walls, allowing photothermal energy to penetrate deep into the cell layers for photothermal steam bio-fermentation. To improve the fermentation quality of the yeast-fermented black tea, the photothermal steam fermentation layer is equipped with two telescopic partitions. When opened, the upper end of the partitions contacts the stainless steel screen conveyor belt, and the lower end contacts the reciprocating screen conveyor belt, thus dividing the photothermal steam fermentation layer into three fermentation chambers: low temperature, medium temperature, and high temperature, for segmented photothermal steam fermentation. After photothermal withering, the tea leaves move gradually to the left on the conveyor belt through the "low temperature photothermal bio-fermentation chamber → medium temperature photothermal bio-fermentation chamber → high temperature photothermal steam bio-fermentation chamber," fermenting and transforming into a large number of fermentation enzymatic hydrolysis products, thereby improving the quality of photothermal steam bio-fermentation.

[0013] 4) Enzyme-enriched oxygen-enhanced rolling: After light and heat withering, the tea leaves are fed into the rolling drum of the rolling machine. The enzyme adder and oxygen supply pipe are turned on. The settings are: cellulase addition amount 0.1-0.3% (ratio to the weight of the rolled leaves), rolling drum speed 16-20 rpm, oxygen supply 0.3-0.5 cubic meters / min, rolling drum temperature 36-40℃, and rolling time 8-12 minutes. This promotes the extraction of tea components and rolls the tea leaves into strips. The beneficial effects of using cellulase-enriched oxygen-enhanced rolling process are: it not only promotes the efficient oxidative hydrolysis reaction between polyphenol oxidase in the tea leaves and exogenous cellulase, decomposing cellulose and softening the leaf texture, which is conducive to rolling into strips, but also transforms into a large amount of pectin, tea polysaccharides, theanine, and aromatic substances, optimizing the quality of yeast black tea. In particular, wooden rolling machines do not cause adverse antagonistic reactions between exogenous cellulase and metal ions, which is conducive to the enzymatic transformation of a large number of enzymatic products and optimizes the quality of yeast black tea.

[0014] Cellulase is a complex enzyme system composed of various hydrolases. Cellulases can be divided into three categories: C1 enzymes, Cx enzymes, and β-glucosidases. C1 enzymes are the initial enzymes acting on cellulose, breaking down the crystalline structure of the cellulose chain. Cx enzymes are cellulases that act on cellulose activated by C1 enzymes, breaking down β-1,4-glycosidic bonds. β-glucosidases can break down cellobiose, cellotriose, and other low-molecular-weight cellodextrins into glucose.

[0015] The described rolling machine is an improved and optimized new type. To avoid adverse antagonistic reactions between the added exogenous cellulase and metal ions, and to overcome the technical obstacle of rolling coarse, old tea buds and leaves with high cellulose content and hard texture into strips, the rolling drum and lid are made of pine wood, while the rolling disc and its ribs are made of nano-ceramic material. This nano-ceramic rolling disc and ribs, being hard and smooth, not only facilitate the rolling of coarse, old tea buds and leaves into strips but also reduce tea breakage. To prevent excessively high tea temperature during pressure rolling, which could reduce polyphenol oxidase activity, a temperature sensor is installed on the lid, extending deep into the rolling drum. Hot and cold air ducts are also provided to adjust the temperature inside the rolling drum. Furthermore, an oxygen supply pipe is installed to deliver oxygen into the rolling drum, and an atomizing enzyme nozzle is provided for adding exogenous enzymes. During the rolling process, exogenous biological enzymes can be added using an atomizing enzyme-adding nozzle for enzymatic rolling, oxygen can be supplied through an oxygen supply pipe for oxygenated rolling, and hot and cold air pipes can be used to regulate the rolling temperature. This promotes the efficient oxidation reaction of polyphenol oxidase in the tea leaves, accelerating the reddening of the buds and leaves. It also promotes the efficient enzymatic hydrolysis of exogenous biological enzymes, hydrolyzing substances such as cellulose, softening the leaf texture to facilitate the rolling of coarse and old tea buds and leaves into strips, and transforming them into a large amount of pectin, tea polysaccharides, theanine, and aromatic substances, thus optimizing the quality of yeast-based black tea. The rolling barrel and lid are made of wood, and the rolling disc is made of ceramic, which will not antagonize the reaction with metal ions, facilitating the efficient enzymatic hydrolysis reaction of exogenous biological enzymes, accelerating the reddening of buds and leaves, and thus forming excellent qualities such as red leaves, red liquor, and sweet aroma.

[0016] 5) De-clumping dual-enzyme fermentation: After kneading and oxygenation with added cellulase, the tea leaves are fed into a de-clumping roller to break up the clumps before being transferred to a fermentation tank for dual-enzyme bio-fermentation. Settings: Leaf thickness 55-60cm, hot air temperature 35-40℃, steam temperature 30-35℃, dual-enzyme fermentation time 1.4-1.6h (closed dual-enzyme fermentation 1-1.1h, open dual-enzyme fermentation 0.4-0.5h). The tea clumps are first broken up by the de-clumping roller and then conveyed onto the screen conveyor belt of the fermentation tank. Closed and open dual-enzyme fermentation occurs under the combined action of polyphenol oxidase and exogenous cellulase. The beneficial effects of this dual-enzyme photothermal bio-fermentation process: Using closed and open dual-enzyme bio-fermentation can enhance the fermentation enzymatic hydrolysis power of the two enzymes, converting them into a large amount of fermentation enzymatic hydrolysis products to optimize the quality of yeast-based black tea, while simultaneously stabilizing the high activity of tea polyphenol oxidase (PPO).

[0017] The de-clumping roller includes an inclined roller body. A screening cage, rotating with the roller body, is housed within the roller body. One end of the screening cage has a tea inlet, and the other end is closed. One end of the roller body has a outlet. De-clumping rollers, moving relative to the screening cage, are located inside the screening cage. Each de-clumping roller is equipped with a dispersing rod. A set of discharge holes are also provided on the surface of the screening cage, through which the dispersed tea leaves fall into the roller body. The discharge holes are elongated structures adapted to the shape of the tea leaves. Tea clumps are continuously broken up by the de-clumping rollers and fall through the discharge holes. If a tea clump cannot fall through the discharge holes, it is further broken up, ensuring thorough de-clumping.

[0018] The fermentation tank is equipped with a screen conveyor belt. After the tea leaves fall, the conveyor belt moves slowly forward, spreading them evenly. To improve fermentation efficiency and quality, the fermentation tank is fitted with three U-shaped supports, each equipped with a quartz infrared electric heat lamp, a small hot air pipe, and a misting humidifier. This allows for photothermal steam dual-enzyme fermentation of the buds and leaves after enzyme addition, kneading, and de-clumping. To facilitate both closed and open fermentation, a nano-bamboo charcoal fiber cover is laid on the U-shaped supports. This allows for closed dual-enzyme fermentation, which enhances the bio-fermentation dynamics of polyphenol oxidase, accelerating the reddening of the buds and leaves, and also improves the enzymatic hydrolysis reaction of exogenous enzymes, converting them into a large number of enzymatic hydrolysis products to optimize the quality of the yeast-infused black tea. Simultaneously, the cover can be opened for open dual-enzyme fermentation, allowing for the dissipation of humid and fermented gases, which is beneficial for subsequent drying and aroma enhancement.

[0019] 6) Hot Air Aroma Enhancement and Initial Drying: After double-enzyme bio-fermentation, the tea leaves are fed into the hot air initial drying and aroma enhancement drum of the integrated hot air drying and vacuum freeze-drying machine. The hot air pipe is turned on, and the hot air temperature is set to 35-40℃, and the hot air aroma enhancement and initial drying time is 20-30 minutes, until the moisture content reaches 18-22%. The low-temperature initial drying and aroma enhancement process achieves beneficial effects: using low-temperature hot air can not only volatilize and remove "fermented odors" and most of the humid heat, but also promote the volatilization of aromatic substances in the tea buds and leaves, enhance the sweet floral aroma, and achieve preliminary drying. This can shorten the subsequent vacuum freeze-drying time by 20-25% and improve freeze-drying efficiency.

[0020] The hot air initial drying and aroma-enhancing drum includes a cylinder body with a feed inlet at one end and a discharge outlet at the other end. A rotating drum is installed inside the cylinder body, and the rotating drum is arranged at an angle. Tea leaves enter from one end of the rotating drum and exit from the other end. The discharge end of the hot air initial drying and aroma-enhancing drum is equipped with a hot air inlet that blows hot air at an angle towards the feed inlet. A hot air fan is connected to the hot air inlet. The hot air fan continuously blows low-temperature hot air at approximately 40°C into the hot air initial drying and aroma-enhancing drum for initial drying, dissipating the "fermented odor" produced during the tea fermentation process and promoting the volatilization of aromatic substances, enhancing the sweet floral aroma. Then, using a freeze dryer, more than 95% of the moisture is removed, and the activity and oxidation reaction of polyphenol oxidase are frozen and solidified, resulting in a high-quality yeast black tea with strong vitality and fermentation power. This machine continuously rotates the drum, causing the tea leaves to tumble and be transported forward. This facilitates the dissipation of moisture from the tea leaves, increases the drying speed, and, under the action of hot air, promotes the dissipation of a large amount of humid heat and "fermented odors," enhances the sweet floral aroma, and reduces the moisture content of the tea leaves by 20-25%, thus completing the initial drying process.

[0021] 7) Vacuum Freeze-Drying: Vitamin C is added to the tea leaves after initial hot air aroma extraction and drying for antioxidant purposes, maintaining the activity of polyphenol oxidase. The amount of vitamin C added is 0.1-0.2% of the tea leaf weight. The tea is then fed into a vacuum freeze dryer, and the refrigeration system, vacuum system, circulation system, control system, hydraulic system, and intermittent vibrator are activated. The settings are as follows: the leaf thickness on the freeze-drying plate is 15-20 cm, the vacuum degree is 30-40 Pa, the freeze-drying temperature is -10 to -16℃, the freeze-drying time is 1-1.5 h, and the vibration frequency of the intermittent vibrator is 60-80 times / min. The vacuum freeze-drying process yields beneficial effects: through intermittent vibration freeze-drying, the internal and external moisture of yeast-treated black tea can be efficiently freeze-dried, freezing and solidifying the oxidative enzymatic hydrolysis reaction and the activity of tea polyphenol oxidase (PPO), maintaining its activity at a relatively high level of 1.5-2 U / G, resulting in a high-quality yeast-treated black tea with high fermentation power, red leaves, red liquor, and a sweet aroma.

[0022] The vacuum freeze dryer is a box-type vacuum freeze dryer, comprising a refrigeration system, a vacuum system, a circulation system, a control system, a hydraulic system, and an intermittent vibrator. Multiple layers of freeze-drying floating baffles are installed inside the chamber to hold the pre-dried and flavor-enhanced yeast black tea for freeze-drying. This machine utilizes vacuum low-temperature drying technology, freezing the yeast black tea at a low temperature and then removing moisture under vacuum to achieve drying. The freeze-drying process is as follows: pretreatment → pre-freezing (quick freezing) → rapid cooling by a water trap → vacuuming of the chamber → drying and sublimation → cold-dried yeast black tea exiting the chamber. To accelerate the freeze-drying of the yeast black tea, a vibrator is installed on the back of the freeze-drying floating baffles inside the chamber. Intermittent vibration causes the yeast black tea placed on the freeze-drying baffles to oscillate and freeze-dry, improving freeze-drying efficiency. Using a vacuum freeze dryer to dry yeast black tea yields beneficial results: it efficiently freeze-dries both internal and external moisture, prevents the leaves from becoming dry and having a strong burnt taste, and maintains high activity of polyphenol oxidase, resulting in yeast black tea with strong fermentation potential.

[0023] The beneficial effects of this invention are as follows: This invention uses a dual-enzyme fermentation process to produce a yeast-based black tea with a strip-shaped appearance, red leaves, red liquor, and sweet aroma. The activity of tea polyphenol oxidase (PPO) is maintained at 1.5-2 U / G, which has a high fermentation enzymatic hydrolysis power. This yeast-based black tea can drive other plant flowers and leaves to carry out mixed fermentation enzymatic hydrolysis reactions to produce high-quality compound black tea.

[0024] This invention employs a three-stage photothermal withering process involving high temperature, medium temperature, and low temperature. By enhancing, stabilizing, and weakening the activity of polyphenol oxidase, it promotes the enzymatic transformation of starch, protein, cellulose, and other substances in fresh tea leaves, resulting in a more pronounced sweet floral aroma and improved photothermal withering quality. Furthermore, it utilizes a three-stage photothermal steam fermentation process involving low temperature, medium temperature, and high temperature. This process stimulates, enhances, and increases the fermentation kinetics of polyphenol oxidase, facilitating the formation of numerous fermentation enzymatic hydrolysis products and optimizing the quality of yeast-infused black tea.

[0025] This invention employs an enzyme-enzyme-assisted oxygenation process for woody kneading and disintegration, which avoids antagonistic reactions with metal materials and rapidly dissolves kneaded tea clumps. This process promotes efficient oxidative hydrolysis of polyphenol oxidase and exogenous cellulose enzymes, decomposing cellulose and softening the leaf material, which is beneficial for kneading into strips. At the same time, it also transforms into a large amount of pectin, tea polysaccharides, theanine, and aromatic substances, optimizing the quality of yeast-based black tea.

[0026] This invention employs a low-temperature initial drying and aroma-enhancing process, which not only eliminates "fermented odors" and most of the damp heat, achieving preliminary drying, but also enhances the sweet floral aroma and shortens the subsequent vacuum freeze-drying time by 20-25%. The vacuum freeze-drying process efficiently freeze-dries the internal and external moisture of yeast-treated black tea, freezing and solidifying the oxidative enzymatic reactions and the activity of tea polyphenol oxidase (PPO), maintaining its activity at a relatively high level of 1.5-2 U / G. This results in a superior yeast-treated black tea with high fermentation power, red leaves, red liquor, and a sweet aroma. Simultaneously, vitamin C is added before vacuum freeze-drying for antioxidant effects, better protecting the activity of polyphenol oxidase during later storage. When exposed to air, oxygen preferentially oxidizes vitamin C before oxidizing polyphenol oxidase, thus better protecting the polyphenol oxidase activity from oxidative damage.

[0027] The present invention will now be described in more detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the present invention.

[0029] Figure 2 This is a front view of the quantitative impurity removal feeding conveyor in this invention.

[0030] Figure 3 This is a front view of the withering fermentation machine in this invention.

[0031] Figure 4 This is a side view of the spiked hot air leaf turner in this invention.

[0032] Figure 5 This is a side view of the ∩-shaped bushing and the infrared electric heating lamp and hot air pipe above it in this invention.

[0033] Figure 6 This is a front view of the telescopic partition in this invention.

[0034] Figure 7 This is a front view of the kneading machine in this invention.

[0035] Figure 8 This is a front view of the disassembly roller in this invention.

[0036] Figure 9 This is a schematic diagram of the elongated material discharge hole on the screening roller in this invention.

[0037] Figure 10 This is a front view of the fermentation tank in this invention.

[0038] Figure 11 This is a side view of the fermentation tank in this invention.

[0039] Figure 12This is a front view of the hot air pre-drying and aroma-enhancing roller in this invention.

[0040] Figure 13 This is a front view of the vacuum freeze dryer in this invention. Detailed Implementation

[0041] Example 1, as Figure 1-13 As shown, a method for preparing yeast black tea using dual-enzyme fermentation aims to produce a yeast black tea product with a strip-shaped appearance, red leaves, red liquor, and a sweet aroma, exhibiting high fermentation enzymatic hydrolysis power. This method can also drive the mixed fermentation and enzymatic hydrolysis of other plant flowers and leaves to create a high-quality compound black tea. The process includes: fresh leaf picking and impurity removal → photothermal withering → photothermal steam bio-fermentation → enzyme-added oxygenation and rolling → de-clumping dual-enzyme fermentation → hot air aroma enhancement and initial drying → vacuum freeze-drying → yeast black tea product.

[0042] The specific steps are as follows:

[0043] 1) Fresh leaf picking and impurity removal: Pick buds and leaves with one bud and 3-4 leaves and paired leaves, and feed the fresh leaves into a quantitative impurity removal feeding conveyor for quantitative impurity removal to remove impurities from the tea leaves;

[0044] 2) Photothermal withering: Weighed and impurity-removed fresh leaves are fed into the photothermal withering layer of the withering fermentation machine for segmented withering. The settings are: leaf thickness is 15-20cm, first withering at a high temperature of 35-42℃ for 1.2-1.5h, then withering at a medium temperature of 34-36℃ for 0.8-1.1h, and finally withering at a low temperature of 30-32℃ for 0.5-0.7h.

[0045] 3) Photothermal steam bio-fermentation: After photothermal withering, the tea leaves are fed into the photothermal steam bio-fermentation layer of the withering fermentation machine for segmented fermentation. The settings are: the leaf thickness is 30-40cm, the fermentation time is 0.3-0.4h in a low temperature environment of 28-32℃, then 0.6-0.7h in a medium temperature environment of 33-36℃, and finally 0.6-0.8h in a high temperature environment of 38-40℃.

[0046] 4) Enzyme-enriched and oxygenated kneading: After the tea leaves have undergone photothermal steam bio-fermentation, they are fed into the kneading drum of the kneading machine, and 0.1-0.3% cellulase is added. Oxygen is introduced, and the tea leaves are kneaded at a temperature of 36-40℃ for 8-12 minutes.

[0047] 5) De-clumping and dual-enzyme fermentation: After adding cellulase and oxygenating the tea clumps through kneading, the clumps are broken up and put into a fermentation tank for dual-enzyme fermentation, which utilizes the polyphenol oxidase naturally present in the tea leaves and the added cellulase for fermentation.

[0048] 6) Hot air aroma enhancement and initial drying: After double enzyme bio-fermentation, the tea leaves are fed into the hot air initial drying and aroma enhancement drum. The hot air temperature is set to 35-40℃, the hot air aroma enhancement and initial drying time is 20-30 minutes, and the moisture content is dried to 18-22%.

[0049] 7) Vacuum freeze drying: Add 0.1-0.2% vitamin C by weight of the tea leaves to the tea leaves after initial drying with hot air for aroma extraction, and then feed them into a vacuum freeze dryer for freeze drying. Set the following parameters: leaf thickness of 15-20cm, vacuum degree of 30-40Pa, freeze drying temperature of -10 to -16℃, and freeze drying time of 1-1.5h.

[0050] The specific equipment structure used in the above steps is as follows:

[0051] The quantitative impurity removal feeding conveyor 1 in step 1) includes a feeding hopper 11, an impurity removal conveyor belt 12 located below the feeding hopper 11, a weighing device 13 located below the feeding hopper 11, and an impurity removal device 14 located on the impurity removal conveyor belt 12. Specifically, the feeding hopper 11 is a "trumpet-shaped" stainless steel structure, positioned at the front end of the impurity removal conveyor belt 12, so that the fresh tea leaves are weighed in the feeding hopper 11 and laid onto the impurity removal conveyor belt 12. The weighing device 13 is an R546H type electronic sensor weigher, installed in the feeding hopper 11 for weighing, in order to achieve quantitative withering and improve withering quality. The impurity removal device 14 includes an electromagnetic roller 141 and an impurity suction hood 142 located above the electromagnetic roller 141, installed at the discharge end of the impurity removal conveyor belt 12, so as to absorb dust, fibers, hair, broken flower leaves, and metal debris carried in the fresh tea leaves during the discharge process. The impurity removal conveyor belt 12 is an 8-10 mesh stainless steel screen conveyor belt, arranged at an upward inclination of 12-15 degrees. Its discharge end is connected to the feed trough of the photothermal withering layer of the withering fermentation machine 2, so that the tea leaves can be screened to remove mud, sand, small insects, insect eggs, and other debris during the conveying process, and the cleaned tea leaves can then undergo photothermal withering. The technical effect of the quantitative impurity removal feeding conveyor of this invention is as follows: by using electromagnetic rollers, impurity suction hoods, and inclined screen conveyor belts, dust, mud, small insects, insect eggs, fibers, hair, broken flower and grass leaves, and metal debris carried in the fresh leaves can be removed, so that the cleaned tea leaves can be quantitatively fed into the photothermal withering layer of the withering fermentation machine for photothermal withering to produce yeast black tea, which helps to ensure product quality and safety.

[0052] The withering and fermentation machine 2 includes a tank 21 made of stainless steel. To ensure a continuous withering and fermentation process for making yeast-based black tea, the tank 21 has a two-layer structure: an upper heat-withering layer 22 and a lower heat-steam fermentation layer 23. The bottom of the heat-withering layer 22 is equipped with a stainless steel mesh conveyor belt 24 that transports tea leaves from left to right. The bottom of the heat-steam fermentation layer 23 is equipped with a reciprocating mesh conveyor belt 25. To ensure the tea leaves can smoothly enter the lower reciprocating mesh conveyor belt 25, a feed chute 26 is provided below the discharge end of the stainless steel mesh conveyor belt 24. One end of the reciprocating mesh conveyor belt 25 extends into the feed chute 26 to receive the tea leaves from the stainless steel mesh conveyor belt 24.

[0053] A feeding trough 210 is provided on the left side of the photothermal withering layer 22. The bottom of the stainless steel screen conveyor belt 24 is made of 20-mesh stainless steel screen. The stainless steel screen conveyor belt 24 is driven by a clockwise rotating belt pulley to move from left to right for photothermal withering. The withered tea leaves are then transported from the feeding trough 26 to the photothermal steam fermentation layer 23 for photothermal steam fermentation. In order to evenly spread the fresh tea leaves on the stainless steel screen conveyor belt 24 and to pierce the cell walls so that the photothermal heat can penetrate into the inner layer of the cells for withering, a stainless steel thorn-shaped leaf-equalizing roller 211 is provided in the feeding trough 210. The roller rotates clockwise to evenly distribute the leaves and break down the cell structure of the buds and leaves. Above the stainless steel screen conveyor belt 24, counter-rotating spiky hot air leaf turners 213 are installed at intervals. Each spiky hot air leaf turner 213 includes a hollow rotating roller 2131 and spiky claws 2132 mounted on the roller. One end of the rotating roller 2131 is connected to a hot air pipe 292 via a rotating joint (existing technology, not described in detail here). Air outlet holes 21311 are provided on the surface of the rotating roller 2131. Through its clockwise and counter-clockwise rotation, it can both turn and blow hot air to heat the tea leaves, and also pierce the cell walls to allow photothermal heat to penetrate into the inner cell layer for photothermal withering.

[0054] To improve the withering quality of yeast-treated black tea, two vertically movable partitions 27 are installed within the photothermal withering layer 22. These partitions 27 divide the photothermal withering layer 22 from left to right into three independent withering chambers: a high-temperature withering chamber 221, a medium-temperature withering chamber 222, and a low-temperature withering chamber 223, achieving segmented photothermal withering. To facilitate control of the vertical movement of the partitions 27, a crossbeam 214 is installed above the photothermal withering layer 22. A cylinder 215 is mounted on the crossbeam 214 to drive the partitions 27 vertically. When separation is required, the cylinder 215 moves the partitions 27 downwards, with their bottoms resting against the stainless steel mesh conveyor belt 24, thus dividing the photothermal withering layer 22 into independent withering chambers. When the tea leaves need to move to the right, the cylinder 215 moves the partitions 27 upwards, facilitating the removal of the tea leaves from the withering chamber.

[0055] To facilitate temperature control in each withering chamber, each withering chamber is equipped with a U-shaped support frame 217. Infrared electric heating lamps 291 and small hot air pipes 292 are mounted on the U-shaped support frame 217. These together form a temperature control device 29. By installing infrared electric heating lamps 291 and hot air pipes 292 with different wattages and inputting hot air at different temperatures, the temperature of each withering chamber is adjusted, allowing for photothermal withering of the fresh tea leaves on the stainless steel mesh conveyor belt 24. The fresh tea leaves on the stainless steel mesh conveyor belt 24 are sequentially withered through a series of chambers: a high-temperature withering chamber 221, a medium-temperature withering chamber 222, and a low-temperature withering chamber 223. First, they pass through the high-temperature withering chamber, where a temperature of approximately 40°C enhances the activity of polyphenol oxidase, causing the buds and leaves to lose water and wither, resulting in a reddish color change. After high-temperature withering, partition 27 moves upward to open, and the stainless steel screen conveyor belt 24 moves to the right, allowing the tea leaves to enter the medium-temperature withering chamber. Partition 27 then moves downward to close, and the medium temperature of approximately 35℃ stabilizes the activity of polyphenol oxidase, promoting the enzymatic transformation of starch, protein, cellulose, and other substances in the fresh tea leaves, resulting in a sweet floral aroma. After the medium-temperature withering process, the stainless steel screen conveyor belt moves to the right, and the tea leaves enter the low-temperature withering chamber. The low temperature of approximately 32℃ weakens the activity of polyphenol oxidase, preventing over-withering, excessive water loss, and leaf dryness. The beneficial effects of using segmented photothermal withering technology include: promoting the enzymatic transformation of starch, protein, cellulose, and other substances in fresh tea leaves, resulting in a sweet floral aroma and improved withering quality.

[0056] The outlet of the photothermal steam fermentation layer 23 is located below the inlet / outlet trough 26. To ensure that the tea leaves in the photothermal withering layer 22 fall smoothly onto the reciprocating screen conveyor belt 25 of the photothermal steam fermentation layer 23, a guide plate 261 is provided in the inlet / outlet trough 26 so that the tea leaves fall directly into the outlet below. In order to evenly spread the tea buds and leaves on the reciprocating screen conveyor belt 25 and to break the cell walls, a spiky leaf-equalizing roller 211 and a steam nozzle 212 are provided in the inlet / outlet trough 26. The spiky leaf-equalizing roller 211 rotates clockwise, and the steam nozzle 212 sprays 40°C steam. This can both heat and humidify the tea leaves after photothermal withering for biological fermentation, and the combined action of the steam force and the spiky leaf-equalizing roller 211 can further break the cell structure of the tea buds and leaves so that the photothermal heat can penetrate into the inner cell layer to stimulate the activity of polyphenol oxidase for biological fermentation. In addition, the reciprocating screen conveyor belt 25 is also equipped with a thorny hot air leaf turner 213 that rotates in both directions. Through its clockwise and counterclockwise rotation, it can both turn the tea leaves and blow hot air to heat them, and it can also pierce the cell wall so that light and heat can penetrate into the inner layer of the cell for photothermal steam bio-fermentation.

[0057] To improve the fermentation quality of yeast-fermented black tea, two telescopic partitions 28 are installed inside the photothermal steam fermentation layer 23. When opened, the telescopic partitions 28 divide the photothermal steam fermentation layer 23 from right to left into three independent fermentation chambers: a low-temperature fermentation chamber 231, a medium-temperature fermentation chamber 232, and a high-temperature fermentation chamber 233. The telescopic partitions 28 and partitions 27 are substantially aligned vertically. When the telescopic partitions 28 are open, their upper ends rest against the underside of the stainless steel screen conveyor belt 24, and their lower ends press against the reciprocating screen conveyor belt 25. This structure allows the light and heat from the lower low-temperature fermentation chamber 231 to reach the lower part of the low-temperature withering chamber 223 through the stainless steel screen conveyor belt 24, thus providing a photothermal effect on the tea leaves in the lower part of the low-temperature withering chamber 223. Similarly, the light and heat from the medium-temperature fermentation chamber 232 can reach the lower part of the medium-temperature withering chamber 222 through the stainless steel screen conveyor belt 24, thus providing a photothermal effect on the tea leaves in the lower part of the medium-temperature withering chamber 222. The light and heat from the high-temperature fermentation chamber 233 can reach the lower part of the high-temperature withering chamber 221 through the stainless steel screen conveyor belt 24, thus providing a photothermal effect on the tea leaves in the lower part of the high-temperature withering chamber 221, overcoming the technical obstacle that the fresh tea leaves at the bottom of the photothermal withering trough cannot receive light and heat.

[0058] The specific installation structure of the telescopic partition 28 is as follows: two transverse rotating shafts 216 are rotatably installed above the photothermal steam fermentation layer 23. The transverse rotating shafts 216 are driven by a motor. Rotating gears 2161 are provided at both ends of the transverse rotating shafts 216. The telescopic partition 28 includes an upper partition 281 and a lower partition 282. Both the upper partition 281 and the lower partition 282 are provided with racks 283 that cooperate with the rotating gears 2161. When the transverse rotating shafts 216 rotate, the upper partition 281 and the lower partition 282 can be opened and closed under the cooperation of the rotating gears 2161 and the racks 283.

[0059] To facilitate temperature control in each fermentation chamber, a U-shaped frame 217 is installed in each chamber. Infrared electric heating lamps 291 and small hot air pipes 292 are mounted on the U-shaped frame 217. These together form a temperature control device 29. By installing infrared electric heating lamps 291 and hot air pipes 292 with different wattages and inputting hot air at different temperatures, the temperature of each fermentation chamber is adjusted, allowing for photothermal steam bio-fermentation of the fresh tea leaves on the reciprocating screen conveyor belt 25. The withered tea leaves move along the reciprocating conveyor belt 25, undergoing fermentation in a progressive manner: "low-temperature fermentation chamber → medium-temperature fermentation chamber → high-temperature fermentation." First, in the low-temperature fermentation chamber 231, the activity of polyphenol oxidase is activated by photothermal stimulation at approximately 31°C, initiating low-temperature fermentation. After low-temperature fermentation, the reciprocating screen conveyor belt 25 moves to the left, feeding the tea leaves into the medium-temperature fermentation chamber 232, where the activity of polyphenol oxidase is enhanced by photothermal stimulation at approximately 35°C, initiating medium-temperature fermentation. After the mesophilic fermentation is completed, the reciprocating screen conveyor belt 25 continues to move to the left, feeding the tea leaves into the high-temperature fermentation chamber 233. High-temperature steam at approximately 40°C enhances the bio-fermentation activity of polyphenol oxidase, resulting in a large amount of fermentation hydrolysis products. The beneficial effects of using a three-stage photothermal steam fermentation process (low temperature, mesophilic temperature, and high temperature) include: enhancing the fermentation activity of polyphenol oxidase, generating a large amount of enzymatic hydrolysis products, and optimizing the quality of yeast-infused black tea.

[0060] To control the temperature and humidity of each withering chamber and fermentation chamber, a control system 220 is also provided, and a temperature sensor 218 and a humidity sensor 219 are installed in each withering chamber and fermentation chamber. The control system 220 receives the signals from the temperature sensor 218 and the humidity sensor 219, and controls the air inlet temperature and air volume of the hot air duct 292 to adjust the temperature and humidity in each withering chamber and fermentation chamber.

[0061] The kneading machine 3 in step 4) includes a kneading drum 31, a kneading disc 32, and a lid 33. The kneading disc 32 is equipped with an openable and closable tea outlet. The matching structure of the kneading drum 31, the kneading disc 32, and the lid 33 is the same as that of existing kneading machines. The lid 33 is an adjustable pressure lid, all of which are existing technologies and will not be described in detail here. To adapt to the processing of yeast black tea, the present invention has made the following improvements to the kneading machine 3: In order to avoid adverse antagonistic reactions between the added exogenous enzymes and the metal materials, and to overcome the technical obstacles of coarse old tea buds and leaves with high cellulose content and hard leaves that are difficult to knead into strips, the kneading drum 31 and the lid 33 are made of pine wood. The kneading disc 32 and the kneading ribs above it are made of nano-ceramic material. When the tea leaves are rotated and kneaded in the nano-ceramic kneading disc, the inclined, hard and smooth ceramic ribs can be used to break the cell walls of the tea buds and leaves, allowing the tea juice to overflow so that it can be kneaded into strips, while also reducing broken tea leaves. To prevent excessively high tea temperatures during pressure kneading from reducing polyphenol oxidase activity, a temperature sensor 35 is installed on the lid 33, extending deep into the kneading drum 31. A hot and cold air duct 36 is also provided to regulate the temperature inside the kneading drum 31. The other end of the hot and cold air duct 36 is connected to a hot and cold air blower, which adjusts the temperature of the hot and cold air to ensure that the tea leaves inside the kneading drum remain within a certain temperature range during kneading, preventing the loss of polyphenol oxidase activity due to high temperatures. Furthermore, an oxygen supply pipe 37 is provided to deliver oxygen into the kneading drum 31, and an atomizing enzyme addition nozzle 38 is provided for adding exogenous enzymes. During the rolling process, exogenous biological enzymes can be added using the atomizing enzyme nozzle 38 for enzymatic rolling, oxygen can be introduced using the oxygen supply pipe 37 for oxygenated rolling, and the rolling temperature can be adjusted using the hot and cold air pipes. This promotes the efficient oxidation reaction of polyphenol oxidase in the tea leaves, accelerates the reddening of the rolling buds and leaves, and also promotes the efficient enzymatic hydrolysis reaction of exogenous biological enzymes to hydrolyze substances such as cellulose, softening the leaf texture to facilitate the rolling of coarse and old tea buds and leaves into strips, and transforming them into a large amount of pectin, tea polysaccharides, theanine, and aromatic substances to optimize the quality of yeast black tea.

[0062] The de-clumping roller 4 includes an inclined roller body 41, which is rotatably mounted on a frame 45 and driven by a motor. Inside the roller body 41 is a screening cage 42 that rotates with it. One end of the screening cage 42 has a tea inlet, and the other end is closed. The roller body 41 has an outlet at the end opposite the tea inlet. Inside the screening cage 42 are de-clumping rollers 43 that move relative to it, each with a dispersing rod 44. The de-clumping rollers 43 can be directly fixed to the frame 45 by a support rod. When the screening cage 42 rotates, the de-clumping rollers 43 remain stationary, achieving relative rotation. The surface of the screening cage also has a set of discharge holes 421. The dispersed tea leaves fall into the roller body 41 through these holes, and under the combined action of the inclination angle and rotational force, the dispersed tea leaves move towards the outlet. The feeding hole 421 is a long strip structure adapted to the tea leaves, which facilitates the falling of the kneaded tea leaves and prevents the tea clumps from falling. The tea clumps are then continuously broken up by the disintegrating roller 43 and fall out of the feeding hole 421, thus ensuring thorough disintegration.

[0063] The fermentation tank 5 is equipped with a screen conveyor belt 51, and a leaf-shaping roller 52 is installed at the feed end of the fermentation tank 5. Through the slow forward movement of the screen conveyor belt 51 and the action of the leaf-shaping roller 52, the tea leaves are evenly spread on the screen conveyor belt 51 for fermentation. In order to carry out dual-enzyme biological fermentation without antagonistic reactions, the fermentation tank 5 is designed with a double-layer structure. Its inner wall is made of fir wood, and its outer wall is a nano-quartz material insulation layer, so as to realize metal-free disintegration and dual-enzyme biological fermentation. To improve the efficiency and quality of fermentation, three U-shaped frames 523 are spaced apart on the fermentation tank 5. Each U-shaped frame 523 is equipped with a quartz infrared electric heat lamp 59, a hot air pipe 510, and an atomizing humidification nozzle 520. This allows for the adjustment of fermentation temperature through light and heat and hot air during fermentation, and the adjustment of fermentation humidity through the atomizing humidification nozzle 520. The tea leaves are then subjected to photothermal steam dual-enzyme fermentation after enzyme addition, kneading and disintegration in the tank. The technical effects of using a photothermal and evaporative heating device are as follows: Infrared light is emitted from infrared electric heating lamps into the buds and leaves in the fermentation tank, stimulating the activity of polyphenol oxidase and exogenous enzymes for dual-enzyme bio-fermentation. Hot air is blown into the tank to enhance the enzymatic fermentation dynamics of the two enzymes, resulting in a large amount of fermentation enzymatic hydrolysis products. Steam nozzles provide heating and humidification during fermentation, stabilizing the bio-enzymatic fermentation dynamics of polyphenol oxidase and exogenous enzymes and preventing the buds and leaves from drying out, which would affect the fermentation quality.

[0064] To achieve both closed and open fermentation, the fermentation tank 5 is equipped with an openable outer cover 53, which can be opened or closed as needed for both types of fermentation. Closed fermentation enhances the bio-fermentation dynamics of polyphenol oxidase, accelerating the reddening of buds and leaves, and also improves the enzymatic hydrolysis reaction of exogenous enzymes, converting them into a large number of enzymatic hydrolysis products that optimize the quality of yeast-based black tea. Open fermentation facilitates the dissipation of humid heat and fermented gases, which is beneficial for subsequent drying and aroma enhancement.

[0065] The hot air pre-drying and aroma-enhancing roller 6 in step 6) includes a cylinder 61 inclinedly arranged on a frame. One end of the cylinder 61 has a feed inlet, and the other end has a discharge outlet. A rotating drum 62 is installed inside the cylinder 61. Tea leaves enter the rotating drum 62 through the feed inlet. The rotation of the rotating drum 62 causes the tea leaves to tumble and be slowly conveyed forward within the rotating drum 62. To achieve dynamic drying, the discharge end of the hot air pre-drying and aroma-enhancing roller 6 is provided with a hot air inlet 63 inclined towards the feed inlet. A hot air blower 64 is connected to the hot air inlet 63. The hot air blower 64 continuously delivers hot air at approximately 40°C into the cylinder 61 through the hot air inlet 63. Combined with the rotation of the rotating drum 12, the tea leaves are dynamically dried with hot air.

[0066] The vacuum freeze dryer 7 in step 7) has a box-type structure. The vacuum freeze dryer 7 contains multiple drawers 71, on which screen receiving frames 73 are placed. The vacuum freeze dryer 7 also has an automatic sensor door 72 for convenient automatic opening and feeding. To allow the tea leaves to move within the screen receiving frames 73 during freeze-drying, thus accelerating the process, the screen of the screen receiving frames 73 is preferably wavy. Simultaneously, support plates 711 are provided on both sides of the drawers 71, and floating plates 712 are mounted on the support plates 711. The screen receiving frames 73 are placed on the floating plates 712. A set of support springs 713 is provided between the floating plates 712 and the support plates 711. A vibrator 76 is also provided on the back of the floating plates 712. The vibration of the vibrator 76 causes the floating plates 712 and the screen receiving frames 73 mounted on the floating plates 712 to vibrate, thus causing the tea leaves to move. The basic principle of the vacuum freeze dryer 7 is the same as that of existing vacuum freeze dryers, and it has a refrigeration system, a vacuum system, a circulation system, a control system, and a hydraulic system. Its freeze-drying process is as follows: pretreatment → pre-freezing (quick freezing) → rapid cooling by a water trap → vacuuming of the chamber → drying and sublimation → freeze-drying and unloading. Using a vacuum freeze dryer to dry yeast black tea yields beneficial results: it not only avoids the dryness and strong burnt flavor that are easily caused by conventional high-temperature drying methods, but also freezes and solidifies the oxidative enzymatic hydrolysis reaction and the activity of tea polyphenol oxidase (PPO), allowing it to maintain high activity and become yeast black tea with strong fermentation power.

[0067] Example 2: A method for preparing black tea yeast products using spring tea includes the following steps:

[0068] 1) Fresh Leaf Harvesting and Impurity Removal: Harvest one bud and 3-4 leaves of coarse, mature buds and paired leaves from the tea tree. Feed the harvested fresh leaves into a quantitative impurity removal conveyor. Settings: Each withering cycle is 85-90 kg; the electromagnetic roller speed is 20-21 rpm; and the suction hood's air volume is 180-190 cubic meters per minute. The electromagnetic roller and suction hood remove dust, fibers, hair, broken leaves, and metal debris from the fresh tea leaves. A 10-mesh screen conveyor belt further removes mud, small insects, insect eggs, and other debris during transport, ensuring the cleaned tea leaves are properly withered using light and heat.

[0069] 2) Photothermal Withering: After weighing and impurity removal, clean the fresh tea leaves and feed them into the photothermal withering layer of the withering fermentation machine. Turn on: the spiky leaf-shaping roller, quartz infrared electric heat lamp, hot air pipe, and spiky hot air leaf turner. Settings: leaf thickness 15-20cm, hot air temperature 38-40℃, withering time 2.5-3.5h, spiky leaf-shaping roller speed 16-20 rpm, spiky hot air leaf turner speed 12-16 rpm, turning the leaves for 1-1.5 minutes every 15-20 minutes. The photothermal withering process is divided into three stages: First, move the fresh tea leaves to the high-temperature photothermal withering chamber, using a high temperature of 37-39℃ for 1.2-1.5h to enhance the activity of polyphenol oxidase, causing the buds and leaves to lose water and wither, resulting in a reddish leaf color. After the high-temperature photothermal withering process, the conveyor belt moves to the right, and the tea leaves are fed into the medium-temperature photothermal withering chamber. At a medium temperature of 34-36℃ for 0.8-1.1 hours, the activity of polyphenol oxidase is stabilized, promoting the enzymatic transformation of starch, protein, cellulose, and other substances in the fresh tea leaves, resulting in a sweet floral aroma. After the medium-temperature photothermal withering process, the conveyor belt continues to move to the right, and the tea leaves are fed into the low-temperature photothermal withering chamber. At a low temperature of 30-32℃ for 0.5-0.7 hours, the activity of polyphenol oxidase is weakened to prevent over-withering, excessive water loss, and leaf dryness. Because the temperature is low during the spring tea season, a process of "thick leaf spreading, high-heat air, and long photothermal withering" is adopted to stimulate polyphenol oxidase activity, enhance the photothermal withering effect, and improve the withering quality.

[0070] 3) Photothermal Steam Bio-fermentation: After photothermal withering, the tea leaves are fed into the inlet / outlet trough of the photothermal steam bio-fermentation layer of the withering and fermentation machine. The settings are: leaf thickness 30-40cm, hot air temperature 35-40℃, steam nozzle temperature 30-40℃, fermentation time 1.1-1.4h, spiky leaf-shaping roller speed 10-14 rpm, spiky hot air leaf-turning device speed 8-12 rpm, with leaf turning every 15-20 minutes for 1-1.5 minutes. The photothermal steam bio-fermentation process is divided into three stages: The photothermal withered tea leaves on the reciprocating conveyor belt are first moved to the left to the low-temperature photothermal bio-fermentation chamber, where they are fermented at approximately 28-32℃ for 0.3-0.4h to stimulate polyphenol oxidase activity and initiate low-temperature photothermal bio-fermentation. After completing the low-temperature photothermal fermentation process, the conveyor belt moves to the left, and the tea leaves are fed into the medium-temperature photothermal biological fermentation chamber. Under photothermal conditions at approximately 33-36℃, the fermentation time is 0.6-0.7 hours, enhancing the activity of polyphenol oxidase and proceeding with medium-temperature photothermal fermentation. After completing the medium-temperature photothermal fermentation process, the conveyor belt continues to move to the left, and the tea leaves are fed into the high-temperature photothermal steam biological fermentation chamber. Utilizing steam at approximately 38-40℃, the fermentation time is 0.6-0.8 hours, further enhancing the activity of polyphenol oxidase and converting it into a large amount of fermentation enzymatic hydrolysis products. After completing the three-stage photothermal steam biological fermentation process, the reciprocating conveyor belt is changed to move to the right, allowing the fermented tea leaves to be output from the inlet and outlet troughs. Due to the lower temperatures during the spring tea season, a process of "thick leaf spreading, high-temperature steam, and long-term fermentation" is adopted to enhance the fermentation dynamics of polyphenol oxidase, converting it into a large amount of enzymatic hydrolysis products and optimizing the quality of the black tea yeast.

[0071] 4) Enzyme-enhanced and oxygenated rolling: After bio-fermentation by light and heat steam, the tea leaves are fed into the inlet of the rolling machine's tea hopper. The enzyme adder and oxygen supply pipe are turned on. The settings are as follows: the amount of cellulase added is 0.15-0.2% of the weight of the rolled tea leaves; the speed of the tea hopper is 19-20 rpm; the oxygen supply is 0.35-0.4 cubic meters / min; the temperature inside the rolling hopper is 36-40℃; and the rolling time is 10-11 minutes, so that the yeast-infused black tea is fully rolled into strips. Because the temperature is low in spring, the cellulose content in the coarse and old tea buds and leaves is relatively low. Therefore, a rolling process of "less cellulase added, more oxygen supplied, and medium temperature" is adopted to enhance the oxidative hydrolysis reaction of polyphenol oxidase and exogenous cellulose bio-enzymes, accelerate the reddening of buds and leaves, and form excellent quality with red leaves, red soup, and sweet aroma.

[0072] 5) De-clumping and dual-enzyme fermentation: After kneading and oxygenation with added cellulase, the tea clumps are de-clumped and fed into a fermentation tank for dual-enzyme fermentation. Infrared electric heating lamps and hot air steaming devices are turned on to conduct dual-enzyme biological fermentation without antagonistic reactions. Settings: Leaf thickness is 55-60cm, hot air temperature is 36-38℃, steam nozzle temperature is 33-35℃, and dual-enzyme fermentation time is 1.4-1.6h (1-1.1h for closed dual-enzyme fermentation and 0.4-0.5h for open dual-enzyme fermentation). Due to the lower temperatures during the spring tea season, a process of "thick leaf spreading, high-temperature steam, and extended closed dual-enzyme fermentation time" is adopted to enhance the fermentation and enzymatic hydrolysis power of the dual enzymes, converting them into a large amount of fermentation enzymatic hydrolysis products to optimize the quality of black tea yeast.

[0073] 6) Hot Air Aroma Enhancement and Initial Drying: After double-enzyme bio-fermentation, the tea leaves are fed into the hot air initial drying and aroma enhancement drum. The hot air pipe is turned on, and the hot air temperature is set to 37-39℃. The hot air aroma enhancement and initial drying time is 25-28 minutes, until the moisture content reaches 18-22%. Due to the low temperature during the spring tea season, the process of "thick leaf spreading, high hot air, and long aroma enhancement and initial drying" is adopted to release a large amount of "fermented odor" and humid heat, which promotes the volatilization of aromatic substances in the buds and leaves, enhancing the sweet floral aroma.

[0074] 7) Vacuum Freeze-Drying: After initial drying with hot air for aroma extraction, add 0.1-0.15% (by weight) of Vitamin C to the tea leaves and input them into a vacuum freeze dryer. Turn on the refrigeration system, vacuum system, circulation system, control system, hydraulic system, and vibrator. Set the following parameters: leaf thickness on the freeze-drying rack to 15-20 cm, vacuum degree to 30-40 Pa, freeze-drying temperature to -10 to -14℃, freeze-drying time to 1-1.5 h, and vibrator frequency to 60-70 times / min. Due to the low temperatures during spring tea season, a process of "conventional freeze-drying temperature, conventional vacuum degree, low vibration frequency, and long freeze-drying time" is adopted to freeze-dry the internal and external moisture of the black tea yeast, freezing and solidifying the oxidative enzymatic hydrolysis reaction to give it high activity and strong fermentation power.

[0075] Example 3: A method for preparing black tea yeast using summer and autumn tea includes the following steps:

[0076] 1) Fresh Leaf Harvesting and Impurity Removal: Harvest one bud and 2-3 tender leaves, along with opposite leaves, from the tea tree. Feed the harvested fresh leaves into a quantitative impurity removal conveyor for quantitative impurity removal. Settings: Each withering cycle is 80-85 kg; the electromagnetic roller speed is 22-24 rpm; and the suction hood's air volume is 190-200 cubic meters per minute. Considering the rapid growth and aging of tea trees during the summer and autumn tea season, and the presence of numerous small insects, insect eggs, dust, and broken flowers and grasses, a conveyor belt with an 8-mesh impurity removal screen is used when harvesting tender buds and leaves. The electromagnetic roller speed and suction hood's air volume are increased to remove impurities, ensuring clean tea leaves for photothermal withering.

[0077] 2) Photothermal Withering: After weighing and impurity removal, clean the fresh tea leaves and feed them into the feeding trough of the photothermal withering layer of the withering fermentation machine. Turn on: the spiky leaf-shaping roller, quartz infrared electric heat lamp, hot air pipe, and spiky hot air leaf turner. Settings: leaf thickness 15-17cm, hot air temperature 35-37℃, withering time 2.5-2.8h, spiky leaf-shaping roller speed 18-20 rpm, spiky hot air leaf turner speed 12-14 rpm, turning the leaves every 15-17 minutes for 1-1.5 minutes. Photothermal withering steps: First, move the fresh tea leaves to the high-temperature photothermal withering chamber. Utilize the high temperature of 35-37℃ for 1.2-1.3h to enhance the activity of polyphenol oxidase, causing the buds and leaves to lose water and wither, resulting in a reddish leaf color. After the high-temperature photothermal withering process, the conveyor belt moves to the right, and the tea leaves are fed into the medium-temperature photothermal withering chamber. At a medium temperature of 31-32℃ for 0.8-0.9 hours, the activity of polyphenol oxidase is stabilized, promoting the enzymatic transformation of starch, protein, cellulose, and other substances in the fresh tea leaves, resulting in a sweet floral aroma. After the medium-temperature photothermal withering process, the conveyor belt continues to move to the right, and the tea leaves are fed into the low-temperature photothermal withering chamber. At a low temperature of 30-31℃ for 0.5-0.6 hours, the activity of polyphenol oxidase is weakened to prevent over-withering, excessive water loss, and leaf dryness. For summer and autumn tea production, where temperatures are higher, a process of "thin leaf spreading, low-temperature hot air, rapid leaf turning, and short-term photothermal withering" is adopted to reduce the intensity of photothermal withering and prevent over-withering from affecting the quality of the yeast-infused black tea.

[0078] 3) Photothermal Steam Bio-fermentation: After photothermal withering, the tea leaves are fed into the inlet / outlet trough of the photothermal steam bio-fermentation layer of the withering and fermentation machine. The following are activated: spiked leaf-shaping roller, steam nozzle, quartz infrared electric heat lamp, hot air pipe, and spiked hot air leaf turner. Settings: leaf thickness 30-35cm, hot air temperature 35-37℃, steam nozzle temperature 34-36℃, fermentation time 0.8-1.1h, spiked leaf-shaping roller speed 10-12 rpm, spiked hot air leaf turner speed 8-10 rpm, turning the leaves every 15-18 minutes for 1-1.5 minutes. The photothermal withered tea leaves are then moved to the low-temperature photothermal bio-fermentation chamber on the conveyor belt. Utilizing 27-29℃ photothermal heat, the fermentation time is 0.2-0.3h to stimulate polyphenol oxidase activity and initiate low-temperature photothermal bio-fermentation. After completing the low-temperature photothermal fermentation process, the conveyor belt moves to the left, and the tea leaves are fed into the medium-temperature photothermal biological fermentation chamber. Fermentation takes place at 31-33℃ for 0.3-0.4 hours, enhancing the activity of polyphenol oxidase. Following this, the conveyor belt continues to move to the left, and the tea leaves are fed into the high-temperature photothermal steam biological fermentation chamber. Fermentation takes place at 34-36℃ for 0.3-0.4 hours, further boosting the fermentation activity of polyphenol oxidase. For summer and autumn tea seasons with higher temperatures, a process of "thinly spreading the leaves, reducing the hot air steam temperature, and shortening the fermentation time" is adopted to stabilize the fermentation activity of polyphenol oxidase and prevent over-fermentation, which would negatively impact the quality of the yeast-fermented black tea.

[0079] 4) Enzyme-enhanced and oxygenated rolling: After photothermal steam bio-fermentation, the tea leaves are fed into the inlet of the rolling machine's tea hopper. The enzyme adder and oxygen supply pipe are turned on. The settings are as follows: cellulase addition is 0.2-0.3% of the weight of the rolled tea leaves; the rolling hopper speed is 16-18 rpm; the oxygen supply is 0.3-0.4 cubic meters / min; the temperature is 40-42℃; and the rolling time is 8-9 minutes. For summer and autumn teas, which have high cellulose content in buds and leaves, a process of "adding more cellulase, less oxygen, increasing temperature, and shortening rolling time" is adopted to decompose cellulose and soften the leaf material, making it easier to roll into strips, reducing bud and leaf breakage, and stabilizing the oxidative hydrolysis reaction of polyphenol oxidase and exogenous cellulose bio-enzymes.

[0080] 5) De-clumping and Double-enzyme Fermentation: After adding cellulase, the tea clumps, steamed, oxygenated, and kneaded, are de-clumped and then fed into a fermentation tank for double-enzyme fermentation. Infrared electric heating lamps and hot air steaming devices are turned on. Settings: Leaf thickness is 50-55cm, hot air temperature is 35-37℃, steam nozzle temperature is 31-33℃, and double-enzyme fermentation time is 1.4-1.6h (closed double-enzyme fermentation 0.8-0.9h, open double-enzyme fermentation 0.6-0.7h). Considering the higher temperatures during the summer and autumn tea season, a process of "thin leaf spreading, lower hot air steam temperature, shorter closed double-enzyme fermentation time, and longer open double-enzyme fermentation time" is adopted to stabilize the double-enzyme fermentation intensity and avoid over-fermentation, which would affect the quality of the yeast-fermented black tea.

[0081] 6) Hot Air Aroma Enhancement and Initial Drying: After double-enzyme bio-fermentation, the tea leaves are fed into the hot air initial drying and aroma enhancement drum. The hot air pipe is turned on, and the initial drying time is set to 22-23 minutes, until the moisture content reaches 20-22%. Considering the higher temperatures during the summer and autumn tea season, a process of "spreading the leaves thinly, reducing the hot air temperature, and shortening the initial drying time" is adopted to quickly dry the moisture and prevent a burnt taste.

[0082] 7) Vacuum Freeze-Drying: After initial drying with hot air for aroma extraction, add 0.15-0.2% (by weight) of Vitamin C to the tea leaves. Input the tea into a vacuum freeze dryer, and activate the refrigeration, vacuum, circulation, control, and hydraulic systems, as well as the vibrator. Set the following parameters: leaf thickness on the freeze-drying rack to 15-16 cm, vacuum level to 38-40 Pa, freeze-drying temperature to -14 to -16℃, vibrator frequency to 78-80 times / min, and freeze-drying time to 1-1.2 hours. For summer and autumn tea seasons with higher temperatures, a process of "thin leaf spreading, increased addition of antioxidant Vitamin C, lower freeze-drying temperature, higher vibration frequency, and shorter freeze-drying time" is adopted to rapidly freeze-dry the internal and external moisture of the black tea yeast, freezing and solidifying the oxidative enzymatic hydrolysis reaction to maintain high activity, strong fermentation power, and the excellent qualities of red leaves, red liquor, and sweet aroma.

[0083] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution; or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A method for preparing yeast black tea using dual-enzyme fermentation, characterized in that, Includes the following steps: 1) Fresh leaf picking and impurity removal: Pick buds and leaves with one bud and 3-4 leaves and paired leaves, and feed the fresh leaves into a quantitative impurity removal feeding conveyor for quantitative impurity removal to remove impurities from the tea leaves; 2) Photothermal withering: Weighed and impurity-removed fresh leaves are fed into the photothermal withering layer of the withering fermentation machine for segmented withering. The settings are: leaf thickness is 15-20cm, first withering at a high temperature of 35-42℃ for 1.2-1.5h, then withering at a medium temperature of 34-36℃ for 0.8-1.1h, and finally withering at a low temperature of 30-32℃ for 0.5-0.7h. 3) Photothermal steam bio-fermentation: After photothermal withering, the tea leaves are fed into the photothermal steam bio-fermentation layer of the withering fermentation machine for segmented fermentation. The settings are: the leaf thickness is 30-40cm, the fermentation time is 0.3-0.4h in a low temperature environment of 28-32℃, then 0.6-0.7h in a medium temperature environment of 33-36℃, and finally 0.6-0.8h in a high temperature environment of 38-40℃. 4) Enzyme-enriched and oxygenated kneading: After the tea leaves have undergone photothermal steam bio-fermentation, they are fed into the kneading drum of the kneading machine, and 0.1-0.3% of cellulase by weight of the tea leaves is added. Oxygen is introduced, and the tea leaves are kneaded at a temperature of 36-40℃ for 8-12 minutes. 5) De-clumping and dual-enzyme fermentation: After adding cellulase and oxygenating the tea clumps through kneading, the clumps are broken up and put into a fermentation tank for dual-enzyme fermentation, which utilizes the polyphenol oxidase naturally present in the tea leaves and the added cellulase for fermentation. 6) Hot air aroma enhancement and initial drying: After double enzyme bio-fermentation, the tea leaves are fed into the hot air initial drying and aroma enhancement drum. The hot air temperature is set to 35-40℃, the hot air aroma enhancement and initial drying time is 20-30 minutes, and the moisture content is dried to 18-22%. 7) Vacuum freeze-drying: After the tea leaves have been initially dried with hot air for aroma enhancement, they are fed into a vacuum freeze dryer for freeze drying. The settings are as follows: leaf thickness is 15-20cm, vacuum degree is 30-40Pa, freeze-drying temperature is -10 to -16℃, and freeze-drying time is 1-1.5h.

2. The method for preparing yeast black tea using dual-enzyme fermentation according to claim 1, characterized in that: The feed ends of the photothermal withering layer and the photothermal steam bio-fermentation layer of the withering fermentation machine are equipped with thorny leaf-equalizing rollers. The thorny leaf-equalizing rollers pierce the surface of the tea leaves and make the tea leaves fall evenly into the photothermal withering layer. A set of thorny hot air leaf turners are also installed in the photothermal withering layer and the photothermal steam bio-fermentation layer. The thorny hot air leaf turners turn the tea leaves and blow hot air to heat them and further pierce the cell walls of the tea leaves.

3. The method for preparing yeast black tea using dual-enzyme fermentation according to claim 1, characterized in that: The cellulase includes C1 enzyme, Cx enzyme, and β-glucosidase.

4. The method for preparing yeast black tea using dual-enzyme fermentation according to claim 1, characterized in that: In step 5), the following settings are made: the leaf thickness is 55-60cm, the hot air temperature is 35-40℃, the steam temperature is 30-35℃, and the dual-enzyme fermentation time is 1.4-1.6h.

5. The method for preparing yeast black tea using dual-enzyme fermentation according to claim 4, characterized in that: The deblocking fermentation tank is equipped with an outer cover that is easy to remove and place. First, cover the tank and carry out closed fermentation for 1-1.1 hours. Then, open the tank and carry out open dual-enzyme fermentation for 0.4-0.5 hours.

6. The method for preparing yeast black tea using dual-enzyme fermentation according to claim 4, characterized in that: In step 7), before the tea leaves are fed into the vacuum freeze dryer, vitamin C is added to the tea leaves through an enzyme addition device to fight oxidation. The amount of vitamin C added is 0.1-0.2% of the weight of the tea leaves.

7. A yeast black tea product prepared using dual-enzyme fermentation, characterized in that: It is prepared by the method described in any one of claims 1 to 5.

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