Black tea and its refining process

Abstract

The application provides a black tea and a refining process thereof, and the process comprises the following steps: S1. light quality induced segmental wilting, S2. rolling, S3. pulsatile positive and negative pressure difference fermentation, S4. microwave hot air synergistic drying, S5. screening and winnowing, S6. picking, S7. re-firing and blending packaging. By introducing specific wavelength blue light and red light combination irradiation in the wilting stage, the secondary metabolism of in vitro fresh leaves is regulated by using light signals as stress factors. In the fermentation link, the pulsatile variable pressure cycle of "vacuum preservation, oxygen pressure preservation" is adopted, the CO2 and hot waste gas generated by anaerobic metabolism in the core are forcedly removed by negative pressure, and fresh O2 is pressed into the micro gap of the strip, so that the uniform penetration of oxygen in the three-dimensional space of the pile body is realized, and the problem of "surface red, core green" caused by insufficient oxygen supply in the core of traditional static fermentation of large leaf species black tea is eliminated from the level of tissue cells, and the product tea soup is bright red and the leaf bottom is uniform red.

Description

Technical Field

[0001] This invention relates to the field of tea processing technology, specifically to a black tea and its refining process. Background Technology

[0002] Black tea is a fully fermented tea, made from fresh tea leaves through a series of processes including withering, rolling (or cutting), fermentation, and drying. Its core flavor characteristics—red liquor, red leaves, and a sweet, mellow taste—mainly originate from the complex oxidation and polymerization reactions of polyphenols during fermentation, catalyzed by polyphenol oxidase, producing theaflavins, thearubigins, and some theabrownins. Based on different tea varieties and product forms, black tea is generally divided into three main categories: Lapsang Souchong, Congou black tea, and broken black tea. Among them, Congou black tea is highly favored in the market due to its tightly rolled and uniform appearance and its high aroma and mellow taste.

[0003] In the production of Gongfu black tea, the initial fermentation process plays a decisive role in the final quality. Traditional fermentation methods often employ static piling or shallow tray spreading, relying on natural ventilation or simple mechanical blowing for oxygen supply. However, existing fermentation processes frequently face the technical challenge of uneven oxygen supply, especially prominent in the processing of large-leaf black tea. Large-leaf tea leaves are rich in nutrients, thick, and tightly rolled after rolling, resulting in a dense internal structure when piled. This means that under static fermentation conditions, while the surface tea leaves have ample contact with oxygen and undergo vigorous oxidation, the core area, due to obstructed airflow, remains in a relatively oxygen-deficient state, with anaerobic metabolism dominating. This leads to a series of quality defects: excessive oxidation of the surface results in a darker, more muted liquor with a weak aroma; while insufficient oxidation in the core results in bluish-green leaves, a light liquor, and a grassy taste—the typical "red on the outside, green on the inside" phenomenon. Even with manual turning or the addition of ventilation ducts, it is difficult to achieve a uniform distribution of oxygen concentration within the three-dimensional space, and turning the pile can easily damage the integrity of the tea leaves, increasing the breakage rate. Therefore, how to break through the limitations of the traditional static oxygen supply mode and achieve uniform penetration and precise control of oxygen during fermentation has become a key issue that urgently needs to be addressed in the upgrading of processing technology for large-leaf black tea. Summary of the Invention

[0004] In view of this, the present invention proposes a black tea and its refining process to solve the above problems.

[0005] The technical solution of this invention is implemented as follows:

[0006] A black tea and its refining process, comprising the following steps:

[0007] S1. Light quality-induced segmented withering: The fresh leaves of one bud and two leaves or one bud and three leaves of the harvested large-leaf tea tree are evenly spread in the withering trough and withered in a segmented manner by light quality-induced withering to obtain withered leaves;

[0008] S2. Rolling: The withered leaves are put into a rolling machine and rolled using a light-heavy-light pressure method to obtain rolled leaves;

[0009] S3. Pulsating positive and negative pressure difference fermentation: The kneaded leaves are evenly spread in the fermentation chamber, and fermentation is carried out by alternating positive and negative pressure difference to obtain fermented leaves;

[0010] S4. Microwave and hot air combined drying: The fermented leaves are sent into a microwave and hot air drying device for microwave and hot air combined drying to obtain the dried raw tea.

[0011] S5. Screening and air separation: The dried tea leaves are graded using a double-layer vibrating screen with 8-mesh and 16-mesh screens, and the tea leaves between 8-mesh and 16-mesh are taken as the main tea leaves; the main tea leaves are sent to an air separator for three-stage sorting.

[0012] S6. Sorting: The selected tea leaves are manually sorted to remove stems and non-tea impurities;

[0013] S7. Re-firing and blending packaging: The sorted clean tea is sent into the re-firing machine and slow-dryed at low temperature; after re-firing and cooling, it is then blended and then put into the blending machine for blending treatment. After blending is completed, it is sealed in aluminum foil bags filled with nitrogen.

[0014] Furthermore, in step S1, the leaf thickness is 8-12cm, and light quality-induced segmented withering is carried out in the following manner: the first stage withering is carried out with hot air at 30-32℃ for 2-2.5h, the second stage withering is carried out with natural wind at 22-25℃ and under specific wavelength blue and red light for 2-3h, and the third stage withering is carried out with natural wind at 22-25℃ for 1-2h.

[0015] Furthermore, the blue light wavelength is 460 nm, the red light wavelength is 660 nm, and the blue light intensity is 60-100 μmol·m⁻¹. -2 .s -1 The intensity of red light is 120-200 μmol·m. -2 .s -1 .

[0016] Furthermore, in step S2, the light-heavy-light method is as follows: knead without kneading for 9-11 minutes, apply light pressure of 0.5-0.8 kN for 13-17 minutes, apply heavy pressure of 1.5-2.0 kN for 18-22 minutes, and finally relax the pressure for 7-9 minutes.

[0017] Furthermore, in step S3, the thickness of the substrate is 15-20cm, and the rhythm of the single cycle of pulsed positive and negative pressure differential oxygen supply is as follows: vacuuming to -0.06MPa → holding pressure for 55-65s → oxygenation and pressurization to +0.15MPa → holding pressure for 55-65s, continuously cycling for 3-5 hours, and controlling the temperature in the fermentation chamber at 28-32℃ and the relative humidity at ≥95%.

[0018] Furthermore, in step S4, the microwave hot air combined drying is carried out as follows: in the first stage, the tea leaves are dried for 8-10 minutes at a hot air temperature of 110-115℃, a microwave frequency of 2450MHz, a power density of 0.5-0.8W / g, and a leaf thickness of 2-3cm; in the second stage, the tea leaves are spread on a bamboo sieve to rehydrate naturally for 30-40 minutes; and in the third stage, the tea leaves are dried for 15-20 minutes at a hot air temperature of 80-85℃ and a leaf thickness of 3-4cm.

[0019] Furthermore, in step S5, the three-stage sorting is as follows: Level 1 wind 2.0-2.5m / s removes fine hairs and light pieces; Level 2 wind 3.5-4.0m / s collects heavy and uniform tea leaves; and Level 3 wind 5.0-5.5m / s removes stems and burnt bits.

[0020] Furthermore, in step S7, the low-temperature slow drying specifically involves: using hot air at 95-100℃ to spread the leaves to a thickness of 2-3cm and drying for 12-15 minutes; sending the sorted clean tea into the re-firing machine and using low-temperature slow drying; after re-firing, cooling to 25-30℃, and blending according to the ratio of 15% 8-mesh tea + 65% 12-mesh tea + 20% 16-mesh tea, and processing at 12-15 rpm for 25-30 minutes during the uniform stacking process.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention introduces a combination of blue and red light of specific wavelengths during the withering stage, utilizing the light signal as an abiotic stress factor to regulate the secondary metabolism of detached fresh leaves. Blue light activates key aroma metabolism enzymes such as terpene synthase, while red light promotes the hydrolysis of amylase to generate soluble sugars. The combination of these two technologies allows the withered leaves to accumulate a high-quality substrate combination of "high aroma precursors + high soluble sugars + moderate polyphenols" while losing water, effectively reducing the phenol-to-amino acid ratio and resulting in a rich, mellow, and refreshing tea soup with significantly reduced bitterness.

[0023] 2. In the fermentation process, this invention adopts a pulsed pressure-variable cycle of "vacuuming → pressure holding → oxygenation and pressurization → pressure holding". By forcibly removing CO2 and hot and humid waste gas generated by anaerobic metabolism in the core of the pile through negative pressure, and forcing fresh O2 into the micro-gap of the tea leaves through positive pressure, the uniform penetration of oxygen in the three-dimensional space of the pile is achieved. This eliminates the problem of "red surface and green core" caused by insufficient oxygen supply in the core of the pile during the traditional static fermentation of large-leaf black tea from the perspective of tissue cells. The finished tea soup is bright red and the tea leaves are uniformly red.

[0024] 3. This invention organically integrates light-induced withering and pulsed positive and negative pressure difference fermentation into a complete process chain. The two form a three-level linkage mechanism of "physical aroma induction → pressure variation and oxygenation → endogenous aroma locking": light-induced withering provides rich terpene aroma precursors and soluble sugar substrates for fermentation, while pulsed fermentation fully transforms the advantages of the substrates into the aroma and taste quality of the finished product. Detailed Implementation

[0025] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0026] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0027] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0028] Example 1

[0029] A black tea and its refining process, comprising the following steps:

[0030] S1. Light-Induced Segmented Withering: One bud and two leaves from the harvested large-leaf tea trees are evenly spread in a withering trough, with a leaf thickness of 12cm. Light-induced segmented withering is employed, following this method: The first stage involves withering in 30℃ hot air for 2.5 hours; the second stage involves withering in 22℃ natural wind under blue light (wavelength 460nm) and red light (wavelength 660nm) for 3 hours, with a blue light intensity of 60μmol / m. -2 .s -1 The intensity of red light is 120 μmol·m. -2 .s -1 The third stage involves withering the leaves at 22℃ under natural wind for 2 hours to obtain withered leaves.

[0031] S2. Rolling: Put the withered leaves into a rolling machine and roll them using a light-heavy-light pressure method. Specifically, roll them as follows: roll them empty for 9 minutes, then apply light pressure of 0.5kN for 17 minutes, then apply heavy pressure of 1.5kN for 22 minutes, and finally loosen the pressure for 7 minutes to obtain rolled leaves.

[0032] S3. Pulsating positive and negative pressure difference fermentation: The kneaded leaves are evenly spread in the fermentation chamber with a thickness of 20cm. Pulsating positive and negative pressure difference alternating oxygen supply is used for fermentation. The rhythm of a single cycle of the pulsating positive and negative pressure difference alternating oxygen supply is: vacuuming to -0.06MPa → holding pressure for 55s → oxygenating and pressurizing to +0.15MPa → holding pressure for 55s, and continuing the cycle for 5 hours. The temperature in the fermentation chamber is controlled at 28℃ and the relative humidity is 95% to obtain fermented leaves.

[0033] S4. Microwave and hot air combined drying: The fermented leaves are sent into a microwave and hot air drying device for microwave and hot air combined drying. The drying is carried out in the following manner: the first stage is drying for 10 minutes at a hot air temperature of 110℃, a microwave frequency of 2450MHZ, a power density of 0.5W / g, and a leaf thickness of 2cm. The second stage is to spread the tea leaves on a bamboo sieve for natural rehydration for 30 minutes. The third stage is to dry for 20 minutes at a hot air temperature of 80℃ and a leaf thickness of 3cm to obtain the dried raw tea.

[0034] S5. Sieving and air separation: The dried tea leaves are graded using a double-layer vibrating sieve with 8-mesh and 16-mesh screens, and the leaves between 8-mesh and 16-mesh are taken as the main tea leaves. The main tea leaves are then sent to an air separator for three-stage sorting, specifically as follows: Level 1 air at 2.0 m / s removes downy hairs and light pieces, Level 2 air at 3.5 m / s collects heavy and uniform tea leaves, and Level 3 air at 5.0 m / s removes stems and burnt dust.

[0035] S6. Sorting: The selected tea leaves are manually sorted to remove stems and non-tea impurities;

[0036] S7. Re-firing and blending packaging: The sorted clean tea leaves are sent to the re-firing machine and dried at a low temperature for 15 minutes using hot air at 95℃ with a leaf thickness of 2cm. After re-firing, the leaves are cooled to 25℃ and then blended in a ratio of 15% 8-mesh tea, 65% 12-mesh tea, and 20% 16-mesh tea. The blended tea leaves are then fed into a blending machine for blending at 12 rpm for 30 minutes. After blending, the tea leaves are sealed in aluminum foil bags filled with nitrogen.

[0037] Example 2

[0038] A black tea and its refining process, comprising the following steps:

[0039] S1. Light-Induced Segmented Withering: One bud and two leaves from the harvested large-leaf tea trees are evenly spread in a withering trough, with a leaf thickness of 10cm. Light-induced segmented withering is employed, following this method: The first stage involves withering in 31℃ hot air for 2.2 hours; the second stage involves withering in 24℃ natural wind under blue light (wavelength 460nm) and red light (wavelength 660nm) for 2.5 hours, with a blue light intensity of 80μmol / m. -2 .s -1 The intensity of red light is 160 μmol·m. -2 .s -1 The third stage involves withering the leaves at 24℃ under natural wind for 1.5 hours to obtain withered leaves.

[0040] S2. Rolling: Put the withered leaves into a rolling machine and roll them using a light-heavy-light pressure method. Specifically, roll them as follows: roll them empty for 10 minutes, then apply light pressure of 0.6kN for 15 minutes, then apply heavy pressure of 1.8kN for 20 minutes, and finally loosen the pressure for 8 minutes to obtain rolled leaves.

[0041] S3. Pulsating positive and negative pressure difference fermentation: The kneaded leaves are evenly spread in the fermentation chamber with a thickness of 18cm. Pulsating positive and negative pressure difference alternating oxygen supply is used for fermentation. The rhythm of a single cycle of the pulsating positive and negative pressure difference alternating oxygen supply is: vacuuming to -0.06MPa → holding pressure for 60s → oxygenating and pressurizing to +0.15MPa → holding pressure for 60s, and continuing the cycle for 4 hours. The temperature in the fermentation chamber is controlled at 30℃ and the relative humidity is 95% to obtain fermented leaves.

[0042] S4. Microwave and hot air combined drying: The fermented leaves are sent into a microwave and hot air drying device for microwave and hot air combined drying. The drying is carried out in the following manner: the first stage is drying for 9 minutes at a hot air temperature of 112℃, a microwave frequency of 2450MHZ, a power density of 0.6W / g, and a leaf thickness of 3cm. The second stage is to spread the tea leaves on a bamboo sieve for natural rehydration for 35 minutes. The third stage is to dry for 18 minutes at a hot air temperature of 83℃ and a leaf thickness of 4cm to obtain the dried raw tea.

[0043] S5. Sieving and air separation: The dried raw tea is graded using a double-layer vibrating sieve with 8-mesh and 16-mesh screens, and the tea between 8-mesh and 16-mesh is taken as the main raw tea. The main raw tea is sent to an air separator for three-stage sorting, specifically according to the following method: the first stage airflow of 2.2 m / s removes hair and light pieces, the second stage airflow of 3.8 m / s collects heavy and uniform tea, and the third stage airflow of 5.3 m / s removes stems and burnt dust.

[0044] S6. Sorting: The selected tea leaves are manually sorted to remove stems and non-tea impurities;

[0045] S7. Re-firing and blending packaging: The sorted clean tea leaves are sent to the re-firing machine and dried at a low temperature for 14 minutes using hot air at 98℃ with a leaf thickness of 3cm. After re-firing, the leaves are cooled to 28℃ and then blended in a ratio of 15% 8-mesh tea, 65% 12-mesh tea, and 20% 16-mesh tea. The blended tea leaves are then fed into a blending machine for blending at 14 rpm for 28 minutes. After blending, the tea leaves are sealed in aluminum foil bags filled with nitrogen.

[0046] Example 3

[0047] A black tea and its refining process, comprising the following steps:

[0048] S1. Light-Induced Segmented Withering: Fresh leaves (one bud and three leaves) from large-leaf tea trees are evenly spread in withering troughs to a thickness of 8 cm. Light-induced segmented withering is then performed as follows: The first stage involves withering in 32℃ hot air for 2 hours; the second stage involves withering in 25℃ natural wind under blue light (wavelength 460 nm) and red light (wavelength 660 nm) for 2 hours, with the blue light intensity being 100 μmol / m. -2 .s -1 The intensity of red light is 200 μmol·m. -2 .s -1 The third stage involves withering the leaves at 25°C under natural wind for 1 hour to obtain withered leaves.

[0049] S2. Rolling: Put the withered leaves into the rolling machine and roll them using a light-heavy-light pressure method. Specifically, roll them as follows: roll them empty for 11 minutes, then apply light pressure of 0.8kN for 13 minutes, then apply heavy pressure of 2.0kN for 18 minutes, and finally loosen the pressure for 9 minutes to obtain rolled leaves.

[0050] S3. Pulsating positive and negative pressure difference fermentation: The kneaded leaves are evenly spread in the fermentation chamber with a thickness of 15cm. Pulsating positive and negative pressure difference alternating oxygen supply is used for fermentation. The rhythm of a single cycle of the pulsating positive and negative pressure difference alternating oxygen supply is: vacuuming to -0.06MPa → holding pressure for 65s → oxygenating and pressurizing to +0.15MPa → holding pressure for 65s, and continuing the cycle for 3 hours. The temperature in the fermentation chamber is controlled at 32℃ and the relative humidity is 95% to obtain fermented leaves.

[0051] S4. Microwave and hot air combined drying: The fermented leaves are sent into a microwave and hot air drying device for microwave and hot air combined drying. The drying is carried out in the following manner: the first stage is drying for 8 minutes at a hot air temperature of 115℃, a microwave frequency of 2450MHZ, a power density of 0.8W / g, and a leaf thickness of 2cm. The second stage is to spread the tea leaves on a bamboo sieve for natural rehydration for 40 minutes. The third stage is to dry for 15 minutes at a hot air temperature of 85℃ and a leaf thickness of 3cm to obtain the dried raw tea.

[0052] S5. Sieving and air separation: The dried tea leaves are graded using a double-layer vibrating sieve with 8-mesh and 16-mesh screens, and the leaves between 8-mesh and 16-mesh are taken as the main tea leaves. The main tea leaves are then sent to an air separator for three-stage sorting, specifically as follows: Level 1 air at 2.5 m / s removes downy hairs and light pieces, Level 2 air at 4.0 m / s collects heavy and uniform tea leaves, and Level 3 air at 5.5 m / s removes stems and burnt dust.

[0053] S6. Sorting: The selected tea leaves are manually sorted to remove stems and non-tea impurities;

[0054] S7. Re-firing and blending packaging: The sorted clean tea leaves are sent to the re-firing machine and dried at a low temperature. Specifically, the leaves are dried for 12 minutes with hot air at 100℃ and spread to a thickness of 2cm. After re-firing, the leaves are cooled to 30℃ and then blended in a ratio of 15% 8-mesh tea, 65% 12-mesh tea, and 20% 16-mesh tea. The blended tea leaves are then fed into a blending machine for blending at 15 rpm for 25 minutes. After blending, the tea leaves are sealed in aluminum foil bags filled with nitrogen.

[0055] Comparative Example 1

[0056] Compared with Example 2, this comparative example differs in that light quality induction is not performed in the S1 withering step, and the withering is carried out in stages as follows: the first stage is withering with hot air at 31°C for 2.2 hours, and the second stage is withering with natural wind at 24°C for 4 hours.

[0057] Comparative Example 2

[0058] Compared with Example 2, this comparative example differs in that, in the light-induced segmented withering process of step S1, only blue light is used for illumination in the second stage. Specifically, withering is carried out for 2.5 hours under natural wind at 24°C and blue light with a wavelength of 460 nm, with a blue light intensity of 80 μmol / m. -2 .s -1 .

[0059] Comparative Example 3

[0060] Compared with Example 2, this comparative example differs in that, in the light-induced segmented withering process of step S1, only red light is used for illumination in the second stage. Specifically, withering is carried out for 2.5 hours under natural wind at 24°C and red light with a wavelength of 660 nm, with a red light intensity of 160 μmol / m. -2 .s -1 .

[0061] Comparative Example 4

[0062] Compared with Example 2, the difference in this comparative example is that static fermentation is used instead of fermentation in step S3. Specifically, the fermentation is carried out as follows: the kneaded leaves are evenly spread in the fermentation tray with a thickness of 18cm. The temperature of the fermentation room is 30℃ and the relative humidity is 95%. Static fermentation is carried out. When the fermentation has been going on for 2.5 hours, the pile is turned manually once. The total fermentation time is 5 hours.

[0063] Experiment 1

[0064] Take 20g of black tea prepared in Examples 1-3 and Comparative Examples 1-3 respectively, grind it through a 40-mesh sieve using a grinder, and collect the sieve-passing material, i.e., tea powder, as a sample. Take 0.5g of each tea powder and determine the total soluble sugar content using the anthrone-sulfuric acid colorimetric method, perform the test 3 times, and take the average value. Take 0.2g of each tea powder and determine the total tea polyphenols using the Folin-Ciocalteu colorimetric method, perform the test 3 times, and take the average value. Take 0.2g of each tea powder and determine the total free amino acids using the ninhydrin colorimetric method, perform the test 3 times, and take the average value. The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As shown in Table 1, the total soluble sugar content of the examples was higher than that of the comparative example. Comparing Example 2 and Comparative Example 1, Example 2 effectively promoted the enzymatic hydrolysis of starch and other polysaccharides into soluble sugars during withering through photo-induced activation, resulting in a significantly higher soluble sugar content than Comparative Example 1. Comparative Example 3, using only red light irradiation, had a higher total soluble sugar content than Comparative Example 2 but lower than Example 2. This is because red light has a better activation effect on amylase activity than blue light, but red light alone is still less effective than blue-red combined light. The total soluble sugar content of Examples 1-3 was significantly higher than that of Comparative Example 3 because the addition of blue light was not redundant but rather produced a synergistic effect with red light—blue light may have increased the efficiency of red light-induced soluble sugar accumulation and retention by regulating cell membrane permeability, promoting the hydrolysis and release of glycosides, or modulating photosynthetic pigment-mediated signaling pathways. The overall gain from the combination of the two exceeded the simple superposition of the effects of a single light source. Furthermore, the tea polyphenol content of the examples was slightly lower than that of the comparative example. Example 2 is slightly lower than Comparative Example 1 because some polyphenols are degraded by enzymatic oxidation or photo-oxidation during light-induced withering. A moderate reduction in polyphenols helps alleviate the bitterness of the finished tea. Comparative Example 2 is slightly higher than Comparative Example 3, indicating that blue light has a more significant regulatory effect on polyphenol metabolism than red light. Regarding the total amount of free amino acids, Examples 1-3 are significantly higher than Comparative Examples 1-3. This may be because blue light activates protease activity or inhibits the conversion of amino acids to catechins, allowing free amino acids to accumulate. Overall, Examples 1-3 have better total soluble sugar and free amino acid content than the comparative examples, while the tea polyphenol content is slightly lower than Comparative Example 1. This indicates that the light-induced withering in stage S1 of this invention can effectively improve the flavor profile of the finished black tea—higher soluble sugar content brings a sweet and mellow taste to the tea soup, higher free amino acid content enhances the freshness of the tea soup, and a moderate reduction in tea polyphenol content can alleviate bitterness. The synergistic optimization of these three indicators provides better substrate conditions for subsequent fermentation processes.

[0068] Experiment 2

[0069] Take 3g of whole tea leaves from the black teas prepared in Examples 1-3 and Comparative Example 4 respectively, add them to 150mL of boiling water and steep for 5min. Then filter the tea soup and cool it to 25℃. Use a benchtop colorimeter in transmission mode to measure the L* value (brightness) and a* value (redness) of the tea soup. Each group was repeated 3 times and the average value was taken. The test results are shown in Table 2.

[0070] Table 2

[0071]

[0072] As shown in Table 2, the L* value (brightness) of the tea soup in Examples 1-3 is significantly higher than that in Comparative Example 4, indicating that the black tea soup produced by the pulsed positive and negative pressure differential fermentation in stage S3 of this invention has a more vibrant and bright red color. In terms of a* value (redness), Examples 1-3 are also significantly higher than the comparative example. The dual improvement in L* and a* values ​​is due to the fact that the pulsed positive and negative pressure differential fermentation achieves three-dimensional homogenization of oxygen supply between the core and surface layers through a pressure-changing cycle of "vacuuming → pressure holding → oxygenation and pressurization → pressure holding": the negative pressure stage forcibly removes CO2 and humid heat waste gas generated by anaerobic metabolism in the core, opening up micro-channels for oxygen permeation; the positive pressure oxygenation stage forces fresh O2 into the micro-gaps of the tea strands, allowing polyphenol oxidase to obtain sufficient oxygen substrate, thereby fully oxidizing and generating theaflavins and thearubigins. The significant increase in theaflavin content is the direct chemical cause of the increased brightness (L* value) of the tea soup, while the full generation of thearubigins gives the tea soup a higher redness (a* value). In contrast, Comparative Example 4 used traditional static fermentation. Due to long-term lack of oxygen in the core area, oxidation was insufficient, resulting in a lack of theaflavins and thearubigins, which caused the soup color to be darker and lighter.

[0073] Sensory evaluation

[0074] A judging panel of 10 internal personnel who had undergone basic sensory evaluation was selected. Selection criteria included normal taste and smell, abstaining from smoking, alcohol, spicy or strongly flavored foods, and the use of perfumes or scented skincare products within 24 hours prior to the evaluation. The evaluation was conducted in a clean, odorless, and well-lit environment with a white tasting table. Tea samples obtained from Examples 1-3 and Comparative Examples 1-4 were randomly assigned three-digit numbers. The tea infusion was prepared as follows: 3.0g of each tea sample was weighed and placed in a 250mL judging cup, 150mL of boiling water was poured in, the cup was covered, and the tea was steeped for 5 minutes. The tea infusion was then filtered out in one go. The evaluation process is as follows: ① Tea liquor observation: Pour the filtered tea liquor into a white evaluation bowl and observe the redness, brightness, and clarity of the liquor; ② Aroma identification: While the tea is still hot (approximately 75℃), take a deep breath near the rim of the cup to smell the aroma, evaluating the intensity of the floral and fruity fragrance and the presence of any off-flavors such as grassy or sour notes; ③ Taste tasting: Take approximately 5mL of tea liquor with a porcelain spoon and place it in your mouth, gently sucking to spread the tea liquor across your tongue, experiencing the richness, bitterness, and aftertaste. Rinse your mouth with water after each sample, with an interval of at least 2 minutes; ④ Leaf evaluation: Pour the remaining tea leaves from the cup into a white porcelain plate and observe the color (bright red or bluish-green) and uniformity of the leaves. A simplified 10-point scoring method is used. Each evaluator independently scores the four factors: tea liquor color, aroma, taste, and leaf appearance. The arithmetic mean of all evaluators' scores is taken as the final score for each factor of the tea sample. If a reviewer's score for a certain factor differs from the average score of other reviewers by more than 3 points, it needs to be reviewed and confirmed. If the difference is significant, the review panel should jointly agree on a unified evaluation standard before re-evaluating or removing the outlier. The sensory evaluation results are shown in Table 3.

[0075] Table 3

[0076]

[0077] As shown in Table 3, Examples 1-3 performed excellently in all four factor scores. Regarding the color of the tea liquor, Examples 1-3 were significantly better than Comparative Example 4, which is consistent with the L* and a* values ​​detected in Experiment 2, further confirming the effect of pulsating fermentation on enhancing the reddish brightness of the tea liquor. Regarding aroma, Examples 1-3 were significantly better than Comparative Examples 1-4. Among them, Comparative Example 1 had the lowest aroma score, indicating that the accumulation of terpene aroma precursors in the withered leaves that were not induced by light quality was insufficient, resulting in a bland floral and fruity aroma in the finished tea. Comparative Example 3 had an aroma score that was better than Comparative Example 1 but lower than the Example. This is because although red light can provide substrates for aroma formation by promoting sugar accumulation, it lacks the activation effect of blue light on key enzymes such as terpene synthase. Comparative Example 2 had the highest aroma score among the three comparative examples because the direct activation effect of blue light on aroma precursors was better than that of red light, but it was still not as good as the synergistic effect of blue-red composite light. Blue light activates the aroma synthesis pathway, and red light provides glycosylation substrates. The combination of the two makes the types and abundance of aroma substances reach the optimal level. In terms of taste, Examples 1-3 were significantly better than Comparative Examples 1-4. This corresponds to the test results in Experiment 1, which showed high total soluble sugar content, moderate tea polyphenol content, and high free amino acid content. This indicates that the light-induced withering effect of "increasing sugar, increasing amino acids, and moderately reducing polyphenols" effectively reduced the phenol-amino acid ratio, resulting in a rich, mellow, and refreshing tea soup without bitterness. Regarding the tea leaves, Examples 1-3 scored 9.1-9.2, while Comparative Example 4 scored only 6.5, a significant difference. This is because Comparative Example 4 used static fermentation, and the long-term lack of oxygen in the core resulted in a mottled appearance of "red surface and green core" in the tea leaves. In contrast, Examples 1-3, after undergoing pulsed pressure-switching fermentation, had a uniform and even oxygen supply, resulting in uniformly bright red tea leaves.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A type of black tea and its refining process, characterized in that, Includes the following steps: S1. Light quality-induced segmented withering: The fresh leaves of one bud and two leaves or one bud and three leaves of the harvested large-leaf tea tree are evenly spread in the withering trough and withered in a segmented manner by light quality-induced withering to obtain withered leaves; S2. Rolling: The withered leaves are put into a rolling machine and rolled using a light-heavy-light pressure method to obtain rolled leaves; S3. Pulsating positive and negative pressure difference fermentation: The kneaded leaves are evenly spread in the fermentation chamber, and fermentation is carried out by alternating positive and negative pressure difference to obtain fermented leaves; S4. Microwave and hot air combined drying: The fermented leaves are sent into a microwave and hot air drying device for microwave and hot air combined drying to obtain the dried raw tea. S5. Screening and air separation: The dried tea leaves are graded using a double-layer vibrating screen with 8-mesh and 16-mesh screens, and the tea leaves between 8-mesh and 16-mesh are taken as the main tea leaves; the main tea leaves are sent to an air separator for three-stage sorting. S6. Sorting: The selected tea leaves are manually sorted to remove stems and non-tea impurities; S7. Re-firing and blending packaging: The sorted clean tea is sent into the re-firing machine and slow-dryed at low temperature; after re-firing and cooling, it is then blended and then put into the blending machine for blending treatment. After blending is completed, it is sealed in aluminum foil bags filled with nitrogen.

2. The black tea and its refining process as described in claim 1, characterized in that, In step S1, the leaf thickness is 8-12cm, and light quality-induced segmented withering is carried out in the following manner: the first stage withering is carried out with hot air at 30-32℃ for 2-2.5h; the second stage withering is carried out with natural wind at 22-25℃ and under specific wavelength blue and red light for 2-3h; and the third stage withering is carried out with natural wind at 22-25℃ for 1-2h.

3. The black tea and its refining process as described in claim 2, characterized in that, The blue light wavelength is 460 nm, the red light wavelength is 660 nm, and the blue light intensity is 60-100 μmol·m⁻¹. -2 .s -1 The intensity of the red light is 120-200 μmol·m⁻¹. -2 .s -1 .

4. The black tea and its refining process as described in claim 1, characterized in that, In step S2, the light-heavy-light method specifically involves: kneading without kneading for 9-11 minutes, applying light pressure of 0.5-0.8 kN for 13-17 minutes, applying heavy pressure of 1.5-2.0 kN for 18-22 minutes, and finally releasing the pressure for 7-9 minutes.

5. The black tea and its refining process as described in claim 1, characterized in that, In step S3, the thickness of the substrate is 15-20cm. The rhythm of the single cycle of the pulsed positive and negative pressure differential oxygen supply is as follows: vacuuming to -0.06MPa → holding pressure for 55-65s → oxygenation and pressurization to +0.15MPa → holding pressure for 55-65s, and continuing the cycle for 3-5 hours. The temperature inside the fermentation chamber is controlled at 28-32℃ and the relative humidity is ≥95%.

6. The black tea and its refining process as described in claim 1, characterized in that, In step S4, the microwave-hot-air co-drying is carried out as follows: in the first stage, the tea leaves are dried for 8-10 minutes at a hot air temperature of 110-115℃, a microwave frequency of 2450MHz, a power density of 0.5-0.8W / g, and a leaf thickness of 2-3cm; in the second stage, the tea leaves are spread on a bamboo sieve to rehydrate naturally for 30-40 minutes; and in the third stage, the tea leaves are dried for 15-20 minutes at a hot air temperature of 80-85℃ and a leaf thickness of 3-4cm.

7. The black tea and its refining process as described in claim 1, characterized in that, In step S5, the three-stage sorting is as follows: Level 1 wind (2.0-2.5 m / s) removes fine hairs and light pieces; Level 2 wind (3.5-4.0 m / s) collects heavy and uniform tea leaves; and Level 3 wind (5.0-5.5 m / s) removes stems and burnt bits.

8. The black tea and its refining process as described in claim 1, characterized in that, In step S7, the low-temperature slow drying specifically involves: using hot air at 95-100℃ to spread the leaves to a thickness of 2-3cm and drying for 12-15 minutes; after re-firing, cooling to 25-30℃, blending the leaves according to the ratio of 15% 8-mesh tea + 65% 12-mesh tea + 20% 16-mesh tea, and processing the mixture at a speed of 12-15 rpm for 25-30 minutes.

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