Novel preparation technology of low-temperature fresh-keeping cold-quenched tea

Abstract

The invention discloses a novel preparation technology of low-temperature fresh-keeping cold-quenched tea, and relates to the field of cold-quenched tea preparation, and the novel preparation technology comprises the following steps: S1, fresh leaves are picked and then are directly subjected to low-temperature freezing treatment, the freezing temperature is-25 DEG C to-15 DEG C, and the freezing time is 20-40 minutes; s2, unfreezing and withering the frozen fresh leaves; s3, performing rocking treatment on the unfrozen and withered tea leaves; s4, rolling the rocked green leaves by adopting a gradient pressure method; s5, carrying out segmented fermentation treatment under temperature and humidity control conditions; s6, after fermentation is completed, performing low-temperature freezing on the tea leaves again; according to the novel preparation process of the low-temperature fresh-keeping cold-quenched tea, the ice crystal form is cooperatively regulated and controlled through staged freezing treatment, cell structure damage is reduced, dynamic rocking and gradient rolling processes are combined, the inclusion release path is accurately controlled, tea polyphenol, theaflavin and flower and fruit aroma components are effectively reserved, and the low-temperature fresh-keeping cold-quenched tea is prepared. And component loss caused by temperature fluctuation or single mechanical force in the traditional process is avoided.

Description

Technical Field

[0001] The present invention relates to the technology for preparing cold-quenched tea, and particularly to a novel preparation process for low-temperature fresh-keeping cold-quenched tea. Background Art

[0002] As a natural and healthy beverage, the fresh-keeping and quality stability of tea have always been technical difficulties in the industry. In traditional tea processing technology, after fresh tea leaves are picked, they need to go through processes such as withering, shaking, rolling, and fermentation. However, during storage, problems such as the degradation of tea polyphenols, the dissipation of aroma substances, and the browning of color are likely to occur due to oxidation reactions, microbial activities, and moisture migration.

[0003] Existing fresh-keeping technologies mostly rely on low-temperature refrigeration or vacuum packaging. However, conventional refrigeration (0 - 4°C) is difficult to completely inhibit enzyme activity, and long-term storage will still lead to the loss of core components such as theaflavins. Although vacuum packaging can delay oxidation, it cannot solve the problems of cell structure damage and uneven transformation of inclusions caused by rough processing during the processing process. In addition, in traditional freezing processes, due to uncontrollable ice crystal formation, it is easy to damage the cell walls of tea leaves, resulting in turbid tea soup and weak taste after rehydration. Therefore, there is an urgent need for a tea processing method that takes into account both efficient fresh-keeping and quality optimization to break through the technical bottlenecks in shelf life, sensory quality, and industrial production of traditional processes. Summary of the Invention

[0004] The purpose of the present invention is to provide a novel preparation process for low-temperature fresh-keeping cold-quenched tea to solve the above deficiencies in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A novel preparation process for low-temperature fresh-keeping cold-quenched tea, comprising the following steps:

[0006] S1. After the fresh tea leaves are picked, they are directly subjected to low-temperature freezing treatment. The freezing temperature is -25°C to -15°C, and the freezing time is 20 - 40 minutes. The cell structure of the fresh tea leaves is quickly fixed by ultra-low temperature quick-freezing, the activity of polyphenol oxidase is inhibited, the respiration after the fresh tea leaves are picked is blocked, chlorophyll degradation and browning reactions are avoided, and at the same time, tiny ice crystals are formed to reduce cell wall damage and retain the original flavor substances for subsequent processes;

[0007] S2. The frozen fresh tea leaves are thawed and withered. The withering process is used to promote the diffusion of the water gradient and the hydrolysis and transformation of inclusions. At the same time, the low-temperature environment inhibits the reproduction of microorganisms and avoids the risk of mildew in traditional withering;

[0008] S3. The thawed and withered tea leaves are subjected to a shaking process to break the cell membranes at the edges of the leaves by mechanical force and accelerate the contact between polyphenolic substances and oxidase;

[0009] S4. Use the gradient pressure method to knead the shaken green leaves. The gradient pressure strategy takes into account both shaping and the extrusion efficiency of inclusions. Low-temperature kneading reduces the premature conversion of fermentation precursor substances, laying a material foundation for subsequent temperature-controlled fermentation.

[0010] S5. Conduct segmented fermentation treatment under temperature and humidity control conditions. The dual-factor regulation of temperature and humidity precisely guides the direction of enzymatic reactions. Segmented fermentation achieves the selective oxidation of catechins and constructs characteristic aroma components.

[0011] S6. After fermentation is completed, freeze the tea leaves at low temperature again and store them sealed in a cold storage at -18°C to -25°C. The secondary freezing terminates the enzymatic reaction and solidifies the quality at the end of fermentation. Ultra-low temperature storage effectively inhibits lipid peroxidation and extends the tea leaf preservation period.

[0012] Furthermore, in step S1, the temperature of the low-temperature freezing treatment is -20°C, and the freezing time is 30 minutes. -20°C is the critical point for ice crystal formation, which can ensure the freezing efficiency while avoiding cell membrane rupture caused by too low temperature and reducing the loss of nutrients due to the leakage of cell sap.

[0013] Furthermore, in step S2, the thawing temperature for thawing withering is controlled at 0 - 15°C, and the withering humidity is 50 - 80%. Specifically, it includes:

[0014] The first stage: Thaw at 0 - 5°C for 2 - 4 hours, keeping the leaf surface dew-covered. The low-temperature slow thawing enables the orderly repair of cell membranes. The dew on the leaf surface forms a water film to block oxygen, delaying enzymatic oxidation and providing a moderate moisture environment for withering at the same time.

[0015] The second stage: Wither at 10 - 15°C for 6 - 8 hours. During this period, turn the leaf layer every 1 hour and introduce an air current with an oxygen concentration of 25 - 28%. Medium-temperature withering combined with an oxygen-rich environment promotes the activity of polyphenol oxidase and improves the conversion efficiency of tea polyphenols.

[0016] Furthermore, the shaking treatment in step S3 adopts dynamic shaking treatment, specifically:

[0017] Conduct shaking 3 - 5 times. Each shaking time is 3 - 5 minutes. The shaking frequency gradually increases from the initial 20 revolutions per minute to 30 revolutions per minute. After each shaking, let it stand for 0.5 - 1 hour. After the end of each standing, extract leaf samples to observe the proportion of red edges at the leaf margin. When the red edge area reaches 20 - 30%, terminate the shaking. The stepped strengthening of mechanical force makes the degree of cell damage match the release rate of inclusions. The standing period is conducive to the accumulation of oxidation products, and the control of the red edge proportion ensures the balance between the freshness and mellow thickness of the tea soup.

[0018] Furthermore, the red-edge area is detected by the artificial sampling method, and the sampling ratio is 3-5% of the weight of each batch of leaves. Through statistically representative sampling, while ensuring the accuracy of quality monitoring, mechanical damage and process delays caused by full inspection are avoided.

[0019] Furthermore, the gradient pressure method described in step S4 is specifically as follows:

[0020] Initial stage: Apply a pressure of 5-8 kg / cm2 for rolling for 10-15 minutes, control the temperature ≤ 20°C. Light pressure rolling promotes the initial deformation of leaf cells, and the low-temperature environment inhibits the activity of pectinase, maintaining the elasticity of the leaves and the subsequent fermentation potential.

[0021] Strengthening stage: Increase the pressure to 12-15 kg / cm2 and roll for 20-25 minutes, maintain the temperature at 25 ± 2°C. The combined action of high pressure and high temperature accelerates the rupture of cell walls, promotes the extrusion of tea juice and its uniform attachment to the leaf surface, forming the material basis for the tea soup concentration.

[0022] Finishing stage: Reduce the pressure to 3-5 kg / cm2 and roll for 5-10 minutes. Low pressure is used to tidy up the tea strip shape, eliminate the lump phenomenon, and at the same time promote the redistribution of pectin substances, enhancing the tightness of the finished tea strips.

[0023] Furthermore, the segmented fermentation treatment described in step S5 includes:

[0024] Primary fermentation: The temperature is 15-20°C, the humidity is 70-80%, and it lasts for 2-3 hours. The low-temperature and high-humidity environment promotes the formation of precursors of theaflavins, and at the same time controls the conversion rate of thearubigins, laying the foundation for the golden and bright color of the tea soup.

[0025] Secondary fermentation: The temperature is 25-30°C, the humidity is 50-60%, the oxygen concentration is 18-20%, and it lasts for 4-5 hours. Increasing the temperature and reducing the humidity accelerates the dehydrogenation polymerization reaction, and a specific oxygen concentration promotes the formation of aldehyde and ketone aroma substances, realizing the gradient evolution of the taste from fresh and brisk to mellow.

[0026] Furthermore, during the fermentation process, an atomized liquid containing 0.02-0.05% of a complex enzyme preparation is sprayed every 30 minutes. The complex enzyme preparation is compounded by tea polyphenol oxidase and pectinase in a ratio of 1:0.3-0.5. The precise supplementation of exogenous enzymes enhances the activity of the endogenous enzyme system. Tea polyphenol oxidase dominates the directional conversion of catechins, and pectinase synergistically improves the smoothness of the tea soup. The enzyme ratio design ensures the synergistic effect of flavor substances and aroma substances.

[0027] Furthermore, the process parameters of low-temperature freezing in step S6 include:

[0028] The vacuum precooling technology is adopted to evacuate the air twice: the first evacuation is to -90 kPa and maintained for 5 minutes, and the second evacuation is to -95 kPa and maintained for 10 minutes. After the leaf temperature drops to -5 °C, it is transferred to a -20 °C cold storage. The stepped vacuum precooling quickly removes the air between the leaves, avoiding ice crystals from piercing the cell structure. The double evacuation ensures the uniformity of water sublimation and reduces freeze damage.

[0029] Further, before step S6 of sealed storage, the tea leaves are subjected to microwave inactivation treatment.

[0030] Compared with the prior art, a novel preparation process of low-temperature fresh-keeping cold-quenched tea provided by the present invention synergistically regulates the ice crystal morphology through staged freezing treatment, reduces cell structure damage, combines the dynamic withering and gradient rolling processes, precisely controls the release path of inclusions, effectively retains tea polyphenols, theaflavins and floral and fruity aroma components, and avoids the component loss caused by temperature fluctuations or single mechanical force in the traditional process;

[0031] Through vacuum precooling, an ultra-low oxygen storage environment is constructed, combined with microwave-targeted inactivation of enzyme activity, delaying the oxidation reaction from both physical blocking and biological inhibition paths, significantly prolonging the shelf life of tea leaves, and avoiding the use of chemical preservatives at the same time;

[0032] Through the gradient regulation of temperature, humidity and oxygen concentration for staged fermentation, the directional activation of polyphenol oxidase and pectinase is realized, and the efficient synthesis of theaflavins and aroma precursor substances is promoted, solving the problems of low efficiency and unstable quality in traditional natural fermentation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0034] Figure 1 It is a flow chart of a novel preparation process of low-temperature fresh-keeping cold-quenched tea provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will further introduce the present invention in detail with reference to the drawings.

[0036] Please refer to Figure 1 , a novel preparation process of low-temperature fresh-keeping cold-quenched tea, comprising the following steps:

[0037] S1. After the fresh leaves are picked, they are directly subjected to low-temperature freezing treatment. The freezing temperature is -25°C to -15°C, and the freezing time is 20 - 40 minutes. Preferably, the freezing temperature is -20°C, and the freezing time is preferably 30 minutes. Tiny ice crystals are formed through rapid freezing to reduce the rupture of cell membranes and retain active substances such as tea polyphenols and amino acids in the fresh leaves. Preferably, quick freezing at -20°C for 30 minutes can balance the freezing efficiency and energy consumption.

[0038] S2. The frozen fresh leaves are thawed and withered. The thawing temperature for thawing and withering is controlled at 0 - 15°C, and the withering humidity is 50 - 80%. Specifically, it includes:

[0039] The first stage: Thaw at 0 - 5°C for 2 - 4 hours, keeping dew on the leaf surface. Low-temperature thawing avoids cell swelling and rupture due to water absorption, and the dew maintains the leaf humidity and activates enzyme activity.

[0040] The second stage: Wither at 10 - 15°C for 6 - 8 hours. During this period, the leaf layer is turned over every 1 hour, and an air flow with an oxygen concentration of 25 - 28% is introduced. Medium-temperature withering combined with an oxygen-rich environment promotes the activity of polyphenol oxidase and improves the conversion efficiency of tea polyphenols.

[0041] S3. The thawed and withered tea leaves are subjected to a shaking green treatment. A dynamic shaking green treatment is adopted, specifically:

[0042] The shaking green is carried out in 3 - 5 times. The shaking green frequency is gradually increased from the initial 20 revolutions per minute to 30 revolutions per minute. After each shaking green, it is left to stand for 0.5 - 1 hour. After the end of each standing, a leaf sample is taken to observe the proportion of the red edge at the leaf margin. When the red edge area reaches 20 - 30%, the shaking green is terminated. The red edge area is detected by the artificial sampling method, and the sampling ratio is 3 - 5% of the weight of each batch of leaves. The leaf margin cells are gradually damaged during the multiple shaking greens, and the shaking green time for each time is 3 - 5 minutes.

[0043] S4. The shaken green leaves are rolled by the gradient pressure method. The gradient pressure method is specifically as follows:

[0044] The initial stage: Apply a pressure of 5 - 8 kg / cm2 for rolling for 10 - 15 minutes, control the temperature ≤ 20°C. Light pressure rolling protects the integrity of the leaves and initially releases the cell inclusions.

[0045] The strengthening stage: The pressure is increased to 12 - 15 kg / cm2 for rolling for 20 - 25 minutes, and the temperature is maintained at 25 ± 2°C. The cell breakage rate is increased, and high pressure accelerates the extrusion of tea juice.

[0046] The final stage: The pressure is reduced to 3 - 5 kg / cm2 for rolling for 5 - 10 minutes to shape the rolling and reduce the broken leaf rate.

[0047] S5. Under temperature and humidity control conditions, a segmented fermentation treatment is carried out. The segmented fermentation treatment includes:

[0048] Primary fermentation: temperature 15 - 20°C, humidity 70 - 80%, duration 2 - 3 hours, the conversion rate of tea polyphenols increases, and low temperature and high humidity activate enzyme activity;

[0049] Secondary fermentation: temperature 25 - 30°C, humidity 50 - 60%, oxygen concentration 18 - 20%, duration 4 - 5 hours, medium temperature and low oxygen inhibit peroxidation reaction;

[0050] Preferably, during the fermentation process, an atomized liquid containing 0.02 - 0.05% complex enzyme preparation is sprayed every 30 minutes. The complex enzyme preparation is compounded by tea polyphenol oxidase and pectinase in a ratio of 1:0.3 - 0.5. Pectinase synergistically degrades the cell wall, and polyphenol oxidase directionally catalyzes the formation of theaflavin;

[0051] S6. After fermentation is completed, the tea leaves are frozen at low temperature again and stored sealed in a cold storage at -18°C to -25°C. The process parameters of low temperature freezing include:

[0052] Vacuum precooling technology is used to evacuate the vacuum in two steps: the first evacuation to -90 kPa and hold for 5 minutes, the second evacuation to -95 kPa and hold for 10 minutes. After the leaf temperature drops to -5°C, it is transferred to a -20°C cold storage, and the vacuum is evacuated in stages to remove the oxygen inside the leaves;

[0053] Preferably, before the sealed storage in step S6, the tea leaves are subjected to microwave inactivation treatment (microwave power 300 - 500 W, treatment time 30 - 60 seconds, so that the residual activity of polyphenol oxidase ≤ 5%).

[0054] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is given.

[0055] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0056] In addition, the experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials and reagents used, unless otherwise specified, can all be obtained from commercial sources. The equipment used in the experiments, unless otherwise specified, are all well-known to those skilled in the art.

[0057] Example:

[0058] A new preparation process for low-temperature fresh-keeping cold-quenched tea, comprising the following steps:

[0059] S1 (Low-temperature freezing treatment): Pick the fresh leaves of one bud and one leaf of the tea tree, and immediately place them in a quick-freezing machine. Reduce the leaf temperature from 25°C to -20°C at a rate of 4°C per minute and keep it for 30 minutes.

[0060] S2 (Thawing and withering): First stage: Thaw at 0°C for 3 hours, keeping the leaf surface dew-covered; Second stage: Wither at 12°C for 7 hours, turning the leaf layer every hour and introducing an air current with an oxygen concentration of 26%, and controlling the humidity at 70%.

[0061] S3 (Dynamic shaking): Shake the leaves 4 times. The first time, the frequency is 20 revolutions per minute, and after shaking for 5 minutes each time, let it stand for 1 hour; For each subsequent shaking, increase the frequency by 5 revolutions per minute (25 → 30 revolutions per minute) until the red edge area reaches 25% (manually sample 5% of the leaves and measure the proportion of the red edge width).

[0062] S4 (Gradient pressure rolling): Initial stage: Roll at 6 kg / cm 2 for 12 minutes at a temperature of 18°C; Strengthening stage: Roll at 14 kg / cm 2 for 22 minutes at a temperature of 25°C; Final stage: Roll at 4 kg / cm 2 for 8 minutes with a cell breakage rate of 88%.

[0063] S5 (Staged fermentation): First-stage fermentation: At 18°C and a humidity of 75%, for 2.5 hours; Second-stage fermentation: At 28°C, a humidity of 55%, an oxygen concentration of 19%, spray an atomized liquid containing 0.03% composite enzyme (tea polyphenol oxidase: pectinase = 1:0.4), and keep it for 4.5 hours.

[0064] S6 (Secondary freezing preservation): Vacuum precooling: First, pump to -90 kPa and keep it for 5 minutes, then pump to -95 kPa and keep it for 10 minutes until the leaf temperature drops to -5°C; Transfer to a -20°C cold storage, seal with a five-layer aluminum foil composite film (oxygen transmission rate 0.05 cm 3 / m 2 ·24 h), and perform microwave inactivation treatment (microwave power 400 W, treatment time 45 seconds).

[0065] Control example (Traditional tea preservation process):

[0066] 1. Picking: After picking the fresh leaves, transport them at room temperature for 2 hours.

[0067] 2. Withering: Naturally spread out at 25°C for 18 hours with a humidity of 60%.

[0068] 3. Shaking: Shake the leaves once for 40 minutes (15 revolutions per minute).

[0069] 4. Rolling: Constant pressure of 10 kg / cm 2 Roll for 40 minutes.

[0070] 5. Fermentation: Stack naturally (temperature 28 - 32°C, humidity 70%) for 12 hours;

[0071] 6. Drying: Dry with hot air at 120°C for 1 hour;

[0072] 7. Storage: Store in a 4°C cold storage and package with PE bags.

[0073] The tea leaves prepared in the above examples and comparative examples were tested and scored. The specific methods are as follows:

[0074] 1. Sensory evaluation: Select 5 tea tasters to conduct blind evaluations on the tea leaves prepared in the examples and comparative examples. Blind evaluations were carried out on the soup color (bright red and bright, 25 - 30 points), aroma (floral and fruity aroma, 35 - 40 points), and taste (mellow, fresh and brisk, 25 - 30 points), and the average score was taken;

[0075] 2. Physicochemical detection: The tea leaves prepared in the examples and comparative examples were detected for the content of theaflavin / thearubigin, trans-β-ionone, moisture content, and polyphenol oxidase activity. Among them, theaflavin / thearubigin was detected by HPLC method (C18 column, gradient elution with acetonitrile - 0.1% phosphoric acid water, detection wavelength 278 nm), trans-β-ionone was detected by GC-MS method (DB-5MS column, electron impact ionization source, target ion m / z 177 for quantification), the moisture content was determined by the constant weight method at 105°C, and the polyphenol oxidase activity was detected by the guaiacol method (absorbance at 420 nm). The data were averaged by taking three parallel measurements;

[0076] The results obtained are shown in Table (1) below:

[0077]

[0078]

[0079] Table (1)

[0080] As can be seen from the above, through the synergistic effects of the double freezing process, dynamic shaking feedback control, and segmented fermentation, the theaflavin content, trans-β-ionone retention rate, and sensory score were significantly improved. The theaflavin content in the example was increased by 157% compared with Comparative Example 1, proving that dynamic shaking and enzyme activators significantly promoted oxidation; the ratio of thearubigin / theaflavin was optimized from 7.1 in the traditional process to 5.0, and the redness of the tea soup was improved; the trans-β-ionone content in the example was increased by 440% compared with Comparative Example 1, attributed to aroma enhancement at low temperature. The polyphenol oxidase activity in the example was reduced by 87% compared with the comparative example. Combining with the moisture content and low-oxygen environment, the shelf life was extended;

[0081] In summary, through the combination of staged freezing treatment and gradient pressure rolling process, the present invention effectively retains the core flavor substances such as tea polyphenols and amino acids in tea leaves, and promotes the directional synthesis of active ingredients such as theaflavins; the dynamic shaking green treatment precisely controls the area of the red edge on the leaf margin, balances the oxidation degree and leaf integrity, making the tea soup present a bright red color, the floral and fruity fragrance more plump, the taste mellow and fresh, and the sensory quality is comprehensively improved;

[0082] Through the double low-temperature freezing technology (quick-freezing of fresh leaves and freezing of final products) in coordination with the vacuum precooling process, an ultra-low oxygen storage environment is constructed, and combined with microwave targeted inactivation of enzyme activity, the oxidation reaction is blocked from both physical oxygen isolation and biological inhibition paths, significantly slowing down the formation of theabrownin and the dissipation of aroma substances. Compared with the traditional cold storage process, the shelf life of tea is extended to more than 18 months, and the color, aroma and taste characteristics close to those of new tea are still maintained after storage;

[0083] By combining the frequency gradient adjustment mechanism of dynamic shaking green and the temperature and humidity control of segmented fermentation, the conversion efficiency and stability of the inclusions during the processing are ensured. The gradient pressure rolling finely regulates the cell breakage rate through the mechanical action of "light - heavy - light", releasing sweet substances while avoiding excessive damage to the leaves. The entire set of process parameters is adapted to industrial equipment, significantly improving production efficiency and product consistency;

[0084] Through process optimization, the use of chemical preservatives is reduced, and the vacuum precooling and microwave inactivation technologies reduce energy consumption. The comprehensive production cost is reduced by about 20% compared with the traditional process. In addition, due to the significant extension of the shelf life, the transportation and storage losses are reduced, further improving economic benefits. This process is not only applicable to black tea, but also can be extended to categories such as green tea and oolong tea, helping the tea processing industry to achieve the transformation from "seasonal dependence" to "annual supply", and providing technical support for the standardized production and global circulation of high-quality tea.

[0085] Only some exemplary embodiments of the present invention have been described above by way of illustration. Undoubtedly, for those of ordinary skill in the art, without departing from the spirit and scope of the present invention, the described embodiments can be modified in various different ways. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A novel preparation process for low-temperature fresh-keeping cold-quenched tea, characterized in that, It includes the following steps: S1. After the fresh leaves are picked, they are directly subjected to cryogenic freezing treatment at a freezing temperature of -25°C to -15°C for 20 - 40 minutes; S2. Thaw and wither the frozen fresh leaves; S3. Perform the shaking green treatment on the thawed and withered tea leaves; S4. Knead the shaken green leaves by using the gradient pressure method; S5. Conduct segmented fermentation treatment under temperature and humidity control conditions; S6. After fermentation is completed, freeze the tea leaves again at a low temperature and store them sealed in a cold storage at -18°C to -25°C.

2. The novel preparation process of a low-temperature fresh-keeping cold-quenched tea according to claim 1, characterized in that, In step S1, the cryogenic freezing treatment temperature is -20°C and the freezing time is 30 minutes.

3. A novel preparation process for a low-temperature fresh-keeping cold-quenched tea according to claim 1, characterized in that, In step S2, the thawing temperature for thawing and withering is controlled at 0 - 15°C, and the withering humidity is 50 - 80%. Specifically, it includes: The first stage: Thaw at 0 - 5°C for 2 - 4 hours, keeping dew on the leaf surface; The second stage: Wither at 10 - 15°C for 6 - 8 hours. During this period, turn the leaf layer every 1 hour and introduce an air flow with an oxygen concentration of 25 - 28%.

4. A novel preparation process for low-temperature fresh-keeping cold-quenched tea according to claim 1, characterized in that, In step S3, the shaking green treatment adopts dynamic shaking green treatment. Specifically: Perform shaking green in 3 - 5 times, with each shaking green time being 3 - 5 minutes. The shaking green frequency gradually increases from the initial 20 revolutions per minute to 30 revolutions per minute. After each shaking green, let it stand for 0.5 - 1 hour. After the end of each standing, extract leaf samples to observe the proportion of red edges at the leaf margin. When the red edge area reaches 20 - 30%, terminate the shaking green.

5. The novel preparation process of a low-temperature fresh-keeping cold-quenched tea according to claim 4, characterized in that, The detection of the red edge area adopts the artificial sampling method, and the sampling ratio is 3 - 5% of the weight of each batch of leaves.

6. A novel preparation process for low-temperature fresh-keeping cold-quenched tea according to claim 1, characterized in that, In step S4, the specific gradient pressure method is: Initial stage: Apply a pressure of 5 - 8 kg / cm 2 and knead for 10 - 15 minutes, controlling the temperature ≤ 20°C; Strengthening stage: The pressure is increased to 12 - 15 kg / cm 2 Roll for 20 - 25 minutes, maintaining the temperature at 25 ± 2 °C; Final stage: The pressure is reduced to 3 - 5 kg / cm 2 Roll for 5 - 10 minutes.

7. A novel preparation process of a low-temperature fresh-keeping cold-quenched tea according to claim 1, characterized in that, In step S5, the segmented fermentation treatment includes: Primary fermentation: Temperature 15 - 20°C, humidity 70 - 80%, lasting for 2 - 3 hours; Secondary fermentation: Temperature 25 - 30°C, humidity 50 - 60%, oxygen concentration 18 - 20%, lasting for 4 - 5 hours.

8. A novel preparation process of a low-temperature fresh-keeping cold-quenched tea according to claim 7, characterized in that, During the fermentation process, spray an atomized liquid containing 0.02 - 0.05% complex enzyme preparation every 30 minutes. The complex enzyme preparation is compounded by tea polyphenol oxidase and pectinase in a ratio of 1:0.3 - 0.

5.

9. A novel preparation process for low-temperature fresh-keeping cold-quenched tea according to claim 1, characterized in that, In step S6, the process parameters of cryogenic freezing include: Adopt vacuum precooling technology to evacuate the vacuum in two times: The first time is pumped to -90 kPa and maintained for 5 minutes, and the second time is pumped to -95 kPa and maintained for 10 minutes. After the leaf temperature drops to -5°C, transfer it to a -20°C cold storage.

10. A novel preparation process of a low-temperature fresh-keeping cold-quenched tea according to claim 1, characterized in that, Before the sealed storage in step S6, perform microwave inactivation treatment on the tea leaves.

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