A low-temperature segmented fixation processing technology and device for improving tea aroma

Abstract

The application discloses a low-temperature segmented fixation processing technology for improving tea aroma, and belongs to the technical field of low-temperature segmented fixation of tea leaves, and comprises the following steps: S1, fresh tea leaves picked are subjected to fixation treatment to make the tea leaves lose water uniformly; S2, the tea leaves after the fixation treatment are placed in a fixation equipment, and two-stage or three-stage temperature gradient is adopted for fixation treatment, wherein the fixation temperature of the last stage is controlled to be 80-120 DEG C. In the application, the low-temperature segmented fixation technology with two-stage or three-stage temperature gradient is adopted, the fixation temperature of the last stage is controlled to be 80-120 DEG C, and the total fixation time is controlled to be 5-20 minutes, so that the residual enzyme activity of polyphenol oxidase and peroxidase in the tea leaves is all reduced to less than 5%, the problem that enzyme activity is not passivated completely under the single low-temperature fixation mode is effectively solved, the quality deterioration phenomena such as red discoloration, dark soup color and aroma deterioration caused by enzyme catalytic oxidation in the subsequent processing or storage process of the tea leaves are avoided, and the long-term stability of the tea quality is ensured.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature segmented fixation technology for tea, specifically a low-temperature segmented fixation process and apparatus for enhancing the aroma of tea. Background Technology

[0002] Fixing is a crucial step in the processing of non-fermented or slightly fermented teas such as green tea and yellow tea. Its core purpose is to rapidly deactivate the activity of endogenous enzymes such as polyphenol oxidase (PPO) and peroxidase (POD) in tea leaves through high temperature, thereby terminating the enzymatic oxidation reaction, fixing the green color of the tea leaves, and preventing quality deterioration such as reddening, darkening of the tea liquor, and deterioration of aroma during subsequent processing and storage. Traditional fixing methods mostly use single-stage high-temperature rapid fixing (usually above 200℃). Although it can deactivate enzyme activity in a short time, high-temperature treatment can easily cause hardening of the tea leaf surface and damage to the cell structure. It also greatly damages the excellent and delicate aroma and flavor substances in tender tea leaves. In recent years, low-temperature fixing technology has attracted attention because it can better preserve the natural aroma and internal substances of tea leaves.

[0003] However, simply using low-temperature fixation often results in incomplete enzyme inactivation, leading to high residual activity of polyphenol oxidase and peroxidase in the tea leaves. This can cause unexpected enzymatic oxidation reactions during subsequent rolling, drying, and storage, severely impacting the long-term stability of tea quality. Furthermore, while traditional low-temperature slow drying (approximately 80℃ for over 60 minutes) helps maintain the tea's shape, prolonged low-temperature treatment causes a significant loss of volatile aroma components unique to tender tea leaves, such as their delicate fragrance and downy aroma. This results in a finished tea with a bland aroma and insufficient freshness, failing to meet the processing requirements of high-quality tea. Therefore, how to ensure sufficient enzyme inactivation while maximizing the preservation of the tea's excellent aroma quality has become a critical issue that urgently needs to be addressed in the field of tea processing technology. Summary of the Invention

[0004] The purpose of this invention is to provide a low-temperature segmented fixation process and apparatus for enhancing the aroma of tea, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature segmented fixation process for enhancing the aroma of tea, comprising the following steps:

[0006] S1: Spread the freshly picked tea leaves out to allow them to lose moisture evenly;

[0007] S2: Place the withered tea leaves in the fixation equipment and use a two-stage or three-stage temperature gradient for fixation treatment. The temperature of the final fixation stage is controlled at 80-120℃, and the total fixation time is controlled at 5-20 minutes, so that the residual enzyme activity of polyphenol oxidase and peroxidase in the tea leaves is reduced to below 5%.

[0008] S3: Quickly spread the tea leaves after fixing to cool to room temperature;

[0009] S4: Knead and shape the cooled tea leaves;

[0010] S5: Place the kneaded tea leaves in a drying device and dry them rapidly at 120-130℃ for 8-15 minutes, until the moisture content of the tea leaves drops to 5-8%.

[0011] S6: The dried tea leaves are then treated to enhance their aroma, resulting in the finished tea product.

[0012] As a further preferred embodiment of this technical solution: S2: The two-stage temperature gradient blanching method described herein is:

[0013] The first stage of blanching should be carried out at a temperature of 140–180℃ for 2–8 minutes.

[0014] The second stage of blanching involves a temperature of 80–120℃ and a blanching time of 3–12 minutes.

[0015] As a further preferred embodiment of this technical solution: S2: The three-stage temperature gradient blanching is as follows: the blanching temperature of the first stage is 160-200℃, and the blanching time is 1-5 minutes;

[0016] The second stage of blanching involves a temperature of 120–160℃ and a blanching time of 2–6 minutes.

[0017] The third stage of blanching involves a temperature of 80–110℃ and a blanching time of 3–8 minutes.

[0018] As a further preferred embodiment of this technical solution: S2: The blanching equipment mentioned is any one or more combinations of a drum blanching machine, a hot air blanching machine, or a microwave blanching machine;

[0019] As a further preferred embodiment of this technical solution: S2: During the fixation process, a transition time of 30 seconds to 2 minutes is set between each stage to allow the tea temperature to drop gradually and avoid damage to the tea cell structure caused by sudden temperature changes.

[0020] As a further preferred embodiment of this technical solution: S1: The conditions for the withering process are: withering temperature 18-25℃, withering humidity 55-75%, withering time 4-12 hours, withering thickness 3-8 cm, until the tea leaves lose 15-25% of their weight.

[0021] As a further preferred embodiment of this technical solution: S3: The cooling process described herein adopts either air cooling or natural cooling, cooling the tea leaves to a temperature ≤30℃, and controlling the cooling time to 10-30 minutes;

[0022] As a further preferred embodiment of this technical solution: S4: The kneading and shaping process adopts a light kneading method, with the kneading pressure controlled at 0.1-0.3 MPa, the kneading time at 10-30 minutes, and the kneading is carried out until the tea cell damage rate is 40-60%;

[0023] As a further preferred embodiment of this technical solution: S6: The temperature for the aroma enhancement process is 80-120℃, and the aroma enhancement time is 5-15 minutes;

[0024] As a further preferred embodiment of this technical solution: the fresh tea leaves are tender tea leaves with one bud and one leaf, one bud and two leaves, or one bud and three leaves, and the finished tea is green tea or yellow tea.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. In this invention, by adopting a two-stage or three-stage temperature gradient low-temperature segmented fixation process, the final fixation temperature is controlled at 80-120℃, and the total fixation time is controlled at 5-20 minutes, so that the residual enzyme activities of polyphenol oxidase and peroxidase in tea leaves are reduced to below 5%, which effectively solves the problem of incomplete enzyme inactivation under a single low-temperature fixation method, and avoids the deterioration of tea quality such as reddening, dark liquor color, and aroma deterioration caused by enzymatic oxidation during subsequent processing or storage, thus ensuring the long-term stability of tea quality.

[0027] Meanwhile, a transition time of 30 seconds to 2 minutes is set between each section to allow the tea temperature to drop gradually, avoiding damage to the tea cell structure caused by sudden temperature changes, and protecting the cell integrity and basic quality of the tea's internal substances to the greatest extent.

[0028] 2. In this invention, a high-temperature rapid drying method (120-130℃, 8-15 minutes) is used after fixation. Compared with the traditional low-temperature slow drying (around 80℃, more than 60 minutes), the drying time is significantly shortened. This effectively avoids the loss of excellent and delicate aroma and flavor substances in tender tea leaves during long-term low-temperature drying. It fully preserves the characteristic aroma of tender tea leaves, such as tender aroma and downy aroma. Combined with cooling, light rolling and aroma-enhancing treatments after fixation, the finished tea leaves have a bright green color, a bright liquor color, a clear and lasting aroma, and a fresh and mellow taste.

[0029] 3. In this invention, the synergistic effect of low-temperature segmented fixation and high-temperature rapid drying ensures the full deactivation of enzyme activity while maximizing the preservation of the excellent aroma and quality of tender tea leaves, significantly improving the overall sensory quality of the finished tea. It is applicable to the processing and production of various tea types such as green tea and yellow tea, and has broad prospects for industrial application and significant economic benefits. Attached Figure Description

[0030] Figure 1 This is a flowchart of a low-temperature segmented fixation process and apparatus for enhancing the aroma of tea, according to the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] Please see Figure 1 As shown, the present invention provides a technical solution: a low-temperature segmented fixation process for enhancing the aroma of tea, comprising the following steps:

[0034] S1 (Withering): Fresh yellow tea leaves with one bud and one leaf are picked as raw materials. The fresh leaves are evenly spread on the withering rack with a thickness of 5cm. Withering is carried out for 8 hours under the conditions of withering temperature of 22℃ and relative humidity of 70% until the weight loss rate of fresh leaves reaches 17%.

[0035] S2 (Low-temperature segmented fixation): The spread tea leaves are placed in a drum fixation machine and fixation is carried out using a two-stage temperature gradient. The first stage fixation temperature is 160℃ and the fixation time is 5 minutes.

[0036] The second stage of fixation is at a temperature of 100℃ and a time of 8 minutes. A 1-minute transition time is set between the two stages to allow the tea temperature to drop gradually. The total fixation time is 13 minutes.

[0037] Tests showed that after fixation, the residual enzyme activity of polyphenol oxidase in tea leaves decreased to 3.5%, and the residual enzyme activity of peroxidase decreased to 4.2%, both below 5%.

[0038] S3 (Cooling): Quickly place the tea leaves after fixation into an air-cooling device to cool until the tea temperature is ≤30℃, and the cooling time is 15 minutes;

[0039] S4 (Kneading and Shaping): The cooled tea leaves are placed in a kneading machine for light kneading. The kneading pressure is controlled at 0.2 MPa, and the kneading time is 20 minutes, until the tea cell damage rate reaches 50%.

[0040] S5 (High-Temperature Rapid Drying): Place the kneaded tea leaves in a hot air dryer and dry them rapidly at 124℃ for 12 minutes, until the moisture content of the tea leaves drops to 6%;

[0041] S6 (Aroma Enhancement Processing): Place the dried tea leaves in an aroma enhancement machine and enhance their aroma at 100℃ for 10 minutes to obtain the finished green tea.

[0042] Tests showed that the finished green tea obtained in this embodiment has a tightly rolled and emerald green appearance, a bright and tender green liquor, a clear and lasting aroma with typical tender chestnut and downy fragrance, and a fresh, mellow, and refreshing taste.

[0043] Example 2

[0044] This embodiment provides a low-temperature segmented fixation process to enhance the aroma of tea, specifically including the following steps:

[0045] S1 (Withering): Using fresh leaves from Longjing 43 tea trees with one bud and two leaves as raw material, the fresh leaves are evenly spread on the withering rack with a thickness of 4 cm. Withering is carried out for 10 hours under the conditions of withering temperature of 20℃ and relative humidity of 68%, until the weight loss rate of the fresh leaves reaches 22%.

[0046] S2 (Low-Temperature Segmented Fixation): The withered tea leaves are placed in a hot air fixation machine, and fixation is performed using a three-stage temperature gradient:

[0047] The first stage of blanching is at a temperature of 180℃ and a blanching time of 3 minutes;

[0048] The second stage of blanching is carried out at a temperature of 140℃ for 4 minutes.

[0049] The third stage of fixation was carried out at a temperature of 95℃ for 6 minutes, with a 1.5-minute transition time between each stage. The total fixation time was 13 minutes. After testing, the residual enzyme activity of polyphenol oxidase in the tea leaves decreased to 2.8%, and the residual enzyme activity of peroxidase decreased to 3.5%, both below 5%.

[0050] S3 (Cooling): After the tea leaves have been processed, spread them out to cool naturally until the tea temperature is ≤30℃. The cooling time is 20 minutes.

[0051] S4 (Kneading and Shaping): The cooled tea leaves are placed in a kneading machine for light kneading. The kneading pressure is controlled at 0.15 MPa, and the kneading time is 25 minutes, until the tea cell damage rate reaches 55%.

[0052] S5 (High-Temperature Rapid Drying): Place the kneaded tea leaves in a drum dryer and dry them rapidly at 126℃ for 10 minutes, until the moisture content of the tea leaves drops to 5.5%.

[0053] S6 (Aroma Enhancement Process): Place the dried tea leaves in an aroma enhancement machine and enhance their aroma at 110℃ for 8 minutes to obtain the finished green tea.

[0054] The finished green tea obtained in this embodiment has a flat and smooth appearance, a clear and bright liquor, a rich and lasting aroma, a prominent chestnut fragrance, and a sweet and mellow taste.

[0055] Example 3

[0056] This embodiment provides a low-temperature segmented fixation process to enhance the aroma of tea, specifically including the following steps:

[0057] S1 (Withering): Fresh leaves of Huangshan group variety tea trees with one bud and three leaves are picked as raw materials. The fresh leaves are evenly spread on the withering rack with a withering thickness of 6cm. Withering is carried out for 6 hours under the conditions of withering temperature of 24℃ and relative humidity of 67% until the weight loss rate of fresh leaves reaches 25%.

[0058] S2 (Low-Temperature Segmented Fixation): The withered tea leaves are placed in a microwave fixation machine, and fixation is performed using a two-stage temperature gradient:

[0059] The first stage of blanching is at a temperature of 170℃ and a blanching time of 4 minutes;

[0060] The second stage of fixation was carried out at a temperature of 110℃ for 6 minutes, with a 1-minute transition time between the two stages. The total fixation time was 10 minutes. After testing, the residual enzyme activity of polyphenol oxidase in the tea leaves decreased to 4.0% and the residual enzyme activity of peroxidase decreased to 4.5%, both below 5%.

[0061] S3 (Cooling): Quickly place the tea leaves after fixation into an air-cooling device to cool until the tea temperature is ≤30℃, and the cooling time is 12 minutes;

[0062] S4 (Kneading and Shaping): The cooled tea leaves are placed in a kneading machine for light kneading. The kneading pressure is controlled at 0.25 MPa, and the kneading time is 15 minutes, until the tea cell damage rate reaches 45%.

[0063] S5 (High Temperature Rapid Drying): Place the kneaded tea leaves in a hot air dryer and dry them rapidly at 120℃ for 14 minutes, until the moisture content of the tea leaves drops to 7%.

[0064] S6 (Aroma Enhancement Process): Place the dried tea leaves in an aroma enhancement machine and enhance their aroma at 95℃ for 12 minutes to obtain the finished green tea.

[0065] The finished green tea obtained in this embodiment has a tightly rolled appearance, a bright green color, a bright liquor, a fresh and lasting aroma, and a mellow and refreshing taste.

[0066] Comparative Example 1

[0067] This comparative example uses traditional green tea processing techniques. The difference between this example and Example 1 is that the fixation process uses the traditional single-stage high-temperature fixation method (fixation temperature 220℃, fixation time 10 minutes).

[0068] The drying process uses a traditional low-temperature slow drying method (drying temperature 80℃, drying time 60 minutes), and the remaining steps are the same as in Example 1.

[0069] Tests showed that the residual polyphenol oxidase activity of the tea leaves after fixation in Comparative Example 1 was 12.6%, and the residual peroxidase activity was 15.3%, which were far higher than the threshold of 5%. The resulting finished tea leaves showed varying degrees of reddening during subsequent storage, with a dark yellow liquor, a weak aroma, and a significant loss of the tender and downy aroma characteristic of young tea leaves. The quality was significantly inferior to that of Example 1.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 2 is that the fixation method used is a low-temperature single-stage fixation method (fixation temperature 100℃, fixation time 13 minutes); the remaining steps are the same as in Example 2.

[0072] Tests showed that the residual polyphenol oxidase activity and the residual peroxidase activity of the tea leaves after fixation in Comparative Example 2 were 8.7% and 9.2%, respectively, both exceeding the threshold of 5%.

[0073] The finished tea leaves exhibited obvious red stems and leaves during subsequent processing and storage, the tea liquor turned reddish, and the aroma had a musty or stale taste, resulting in a significant decline in quality.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 3 is that the drying method used is the traditional low-temperature slow drying method (drying temperature 80°C, drying time 60 minutes); the remaining steps are the same as in Example 3.

[0076] According to the test results, although the enzyme activity of the finished tea obtained in Comparative Example 3 was fully deactivated, due to the low temperature and long drying time, a large amount of the excellent and delicate aroma and downy aroma substances in the tender tea leaves were lost. The finished tea had a bland aroma, lacked freshness, and tasted less fresh and refreshing. The overall quality was significantly lower than that of Example 3.

[0077] Comparative Example 4

[0078] The difference between this comparative example and Example 1 is that: the fixation method is the traditional single-stage high-temperature fixation method (fixation temperature 220℃, fixation time 10 minutes), and the drying method is the high-temperature rapid drying method (drying temperature 125℃, drying time 12 minutes). The remaining steps are the same as in Example 1.

[0079] Tests showed that the residual polyphenol oxidase activity of the tea leaves after fixation in Comparative Example 4 was 11.8%, and the residual peroxidase activity was 14.6%, both far exceeding the 5% threshold. Although high-temperature rapid drying preserved some aroma to a certain extent, the enzyme activity was not completely deactivated during the fixation stage, and the finished tea still underwent unexpected enzymatic oxidation during storage, resulting in a gradual reddening of the tea liquor, deterioration of aroma, and poor quality stability.

[0080] Effect verification

[0081] The finished tea products obtained in Examples 1 to 3 were compared and evaluated with those obtained in Comparative Examples 1 to 4. The results are shown in the table below:

[0082]

[0083] The above results show that the low-temperature segmented fixation process of the present invention, through the reasonable design of a two-stage or three-stage temperature gradient, can fully inactivate the activity of polyphenol oxidase and peroxidase under low-temperature conditions (the residual enzyme activity is less than 5%), effectively solving the problem of incomplete enzyme inactivation at low temperature leading to subsequent reddening. At the same time, the present invention adopts a high-temperature rapid drying method (120-130℃, 10-14 minutes) in the drying stage, avoiding the loss of the excellent and delicate aroma and flavor of tender tea leaves caused by traditional low-temperature slow drying. The finished tea products obtained in Examples 1 to 3 are of excellent quality, with a clear and lasting aroma and bright liquor color, showing significant advantages compared with the comparative examples.

[0084] In summary, the present invention provides a low-temperature segmented fixation process for enhancing the aroma of tea leaves. Through the synergistic effect of low-temperature segmented fixation and high-temperature rapid drying, it ensures the full deactivation of enzyme activity while maximizing the preservation of the excellent aroma quality of tender tea leaves, and has significant industrial application value.

[0085] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-temperature segmented fixation process for enhancing the aroma of tea, characterized in that, Includes the following steps: S1: Spread the freshly picked tea leaves out to allow them to lose moisture evenly; S2: Place the withered tea leaves in the fixation equipment and use a two-stage or three-stage temperature gradient for fixation treatment. The temperature of the final fixation stage is controlled at 80-120℃, and the total fixation time is controlled at 5-20 minutes, so that the residual enzyme activity of polyphenol oxidase and peroxidase in the tea leaves is reduced to below 5%. S3: Quickly spread the tea leaves after fixing to cool to room temperature; S4: Knead and shape the cooled tea leaves; S5: Place the kneaded tea leaves in a drying device and dry them rapidly at 120-130℃ for 8-15 minutes, until the moisture content of the tea leaves drops to 5-8%. S6: The dried tea leaves are then treated to enhance their aroma, resulting in the finished tea product.

2. The method according to claim 1, characterized in that: S2: the two-stage temperature gradient blanching is as follows: The first stage of blanching should be carried out at a temperature of 140–180℃ for 2–8 minutes. The second stage of blanching involves a temperature of 80–120℃ and a blanching time of 3–12 minutes.

3. The method according to claim 1, characterized in that: S2: the three-stage temperature gradient blanching is: the blanching temperature of the first stage is 160-200℃, and the blanching time is 1-5 minutes; The second stage of blanching involves a temperature of 120–160℃ and a blanching time of 2–6 minutes. The third stage of blanching involves a temperature of 80–110℃ and a blanching time of 3–8 minutes.

4. The method according to claim 1, wherein the blanching equipment in step S2 is any one or more combinations of a drum blanching machine, a hot air blanching machine, or a microwave blanching machine.

5. The method according to claim 1, characterized in that: in the fixing process described in S2, a transition time of 30 seconds to 2 minutes is set between each stage to allow the tea temperature to drop gradually and avoid damage to the tea cell structure caused by sudden temperature changes.

6. The method according to claim 1, characterized in that: the conditions for the withering process in S1 are: withering temperature 18-25℃, withering humidity 55-75%, withering time 4-12 hours, withering thickness 3-8 cm, until the weight loss rate of the tea leaves reaches 15-25%.

7. The method according to claim 1, characterized in that: in step S3: the cooling is carried out by air cooling or natural cooling, and the tea temperature is cooled to ≤30℃, and the cooling time is controlled within 10 to 30 minutes.

8. The method according to claim 1, characterized in that: in S4: the kneading and shaping is carried out by light kneading, the kneading pressure is controlled at 0.1-0.3 MPa, the kneading time is 10-30 minutes, and the tea cell damage rate is 40-60%.

9. The method according to claim 1, wherein the aroma-enhancing treatment in step S6 is performed at a temperature of 80–120°C for 5–15 minutes.

10. The method according to claim 1, characterized in that: The fresh tea leaves are tender tea leaves with one bud and one leaf, one bud and two leaves, or one bud and three leaves, while the finished tea is green tea or yellow tea.

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