Processing method of three-leaf green tea with high freshness and low bitterness

Abstract

The present application relates to the technical field of food processing, and discloses a processing method of three-leaf green tea with high freshness and low bitterness, which comprises the following steps: placing three-leaf green tea fresh leaves for controlled wilting until the moisture content is 60%-65% to obtain wilted leaves; performing first rolling, second rolling, third rolling and fourth rolling on the wilted leaves to obtain rolled leaves; performing temperature-variable fermentation on the rolled leaves in the order of high temperature first and then low temperature; and baking the fermented leaves at low temperature until the moisture content is 4%-7% to obtain the three-leaf green tea. Through the synergistic effect of controlled wilting, segmented variable-speed and variable-pressure rolling, temperature-variable fermentation and low-temperature baking, the content of flavonoid bitter substances is significantly reduced while the freshness substances such as free amino acids are fully retained, and the obtained three-leaf green tea has low bitterness, high freshness, sweet and mellow taste and unique medicinal aroma.

Description

Technical Field

[0001] This invention relates to the field of beverage production technology, and in particular to a processing method for San Ye Qing tea with high freshness and low bitterness. Background Technology

[0002] *Tetrastigma hemsleyanum* Diels et Gilg, also known as Golden Thread Hanging Gourd, Snake Aconite, and Stone Mouse, is a herbaceous vine belonging to the Vitaceae family of the Rhamnales order. The entire plant can be used medicinally, with the underground tubers and fruits yielding the best medicinal effects. Currently, *Tetrastigma hemsleyanum* typically requires more than four years to harvest, and the development of *Tetrastigma hemsleyanum* products mainly focuses on the underground medicinal tubers. During this four-year cultivation and management period, growers rarely reap profits, and a large amount of the above-ground leaves are discarded during harvesting. Research shows that the medicinal components of the above-ground parts of *Tetrastigma hemsleyanum* are similar to those of the underground parts, possessing similar medicinal efficacy. It contains abundant flavonoids, polysaccharides, and kaempferol, accounting for approximately 70% of the content found in the underground medicinal parts. However, almost 100% of the above-ground parts of *Tetrastigma hemsleyanum* are discarded in planting areas or on mountainsides, remaining unutilized and resulting in a significant waste of resources. Toxicological studies have shown that the entire *Trifolium repens* plant is non-toxic and possesses significant medicinal value, exhibiting effects in anti-tumor activity, immune system enhancement, and anti-infection. Existing related health products have received positive market feedback, and there is no long-term cumulative poisoning or genotoxicity. Its applications are wide-ranging, and its market value is immeasurable. Therefore, deep processing and refining of *Trifolium repens* leaves, turning waste into treasure and developing *Trifolium repens* leaf resources, can not only increase farmers' income but also meet the health needs of a broad consumer base.

[0003] Traditionally, dried leaves of *Trifolium repens* (also known as Chinese privet) are used to make tea. However, modern research shows that the flavonoids, terpenoids, and sterols in *Trifolium repens* leaves are heat-sensitive and their structure becomes unstable under high temperatures and sunlight, thus destroying their medicinal properties. The traditional processing method for *Trifolium repens* tea is pan-frying and drying. During this process, many active medicinal components are destroyed due to high temperatures and oxidation, significantly reducing the tea's medicinal efficacy. Furthermore, simply pan-frying and drying *Trifolium repens* has a bitter taste, severely impacting the consumer experience.

[0004] Therefore, there is an urgent need to find a processing method that can overcome the limitations of bitterness, raw green odor, and loss of active ingredients in *Trifolium repens*, while maintaining its medicinal properties and producing a health-promoting tea substitute with good taste and appearance. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a processing method for San Ye Qing tea with high freshness and low bitterness, so as to solve the problems of large loss of active ingredients, raw taste, and bitterness in the processing of San Ye Qing tea in the prior art.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] In a first aspect, the present invention provides a method for processing three-leaf green tea with high freshness and low bitterness, comprising the following steps:

[0008] S1. Controlled wilting: Spread out fresh leaves of *Trifolium repens* for controlled wilting until the moisture content is 60%-65%, and obtain wilted leaves.

[0009] S2. Segmented variable speed and pressure kneading: The withered leaves are kneaded in the first, second, third and fourth kneading processes to obtain kneaded leaves;

[0010] S3. Variable temperature fermentation: The kneaded leaves are subjected to variable temperature fermentation, first at high temperature and then at low temperature, to obtain fermented leaves;

[0011] S4. Low-temperature baking: The fermented leaves are baked at a low temperature until the moisture content is 4%-7% to obtain Sanye green tea.

[0012] Preferably, in step S1, the controlled withering environment temperature is 18-26℃, the relative humidity is 60%-80%, the withering time is 2-4 hours, and the leaf thickness is 3-8 cm.

[0013] Preferably, in step S2, the rotation speed of the first kneading is 40 rpm, the rotation speed of the second kneading is 45 rpm, the rotation speed of the third kneading is 50 rpm, and the rotation speed of the fourth kneading is 40 rpm. After kneading, the cell damage rate is 30%-50% and the strip formation rate is above 60%.

[0014] The drive motor of the kneading machine is controlled by a frequency converter. By adjusting the output frequency of the frequency converter, the kneading machine can run at 40 rpm, 45 rpm, 50 rpm and 40 rpm respectively in each kneading stage.

[0015] Preferably, the first kneading time is 6-10 minutes, the second kneading time is 6-8 minutes, the third kneading time is 4-6 minutes, the fourth kneading time is 4-6 minutes, and the total kneading time is 20-30 minutes; the first kneading pressure is light pressure, the second kneading pressure is medium pressure, the third kneading pressure is heavy pressure, and the fourth kneading pressure is light pressure.

[0016] The terms "light pressure," "medium pressure," and "heavy pressure" used in this application refer to relative pressure levels in the tea rolling process, categorized according to the operating state of the rolling machine's pressurizing device. They are not fixed absolute pressure values ​​independent of the equipment and the amount of tea leaves added. When using the same model of rolling machine and maintaining a consistent amount of tea leaves and loading level, the pressure levels of light, medium, and heavy pressure increase sequentially. Light pressure is used to initially curl the buds and leaves or to shape them into strips in the later stages of rolling; medium pressure is used to moderately damage the cell tissue of the buds and leaves and to allow a small amount of tea juice to leak out; heavy pressure is used to further curl the leaves into strips and increase the degree of cell tissue damage. The pressure at each stage is controlled by the corresponding light, medium, and heavy pressure operating states of the rolling machine's pressurizing handwheel, pressurizing cover, counterweight mechanism, or pneumatic pressurizing device.

[0017] Preferably, in step S3, the variable temperature fermentation is performed by first fermenting at 40-45℃ and relative humidity above 90% for 1-2 hours, and then fermenting at 30-35℃ and relative humidity above 90% for 2-3 hours.

[0018] Preferably, in step S4, the low-temperature baking temperature is 60-80℃ and the baking time is 1.5-3 hours.

[0019] Preferably, before step S1, a harvesting step is included: selecting tender leaves of 1-3 year old Trifolium repens harvested from April to June each year as the fresh leaves of Trifolium repens.

[0020] Preferably, after the picking step and before S1, a cleaning and impurity removal step is also included: removing rotten, deteriorated, insect-infested, and fungal-spotted leaves, removing dust, mud, insect eggs and impurities, and spreading them out until there are no obvious water droplets on the surface of the buds and leaves.

[0021] Preferably, step S4 is followed by a screening step: cooling the low-temperature roasted San Ye Qing tea to room temperature, sifting out broken pieces, leaf stems and impurities, and packaging.

[0022] Secondly, the present invention provides a three-leaf green tea with high freshness and low bitterness, which is prepared by the processing method of the three-leaf green tea.

[0023] The beneficial effects of this invention are:

[0024] (1) The present invention significantly reduces the content of bitter flavonoids in San Ye Qing tea (10.69 mg / g, P<0.05) by the synergistic effect of controlled withering, variable temperature fermentation and low temperature baking: compared with fresh leaves (31.64 mg / g), it is reduced by 66.2%.

[0025] (2) The process of the present invention has a good retention effect on free amino acids. The content of free amino acids in the three-leaf green tea (47.49mg / g) is not significantly different from that in fresh leaves (48.81mg / g) (P>0.05).

[0026] (3) Sensory evaluation of each tea sample. The three-leaf green tea obtained by this invention has a bright yellow color, a sweet and mellow taste, and a unique medicinal aroma. The total sensory evaluation score is higher than that of conventional drying process.

[0027] (4) This invention uses the large amount of discarded leaves of the ground of *Trifolium repens* as raw material, turning waste into treasure. The product is caffeine-free and contains rich *Trifolium repens* flavonoids, polysaccharides, kaempferol and other ingredients. It has health benefits such as anti-tumor and immune enhancement, and has no toxic side effects. It is suitable for all ages and can be consumed after soaking. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] This invention focuses on reducing the bitterness and astringency of San Ye Qing Cha (a type of green tea) while maintaining a fresh, mellow, and smooth flavor. It sequentially implements controlled withering, segmented rolling with varying speed and pressure, variable-temperature fermentation (high temperature followed by low temperature), and low-temperature baking, ensuring that the state of the buds and leaves formed in the previous process is consistent with the processing conditions in the next. The following process relationships illustrate the coordination of each step.

[0030] Example 1

[0031] This embodiment provides a processing method for three-leaf green tea, the specific steps of which are as follows:

[0032] I. Raw Material Selection and Pretreatment

[0033] 1. Harvesting: Select fresh, disease-free, and tender green shoots and leaves of *Trifolium repens* harvested from April to June each year. Tender shoots and leaves with individual leaves measuring 2-4 cm in length, or tender vines with 1-3 unfolded leaves, are preferred. Processing should be done promptly after harvesting. If immediate processing is not possible, spread the raw materials evenly in a cool, well-ventilated indoor environment where the temperature is below 25℃, ensuring the thickness does not exceed 6 cm to prevent overheating and spoilage.

[0034] 2. Cleaning and impurity removal: Use the sorting method to remove impurities from the collected leaves of *Trifolium repens*, removing rotten, deteriorated, insect-infested, and fungal-spotted leaves, as well as dust, mud, insect eggs, and other impurities attached to the leaves and vines. Spread them out in a ventilated place until there are no obvious water droplets on the surface of the buds and leaves before proceeding to the next step.

[0035] II. Controlled Wilting

[0036] After cleaning, spread the three-leaf greens evenly on bamboo sieves, bamboo mats, or withering troughs, controlling the thickness of the leaves to be 3-8 cm. The withering environment should be cool, well-ventilated, and free from direct sunlight, with an ambient temperature of 18-26℃ and a relative humidity of 60%-80%, for 2-4 hours. During the withering process, gently turn the leaves 1-2 times to ensure even distribution and prevent localized heating and spoilage. Wither until the surface moisture of the leaves has fully evaporated, the leaves soften, the grassy smell gradually dissipates and a faint fragrance is emitted, the leaves turn dark green, and the moisture content drops to 60%-65%, at which point the withered leaves are obtained.

[0037] The withering step is limited by the processing time and the state of the buds and leaves, with a processing time range of 2-4 hours. A moisture content of 60%-65% and softened leaves are the conditions for entering the rolling process. Its coordination with subsequent rolling is as follows: first, withering adjusts the moisture content and softness of the buds and leaves; then, the withered leaves undergo moderate tissue damage, ensuring that the subsequent variable-temperature fermentation treatment uses withered and moderately rolled buds and leaves. The listed 20-minute and 17-hour withering controls are used to compare the finished product performance of the entire process under different withering degrees; longer withering time is not equated with better quality.

[0038] III. Kneading

[0039] The withered leaves are placed in a rolling machine and rolled for 20-30 minutes, using a "light, medium, heavy, light" pressure principle: Initially, lightly roll for 6-10 minutes at 40 rpm to initially curl the buds and leaves; gradually increase pressure to medium for 6-8 minutes at 45 rpm to moderately break down the cell tissue; continue increasing pressure to heavy for 4-6 minutes at 50 rpm to curl the leaves into strips and further break down the cell tissue, preparing for the next fermentation step; finally, reduce pressure to light for 4-6 minutes at 40 rpm to allow the tea strips to absorb the juice and curl into strips. The amount of leaves should be enough to fill the rolling drum, but not too tightly to avoid damaging the tender leaves. Rolling continues until the buds and leaves are curled into strips, the cells are moderately broken, a small amount of juice slightly adheres to the leaf surface, the cell breakage rate is 30%-50%, and the strip formation rate is over 60%, at which point the rolled leaves are obtained.

[0040] In this process, rolling connects withering and fermentation: Withered leaves in their aforementioned moisture state are used as the treatment target. A cell damage rate of 30%-50% and slight sap overflow adhering to the leaf surface are used as indicators of appropriate damage. The resulting rolled leaves are then transferred to a variable-temperature fermentation process. Therefore, the withering endpoint, the degree of rolling, and subsequent fermentation conditions collectively define the processing procedure; the same rolling time alone cannot be used to determine that the buds and leaves entering fermentation are in the same state.

[0041] IV. Variable Temperature Fermentation

[0042] Place the kneaded leaves in a bamboo basket, fermentation machine, or fermentation room, cover with a damp cloth, and use a variable-temperature fermentation method: first ferment at 40-45℃ and relative humidity above 90% for 1-2 hours, then ferment at 30-35℃ and relative humidity above 90% for 2-3 hours. During fermentation, gently turn the leaves 1-2 times to ensure even distribution and prevent localized overheating. Fermentation continues until the grassy smell disappears and a faint sweet and medicinal aroma emerges, yielding fermented leaves.

[0043] This step combines the initial treatment at 40-45℃ for 1-2 hours with the subsequent treatment at 30-35℃ for 2-3 hours in a sequential manner, and applies this to the processed products obtained from the withering and rolling processes. From a process design perspective, the initial treatment promotes the dissipation of grassy odor and related flavor transformation, while the subsequent treatment reduces the duration of continuous high temperatures by lowering the processing temperature, thus balancing the preservation of mellow flavor and freshness-related components. The 30℃ constant-temperature sample exhibited a green and raw taste, the 45℃ constant-temperature sample exhibited a cooked and musty taste with a slightly acidic flavor, while the variable-temperature sample showed a mellow and sweet taste. These results support the use of segmented temperature arrangements to balance flavor defects under different constant-temperature treatments. The above mechanistic explanation is not equivalent to the confirmed selective decomposition of flavonoids, accumulation of free amino acids, or changes in specific enzyme activity.

[0044] V. Low-temperature baking

[0045] Spread the fermented leaves evenly to dry, then roast at a low temperature to enhance aroma: roast at 60-80℃ for 1.5-3 hours, using a slow, low-temperature roasting method to gradually remove moisture from the buds and leaves, controlling the changes in aroma and flavor during the drying process. Ensure even heating during roasting. Roast until the buds and leaves are dry, can be easily rubbed into powder by hand, have a delicate and lasting aroma, and a finished product moisture content of 4%-7%. After the finished product cools to room temperature, sift to remove dust, impurities, fragments, leaf stems, and other debris, then package to obtain the finished San Ye Qing Cha (Three-Leaf Green Tea).

[0046] Low-temperature baking uses the fermented leaves obtained from the aforementioned variable-temperature fermentation as the treatment material. Its coordination with the fermentation process is as follows: the fermentation stage first develops a relatively mellow flavor and sweet, medicinal aroma; then, the baking stage gradually dehydrates the leaves at 60-80℃ until the finished product's moisture content is 4%-7%, balancing drying requirements with the flavor characteristics developed in the previous stage. The listed high-temperature short-time drying control showed a strong roasted / fired flavor, while the low-temperature baked samples scored higher in aroma and flavor.

[0047] Comparative Example 1 (20-minute short-time withering process)

[0048] The only difference from Example 1 is that the withering is a short withering of 20 minutes (all other conditions are the same as in Example 1).

[0049] Comparative Example 2 (17h ultra-long withering process)

[0050] The only difference from Example 1 is that the withering is an extra-long withering of 17 hours (all other conditions are the same as in Example 1).

[0051] Comparative Example 3 (Constant Speed ​​and Pressure Kneading)

[0052] The only difference from Example 1 is that the kneading is performed at a constant speed of 45 rpm and a constant pressure of light pressing.

[0053] Comparative Example 4 (30℃ constant temperature fermentation process)

[0054] The only difference from Example 1 is that the fermentation is carried out at a constant temperature of 30°C (the other conditions are the same as in Example 1).

[0055] Comparative Example 5 (45℃ constant temperature fermentation process)

[0056] The only difference from Example 1 is that the fermentation is carried out at a constant temperature of 45°C (the other conditions are the same as in Example 1).

[0057] Comparative Example 6 (High-Temperature Short-Time Drying Process)

[0058] The only difference from Example 1 is that the baking process uses a high temperature and short time (100-110℃, 30-60 minutes) (the other conditions are the same as in Example 1).

[0059] Comparative Example 7 (Constant speed and pressure kneading + 30℃ constant temperature fermentation)

[0060] The difference from Example 1 is that: during the kneading process, a constant speed of 45 rpm and constant pressure kneading with light pressure are used, and the total kneading time is the same as in Example 1; during the fermentation process, a constant temperature of 30°C is used for fermentation, and the total fermentation time is the same as the total fermentation time of the two stages in Example 1, with the relative humidity maintained above 90%; the other raw materials, withering and low-temperature baking conditions are the same as in Example 1.

[0061] Sensory evaluation and physicochemical index testing

[0062] I. Sensory Evaluation Method: Referring to GB / T 23776-2018 "Sensory Evaluation Method for Tea", an evaluation panel composed of 5 qualified tea evaluators will score five factors: appearance, liquor color, aroma, taste, and infused leaf appearance. Each factor has a maximum score of 100 points, and the average score of each factor will be the average of the evaluators' scores. The overall score will be calculated according to the weights listed in the test table for this group: Overall Score = Appearance × 25% + Liquor Color × 10% + Aroma × 25% + Taste × 30% + Infused Leaf Appearance × 10%.

[0063] II. Physicochemical index testing methods: Moisture content was determined by direct drying method (101℃-105℃), referring to GB 5009.3-2016; total flavonoids were determined according to DB 43 / T 476-2009 (Determination of total flavonoids in plant-derived foods); total free amino acids were determined by ninhydrin colorimetric method, referring to GB / T 8314-2013 (Determination of total free amino acids in tea).

[0064] 1. Comparison of withering processes

[0065] Table 1

[0066]

[0067] 2. Comparison of kneading processes

[0068] Table 2

[0069]

[0070] 3. Comparison of Fermentation Processes

[0071] Table 3

[0072]

[0073] 4. Comparison of drying processes

[0074] Table 4

[0075]

[0076] 5. Sensory evaluation results of the combined process

[0077] Table 5

[0078]

[0079] 6. Results of testing main physicochemical components

[0080] Table 6

[0081]

[0082] This invention uses the moderate transformation of internal substances after withering and the degree of damage during kneading as pretreatment conditions for variable-temperature fermentation. The fermentation temperature is arranged from high to low to balance the reduction of grassy odor with the formation of a mellow and sweet flavor. Low-temperature baking is then used to complete dehydration while preserving the flavor developed in the previous stages. This continuous processing demonstrates the synergy between each step in achieving the same flavor objective.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A method for processing three-leaf green tea with high freshness and low bitterness, characterized in that, Includes the following steps: S1. Controlled wilting: Spread out fresh leaves of *Trifolium repens* for controlled wilting until the moisture content is 60%-65%, and obtain wilted leaves. S2. Segmented variable speed and pressure kneading: The withered leaves are kneaded in the first, second, third and fourth kneading processes to obtain kneaded leaves; S3. Variable temperature fermentation: The kneaded leaves are subjected to variable temperature fermentation, first at high temperature and then at low temperature, to obtain fermented leaves; S4. Low-temperature baking: The fermented leaves are baked at a low temperature until the moisture content is 4%-7% to obtain Sanye green tea.

2. The processing method of San Ye Qing Cha according to claim 1, characterized in that, In step S1, the controlled withering environment temperature is 18-26℃, the relative humidity is 60%-80%, the withering time is 2-4 hours, and the leaf thickness is 3-8 cm.

3. The processing method of San Ye Qing Cha according to claim 1, characterized in that, In step S2, the rotation speed of the first kneading is 40 rpm, the rotation speed of the second kneading is 45 rpm, the rotation speed of the third kneading is 50 rpm, and the rotation speed of the fourth kneading is 40 rpm. After kneading, the cell damage rate is 30%-50% and the strip formation rate is over 60%.

4. The processing method of San Ye Qing Cha according to claim 3, characterized in that, The first kneading time is 6-10 minutes, the second kneading time is 6-8 minutes, the third kneading time is 4-6 minutes, the fourth kneading time is 4-6 minutes, and the total kneading time is 20-30 minutes; The first kneading pressure is light, the second kneading pressure is medium, the third kneading pressure is heavy, and the fourth kneading pressure is light.

5. The processing method of San Ye Qing Cha according to claim 1, characterized in that, In step S3, the variable temperature fermentation is as follows: first fermentation at 40-45℃ and relative humidity above 90% for 1-2 hours, and then fermentation at 30-35℃ and relative humidity above 90% for 2-3 hours.

6. The processing method of San Ye Qing Cha according to claim 1, characterized in that, In step S4, the low-temperature baking temperature is 60-80℃ and the baking time is 1.5-3 hours.

7. The processing method of San Ye Qing Cha according to claim 1, characterized in that, Before step S1, there is also a harvesting step: selecting tender leaves of 1-3 year old Trifolium repens harvested from April to June each year as the fresh leaves of Trifolium repens.

8. The processing method of San Ye Qing Cha according to claim 7, characterized in that, After the picking step and before S1, there is also a cleaning and impurity removal step: removing rotten, deteriorated, insect-infested, and fungal-damaged leaves, removing dust, mud, insect eggs and impurities, and spreading them out until there are no obvious water droplets on the surface of the buds and leaves.

9. The processing method of San Ye Qing Cha according to claim 1, characterized in that, The step S4 is followed by a screening step: cooling the low-temperature roasted San Ye Qing Cha to room temperature, sifting out broken pieces, leaf stems and impurities, and then packaging it.

10. A type of three-leaf green tea with high freshness and low bitterness, characterized in that... It is prepared by the processing method of the three-leaf green tea according to any one of claims 1-8.

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