Sugar-flavor congou black tea and fermentation preparation method thereof

Abstract

The invention provides sugar-flavor Congou black tea, which relates to the field of fermentation preparation of Congou black tea and is obtained by a preparation process of withering, rolling, fermenting and continuous light fermentation drying. Wherein in the step of rolling, the withered leaves are circularly rolled in a pressing mode of light pressing, heavy pressing and light pressing, so that rolled leaves are obtained; fermentation: the rolled leaves are deblocked, the deblocked rolled leaves are placed in a fermentation chamber or a fermentation machine to be fermented, the fermentation temperature is 28-30 DEG C, the fermentation humidity is not lower than 90%, the fermentation time is 3 h, turning and stirring are conducted once every 1 h, and fermented leaves are obtained; and after fermentation, carrying out continuous light fermentation and drying to obtain the sugar-flavor congou black tea. The congou black tea is subjected to a specific tea making technology, namely, after fermentation, dry mixed gas is introduced for continuous light fermentation drying, light fermentation in the drying process is achieved, fermentation runs through the whole drying technology, the durability of the fermentation process is improved, excessive oxidation fermentation of a tea sample is avoided, and the long-term effect and stability of fermentation are guaranteed.

Description

[0001] This invention is a divisional application of patent application number 202510181326.7, entitled "An efficient fermentation preparation method for Gongfu black tea". Technical Field

[0002] This invention relates to the field of fermentation preparation technology of black tea, specifically to a sugar-flavored black tea and its fermentation method. Background Technology

[0003] Congou black tea originated in Wuyi Mountain, Fujian Province in the 16th century. It is a unique fully fermented tea in my country, improved from Lapsang Souchong. Congou black tea has a tightly rolled and uniform appearance, a dark and lustrous color, a rich aroma, a mellow and sweet taste, and a bright red liquor. It also offers health benefits such as helping to regulate cardiovascular health, providing mild antioxidant effects, refreshing the mind, improving concentration, and supporting gastrointestinal health. The main representative varieties of Congou black tea in my country are Qihong, Dianhong, and Yihong. The production process of Congou black tea mainly includes fresh leaf picking, withering, rolling, fermentation, drying, and refining. The process involves several steps: Fresh leaf picking: primarily using one bud and two or three leaves, requiring them to be tender and uniform; Withering: evenly dissipating appropriate amounts of moisture from the fresh leaves, softening them to facilitate rolling into strips, and simultaneously enhancing enzyme activity to create conditions for fermentation; Rolling: under mechanical force, the withered leaves are rolled into strips, breaking down leaf cell tissue and releasing tea juice; Fermentation: a key process that develops the distinctive color, aroma, and flavor of black tea, primarily aimed at oxidizing tea polyphenols to form a red liquor and red leaves; Drying: using a drying method to evaporate moisture, tighten the tea strips, deactivate enzymes, fix fermentation quality, and develop aroma; Refining: through processes such as shaking, sieving, winnowing, and hand sorting, the tea is graded and finally blended to produce a finished product with a tight appearance and stable internal quality. In existing tea-making processes, the drying process often involves prolonged high temperatures, which can easily lead to a "high-fired" taste in the finished product. This results in black tea exhibiting a slightly astringent taste, low sweetness, and poor aroma. Furthermore, directly replacing the high temperature in the drying process with a lower temperature not only increases the drying time and prolongs the tea-making cycle but also makes the tea prone to moisture absorption and other problems. This is not conducive to the transformation of astringent substances, resulting in a bitter and astringent taste and poor aroma in the final tea. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a sweet-scented black tea. This black tea, through a specific tea-making process, effectively avoids issues such as slightly astringent taste, insufficient sweetness, and unpleasant aroma, resulting in a sweet-scented black tea with a mellow and rich flavor. Furthermore, the present invention also provides a fermentation method for the aforementioned sweet-scented black tea.

[0005] The objective of this invention is achieved through the following technical solution: A sweet-scented black tea and its fermentation method are characterized by the following steps: withering, rolling, fermentation, and continuous light fermentation drying. The fermentation involves breaking up the rolled leaves and placing them in a fermentation chamber or machine for fermentation at a temperature of 28-30°C and a humidity of not less than 90%. The fermentation time is 3 hours, with the leaves being turned over every hour to obtain fermented leaves. After fermentation, continuous light fermentation drying is performed: drying at 73-77°C with a continuous flow of a drying mixed gas, followed by stopping the gas flow and roasting the dried leaves at 95-105°C to enhance aroma. This process achieves light fermentation during drying, allowing fermentation to continue throughout the entire process and improving the persistence of the fermentation. It also avoids excessive oxidation and fermentation of the tea sample, preventing the excessive conversion of bitter and astringent flavor compounds and low-boiling-point aroma compounds such as floral notes. This ensures the long-term effectiveness and stability of the fermentation, guaranteeing a high-aroma, mellow-tasting tea with appropriate transformation of flavor compounds. More specifically, a sweet-scented black tea and its fermentation method, including: Step S1, Fresh Leaf Harvesting: In autumn (September-October), when most of the new tea shoots have one bud and two or three leaves, fresh leaves are harvested and then promptly spread out to cool. Step S2, Withering: The harvested and cooled tea leaves are placed in a withering trough for withering to obtain withered leaves. Step S3, Rolling: The withered leaves are rolled in a cycle of light pressure-heavy pressure-light pressure to obtain rolled leaves. Step S4, Fermentation: The rolled leaves are placed in a fermentation chamber or fermentation machine for fermentation to obtain fermented leaves. Step S5, Drying: First, a dry mixed gas is introduced into the drying chamber to fill it completely. Then, the fermented leaves are placed in the drying chamber and dried at 73-77℃, with the dry mixed gas continuously introduced during the drying process. Finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 95-105℃ to enhance their aroma, yielding the finished tea.

[0006] Based on further optimization of the above scheme, the fresh leaf varieties in step S1 are selected from oolong tea varieties such as Jin Guanyin and Jin Mudan, or Sichuan small and medium leaf group varieties, Fuding Da Bai tea, and Shu Yong series varieties (including Shu Yong No. 1, Shu Yong No. 2, Shu Yong No. 3, Shu Yong 703, etc.).

[0007] Based on further optimization of the above scheme, the ambient humidity of the withering process is 65% to 70%, the leaf thickness is 5 to 10 cm, and the spreading time is 8 to 12 hours; the leaves are turned and shaken once every 1 hour in the early stage of withering and once every 2 hours in the later stage of withering.

[0008] Based on further optimization of the above scheme, during the kneading process, the average downward movement of the cap during light pressing is 0.5–1 cm, and the average downward movement of the cap during heavy pressing is 10–15 cm; the first light pressing time is 18–22 min, the second light pressing time is 11–15 min, and the heavy pressing time is 5–8 min; the total kneading cycle time is 100–120 min. After kneading and before fermentation, the kneaded leaves are broken up to ensure the uniformity and sufficiency of the fermentation process.

[0009] Based on further optimization of the above scheme, the drying mixed gas is a combination of nitrogen and oxygen, with a volume percentage of 85%–90%: 10%–15%; during the drying process, the flow rate of the drying mixed gas is 10–20 mL / min.

[0010] This invention employs a drying process combining relatively low-temperature drying with high-temperature baking, along with a continuous flow of a combination of nitrogen and oxygen during the drying process. This not only utilizes the low oxygen content to inhibit oxidative fermentation during drying, thus preventing excessive oxidation and fermentation of the tea sample, allowing fermentation to continue throughout the entire drying process and enhancing its persistence, but also effectively removes water vapor from the surface of the tea sample during drying. This prevents the tea sample from absorbing moisture and becoming damp under low-temperature drying, which would inhibit the transformation of astringent substances. Furthermore, the continuously introduced drying mixed gas effectively cools the tea sample, ensuring drying efficiency while preventing substances such as linalool and geraniol from being transformed or volatilized under continuous high temperatures, thereby enhancing and fixing the sweet aroma of the tea.

[0011] Based on further optimization of the above scheme, the drying process takes 6 to 8 hours, and the baking and aroma-enhancing time is 23 to 27 minutes.

[0012] The following are the technical effects of this invention: This invention prepares a sweet-scented black tea through a process of fresh leaf harvesting, withering, rolling, fermentation, and drying. In particular, the fermentation and drying process involves continuous light fermentation and drying after fermentation: drying at a lower temperature followed by baking at a higher temperature to enhance aroma, and introducing a specific drying mixture during the drying process. This achieves light fermentation during the drying process, allowing fermentation to continue throughout the entire drying process, improving the persistence of the fermentation process, and avoiding excessive oxidation and fermentation of the tea sample. This avoids the excessive conversion of bitter and astringent flavor substances and low-boiling-point aroma substances such as light floral fragrances, ensuring the long-lasting and stable fermentation, and ensuring that the tea sample has a high aroma and mellow taste with appropriate conversion of flavor substances. By employing the aforementioned fermentation and drying method, not only can the conversion or volatilization of sweet-smelling substances such as linalool and geraniol in the tea sample be avoided due to high temperatures, effectively preserving and fixing the aroma in the tea sample; it also avoids problems such as moisture absorption and rehydration that occur during low-temperature drying, which would inhibit the conversion of astringent substances in the tea sample; in addition, it avoids excessive oxidative fermentation of the tea sample (i.e., avoiding the problems of bitterness and astringency and the conversion of aroma substances caused by excessive fermentation), ensuring the long-term effectiveness and stability of fermentation, thereby ensuring the conversion of functional substances in the tea sample and inhibiting the conversion of other substances.

[0013] This invention effectively balances the adverse effects of low-temperature drying and high-temperature drying on the aroma and taste of tea during the preparation of Gongfu black tea by combining fermentation and drying. It promotes the transformation of astringent substances in the tea sample and preserves the aroma substances in the tea sample, ultimately obtaining Gongfu black tea with a mellow and sweet taste and a strong sweet or sugary aroma. Attached Figure Description

[0014] Figure 1 The figure shows the PCA analysis results of the black tea prepared in the embodiments and comparative examples of the present invention.

[0015] Figure 2 This is a correlation diagram of flavor characteristics and differential metabolites in black tea prepared under the traditional drying process and in Example 2 of the present invention. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0017] Example 1: A sweet-scented black tea and its fermentation method, comprising: Step S1, Fresh Leaf Harvesting: In autumn (September-October), select Jin Guan Yin as the raw material for fresh leaves. Harvest the fresh leaves when most of the new shoots of the tea tree have one bud and two or three leaves. Spread the harvested fresh leaves out to cool in time (using conventional cooling methods in this field is sufficient). Step S2, Withering: Place the harvested and cooled tea leaves in a withering trough for withering. The ambient humidity is 65%, the leaf thickness is 5cm, and the spreading time is 8 hours. In the early stage of withering (i.e., within the first 4 hours), turn and shake the leaves once every 1 hour. In the later stage of withering (i.e., within the last 4 hours), turn and shake the leaves once every 2 hours. Throughout the entire withering process, gently turn the leaves once every 2 hours or so. Obtain the withered leaves. Step S3, Kneading: The withered leaves are kneaded cyclically using a pressure pattern of 18 minutes of light pressure, 5 minutes of heavy pressure, and 11 minutes of light pressure (a 25-type kneading machine is sufficient). The total kneading time is 102 minutes, yielding kneaded leaves. The average downward displacement of the pressure cap during light pressure is 0.5 cm, and the average downward displacement during heavy pressure is 10 cm. Step S4, Fermentation: The kneaded leaves are broken up (using conventional methods in this field). The broken-up leaves are then placed in a fermentation chamber or fermentation machine for fermentation at 28°C and a humidity of at least 90%. The fermentation time is 3 hours, with the leaves turned over every hour to obtain fermented leaves. Step S5, Drying: First, introduce a drying mixture into the drying chamber until it is full (the flow rate of the drying mixture is not limited during this process; it is sufficient to quickly fill the drying chamber with the drying mixture). The drying mixture is a combination of nitrogen and oxygen, with a volume percentage of 85%:15%. Then, place the fermented leaves in the drying chamber and dry them at 73°C for 8 hours. During the drying process, the drying mixture is continuously introduced, and the flow rate of the drying mixture is adjusted to 10 mL / min. Finally, stop the introduction of the drying mixture and bake the dried leaves at 95°C for 27 minutes to enhance their aroma, thus obtaining the finished tea.

[0018] Example 2: A sweet-scented black tea and its fermentation method, comprising: Step S1, Fresh Leaf Harvesting: In autumn (September-October), select small-leaf tea varieties from Sichuan as raw materials. Harvest fresh leaves when most of the new shoots of the tea trees have one bud and two or three leaves. Immediately spread the harvested fresh leaves to cool (using conventional cooling methods). Step S2, Withering: Place the harvested and cooled tea leaves in a withering trough for withering. The ambient humidity is 68%, the leaf thickness is 7cm, and the spreading time is 10 hours. During the early withering stage (the first 5 hours), turn the leaves once every 1 hour; during the later withering stage (the last 5 hours), turn the leaves once every 2 hours. Throughout the entire withering process, gently turn the leaves approximately every 2 hours to obtain withered leaves. Step S3, Kneading: The withered leaves are kneaded cyclically using a pressure cycle of 20 minutes of light pressure, 6 minutes of heavy pressure, and 13 minutes of light pressure (a 25-type kneading machine is sufficient). The total kneading cycle takes 117 minutes to obtain kneaded leaves. The average downward displacement of the pressure cap during light pressure is 0.7 cm, and the average downward displacement during heavy pressure is 12.5 cm. Step S4, Fermentation: The kneaded leaves are broken up (using conventional methods in this field). The broken-up leaves are then placed in a fermentation chamber or fermentation machine for fermentation at 29°C and a humidity of at least 90%. The fermentation time is 3 hours, with the leaves turned over every hour to obtain fermented leaves. Step S5, Drying: First, introduce a drying mixture into the drying chamber until it is full (the flow rate of the drying mixture is not limited during this process; it is sufficient to quickly fill the drying chamber with the drying mixture). The drying mixture is a combination of nitrogen and oxygen, with a volume percentage of 87%:13%. Then, place the fermented leaves in the drying chamber and dry them at 75°C for 7 hours. During the drying process, the drying mixture is continuously introduced, and the flow rate of the drying mixture is adjusted to 15 mL / min. Finally, stop the introduction of the drying mixture and roast the dried leaves at 100°C for 25 minutes to enhance their aroma, thus obtaining the finished tea.

[0019] Example 3: A sweet-scented black tea and its fermentation method, comprising: Step S1, Fresh Leaf Harvesting: In autumn (September-October), select Shuyong series varieties (including Shuyong No. 1, Shuyong No. 2, Shuyong No. 3, Shuyong 703, etc.) as fresh leaf raw materials. Harvest fresh leaves when most of the new shoots of the tea trees have one bud and two or three leaves. Spread the harvested fresh leaves out to cool in time (using conventional cooling methods in this field is sufficient). Step S2, Withering: Place the harvested and cooled tea leaves in a withering trough for withering. The ambient humidity is 70%, the leaf thickness is 10cm, and the spreading time is 12h. In the early stage of withering (i.e., within the first 6h), turn and shake once every 1h; in the later stage of withering (i.e., within the last 6h), turn and shake once every 2h. Throughout the entire withering process, gently turn the leaves about once every 2h; obtain withered leaves. Step S3, Kneading: The withered leaves are kneaded cyclically using a pressure pattern of 22 minutes of light pressure, 8 minutes of heavy pressure, and 15 minutes of light pressure (a 25-type kneading machine is sufficient). The total kneading time is 120 minutes, yielding kneaded leaves. During light pressure, the average downward displacement of the pressure cap is 1 cm, and during heavy pressure, it is 15 cm. Step S4, Fermentation: The kneaded leaves are broken up (using conventional methods in this field). The broken-up leaves are then placed in a fermentation chamber or fermentation machine for fermentation at 30°C and a humidity of at least 90%. The fermentation time is 3 hours, with the leaves turned over every hour to obtain fermented leaves. Step S5, Drying: First, introduce a drying mixture into the drying chamber until it is full (the flow rate of the drying mixture is not limited during this process; it is sufficient to quickly fill the drying chamber with the drying mixture). The drying mixture is a combination of nitrogen and oxygen, with a volume percentage of 90%:10%. Then, place the fermented leaves in the drying chamber and dry them at 77°C for 6 hours. During the drying process, the drying mixture is continuously introduced, and the flow rate of the drying mixture is adjusted to 20 mL / min. Finally, stop the introduction of the drying mixture and roast the dried leaves at 105°C for 23 minutes to enhance their aroma, thus obtaining the finished tea.

[0020] Comparative Example 1: A method for preparing Gongfu black tea, comprising: Step S1, Fresh Leaf Harvesting: Same as Step S1 in Example 2. Step S2, Withering: Same as Step S2 in Example 2. Step S3, Rolling: Same as Step S3 in Example 2. Step S4, Fermentation: Same as Step S4 in Example 2. Step S5, Drying: First, place the fermented leaves in a drying oven and dry at 75℃ for 7 hours; then, bake the dried leaves at 100℃ for 25 minutes to enhance aroma, thus obtaining the finished tea.

[0021] Comparative Example 2: A method for preparing Gongfu black tea, comprising: Step S1, Fresh Leaf Harvesting: Same as Step S1 in Example 2. Step S2, Withering: Same as Step S2 in Example 2. Step S3, Rolling: Same as Step S3 in Example 2. Step S4, Fermentation: Same as Step S4 in Example 2. Step S5, Drying: First, place the fermented leaves in a drying oven and dry at 75℃ for 7 hours. During the drying process, continuously circulate air (i.e., conventional air with 78% nitrogen and 21% oxygen) at a flow rate of 15 mL / min. Then, stop the air circulation and bake the dried leaves at 100℃ for 25 minutes to enhance aroma, thus obtaining the finished tea.

[0022] Comparative Example 3: A method for preparing Gongfu black tea, comprising: Step S1, Fresh Leaf Harvesting: Same as Step S1 in Example 2. Step S2, Withering: Same as Step S2 in Example 2. Step S3, Rolling: Same as Step S3 in Example 2. Step S4, Fermentation: Same as Step S4 in Example 2. Step S5, Drying: First, introduce a drying mixture into the drying chamber until it is full (the flow rate of the drying mixture is not limited; it is sufficient to quickly fill the drying chamber). The drying mixture is a combination of nitrogen and oxygen, with a volume percentage of 87%:13%. Then, place the fermented leaves in the drying chamber and dry at 100°C for 25 minutes. During the drying process, continuously introduce the drying mixture, adjusting the flow rate to 15 mL / min. Finally, stop introducing the drying mixture and bake the dried leaves at 75°C for 7 hours to obtain the finished tea.

[0023] Comparative Example 4: A method for preparing Gongfu black tea, comprising: Step S1, Fresh Leaf Harvesting: Same as Step S1 in Example 2. Step S2, Withering: Same as Step S2 in Example 2. Step S3, Rolling: Same as Step S3 in Example 2. Step S4, Fermentation: Same as Step S4 in Example 2. Step S5, Drying: First, place the fermented leaves in a drying oven and dry at 100℃ for 25 minutes; then, bake the dried leaves at 75℃ for 7 hours. During baking, a drying mixed gas (nitrogen and oxygen) is simultaneously introduced into the drying oven at a volume percentage of 87%:13% and a flow rate of 15 mL / min to obtain the finished tea.

[0024] Comparative Example 5: A method for preparing Gongfu black tea, comprising: Step S1, Fresh Leaf Harvesting: Same as Step S1 in Example 2. Step S2, Withering: Same as Step S2 in Example 2. Step S3, Rolling: Same as Step S3 in Example 2. Step S4, Fermentation: Same as Step S4 in Example 2. Step S5, Drying: First, introduce a drying mixture into the drying chamber until it is full (the flow rate of the drying mixture is not limited; it is sufficient to quickly fill the drying chamber). The drying mixture is a combination of nitrogen and oxygen, with a volume percentage of 87%:13%. Then, place the fermented leaves in the drying chamber and dry at 75°C for 7 hours. During the drying process, continuously introduce the drying mixture, adjusting the flow rate to 8 mL / min. Finally, stop introducing the drying mixture and bake the dried leaves at 100°C for 25 minutes to enhance their aroma, thus obtaining the finished tea.

[0025] Comparative Example 6: A method for preparing Gongfu black tea, comprising: Step S1, Fresh Leaf Harvesting: Same as Step S1 in Example 2. Step S2, Withering: Same as Step S2 in Example 2. Step S3, Rolling: Same as Step S3 in Example 2. Step S4, Fermentation: Same as Step S4 in Example 2. Step S5, Drying: First, introduce a drying mixture into the drying chamber until it is full (the flow rate of the drying mixture is not limited; it is sufficient to quickly fill the drying chamber). The drying mixture is a combination of nitrogen and oxygen, with a volume percentage of 87%:13%. Then, place the fermented leaves in the drying chamber and dry at 75°C for 7 hours. During the drying process, continuously introduce the drying mixture, adjusting the flow rate to 22 mL / min. Finally, stop introducing the drying mixture and bake the dried leaves at 100°C for 25 minutes to enhance their aroma, thus obtaining the finished tea.

[0026] The appearance, liquor color, aroma, taste, and infused leaf appearance of the black teas in Examples 1-3 and Comparative Examples 1-6 were described and scored using traditional expert sensory evaluation (evaluation standards refer to GB / T23776-2018). The sensory evaluation of the samples was conducted using a coded evaluation method. The results are shown in Table 1 below: Table 1

[0027] Based on the above sensory evaluation form, it can be concluded that in the preparation process of Gongfu black tea, the drying method adopts low-temperature drying + high-temperature baking. Combined with the introduction of a combination of nitrogen and oxygen gas in a specific ratio and flow rate during the low-temperature drying process, Gongfu black tea can present a rich and sweet aroma, mellow and sweet taste, and no bitterness.

[0028] Aroma components of the black tea prepared in Examples 1-3 and Comparative Examples 1-6 were analyzed using GC-MS combined with multivariate statistical analysis. Specifically: Step A, Sample Pretreatment: Remove the sample from the -80℃ freezer and grind it with liquid nitrogen, vortexing until homogeneous. Step B, HS-SPME Extraction Conditions: Weigh 500 mg of sample into a headspace vial, add saturated NaCl solution and 20 µL (10 µg / mL) internal standard solution, shake at 60℃ for 5 min, insert a 120 µm DVB / CWR / PDMS extraction head into the sample headspace vial, perform headspace extraction for 15 min, and then desorb at 250℃ for 5 min. Step C, Chromatographic Conditions: Use a DB-5MS capillary column (30 m × 0.25 mm × 0.25 µm, Agilent J&W Scientific, Folsom, CA, USA), high-purity helium (purity not less than 99.999%) as carrier gas, constant flow rate of 1.2 mL / min, injection port temperature of 250℃, splitless injection, and solvent delay of 3.5 min. Temperature program: Hold at 40℃ for 3.5 min, increase to 100℃ at 10℃ / min, then to 180℃ at 7℃ / min, and finally to 280℃ at 25℃ / min, hold for 5 min. Step D, Mass spectrometry conditions: Electron impact ionization (EI) source, ion source temperature 230℃, quadrupole temperature 150℃, mass spectrometer interface temperature 280℃, electron energy 70 eV, scan mode selected ion detection (SIM), precise scanning of qualitative and quantitative ions (GB 23200.8-2016). Step E, Metabolite qualitative and quantitative analysis: Based on multiple species, literature, some standards, and retention indices, a self-established database was built, containing determined RT and qualitative and quantitative ions for precise scanning using selected ion detection mode. For each compound, one quantitative ion and two to three qualitative ions were selected. All ions to be detected in each group are detected separately in the order of peak elution and at different time periods. If the retention time of the detected ions is consistent with the standard reference and all selected ions appear in the sample mass spectrum after background subtraction, the substance is identified. Quantitative ions are selected for integration and calibration to enhance the accuracy of quantification.

[0029] For Examples 1-3 and Comparative Examples 1-6, the raw data were analyzed using Excel; metabolite content data were processed using unit variance scaling (UV); PCA analysis, heatmap plotting, and hierarchical cluster analysis (HCA) of metabolites were performed using the prcomp function and ComplexHeatmap package in R software; and the relative odor activity value (rOAV) was used to elucidate the contribution of each aroma compound to the overall aroma characteristics of the sample.

[0030] Figure 1 The PCA analysis results for the black tea prepared in Examples 1-3 and Comparative Examples 1-6 are shown in the figure. PCA (Principal Component Analysis) revealed that the drying method of this invention employs a combination of low-temperature drying and high-temperature roasting. The combination of nitrogen and oxygen gas at a specific ratio and flow rate introduced during the low-temperature drying process resulted in maximum values ​​in both PC1 and PC2 directions. A correlation analysis was performed between the sensory flavor characteristics and differential metabolites of the black tea prepared in Example 2 and the traditional drying process (i.e., drying without introducing any gas, using a high-temperature initial drying followed by a low-temperature final drying, i.e., first high-temperature drying above 100°C, then low-temperature drying at around 70°C). The results are as follows. Figure 2 As shown. By Figure 2 As can be seen, compared with the traditional drying process, Example 2 of the present invention produced 17 aroma compounds, mainly including ethyl hexyl acetoacetate, 2-undecenal, 3-octanol, 3-methyl-2-(2-methyl-2-butenyl)furan, 1-ethyl-1H-pyrrole, etc., exhibiting various aroma types such as fruity aroma, roasted aroma, rose aroma, and sweet aroma. Through the drying treatment of the present invention, the aroma sensory evaluation score of the black tea was significantly improved (see Table 1 for details), and the sweet aroma became stronger; in addition, aroma analysis showed that the new drying process produced 17 substances with floral and fruity aroma, sweet aroma, and roasted aroma. Specifically, in sensory evaluation of tea, the black tea prepared in Example 2 of this invention significantly increased the sweet aroma concentration (P<0.05), and the aroma changed from "low sweet aroma" of traditional drying process to "strong sweet aroma"; and after processing the tea sample prepared in Example 2 of this invention, aroma analysis showed that the tea sample in Example 2 produced 17 aroma compounds, including ethyl hexyl acetoacetate, 2-undecenal, 3-octanol, 3-methyl-2-(2-methyl-2-butenyl)furan, and 1-ethyl-1H-pyrrole, mainly exhibiting various aroma types such as floral and fruity aroma, roasted aroma, and sweet aroma (e.g. Figure 2(As shown). Sensory evaluation and aroma analysis results both indicate that the preparation method of the present invention can, to a certain extent, increase the concentration of sweet aroma, the content and quantity of metabolites with sweet and floral aromas, thereby improving the sweet aroma quality of Gongfu black tea and producing high-aroma Gongfu black tea.

Claims

1. A sweet-scented black tea, characterized in that: The tea is prepared through a process of withering, rolling, fermentation, and continuous light fermentation drying. Rolling involves cyclically rolling the withered leaves using a light-heavy-light pressure method to obtain rolled leaves. Light pressure refers to an average downward movement of the cap by 0.5–1 cm, while heavy pressure refers to an average downward movement of the cap by 10–15 cm. The first light pressure lasts 18–22 minutes, the second light pressure lasts 11–15 minutes, and the heavy pressure lasts 5–8 minutes, with the entire rolling cycle lasting 100–120 minutes. Fermentation involves breaking up the rolled leaves and placing them in a fermentation chamber or fermentation machine for fermentation. The fermentation temperature is 28–30℃, the fermentation humidity is not less than 90%, and the fermentation time is 3 hours, with stirring every hour to obtain fermented leaves. After fermentation, continuous light fermentation drying is performed to obtain the sweet-scented black tea.

2. The sweet-scented black tea according to claim 1, characterized in that: The process of continuous light fermentation and drying after fermentation involves placing the fermented leaves in a drying oven and drying them at 73-77°C, while continuously introducing a drying mixed gas during the drying process. Finally, the introduction of the drying mixed gas is stopped, and the dried leaves are roasted at 95-105°C to enhance their aroma, thus obtaining the finished tea.

3. The sweet-scented black tea according to claim 2, characterized in that: The drying mixture is a combination of nitrogen and oxygen, with a volume percentage of 85%–90%:10%–15%; during the drying process, the flow rate of the drying mixture is 10–20 mL / min.

4. The fermentation method for a sweet-scented black tea according to claim 1 or 3, characterized in that: include: Step S1: Fresh leaf harvesting: In autumn, when most of the new tea shoots have one bud and two or three leaves, fresh leaves are harvested and then spread out to cool in time. Step S2, withering: Place the harvested and cooled fresh tea leaves in a withering trough for withering to obtain withered leaves; Step S3, Kneading: The withered leaves are kneaded in a cycle of light pressure-heavy pressure-light pressure to obtain kneaded leaves; the light pressure means that the average downward movement of the cap is 0.5-1cm, the heavy pressure means that the average downward movement of the cap is 10-15cm, the first light pressure time is 18-22min, the second light pressure time is 11-15min, the heavy pressure time is 5-8min, and the entire cycle of kneading takes 100-120min; Step S4, Fermentation: Break up the tumbled leaves and place them in a fermentation chamber or fermentation machine for fermentation. The fermentation temperature is 28-30℃, the fermentation humidity is not less than 90%, the fermentation time is 3 hours, and the leaves are turned over once every 1 hour to obtain fermented leaves. Step S5, Drying: First, introduce a drying mixture into the drying chamber until it is full; then, place the fermented leaves in the drying chamber and dry them at 73-77℃. During the drying process, continuously introduce the drying mixture, which is a combination of nitrogen and oxygen with a volume percentage of 85%-90%:10%-15%; the flow rate of the drying mixture during the drying process is 10-20 mL / min; finally, stop introducing the drying mixture and roast the dried leaves at 95-105℃ to enhance their aroma, thus obtaining the finished tea.

5. The fermentation method for a sweet-scented black tea according to claim 4, characterized in that: In step S1, the fresh leaf varieties selected are Jin Guanyin, Jin Mudan Oolong tea, or Sichuan small and medium leaf group variety, Fuding Da Bai tea, and Shu Yong series varieties.

6. The fermentation method for a sweet-scented black tea according to claim 4, characterized in that: The ambient humidity during the withering process is 65%–70%, the leaf thickness is 5–10 cm, and the spreading time is 8–12 hours. The leaves are turned and shaken once every 1 hour in the early stage of withering and once every 2 hours in the later stage of withering. Throughout the entire withering process, the leaves are turned lightly once every 2 hours.

7. The fermentation method for a sweet-scented black tea according to claim 4, characterized in that: The drying process takes 6–8 hours, and the baking and aroma-enhancing process takes 23–27 minutes.

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