A high-efficiency fermentation preparation method for Gongfu black tea

Abstract

The invention provides a high-efficiency fermentation preparation method of Gongfu black tea, comprising: withering, rolling, fermentation, and continuous light fermentation and drying; the fermentation comprises: deblocking rolled leaves, placing the deblocked rolled leaves in a fermentation chamber or a fermentation machine for fermentation, wherein the fermentation temperature is 28 DEG C, the fermentation humidity is not less than 90%, the fermentation time is 3 hours, and the leaves are stirred every hour to obtain fermented leaves; after fermentation, continuous light fermentation and drying are performed: a drying method of filling with a specific dry mixed gas, drying at a lower temperature, and baking at a higher temperature for aroma enhancement during the drying process is adopted, thereby achieving light fermentation during the drying process, allowing fermentation to run through the entire drying process, improving the durability of the fermentation process, avoiding excessive oxidation and fermentation of tea samples, that is, avoiding the bitter taste presented by excessive fermentation and the conversion of aromatic substances, thereby ensuring the long-term and stable fermentation, thereby ensuring the conversion of functional substances in the tea samples and inhibiting the conversion of other substances.

Description

Technical Field

[0001] The invention relates to the technical field of Gongfu black tea preparation, and in particular to a high-efficiency fermentation preparation method for high-fragrance Gongfu black tea. Background Art

[0002] Gongfu black tea is China's second-best-selling tea. Its tight, straight leaves, rich aroma, and mellow, sweet flavor, along with a vibrant red liquor, are known for their health benefits. Currently, Qihong, Dianhong, and Yihong are the main varieties of Gongfu black tea in my country. High-quality Gongfu black tea typically possesses a rich, lingering sweet, floral, sugary, or honey aroma, along with a mellow flavor, but these teas are currently in short supply.

[0003] The production process of Gongfu black tea mainly includes withering, rolling, fermentation, drying, etc.; among them, withering is to evenly disperse the appropriate amount of water from the fresh leaves, soften the leaves, and facilitate rolling into strips, while enhancing the activity of enzymes to create conditions for fermentation, which includes natural withering, artificial heating withering and withering in a withering machine; rolling is to curl the withered leaves into strips under the action of mechanical force, destroy the leaf cell tissue, let the tea juice overflow, and promote fermentation; fermentation is the key process to form the color, aroma and taste quality characteristics of black tea, including fermentation in the fermentation room, fermentation in the fermentation frame and fermentation in the fermentation vehicle; drying is to use drying method to evaporate water, tighten the tea strips, deactivate the activity of enzymes, and fix the fermentation quality. In traditional tea-making technology, the drying process often uses long-term high temperature, which can easily lead to a "high-fire taste" in the finished product, which in turn makes the Gongfu black tea exhibit problems such as slightly astringent taste, low sweetness purity, and poor aroma; at the same time, if the high temperature in the drying process is directly replaced with a lower temperature, it will not only increase the drying time and lengthen the tea-making cycle, but also easily cause problems such as tea moisture regain and moisture absorption, which is not conducive to the conversion of astringent substances, resulting in the final prepared tea having a bitter taste and poor aroma. Summary of the Invention

[0004] In view of the problems existing in the above-mentioned prior art, the object of the present invention is to provide a fermentation preparation method for high-fragrance Gongfu black tea. The Gongfu black tea prepared by this method can effectively avoid the problems of slightly astringent taste, low sweetness purity, and poor aroma in traditional tea making processes. The prepared Gongfu black tea has a strong sweet or sugary aroma and a mellow and rich taste.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The invention relates to a method for preparing Gongfu black tea by fermentation, characterized in that the method comprises withering, rolling, fermenting, and continuous light fermentation and drying. The fermentation comprises the following steps: deblocking the rolled leaves, placing the deblocked rolled leaves in a fermentation chamber or a fermentation machine, and fermenting the leaves at a fermentation temperature of 28-30°C, a fermentation humidity of not less than 90%, a fermentation time of 3 hours, and stirring the leaves every hour to obtain the fermented leaves. The method further comprises the following steps: drying the leaves at 73-77°C, continuously introducing a certain flow of dry mixed gas, then stopping the introduction of the dry mixed gas, and baking the dried leaves at 95-105°C to enhance the aroma. This achieves light fermentation during the drying process, allows the fermentation to run through the entire drying process, improves the durability of the fermentation process, and avoids excessive oxidation and fermentation of the tea sample, i.e., avoids excessive conversion of bitter flavor substances and low-boiling point flavor substances such as fragrant floral fragrance, thereby ensuring long-term and stable fermentation and ensuring the moderate conversion of high-fragrance and mellow flavor substances of the tea sample.

[0007] More specifically, a highly efficient fermentation preparation method for high-flavor Gongfu black tea comprises:

[0008] Step S1, fresh leaf harvesting: in autumn (September-October), when most of the new shoots of tea trees are in the form of one bud, two or three leaves, fresh leaves are harvested; and the harvested fresh leaves are spread out to cool in time;

[0009] Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering to obtain withered leaves;

[0010] Step S3, rolling: the withered leaves are cyclically rolled using a pressure method of light pressure-heavy pressure-light pressure to obtain rolled leaves;

[0011] Step S4, fermentation: placing the rolled leaves in a fermentation chamber or a fermentation machine for fermentation to obtain fermented leaves;

[0012] Step S5, drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven; then, the fermented leaves are placed in the drying oven and dried at 73-77°C, 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°C to enhance aroma, thereby obtaining finished tea.

[0013] 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, Jin Mudan, or Sichuan small and medium-leaf group varieties, Fuding Da Baicha, and Shuyong series varieties (including Shuyong No. 1, Shuyong No. 2, Shuyong No. 3, Shuyong 703, etc.).

[0014] 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 bucket is turned over every 1 hour in the early withering stage and shaken every 2 hours in the late withering stage.

[0015] Based on further optimization of the above scheme, during the kneading process, the average downward movement height of the light pressure, i.e., the pressure cover, is 0.5 to 1 cm, and the average downward movement height of the heavy pressure, i.e., the pressure cover, is 10 to 15 cm; the first light pressure time is 18 to 22 minutes, the second light pressure time is 11 to 15 minutes, and the heavy pressure time is 5 to 8 minutes; the time for the entire cycle kneading is 100 to 120 minutes.

[0016] Based on the further optimization of the above scheme, the rolled leaves are also deblocked after rolling and before fermentation to ensure the uniformity and sufficiency of the fermentation process.

[0017] Based on further optimization of the above scheme, the dry mixed gas is a combination gas of nitrogen and oxygen, and the volume percentage between them is 85% to 90%:10% to 15%; during the drying process, the flow rate of the dry mixed gas is 10 to 20 mL / min.

[0018] The present invention adopts a drying process of relatively low temperature drying + high temperature baking, and continuously introduces a certain flow of nitrogen and oxygen combined gas during the drying process. It not only uses low-content oxygen to inhibit oxidative fermentation during the drying process, that is, to avoid excessive oxidative fermentation of the tea sample during the drying process, so that fermentation runs through the entire drying process and improves the durability of the fermentation process, but also effectively removes water vapor on the surface of the tea sample during the drying process, and avoids the tea sample absorbing moisture and regaining moisture under low-temperature drying, thereby inhibiting the conversion of astringent substances; in addition, the continuously introduced dry mixed gas can also effectively cool the tea sample, ensuring the drying efficiency while avoiding the conversion or volatilization of substances such as linalool and geraniol in the tea sample under the action of continuous high temperature, thereby enhancing and fixing the sweet aroma of the tea.

[0019] 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.

[0020] The following are the technical effects of the present invention:

[0021] The present invention prepares Gongfu black tea through fresh leaf harvesting, withering, rolling, fermentation, and drying. During the drying process, a combination of relatively low-temperature drying and relatively high-temperature baking for aroma enhancement is employed, followed by the introduction of a specific dry mixed gas. This method, firstly, prevents the conversion or volatilization of sweet-smelling substances such as linalool and geraniol in the tea sample caused by high temperatures, effectively preserving and fixing the aroma of the tea sample. Secondly, it prevents moisture absorption and resurgence during the low-temperature drying process, which inhibits the conversion of astringent substances in the tea sample. Thirdly, it prevents excessive oxidative fermentation (i.e., the bitterness and conversion of aromatic substances caused by excessive fermentation), ensuring long-term and stable fermentation, thereby ensuring the conversion of functional substances in the tea sample and inhibiting the conversion of other substances. In other words, the present invention effectively balances the adverse effects of low-temperature and high-temperature drying on the tea aroma and taste during the Gongfu black tea production process, promoting the conversion of astringent substances and preserving aromatic substances in the tea sample. The result is a Gongfu black tea with a mellow, sweet, and rich aroma, and a strong sweet or sugary aroma. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Graph showing PCA analysis results of the Gongfu black tea prepared in the examples of the present invention and the comparative examples.

[0023] Figure 2 This is a correlation analysis diagram of the flavor characteristics and differential metabolites of Gongfu black tea prepared by Example 2 of the present invention and the traditional drying process. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Example 1:

[0026] A highly efficient fermentation preparation method for high-fragrance Gongfu black tea, comprising:

[0027] Step S1, fresh leaf harvesting: In autumn (September-October), Jin Guanyin tea is selected as the fresh leaf raw material, and fresh leaves are harvested when most of the new shoots of the tea tree have one bud and two or three leaves; and the harvested fresh leaves are promptly spread out to cool (using a conventional cooling method in the art);

[0028] Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering, with an ambient humidity of 65%, a leaf thickness of 5 cm, and a spreading time of 8 hours; turning the tank every 1 hour during the early withering period (i.e., within the first 4 hours), and shaking the tank every 2 hours during the late withering period (i.e., within the last 4 hours); obtaining withered leaves;

[0029] Step S3, rolling: The withered leaves are subjected to cyclic rolling (using a 25-type rolling machine) using a pressure-applying method of light pressure for 18 minutes, heavy pressure for 5 minutes, and light pressure for 11 minutes. The entire rolling cycle takes 102 minutes to obtain rolled leaves. The average downward movement height of the cover during light pressure is 0.5 cm, and the average downward movement height of the cover during heavy pressure is 10 cm.

[0030] Step S4, fermentation: deblocking the rolled leaves (using conventional deblocking methods in the art), placing the deblocked rolled leaves in a fermentation chamber or fermentation machine for fermentation at a temperature of 28° C. and a humidity of not less than 90% for 3 hours with stirring every hour to obtain fermented leaves;

[0031] Step S5, Drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven (during this process, the flow rate of the dry mixed gas is not limited, it only needs to be quickly filled with the dry mixed gas). The dry mixed gas is a combination of nitrogen and oxygen, and the volume percentage between them is 85%:15%. Then, the fermented leaves are placed in the drying oven and dried at 73°C for 8 hours. The dry mixed gas is continuously introduced during the drying process, and the dry mixed gas flow rate is adjusted to 10mL / min. Finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 95°C for 27 minutes to enhance the aroma, thereby obtaining the finished tea.

[0032] Example 2:

[0033] A highly efficient fermentation preparation method for high-fragrance Gongfu black tea, comprising:

[0034] Step S1, fresh leaf harvesting: In autumn (September-October), select Sichuan small- and medium-leaf tea varieties as fresh leaf raw materials, and harvest fresh leaves when most of the new shoots of tea trees have one bud and two or three leaves; and spread the harvested fresh leaves to cool in time (using conventional cooling methods in the art);

[0035] Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering, with an ambient humidity of 68%, a leaf thickness of 7 cm, and a spreading time of 10 hours; turning the tank once every hour in the early withering stage (i.e., within the first 5 hours), and shaking once every 2 hours in the late withering stage (i.e., within the last 5 hours), and gently turning the tank once every 2 hours or so during the entire withering process; thereby obtaining withered leaves;

[0036] Step S3, rolling: The withered leaves are subjected to cyclic rolling (using a 25-type rolling machine) using a pressure-applying method of light pressure for 20 minutes, heavy pressure for 6 minutes, and light pressure for 13 minutes. The entire rolling cycle takes 117 minutes to obtain rolled leaves. The average downward movement height of the gland under light pressure is 0.7 cm, and the average downward movement height of the gland under heavy pressure is 12.5 cm.

[0037] Step S4, fermentation: deblocking the rolled leaves (using conventional deblocking methods in the art), placing the deblocked rolled leaves in a fermentation chamber or fermentation machine for fermentation at a temperature of 29° C. and a humidity of not less than 90% for 3 hours with stirring every hour to obtain fermented leaves;

[0038] Step S5, Drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven (during this process, the flow rate of the dry mixed gas is not limited, it only needs to be quickly filled with the dry mixed gas). The dry mixed gas is a combination of nitrogen and oxygen, and the volume percentage between them is 87%:13%; then, the fermented leaves are placed in the drying oven and dried at 75°C for 7 hours. The dry mixed gas is continuously introduced during the drying process, and the dry mixed gas flow rate is adjusted to 15mL / min. Finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 100°C for 25 minutes to enhance the aroma, thereby obtaining the finished tea.

[0039] Example 3:

[0040] A highly efficient fermentation preparation method for high-fragrance Gongfu black tea, comprising:

[0041] 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, and harvest fresh leaves when most of the new shoots of tea trees have one bud and two or three leaves; and spread the harvested fresh leaves to cool in time (using conventional cooling methods in the art);

[0042] Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering, with an ambient humidity of 70%, a leaf thickness of 10 cm, and a spreading time of 12 hours; turning the tank once every hour in the early withering stage (i.e., within the first 6 hours), and shaking once every 2 hours in the late withering stage (i.e., within the last 6 hours), and gently turning the tank once every 2 hours or so during the entire withering process; obtaining withered leaves;

[0043] Step S3, rolling: The withered leaves are subjected to cyclic rolling (using a 25-type rolling machine) using a pressure-applying method of light pressure for 22 minutes, heavy pressure for 8 minutes, and light pressure for 15 minutes. The entire rolling cycle lasts for 120 minutes to obtain rolled leaves. The average downward movement height of the cover during light pressure is 1 cm, and the average downward movement height of the cover during heavy pressure is 15 cm.

[0044] Step S4, fermentation: deblocking the rolled leaves (using conventional deblocking methods in the art), placing the deblocked rolled leaves in a fermentation chamber or fermentation machine for fermentation at a temperature of 30° C. and a humidity of not less than 90% for 3 hours with stirring every hour to obtain fermented leaves;

[0045] Step S5, Drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven (during this process, the flow rate of the dry mixed gas is not limited, it only needs to be quickly filled with the dry mixed gas). The dry mixed gas is a combination of nitrogen and oxygen, with the volume percentage of the nitrogen and oxygen being 90%:10%. Then, the fermented leaves are placed in the drying oven and dried at 77°C for 6 hours. The dry mixed gas is continuously introduced during the drying process, and the flow rate of the dry mixed gas is adjusted to 20 mL / min. Finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 105°C for 23 minutes to enhance aroma, thereby obtaining the finished tea.

[0046] Comparative Example 1:

[0047] A method for preparing Gongfu black tea, comprising:

[0048] Step S1, fresh leaf harvesting: the same as step S1 in Example 2;

[0049] Step S2, withering: the same as step S2 in Example 2;

[0050] Step S3, kneading: the same as step S3 in Example 2;

[0051] Step S4, fermentation: the same as step S4 in Example 2;

[0052] Step S5, drying: first, the fermented leaves are placed in a drying oven and dried at 75°C for 7 hours; then, the dried leaves are roasted at 100°C for 25 minutes to enhance the aroma, thereby obtaining the finished tea.

[0053] Comparative Example 2:

[0054] A method for preparing Gongfu black tea, comprising:

[0055] Step S1, fresh leaf harvesting: the same as step S1 in Example 2;

[0056] Step S2, withering: the same as step S2 in Example 2;

[0057] Step S3, kneading: the same as step S3 in Example 2;

[0058] Step S4, fermentation: the same as step S4 in Example 2;

[0059] Step S5, drying: first, the fermented leaves are placed in a drying oven and dried at 75°C for 7 hours. During the drying process, air (i.e., conventional air with a nitrogen content of 78% and an oxygen content of 21%) is continuously introduced at a flow rate of 15 mL / min. Then, the introduction of air is stopped, and the dried leaves are roasted at 100°C for 25 minutes to enhance the aroma, thereby obtaining the finished tea.

[0060] Comparative Example 3:

[0061] A method for preparing Gongfu black tea, comprising:

[0062] Step S1, fresh leaf harvesting: the same as step S1 in Example 2;

[0063] Step S2, withering: the same as step S2 in Example 2;

[0064] Step S3, kneading: the same as step S3 in Example 2;

[0065] Step S4, fermentation: the same as step S4 in Example 2;

[0066] Step S5, Drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven (during this process, the flow rate of the dry mixed gas is not limited, it only needs to be quickly filled with the dry mixed gas). The dry mixed gas is a combination of nitrogen and oxygen, and the volume percentage between them is 87%:13%; then, the fermented leaves are placed in the drying oven and dried at 100°C for 25 minutes. The dry mixed gas is continuously introduced during the drying process, and the dry mixed gas flow rate at this time is adjusted to 15mL / min; finally, the introduction of the dry mixed gas is stopped, and the dried leaves are baked at 75°C for 7 hours to obtain the finished tea.

[0067] Comparative Example 4:

[0068] A method for preparing Gongfu black tea, comprising:

[0069] Step S1, fresh leaf harvesting: the same as step S1 in Example 2;

[0070] Step S2, withering: the same as step S2 in Example 2;

[0071] Step S3, kneading: the same as step S3 in Example 2;

[0072] Step S4, fermentation: the same as step S4 in Example 2;

[0073] Step S5, drying: First, the fermented leaves are placed in a drying oven and dried at 100°C for 25 minutes; then, the dried leaves are baked at 75°C for 7 hours. During the baking process, a dry mixed gas is introduced into the drying oven. The dry mixed gas is a combination of nitrogen and oxygen in a volume percentage of 87%:13%. The flow rate of the dry mixed gas is 15 mL / min, and the finished tea is obtained.

[0074] Comparative Example 5:

[0075] A method for preparing Gongfu black tea, comprising:

[0076] Step S1, fresh leaf harvesting: the same as step S1 in Example 2;

[0077] Step S2, withering: the same as step S2 in Example 2;

[0078] Step S3, kneading: the same as step S3 in Example 2;

[0079] Step S4, fermentation: the same as step S4 in Example 2;

[0080] Step S5, Drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven (during this process, the flow rate of the dry mixed gas is not limited, it only needs to be quickly filled with the dry mixed gas). The dry mixed gas is a combination of nitrogen and oxygen, and the volume percentage between them is 87%:13%; then, the fermented leaves are placed in the drying oven and dried at 75°C for 7 hours. The dry mixed gas is continuously introduced during the drying process, and the dry mixed gas flow rate is adjusted to 8 mL / min. Finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 100°C for 25 minutes to enhance the aroma, thereby obtaining the finished tea.

[0081] Comparative Example 6:

[0082] A method for preparing Gongfu black tea, comprising:

[0083] Step S1, fresh leaf harvesting: the same as step S1 in Example 2;

[0084] Step S2, withering: the same as step S2 in Example 2;

[0085] Step S3, kneading: the same as step S3 in Example 2;

[0086] Step S4, fermentation: the same as step S4 in Example 2;

[0087] Step S5, Drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven (during this process, the flow rate of the dry mixed gas is not limited, it only needs to be quickly filled with the dry mixed gas). The dry mixed gas is a combination of nitrogen and oxygen, and the volume percentage between them is 87%:13%; then, the fermented leaves are placed in the drying oven and dried at 75°C for 7 hours. The dry mixed gas is continuously introduced during the drying process, and the dry mixed gas flow rate is adjusted to 22 mL / min. Finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 100°C for 25 minutes to enhance the aroma, thereby obtaining the finished tea.

[0088] The appearance, soup color, aroma, taste, and leaf base of the Gongfu black tea in Examples 1 to 3 and Comparative Examples 1 to 6 were described and scored using traditional expert sensory evaluation (evaluation standards refer to GB / T23776-2018). The sensory evaluation of the samples was performed using a password review, and the results are shown in Table 1 below:

[0089] Table 1

[0090]

[0091] The above sensory evaluation table shows that during the preparation 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 at a specific ratio and flow rate during the low-temperature drying process, the Gongfu black tea can have a rich and sweet aroma, and a mellow and sweet taste without bitterness.

[0092] The aroma components of the Gongfu black tea prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were analyzed by GC-MS combined with multivariate statistical analysis. Specifically,

[0093] Step A, sample pretreatment: take out the sample from the -80℃ freezer, grind it in liquid nitrogen, and vortex to mix it evenly;

[0094] 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°C for 5 min, insert a 120 µm DVB / CWR / PDMS extraction tip into the sample headspace vial, extract in the headspace for 15 min, and desorb at 250°C for 5 min.

[0095] Step C, Chromatographic Conditions: A DB-5MS capillary column (30 m × 0.25 mm × 0.25 µm, Agilent J&W Scientific, Folsom, CA, USA) was used, with high-purity helium (≥99.999%) as the carrier gas, at a constant flow rate of 1.2 mL / min, an inlet temperature of 250°C, splitless injection, and a solvent delay of 3.5 min. The temperature program was as follows: 40°C for 3.5 min, then increased to 100°C at 10°C / min, then to 180°C at 7°C / min, and finally to 280°C at 25°C / min, where it was held for 5 min.

[0096] Step D, mass spectrometry conditions: electron impact ion source (EI), ion source temperature 230°C, quadrupole temperature 150°C, mass spectrometer interface temperature 280°C, electron energy 70 eV, selected ion detection (SIM) scanning mode, qualitative and quantitative ion precise scanning (GB 23200.8-2016);

[0097] Step E: Metabolite Qualitative and Quantitative Identification: Based on multiple species, literature, some standard products, and retention indices, a database is independently established, including the determined RT and qualitative and quantitative ions for precise scanning in selected ion detection mode. For each compound, one quantitative ion and two to three qualitative ions are selected. All ions in each group to be detected are detected separately in the order of peak elution and in different time periods. If the detected retention time is consistent with the standard reference and the selected ions appear in the sample mass spectrum after background subtraction, the substance is identified. The quantitative ions are selected for integration and correction to enhance the accuracy of quantification.

[0098] For Examples 1-3 and Comparative Examples 1-6, the raw data were analyzed using Excel. The metabolite content data were processed using UV (unit variance scaling), and PCA analysis, heat map creation, and hierarchical cluster analysis (HCA) of metabolites were performed using the prcomp function and the ComplexHeatmap package in R software. The relative odor activity value (rOAV) was used to illustrate the contribution of each aroma compound to the overall aroma characteristics of the sample.

[0099] Figure 1 The PCA analysis results of the Gongfu black tea prepared in Examples 1 to 3 and Comparative Examples 1 to 6 are shown. PCA (Principal Component Analysis) shows that the drying method of the present invention adopts low-temperature drying + high-temperature baking. The combination of nitrogen and oxygen at a specific ratio and specific flow rate during the low-temperature drying process is maximized in the directions of PC1 and PC2.

[0100] Correlation analysis was conducted between the sensory flavor characteristics and differential metabolites of the Gongfu black tea prepared in Example 2 and the traditional drying process (i.e., direct drying without introducing any gas during the drying process, and using a high-temperature rough fire and low-temperature full fire drying method, i.e., first drying at a high temperature of more than 100°C and then drying at a low temperature of about 70°C). The results are as follows: Figure 2 As shown. Figure 2 It can be seen that compared with the traditional drying process, Example 2 of the present invention produces 17 aroma compounds, mainly including ethyl n-hexyl acetoacetate, 2-undecenal, 3-octanol, 3-methyl-2-(2-methyl-2-butenyl) furan, 1-ethyl-1H-pyrrole and other substances, which have various aroma types such as fruity aroma, baking aroma, rose aroma and sweet aroma.

[0101] Through the drying treatment of the present invention, the aroma sensory evaluation score of Gongfu black tea is significantly improved (see Table 1 for details), and the sweet aroma becomes stronger; in addition, the aroma analysis shows that the new drying process produces 17 substances with floral, fruity, sweet and baking aromas. Specifically, in the sensory evaluation of tea leaves, the Gongfu black tea prepared in Example 2 of the present invention significantly increases the sweet aroma concentration (P<0.05), and the aroma is transformed from the "low sweet aroma" of the traditional drying process to the "strong sweet aroma"; and the tea samples prepared in Example 2 of the present invention are treated and then subjected to aroma analysis. The results show that the tea samples in Example 2 produce 17 aroma compounds such as ethyl n-hexyl acetoacetate, 2-undecenal, 3-octanol, 3-methyl-2-(2-methyl-2-butenyl) furan, 1-ethyl-1H-pyrrole, etc., which mainly present a variety of aroma types such as floral, fruity, baking and sweet (such as Figure 2 shown).

[0102] The results of sensory evaluation and aroma analysis both indicate that the preparation method of the present invention can, to a certain extent, increase the sweet aroma concentration, and the content and quantity of metabolites with sweet and floral aromas, thereby improving the sweet aroma quality of Gongfu black tea and producing high-aromatic Gongfu black tea.

Claims

1. A fermentation method for preparing Gongfu black tea, characterized by: include: Withering, rolling, fermentation, and continuous light fermentation and drying; the fermentation comprises: deblocking the rolled leaves, placing the deblocked rolled leaves in a fermentation chamber or a fermentation machine, and fermenting the leaves at a fermentation temperature of 28-30°C, a fermentation humidity of not less than 90%, a fermentation time of 3 hours, and stirring the leaves every hour to obtain fermented leaves; after fermentation, continuous light fermentation and drying are performed: drying at 73-77°C, continuously introducing a certain flow of dry mixed gas, wherein the dry mixed gas is a combination gas of nitrogen and oxygen, and the volume percentage between the nitrogen and oxygen is 85%-90%:10%-15%, and the flow rate of the dry mixed gas is 10-20 mL / min during the drying process; then, the introduction of the dry mixed gas is stopped, and the dried leaves are baked at 95-105°C to enhance aroma.

2. The fermentation method for preparing Gongfu black tea according to claim 1, characterized in that: Specifically include: Step S1, fresh leaf harvesting: in autumn, when most of the new shoots of tea trees are in the form of one bud, two or three leaves, fresh leaves are harvested; and the harvested fresh leaves are spread out to cool in time; Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering to obtain withered leaves; Step S3, rolling: the withered leaves are cyclically rolled using a pressure method of light pressure-heavy pressure-light pressure to obtain rolled leaves; Step S4, fermentation: deblocking the rolled leaves, and placing the deblocked rolled leaves in a fermentation chamber or a fermentation machine for fermentation to obtain fermented leaves; Step S5, drying: First, a dry mixed gas is introduced into the drying oven to fill the drying oven; then, the fermented leaves are placed in the drying oven and dried at 73-77°C, 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°C to enhance aroma, thereby obtaining finished tea.

3. The fermentation method for preparing Gongfu black tea according to claim 2, characterized in that: The fresh leaf varieties in step S1 are selected from Jin Guanyin, Jin Mudan Oolong tea varieties or Sichuan small and medium leaf group varieties, Fuding Da Baicha, and Shuyong series varieties.

4. The fermentation method for preparing Gongfu black tea according to claim 2 or 3, characterized in that: The environmental 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 bucket is turned over once every 1 hour in the early withering stage, and shaken once every 2 hours in the late withering stage. During the entire withering process, the bucket is lightly turned over every 2 hours.

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