Efficient fermentation preparation method of congou black tea

Abstract

The invention provides an efficient fermentation preparation method of congou black tea. The efficient fermentation preparation method comprises the following steps: withering, rolling, fermenting and continuously lightly fermenting and drying, in the fermentation step, 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 DEG C, the fermentation humidity is not lower than 90%, the fermentation time is 3 h, the rolled leaves are turned and stirred once every 1 h, and the fermented leaves are obtained; in the drying process, a specific drying mixed gas is filled, drying is carried out at a low temperature, baking and fragrance extraction are carried out at a high temperature, so that light fermentation in the drying process is realized, the fermentation runs through the whole drying process, the durability of the fermentation process is improved, and the production efficiency is improved. The tea sample is prevented from being excessively oxidized and fermented, that is, the problems of bitter taste, conversion of flavor substances and the like caused by excessive fermentation are avoided, and the long-term effect and stability of fermentation are ensured, so that conversion of functional substances in the tea sample is ensured, and conversion of other substances is inhibited.

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 the second most sold tea in China. It has tight and straight leaves, rich aroma, mellow and sweet taste, bright red soup color, and has certain health benefits. At present, my country's Gongfu black tea is mainly represented by Qihong, Dianhong and Yihong. High-quality Gongfu black tea usually has a strong and lasting sweet, floral, sugary or honey aroma, and a mellow taste, but it is currently lacking in the market.

[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, so that the leaves become soft and easy to roll 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 the fermentation process; 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 car; drying is to use drying method to evaporate water, tighten the tea leaves, 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 transformation 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 prior art, the purpose of the present invention is to provide a fermentation preparation method of high-fragrance Gongfu black tea. The Gongfu black tea prepared by the method can effectively avoid the problems of slightly astringent taste, low sweetness purity, poor aroma, etc. in the traditional tea making process. The prepared Gongfu black tea has a strong sweet or sugary aroma and a mellow and sweet taste.

[0005] The purpose of the present invention is achieved through the following technical solutions: The invention discloses a highly efficient fermentation preparation method of Gongfu black tea, characterized in that it comprises 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, wherein the fermentation temperature is 28-30°C, the fermentation humidity is not less than 90%, the fermentation time is 3 hours, and the leaves are turned over every 1 hour to obtain the fermented leaves; after the fermentation, continuous light fermentation and drying are performed: drying at 73-77°C, continuously introducing a certain flow of dry mixed gas, and then stopping the introduction of the dry mixed gas, and baking the dried leaves at 95-105°C for aroma enhancement, so as to achieve light fermentation in the drying process, allow the fermentation to run through the entire drying process, improve the durability of the fermentation process, and avoid excessive oxidation fermentation of the tea sample, that is, avoid excessive conversion of bitter flavor substances and low-boiling point flavor substances such as fragrant flower fragrance produced by excessive fermentation, thereby ensuring the long-term and stable fermentation and ensuring the moderate conversion of high-fragrance and mellow flavor substances of the tea sample. More specifically, a highly efficient fermentation preparation method for high-flavor Gongfu black tea comprises: Step S1, harvesting fresh leaves: 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; 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 pressurization method of light pressure-heavy pressure-light pressure to obtain rolled leaves; Step S4, fermentation: placing the rolled leaves in a fermentation room or a fermentation machine for fermentation to obtain fermented leaves; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven; then, place the fermented leaves in the drying oven and dry them at 73-77°C, and continue to introduce dry mixed gas during the drying process; finally, stop introducing the dry mixed gas, and bake the dried leaves at 95-105°C to enhance the aroma, so as to obtain 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 Baicha, and Shuyong series varieties (including Shuyong No. 1, Shuyong No. 2, Shuyong No. 3, Shuyong 703, etc.).

[0007] Based on further optimization of the above scheme, 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 every 1 hour in the early stage of withering, and shaken every 2 hours in the late stage of withering.

[0008] 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.

[0009] Based on the further optimization of the above scheme, after rolling and before fermentation, the rolled leaves are also deblocked to ensure the uniformity and sufficiency of the fermentation process.

[0010] 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.

[0011] 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 tea samples during the drying process, so that fermentation runs through the entire drying process and improves the durability of the fermentation process, but also effectively takes away water vapor on the surface of the tea samples during the drying process, and avoids moisture absorption and rehumidification of the tea samples under low-temperature drying to inhibit the conversion of astringent substances; in addition, the continuously introduced dry mixed gas can also effectively cool the tea samples, ensure the drying efficiency, and avoid substances such as linalool and geraniol in the tea samples from being converted or volatilized under the action of continuous high temperature, thereby enhancing and fixing the sweet fragrance of the tea leaves.

[0012] 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.

[0013] The following are the technical effects of the present invention: The invention prepares Gongfu black tea through fresh leaf harvesting, withering, rolling, fermentation and drying processes, and in the drying process, a drying method is used in which a relatively low temperature drying + a relatively high temperature baking is used to enhance the aroma, and a specific dry mixed gas is filled in the drying process. First, the high temperature is avoided to cause the sweet and fragrant substances such as linalool and geraniol in the tea sample to be transformed or volatilized, and the aroma in the tea sample is effectively retained and fixed; second, the problems of moisture absorption and moisture resurgence in the tea sample during the low-temperature drying process are avoided, resulting in the inhibition of the transformation of astringent substances in the tea sample; third, the excessive oxidation and fermentation of the tea sample is avoided (i.e., the bitter taste presented by excessive fermentation and the transformation of aromatic substances are avoided), and the long-term and stable fermentation is ensured, thereby ensuring the transformation of functional substances in the tea sample and inhibiting the transformation of other substances. That is, the invention effectively balances the adverse effects of low-temperature drying and high-temperature drying on the tea aroma and taste in the preparation process of Gongfu black tea through a specific drying method, promotes the transformation of astringent substances in the tea sample, and retains the aromatic substances in the tea sample, and finally obtains Gongfu black tea with a mellow taste, sweet and strong aroma, and a strong sweet or sugary aroma. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The PCA analysis results of the Gongfu black tea prepared in the examples of the present invention and the comparative examples are shown in FIG.

[0015] 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

[0016] The technical solutions in the embodiments of the present invention will be described clearly and completely 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.

[0017] Embodiment 1: A highly efficient fermentation preparation method for high-fragrance Gongfu black tea, comprising: Step S1, harvesting fresh leaves: In autumn (September-October), select Jin Guanyin as the fresh leaf raw material, 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 the conventional cooling method in the art); Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering, with an environmental humidity of 65%, a leaf thickness of 5 cm, and a spreading time of 8 hours; turning the tank once every 1 hour in the early withering period (i.e., within the first 4 hours), and shaking once every 2 hours in the late withering period (i.e., within the last 4 hours); obtaining withered leaves; Step S3, rolling: the withered leaves are rolled in a cycle (a 25-type rolling machine can be used for rolling) by a pressurizing method of light pressing for 18 minutes, heavy pressing for 5 minutes, and light pressing for 11 minutes. The entire cycle rolling time is 102 minutes to obtain rolled leaves. The average downward movement height of the cover under light pressure is 0.5 cm, and the average downward movement height of the cover under heavy pressure is 10 cm. Step S4, fermentation: deblocking the rolled leaves (using conventional deblocking means in the art), and placing the deblocked rolled leaves in a fermentation room or a fermentation machine for fermentation at a fermentation temperature of 28° C. and a fermentation humidity of not less than 90%. The fermentation time is 3 hours and the leaves are turned over every hour to obtain fermented leaves; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven (in this process, the flow rate of the dry mixed gas is not limited, it is only necessary to quickly fill the drying oven 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. During the drying process, the dry mixed gas is continuously introduced, and the flow rate of the dry mixed gas 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 obtain finished tea.

[0018] Embodiment 2: A highly efficient fermentation preparation method for high-fragrance Gongfu black tea, comprising: Step S1, fresh leaf harvesting: in autumn (September-October), select Sichuan small and medium-leaf group species 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); Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering, the environmental humidity is 68%, the leaf thickness is 7 cm, and the spreading time is 10 hours; turning the bucket once every 1 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 bucket once every 2 hours or so during the whole withering process; obtaining withered leaves; Step S3, rolling: the withered leaves are rolled in a cycle (a 25-type rolling machine can be used for rolling) by a pressurizing method of light pressing for 20 minutes, heavy pressing for 6 minutes, and light pressing for 13 minutes. The entire cycle rolling time is 117 minutes to obtain rolled leaves. The average downward movement height of the cover under light pressure is 0.7 cm, and the average downward movement height of the cover under heavy pressure is 12.5 cm. Step S4, fermentation: deblocking the rolled leaves (using conventional deblocking means in the art), and placing the deblocked rolled leaves in a fermentation room or a fermentation machine for fermentation at a fermentation temperature of 29° C. and a fermentation humidity of not less than 90%. The fermentation time is 3 hours and the leaves are turned over every hour to obtain fermented leaves; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven (in this process, the flow rate of the dry mixed gas is not limited, it is only necessary to make the dry mixed gas quickly fill the drying oven), 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. During the drying process, the dry mixed gas is continuously introduced, and the flow rate of the dry mixed gas 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 obtain finished tea.

[0019] Embodiment 3: A highly efficient fermentation preparation method for high-fragrance Gongfu black tea, 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, 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 the conventional cooling method in the art); Step S2, withering: placing the harvested and cooled fresh tea leaves in a withering tank for withering, with an environmental humidity of 70%, a leaf thickness of 10 cm, and a spreading time of 12 hours; turning the bucket once every 1 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 bucket once every 2 hours or so during the whole withering process; obtaining withered leaves; Step S3, rolling: the withered leaves are rolled in a cycle (a 25-type rolling machine can be used for rolling) by a pressurizing method of light pressing for 22 minutes, heavy pressing for 8 minutes, and light pressing for 15 minutes. The entire cycle rolling time is 120 minutes to obtain rolled leaves. The average downward movement height of the cover under light pressure is 1 cm, and the average downward movement height of the cover under heavy pressure is 15 cm. Step S4, fermentation: deblocking the rolled leaves (using conventional deblocking means in the art), and placing the deblocked rolled leaves in a fermentation room or a fermentation machine for fermentation at a fermentation temperature of 30° C. and a fermentation humidity of not less than 90% for 3 hours with stirring every 1 hour to obtain fermented leaves; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven (in this process, the flow rate of the dry mixed gas is not limited, it is only necessary to quickly fill the drying oven with the dry mixed gas), the dry mixed gas is a combination of nitrogen and oxygen, and the volume percentage between them is 90%:10%; then, the fermented leaves are placed in the drying oven and dried at 77°C for 6 hours. During the drying process, the dry mixed gas is continuously introduced, and the flow rate of the dry mixed gas is adjusted to 20mL / min; finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 105°C for 23 minutes to obtain finished tea.

[0020] Comparative Example 1: A method for preparing Gongfu black tea, comprising: Step S1, fresh leaf harvesting: the same as step S1 in Example 2; Step S2, withering: the same as step S2 in Example 2; Step S3, kneading: the same as step S3 in embodiment 2; Step S4, fermentation: the same as step S4 in Example 2; Step S5, drying: firstly, the fermented leaves are placed in a drying oven and dried at 75°C for 7 hours; then, the dried leaves are baked at 100°C for 25 minutes to obtain finished tea.

[0021] Comparative Example 2: A method for preparing Gongfu black tea, comprising: Step S1, fresh leaf harvesting: the same as step S1 in Example 2; Step S2, withering: the same as step S2 in Example 2; Step S3, kneading: the same as step S3 in embodiment 2; Step S4, fermentation: the same as step S4 in Example 2; 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 baked at 100°C for 25 minutes to obtain finished tea.

[0022] Comparative Example 3: A method for preparing Gongfu black tea, comprising: Step S1, fresh leaf harvesting: the same as step S1 in Example 2; Step S2, withering: the same as step S2 in Example 2; Step S3, kneading: the same as step S3 in embodiment 2; Step S4, fermentation: the same as step S4 in Example 2; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven (in this process, the flow rate of the dry mixed gas is not limited, it is only necessary to quickly fill the drying oven 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. During the drying process, the dry mixed gas is continuously introduced, and the flow rate of the dry mixed gas 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 finished tea.

[0023] Comparative Example 4: A method for preparing Gongfu black tea, comprising: Step S1, fresh leaf harvesting: the same as step S1 in Example 2; Step S2, withering: the same as step S2 in Example 2; Step S3, kneading: the same as step S3 in embodiment 2; Step S4, fermentation: the same as step S4 in Example 2; 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, and during the baking process, a dry mixed gas is introduced into the drying oven simultaneously. The dry mixed gas is a combination of nitrogen and oxygen, and the volume percentage between them is 87%:13%. The flow rate of the dry mixed gas is 15mL / min, and the finished tea is obtained.

[0024] Comparative Example 5: A method for preparing Gongfu black tea, comprising: Step S1, fresh leaf harvesting: the same as step S1 in Example 2; Step S2, withering: the same as step S2 in Example 2; Step S3, kneading: the same as step S3 in embodiment 2; Step S4, fermentation: the same as step S4 in Example 2; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven (in this process, the flow rate of the dry mixed gas is not limited, it is only necessary to quickly fill the drying oven 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. During the drying process, the dry mixed gas is continuously introduced, and the flow rate of the dry mixed gas is adjusted to 8mL / min; finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 100°C for 25 minutes to obtain finished tea.

[0025] Comparative Example 6: A method for preparing Gongfu black tea, comprising: Step S1, fresh leaf harvesting: the same as step S1 in Example 2; Step S2, withering: the same as step S2 in Example 2; Step S3, kneading: the same as step S3 in embodiment 2; Step S4, fermentation: the same as step S4 in Example 2; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven (in this process, the flow rate of the dry mixed gas is not limited, it is only necessary to make the dry mixed gas quickly fill the drying oven), 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. During the drying process, the dry mixed gas is continuously introduced, and the flow rate of the dry mixed gas is adjusted to 22mL / min; finally, the introduction of the dry mixed gas is stopped, and the dried leaves are roasted at 100°C for 25 minutes to obtain finished tea.

[0026] The appearance, soup color, aroma, taste and leaf bottom 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 password evaluation, and the results are shown in Table 1: Table 1

[0027] It can be concluded from the above sensory evaluation table that in the preparation process of Gongfu black tea, the drying method adopts low-temperature drying + high-temperature baking methods, combined with the introduction of a combination of nitrogen and oxygen in a specific proportion and specific flow rate during the low-temperature drying process, which can make the Gongfu black tea have a strong sweet aroma, a mellow and sweet taste, and no bitterness.

[0028] 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: Step A, sample pretreatment: take out the sample from the -80°C refrigerator, grind it with liquid nitrogen, and vortex to mix it evenly; Step B, HS-SPME extraction conditions: weigh 500 mg of sample into a headspace bottle, 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 head into the sample headspace bottle, extract at headspace for 15 min, and analyze at 250 °C for 5 min; Step C, chromatographic conditions: DB-5MS capillary column (30 m×0.25 mm×0.25 µm, Agilent J&W Scientific, Folsom, CA, USA), carrier gas was high-purity helium (purity not less than 99.999%), constant flow rate was 1.2 mL / min, injection port temperature was 250°C, non-split injection, solvent delay was 3.5 min. Program temperature rise: 40°C for 3.5 min, then increased to 100°C at 10°C / min, then increased to 180°C at 7°C / min, and finally increased to 280°C at 25°C / min, and maintained for 5 min; Step D, mass spectrometry conditions: electron impact ion source (EI), ion source temperature 230°C, quadrupole temperature 150°C, mass spectrometry interface temperature 280°C, electron energy 70eV, scanning mode selected ion detection mode (SIM), qualitative and quantitative ion precise scanning (GB 23200.8-2016); Step E, qualitative and quantitative identification of metabolites: Based on multiple species, literature, some standards and retention indexes, a database is independently established, including the determined RT and qualitative and quantitative ions for precise scanning in the selected ion detection mode. One quantitative ion and 2 to 3 qualitative ions are selected for each compound. All ions to be detected in each group are detected 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, it is determined to be the substance; select the quantitative ions for integration and correction to enhance the accuracy of quantification.

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

[0030] 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. Through PCA (Principal Component Analysis), it is known that the drying method of the present invention adopts the method of low-temperature drying + high-temperature baking, and the combined gas of nitrogen and oxygen at a specific ratio and a specific flow rate during the low-temperature drying process is the largest in the directions of PC1 and PC2.

[0031] The sensory flavor characteristics and differential metabolites of the Gongfu black tea prepared in Example 2 and the traditional drying process (i.e., no gas is introduced during the drying process, the drying is carried out directly, and a high-temperature rough fire and a low-temperature full fire drying method is used, i.e., high-temperature drying above 100°C is first performed, and then low-temperature drying at about 70°C is performed) are correlated and analyzed. The results are as follows Figure 2 As shown. Figure 2 It can be seen that compared with the traditional drying process, 17 aroma compounds are produced in Example 2 of the present invention, 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, showing a variety of aroma types such as fruity aroma, baking aroma, rose aroma and sweet aroma.

[0032] 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, 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 improves the sweet aroma concentration (P<0.05), and the aroma is transformed from the "low sweet aroma" of the traditional drying process to "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 aromas (such as Figure 2 as shown).

[0033] 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, 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 highly efficient fermentation method for preparing Gongfu black tea, characterized in that: include: Withering, rolling, fermentation, and continuous light fermentation and drying; the fermentation is to deblock the rolled leaves, and place the deblocked rolled leaves in a fermentation room or a fermentation machine for fermentation, the fermentation temperature is 28-30°C, the fermentation humidity is not less than 90%, the fermentation time is 3 hours and the leaves are stirred every 1 hour to obtain fermented leaves; after fermentation, continuous light fermentation and drying is performed: drying 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 for aroma enhancement.

2. The method for preparing Gongfu black tea by efficient fermentation 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 pressurization method of light pressure-heavy pressure-light pressure to obtain rolled leaves; Step S4, fermentation: placing the rolled leaves in a fermentation room or a fermentation machine for fermentation to obtain fermented leaves; Step S5, drying: first, introduce dry mixed gas into the drying oven to fill the drying oven; then, place the fermented leaves in the drying oven and dry them at 73-77°C, and continue to introduce dry mixed gas during the drying process; finally, stop introducing the dry mixed gas, and bake the dried leaves at 95-105°C to enhance the aroma, so as to obtain finished tea.

3. The method for preparing Gongfu black tea by efficient fermentation according to claim 2, characterized in that: 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.

4. The method for preparing Gongfu black tea by efficient fermentation 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 or so.

5. The method for preparing Gongfu black tea by efficient fermentation according to claim 2 or 4, characterized in that: After rolling and before fermentation, the rolled leaves are also deblocked to ensure uniformity and sufficiency of the fermentation process.

6. The method for preparing Gongfu black tea by efficient fermentation according to claim 5, characterized in that: The dry mixed gas is a combination 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.

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