Processing method for reducing grass smell and astringent taste of white tea and white tea

Abstract

The invention relates to the technical field of tea processing, in particular to a processing method for reducing green grass smell and astringent taste of white tea and the white tea, and the processing method comprises the following steps: picking fresh white tea leaf raw materials; withering the fresh leaves in a heating and dehumidifying withering chamber for 32 hours; treating the withered tea leaves at 90-100 DEG C for 5-8 minutes; performing piling treatment on the tea leaves subjected to the short-time high-temperature treatment; and drying the piled tea leaves until the water content of the tea leaves is less than 5%. The processing method has the beneficial effects that under the condition that the withering time is shortened, high-temperature treatment is performed after withering is performed for 32 hours, at the moment, the moisture content of withered leaves is not high, the enzyme activity is relatively weak, fermentation cannot be promoted, and the withering time is shortened while the normal flavor of the white tea is maintained.

Description

Technical Field

[0001] The present invention relates to the technical field of tea processing, and specifically relates to a processing method for reducing the grassy smell and astringency of white tea and white tea. Background Art

[0002] White tea is one of the six major tea categories in China. Its primary processing process is: picking fresh white tea leaves as raw materials → withering → piling up → drying. Among them, withering is the most critical process for white tea, which normally takes about 48 hours. During the withering process, as the water slowly evaporates, various components in the leaves are transformed, and finally, the white tea has the flavor quality characteristics of fresh fragrance, pekoe fragrance, and mellow taste.

[0003] Most of the tea production enterprises in the main production areas of white tea in Fuding and Zhenghe, China, are small enterprises. The characteristics of long withering time and large floor area of the white tea withering process lead to low primary processing capacity. In order to meet the rapidly growing output demand, some tea enterprises use high-power dehumidifiers and exhaust fans to accelerate the water loss speed during withering. Although the withering time is shortened, the substances inside the tea leaves are not fully transformed, resulting in defects such as grassy smell and bitterness in white tea. Controlling temperature and humidity requires good equipment and reasonable factory design, with a large capital investment, and most small-scale tea factories cannot achieve this. Therefore, it is necessary to develop a white tea processing method that can improve work efficiency and ensure quality, and is easy to implement, so as to optimize the white tea processing technology for small-scale tea factories, scientifically improve the work efficiency of white tea and the excellent rate of rough tea. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to provide a processing method for white tea that can improve work efficiency while reducing the grassy smell and astringency of white tea, and white tea.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: to provide a processing method for reducing the grassy smell and astringency of white tea, including the following steps: Step 1: Picking fresh white tea leaves as raw materials; Step 2: Withering treatment: Withering the fresh leaves in a withering room for 30 - 32 hours; Step 3: Short-time high-temperature treatment: Treating the withered tea leaves at 90 - 100 °C for 5 - 8 minutes; Step 4: Piling up: Piling up the tea leaves after short-time high-temperature treatment; Step 5: Drying: Drying the piled-up tea leaves until the water content of the tea leaves is less than 5%.

[0006] Further, in the above processing method for reducing the grassy smell and astringency of white tea, the specific content of Step 1 is: on a sunny day, picking fresh leaves of one bud and two leaves of Fuding Dabaicha.

[0007] Further, in the above processing method for reducing the grassy odor and astringency of white tea, step 2 is specifically as follows: Evenly spread the fresh leaves on a withering sieve with a thickness of 2 - 3 cm, and carry out withering in a withering room for 32 h.

[0008] Further, in the above processing method for reducing the grassy odor and astringency of white tea, step 3 is specifically as follows: Set the oven temperature to 90 °C. When the oven temperature reaches 90 °C, put the withered tea leaves into the oven, start timing, and take them out after 7 min.

[0009] The above is a preferred short - time high - temperature treatment. If the temperature is too low or the time is too short, the effect of removing the grassy odor cannot be achieved. If the temperature is too high or the time is too long, the tea leaves will have a fired aroma or burnt smell, which is not the typical flavor characteristic of white tea.

[0010] Further, in the above processing method for reducing the grassy odor and astringency of white tea, step 4 is specifically as follows: Put the tea leaves after short - time high - temperature treatment into a clean and breathable piling trough, with a pile height of 25 cm, and pile for 12 days.

[0011] Further, in the above processing method for reducing the grassy odor and astringency of white tea, step 5 is specifically as follows: Put the piled tea leaves into the oven, set the temperature to 70 °C, and bake until completely dry, that is, the moisture content of the tea leaves is less than 5%.

[0012] Further, the above processing method for reducing the grassy odor and astringency of white tea specifically includes the following steps: Step 1: On a sunny day, pick the fresh leaves of one bud and two leaves of Fuding Dabaicha. Step 2: Withering treatment: Evenly spread the fresh leaves on a withering sieve with a thickness of 2 - 3 cm, and carry out withering in a withering room for 32 h.

[0013] Step 3: Short - time high - temperature treatment: Set the oven temperature to 90 °C. When the oven temperature reaches 90 °C, put the withered tea leaves into the oven, start timing, and take them out after 7 min.

[0014] Step 4: Piling: Put the tea leaves after short - time high - temperature treatment into a clean and breathable piling trough, with a pile height of 25 cm, and pile for 12 days.

[0015] Step 5: Drying: Put the piled tea leaves into the oven, set the temperature to 70 °C, and bake until completely dry, that is, the moisture content of the tea leaves is less than 5%.

[0016] Another technical solution of the present invention is to provide a white tea processed by the above processing method for reducing the grassy odor and astringency of white tea.

[0017] The beneficial effects of the present invention are as follows: White tea belongs to slightly fermented tea, and appropriate temperature conditions are required during the withering process. If the temperature exceeds 35 °C during withering, it will cause excessive fermentation, too much red change in the leaves, and a fermented smell in the aroma, which does not conform to the normal flavor of white tea. The processing method for reducing the grassy smell and astringency of white tea in the present invention shortens the withering time. After withering for 32 hours, high-temperature treatment is carried out. At this time, the water content of the withered leaves is not high, and the enzyme activity is weak, which will not promote fermentation. While maintaining the normal flavor of white tea, the withering time is shortened and the work efficiency is improved.

[0018] Furthermore, considering that most of the grassy smell substances in tea leaves have relatively low boiling points, higher temperatures are used to promote the volatilization of grassy smell substances in the tea leaves, thereby reducing the grassy smell and astringency of the finished tea. The inventor also conducted single-factor experiments on two key factors, the high-temperature treatment temperature and time, and set 3 temperature gradients (80 °C, 90 °C, 100 °C) and 3 time gradients (4 min, 7 min, 10 min). The results show that the effect of high-temperature treatment at 90 °C for 7 min is the best, which can effectively reduce the grassy smell of the tea leaves and maintain the unique flavor characteristics of white tea.

[0019] The processing method for reducing the grassy smell and astringency of white tea in the present invention specifically has the following advantages: (1) significantly reducing the volatile components with a grassy smell in white tea, such as cis-3-hexen-1-ol, 2-n-amylfuran, decane, 3,5-octadien-2-one, 2-methyldecane, etc., and increasing the volatile components with floral and fruity aromas, such as benzyl alcohol, phenethyl alcohol, hexyl acetate, ethyl laurate, etc., so as to reduce the grassy smell of white tea, make the fresh and floral aromas more obvious, and improve the aroma quality characteristics of white tea; (2) significantly reducing the astringency of the taste of white tea and improving the taste quality of white tea; (3) this technology is simple and easy to implement and has good popularization. Description of the Drawings

[0020] Figure 1 The following shows the heat map of the aroma components of the white tea samples obtained from the examples and comparative examples of the specific embodiments of the present invention; among them, I1, I2, and I3 are the white tea samples obtained from Example 1, Example 2, and Example 3 respectively, and C1, C2, and C3 are the white tea samples obtained from Comparative Example 1, Comparative Example 2, and Comparative Example 3 respectively. Specific Embodiments

[0021] To illustrate the technical content, the achieved objectives and effects of the present invention in detail, the following is described in conjunction with the embodiments and with reference to the drawings.

[0022] The key principle of the processing method for reducing the grassy smell and astringency of white tea in the present invention: Green tea is unfermented tea, and high-temperature fixation is carried out soon after picking to inactivate enzyme activity. White tea belongs to slightly fermented tea, and appropriate temperature conditions are required during the withering process. If the temperature exceeds 35 °C during withering, it will cause excessive fermentation, too much red change in the leaves, and a fermented smell in the aroma, which is not the normal flavor of white tea.

[0023] The processing method for reducing the grassy smell and astringency of white tea according to the present invention, under the condition of shortening the withering time, after withering for 32 h, high-temperature treatment is carried out. At this time, the water content of the withered leaves is not high, and the enzyme activity is weak, which will not promote fermentation. While maintaining the normal flavor of white tea, the withering time is shortened.

[0024] During the withering process of white tea, the present invention appropriately promotes the conversion of internal substances by using enzyme activity, controls the temperature well, and prevents the tea leaves from being mechanically damaged to prevent excessive fermentation. It also uses high temperature to promote the volatilization of low-boiling grassy gas components in the tea leaves, thereby reducing the grassy smell and astringency of white tea, improving the quality of white tea, and increasing the income of tea farmers.

[0025] In the traditional primary processing process of white tea, only a relatively high temperature is used for drying in the final drying process, and the semi-finished tea mostly has a grassy smell and astringency, which seriously affects the sensory quality. After the withered leaves are subjected to short-term high-temperature treatment, the content of volatile components with a grassy smell in them is significantly reduced, such as cis-3-hexen-1-ol, 2-n-pentylfuran, decane, 3,5-octadien-2-one, 2-methyldecane, etc., while the volatile components with floral and fruity aromas increase, such as benzyl alcohol, phenethyl alcohol, hexyl acetate, ethyl laurate, etc., so that the grassy smell of white tea fades, and the fresh and floral aromas are more obvious, improving the aroma quality characteristics of white tea. At the same time, the high-temperature treatment promotes the conversion of tea polyphenol substances, reduces the astringency of the taste of white tea, and improves the taste quality of white tea.

[0026] Example 1 A processing method for reducing the grassy smell and astringency of white tea, comprising the following steps: Step 1: On a sunny day, pick the fresh leaves of one bud and two leaves of Fuding Dabaicha. Step 2: Evenly spread the fresh leaves on a withering sieve with a thickness of 2-3 cm, and wither for 32 h in a temperature-controlled and humidity-extracted withering room at a temperature of 33-35 °C. Step 3: Put the withered leaves into an oven for short-term high-temperature treatment to promote the volatilization of grassy gas substances. The oven temperature is set at 90 °C. When the oven temperature reaches 90 °C, put the withered leaves into the oven and start timing, and take them out after 7 min. Step 4: Carry out piling treatment on the withered leaves after high-temperature treatment. Put the tea leaves into a clean and breathable piling tank with a pile height of about 25 cm and pile for 12 days. Step 5: Dry. Put the piled tea leaves into an oven (temperature 70 °C) and bake until completely dry, that is, the water content of the tea leaves is less than 5%.

[0027] Example 2 A processing method for reducing the grassy odor and astringency of white tea, comprising the following steps: The rest is the same as in Example 1, except that in step 1, the fresh leaves of one bud and two leaves of Fuding Dahao tea are picked, and in step 4, it is piled up for 10 days.

[0028] Example 3 A processing method for reducing the grassy odor and astringency of white tea, comprising the following steps: Step 1: On a light rainy day, pick the fresh leaves of one bud and two leaves of Fuding Dabaicha; Step 2: Evenly spread the fresh leaves on a withering sieve with a thickness of 1.5 - 2.5 cm, and wither in a temperature-controlled and humidity-extracted withering chamber for 32 h, with the temperature controlled at 33 - 35 °C; Step 3: Put the withered leaves into an oven for short-term high-temperature treatment to promote the volatilization of the grassy odor substances. Set the oven temperature to 100 °C. When the oven temperature reaches 100 °C, put the withered leaves into the oven and start timing. Take them out after 7 min; Step 4: Conduct piling treatment on the withered leaves after high-temperature treatment. Put the tea leaves into a clean and breathable piling tank with a pile height of about 25 cm and pile them up for 12 days; Step 5: Dry. Put the piled-up tea leaves into an oven (temperature 70 °C) and bake until fully dry, that is, the water content of the tea leaves is less than 5%.

[0029] Comparative Example 1 A white tea processing method, comprising the following steps: The rest is the same as in Example 1, except that in step 3, the oven temperature is set to 80 °C.

[0030] Comparative Example 2 A white tea processing method, comprising the following steps: The rest is the same as in Example 1, except that in step 3, the timing is 4 min.

[0031] Comparative Example 3 A white tea processing method, comprising the following steps: The rest is the same as in Example 1, except that in step 3, the timing is 10 min.

[0032] Aroma component detection Use headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) to detect the aroma components of the white tea samples in Examples 1 - 3 and Comparative Examples 1 - 3. The specific method is as follows: Sample extraction process: Place the dried tea sample (moisture content ≤ 5%) in a grinder and grind it into a uniform powder (passing through a 60-mesh sieve) at room temperature. After mixing well in a vortex mixer, take 1000 mg of the solid sample and put it into a headspace vial, and add saturated NaCl solution and 20 μL of internal standard solution (10 μg / mL).

[0033] HS-SPME extraction conditions: Under the constant temperature condition of 80 °C, shake for 20 min, insert the extraction head into the sample headspace vial, perform headspace extraction for 40 min, desorb at 250 °C for 5 min, and then carry out GC-MS separation and identification. The new fiber head needs to be pre-aged for 2 hours and re-aged for 5 minutes before each use to avoid contamination.

[0034] Optimization of chromatographic separation conditions: Use high-purity helium as the carrier gas, with a constant flow rate of 1 mL / min, the inlet temperature is 250 °C, splitless injection, and a solvent delay of 3.5 min. The specific temperature programming operation is to hold at 40 °C for 1 minute first, and then rise to 280 °C at a rate of 5 °C / min and hold for 5 min.

[0035] Setting of mass spectrometry detection parameters: The mass spectrometry analysis system is equipped with an advanced electron impact ionization source (EI), and its ion source temperature, quadrupole temperature, and mass spectrometry interface temperature are accurately set to 230 °C, 150 °C, and 280 °C respectively. The electron energy is adjusted to 70 electron volts, and the full scan mode (SCAN) is used to analyze the mass range of the sample, and the scanning range covers m / z 50 to 500 atomic mass units.

[0036] Qualitative and quantitative analysis of aroma components: Use the database established by the Research Center for Horticultural Plant Biology and Metabolomics of Fujian Agriculture and Forestry University to perform mass spectrometry qualitative and quantitative analysis on the metabolites of the samples.

[0037] Detection of internal components in tea: Perform internal component analysis on the white tea samples of Examples 1-3 and Comparative Examples 1-3. Among them, for tea polyphenols, use GB / T 8313—2018 "Methods for the Determination of Tea Polyphenols and Catechins Contents"; for free amino acids, refer to GB / T 8314—2013 "Determination of Total Free Amino Acids in Tea" and use the ninhydrin colorimetric method; for flavonoids, use the aluminum trichloride colorimetric method.

[0038] Sensory evaluation of tea: Refer to the standard of GB / T 23776-2018, namely "Methods for Sensory Evaluation of Tea", to perform sensory evaluation on the white tea samples of Examples 1-3 and Comparative Examples 1-3. The specific operation is as follows: Weigh 3 grams of tea samples and put them into a 150-mL standard evaluation tea cup, and soak them with boiling water for 5 minutes. Three professional tea tasters evaluate the aroma and taste of the tea samples.

[0039] Data analysis Each group of experiments was repeated three times, and the results were expressed as mean ± standard deviation. SPSS Statistics 19.0 software and Excel software were used to analyze the experimental data. The LSD method was used for significant comparison between data, with a detection limit of 0.05. P < 0.05 indicates significant difference.

[0040] Table 1 shows the comparison of the contents of common internal components of white tea samples in the examples and comparative examples, and Table 2 shows the sensory quality evaluation results of white tea samples in the examples and comparative examples.

[0041] Table 1

[0042] Table 2

[0043] From Figure 1 it can be seen that the main component with a green odor characteristic, cis-3-hexen-1-ol, has the highest content in Comparative Example 1 and the lowest content in Example 3, indicating that the higher the temperature, the more cis-3-hexen-1-ol volatilizes during the hot air treatment. Other components with green odor characteristics, such as 2-n-amylfuran, decane, 3,5-octadien-2-one, 2-methyldecane, etc., also have relatively high contents in Comparative Example 1 and Comparative Example 2. Combining with the sensory evaluation results in Table 1, Comparative Example 1 has an obvious green odor, and Comparative Example 2 also has a green odor and a lower aroma score. In Examples 1 and 2 with higher aroma scores, the contents of volatile components with fruity and floral aromas are relatively high, such as ethyl hexanoate, phenethyl alcohol, geraniol, ethyl hexanoate, ethyl nonanoate, β-ionone, dihydroactinidiolide, ethyl laurate, etc. Tea polyphenols are the main quality components of tea, which are closely related to the intensity and bitterness of tea taste. When the content is moderate, the tea taste is mellow; when the content is too low, the taste is light; when the content is high, it will be bitter and astringent.

[0044] Tables 1 and 2 show that the tea polyphenol contents in Comparative Example 1 and Comparative Example 2 are higher than those in the three examples, and Comparative Example 1 has astringency. Amino acids are the main factors affecting the sweet and fresh taste of tea, and a high content is beneficial to the tea taste. The amino acid contents in the three examples are all higher than those in the comparative examples. The sensory evaluation results show that the white tea in Examples 1 and 2 has good quality, and both the aroma and taste have typical white tea flavor characteristics, with a fresh aroma and a hairy aroma, no green grass odor, a mellow and refreshing taste, and no astringency. The comprehensive quality meets the quality requirements of first-class white peony. In Comparative Example 1, the hot air treatment temperature is relatively low (80 °C), the aroma still has a green odor, and the taste also has astringency, and the comprehensive score is also relatively low.

[0045] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. All equivalent transformations made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in the relevant technical fields, are equally included in the patent protection scope of the present invention.

Claims

1. A processing method for reducing the green grassy odor and astringency of white tea, characterized in that, It includes the following steps: Step 1: Pick the fresh leaves of white tea as raw materials; Step 2: Withering treatment: Withering the fresh leaves in the withering room for 30 - 32h; Step 3: Short-time high-temperature treatment: Treating the withered tea leaves at 90 - 100°C for 5 - 8 minutes; Step 4: Piling: Piling the tea leaves after short-time high-temperature treatment; Step 5: Drying: Drying the piled tea leaves until the water content of the tea leaves is less than 5%.

2. The processing method for reducing the grassy odor and astringency of white tea according to claim 1, characterized in that, Specifically, step 1 is: On a sunny day, pick the fresh leaves of one bud and two leaves of Fuding Dabaicha.

3. The processing method for reducing the grassy odor and astringency of white tea according to claim 1, characterized in that, Specifically, step 2 is: Evenly spread the fresh leaves on the withering sieve with a thickness of 2 - 3 cm and wither them in the withering room for 32h.

4. The processing method for reducing the grassy odor and astringency of white tea according to claim 1, characterized in that, Specifically, step 3 is: Set the oven temperature to 90°C. When the oven temperature reaches 90°C, put the withered tea leaves into the oven, start timing, and take them out after 7 minutes.

5. The processing method for reducing the grassy odor and astringency of white tea according to claim 1, characterized in that, Specifically, step 4 is: Put the tea leaves after short-time high-temperature treatment into a clean and breathable piling trough, pile them up to a height of 25 cm, and stack them for 12 days.

6. The processing method for reducing the grassy odor and astringency of white tea according to claim 1, wherein, Specifically, step 5 is: Put the piled tea leaves into the oven, set the temperature to 70°C, and dry them until they are completely dry, that is, the water content of the tea leaves is less than 5%.

7. The processing method for reducing the grassy odor and astringency of white tea according to claim 1, characterized in that, Specifically, it includes the following steps: Step 1: On a sunny day, pick the fresh leaves of one bud and two leaves of Fuding Dabaicha; Step 2: Withering treatment: Evenly spread the fresh leaves on the withering sieve with a thickness of 2 - 3 cm and wither them in the withering room for 32h; Step 3: Short-time high-temperature treatment: Set the oven temperature to 90°C. When the oven temperature reaches 90°C, put the withered tea leaves into the oven, start timing, and take them out after 7 minutes; Step 4: Piling: Put the tea leaves after short-time high-temperature treatment into a clean and breathable piling trough, pile them up to a height of 25 cm, and stack them for 12 days; Step 5: Drying: Put the piled tea leaves into the oven, set the temperature to 70°C, and dry them until they are completely dry, that is, the water content of the tea leaves is less than 5%.

8. White tea processed by the processing method for reducing the grassy smell and astringency of white tea according to any one of claims 1 - 7.

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