Preparation method of rock tea freeze-dried powder through high-low temperature composite extraction and application of rock tea freeze-dried powder

Abstract

The invention provides a preparation method and application of rock tea freeze-dried powder through high and low temperature composite extraction. The preparation method comprises the following steps: removing moisture and aging taste through medium-fire short-time re-baking to improve fragrance, adopting a composite extraction mode of combining low-temperature extraction and high-temperature short-time extraction, and then carrying out disc centrifugation, ultrafiltration, Ro concentration, vacuum freeze-drying and the like to prepare the freeze-dried powder. The method solves the problems that the rock tea powder is easy to bitterness, miscellaneous in taste and stuffy and single in aroma, the flavor quality of the rock tea powder is improved, the method has the advantages of low-temperature extraction for aroma preservation and high-temperature extraction for flavor enhancement, and meanwhile, the tea cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of tea processing, and in particular relates to a preparation method of high-low temperature composite extraction rock tea freeze-dried powder and application thereof. Background Art

[0002] The existing extraction technology of instant rock tea powder is mostly single high-temperature extraction. The traditional tea soup extraction method is generally divided into low-temperature extraction and high-temperature extraction. Low-temperature extraction can well preserve the aroma of tea, but the tea soup extracted by low-temperature extraction has a low concentration and a weak taste, and has a large loss of tea content; high-temperature extraction can extract most of the internal substances in tea, with a strong taste, but it has a large loss of tea aroma.

[0003] In the application publication number CN108157551A, the invention name is "A tea extract, tea beverage and preparation method thereof prepared by ice extraction technology", although the low-temperature extraction technology is disclosed, it cannot solve the problem that rock tea powder is easily bitter, has mixed taste, and has a dull and single aroma. In the application publication number CN116746626A, the invention name is "A method for preparing low-temperature countercurrent ice extraction coffee concentrate", although it discloses the steps of raw material processing, baking, grinding (obtaining ground coffee powder with a specific particle size distribution), ice extraction water preparation, countercurrent ice extraction, recovery, slag removal, concentration, etc., this method is for coffee extraction and does not involve rock tea powder extraction, and cannot solve the problem that rock tea powder is easily bitter, has mixed taste, and has a dull and single aroma.

[0004] Therefore, it is urgent to develop a preparation method of rock tea freeze-dried powder, which can increase the concentration and flavor of tea soup while retaining the aroma of tea, reduce the loss of substances contained in tea, and improve the aroma quality of tea, so as to solve the problems that rock tea powder is easy to be bitter, has a mixed taste, and has a dull and single aroma. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a preparation method of rock tea freeze-dried powder through high-low temperature composite extraction and application thereof, which removes moisture and stale taste and enhances aroma through short-time repeated baking at medium fire, adopts a composite extraction method combining low-temperature extraction and high-temperature short-time extraction, and then works together through disc centrifugation, ultrafiltration, Ro concentration and vacuum freeze drying, thereby effectively improving the quality of rock tea freeze-dried powder, solving the problems that rock tea powder is easily bitter, has mixed taste, and has a dull and single aroma, and has the advantages of improving the flavor quality of rock tea powder, having both the advantages of low-temperature extraction to preserve fragrance and high-temperature extraction to enhance flavor, while saving the cost of tea.

[0006] In order to achieve the above object, the present invention adopts the following scheme:

[0007] In one aspect, the present invention provides a method for preparing freeze-dried rock tea powder, characterized in that it comprises the following steps:

[0008] (1) before extracting tea soup, the tea leaves are roasted for a short time at medium heat;

[0009] (2) obtaining the first extract and the second extract by high and low temperature composite extraction;

[0010] (3) rapidly cooling the second extract tea soup, and mixing it with the first extract tea soup to obtain a final extract, which is used to prepare rock tea freeze-dried powder;

[0011] In the medium-fire short-time re-roasting process adopted in step (1), the re-roasting temperature of the tea leaves is 90-110° C. and the re-roasting time is 10-20 minutes.

[0012] In some embodiments, the present invention proposes a new rock tea powder production process, which uses medium-fire short-time double roasting before tea extraction, uses a combination of low-temperature extraction and high-temperature short-time extraction to extract tea soup, and uses vacuum freeze-drying to dry.

[0013] In the traditional rock tea powder processing technology, due to the limitations of the cognition of traditional technology and the basic satisfaction of traditional technology with tea quality, for example, in the traditional technology, the role of re-baking in significantly improving the aroma of rock tea, removing moisture and stale taste, and improving the taste is not deeply understood. The traditional concept focuses more on the influence of the basic extraction method of tea (such as low temperature or high temperature extraction) on the quality of tea soup, but does not fully realize the importance of re-baking in improving the overall quality, and does not carry out the "medium fire short time re-baking" process. Therefore, in order to verify the necessity of the "medium fire short time re-baking" process of the present invention, a comparative test is carried out in the present invention, and the quality of the final rock tea powder is sensory evaluated and related components are detected. The results show that the "medium fire short time re-baking" process is very necessary in the processing technology of rock tea powder. This process can effectively remove moisture and stale taste generated during the storage of tea leaves, significantly improve the aroma of rock tea, retain the floral and fruity aroma of rock tea, make the taste more mellow and smooth, and show rock rhyme, thereby improving the quality of rock tea powder. The traditional process does not adopt this process due to insufficient understanding of the effect of double roasting and basic satisfaction with existing quality. However, through the comparative test of this embodiment, we can clearly see the advantages brought by the double roasting process, which provides a strong basis for the improvement of the rock tea powder processing technology.

[0014] Furthermore, in the step (2), the tea soup extraction adopts an extraction method combining low-temperature extraction and high-temperature short-time extraction, wherein the first extraction adopts low-temperature extraction, the tea soup is filtered and refrigerated for later use, and the tea leaves are retained; the second extraction adopts high-temperature extraction, and after the second extraction is completed, the tea soup is quickly cooled and mixed with the first extraction tea soup to obtain the final extract.

[0015] The traditional tea soup extraction method is generally divided into low-temperature extraction and high-temperature extraction. These two extraction methods have their own advantages and disadvantages. Low-temperature extraction can well preserve the aroma of tea, but the tea soup extracted at low temperature has a low concentration and a thin taste, and the loss of tea content is large; high-temperature extraction can extract most of the connotation substances in tea, and the taste is strong, but the loss of tea aroma is large. The composite extraction tea soup of the present invention adopts a high-low temperature combined extraction method, which has the advantages of both extraction methods, one is low-temperature extraction, and the other is high-temperature extraction. The main extraction tea soup is low temperature, and has the unique aroma of rock tea extracted at low temperature, and the high-temperature extraction tea soup is supplemented to increase its pyrotechnics and mellow taste, and the low-temperature drying method is used to retain the tea aroma to the greatest extent, which not only improves the flavor quality of rock tea powder, but also saves tea costs compared to low-temperature extraction.

[0016] In some embodiments of the present invention, the necessity of using high and low temperature composite extraction in the present invention is also verified by a test. The results show that the tea powder using the "high and low temperature composite extraction" of the present invention is significantly superior to the tea powder using "high temperature extraction", "low temperature extraction" and "high temperature first and low temperature extraction" in terms of aroma and taste. Although the tea soup of the tea powder using "high temperature extraction" is thicker, the aroma is weaker and more stuffy, and more bitter; the tea powder using "low temperature extraction" has too low an extraction rate, which results in the subsequent concentration and other processing processes taking too long and also causes aroma loss. Although the tea powder has a good aroma, it has a thin and weak taste and a high cost. For the tea powder using "high temperature first and low temperature extraction later", the first high temperature extraction may cause some aroma components in the tea to be lost at high temperature, so that the aroma of the final tea powder has a roasted aroma but is weak and has a burnt taste. At the same time, the first high temperature treatment may cause some components in the tea to change, affecting the extraction of the effective components in the tea during the subsequent low temperature extraction, resulting in a thicker taste but with bitterness and miscellaneous flavors, which also affects the quality of the final tea powder. Therefore, only by adopting the "high-low temperature composite extraction" method of the present invention can the quality of traditional tea powder be effectively improved.

[0017] Furthermore, the extraction temperature is 0-15°C, and the extraction time is 30-120 minutes.

[0018] Furthermore, the secondary extraction temperature is 85-100° C., and the extraction time is 5-10 minutes.

[0019] Furthermore, the ratio of tea to water is 1:7-1:15, and the ratio of tea to ice is 1:3-1:35.

[0020] Furthermore, the ratio of the two extractions of tea to water is 1:5-1:15.

[0021] Furthermore, after the second extraction, the tea soup is rapidly cooled to a temperature of 0-5°C.

[0022] In some embodiments, in order to further verify the necessity and uniqueness of the process of "high and low temperature composite extraction" of the present invention, the Chinese invention patent with the authorization announcement number "CN104106696B" and the invention name "a tea beverage and its manufacturing method" (comparative document 1) and the Chinese invention patent with the authorization announcement number "CN101164424B" and the invention name "a method for preparing instant tea powder" (comparative document 2) are used for comparative verification. Among them, comparative document 1 also mentions the use of "high and low temperature composite extraction method", but in fact, the extraction temperature of the first extraction is 50-85°C, the extraction time is 10-30min, and the tea-water ratio is 1: (50-80); the second extraction temperature conditions are complex (such as 75°C at the top of the tower and 55°C for the feed), and the overall temperature range is relatively high. In the present invention, the first extraction temperature is 0-15°C, the extraction time is 30-120min, the tea-water ratio is 1:7-1:15, and the tea-ice ratio is 1:3-1:35; the second extraction temperature is 85-100°C, the extraction time is 5-10min, and the tea-water ratio is 1:5-1:15. Therefore, in the final tea quality test, although the tea powder prepared by the comparative document 1 can extract more internal substances, the aroma is relatively low and dull, and the roasted aroma is the main flavor. The taste is thick but the bitter taste is heavy, and it has the disadvantages of high caffeine and tea polyphenol content. It is completely inferior to the tea powder prepared by the present invention in terms of aroma and taste balance and the rationality of the ingredient content. This may be because the first extraction temperature is 50-85℃, which is relatively high and not conducive to the retention of aroma, and the first extraction time is 10-20min, which is relatively short and may not be able to fully extract the aroma components in the tea leaves. The subsequent operation is to directly mix the first extract and the second extract after clarification (weight ratio: 350:1). This mixing method may not be able to blend the advantages of the two extracts well, thus affecting the quality of the tea powder.

[0023] Although the three-stage temperature extraction method is adopted in Comparative Document 2, in fact, it is completely different from the "high-low temperature composite extraction" of the present invention. The extraction temperature of the first extraction is 20-30℃, the extraction time is 20-30min, and the tea-water ratio is 1:(4-6); the extraction temperature of the second extraction is 40-70℃, the extraction time is 10-15min, and the tea-water ratio is 1:(10-15); the extraction temperature of the third extraction is 85-100℃, the extraction time is 5-10min, and the tea-water ratio is 1:(4-6). But in fact, it is completely different from the "high-low temperature composite extraction" of the present invention. In the present invention, the temperature of the first extraction is 0-15℃, the extraction time is 30-120min, the tea-water ratio is 1:7-1:15, and the tea-ice ratio is 1:3-1:35; the temperature of the second extraction is 85-100℃, the extraction time is 5-10min, and the tea-water ratio is 1:5-1:15. Therefore, in the final tea quality test, although the tea powder prepared by the comparative document 2 can extract different components of tea at different temperature stages by using three-stage temperature extraction, the operation is complicated, and the subsequent processing steps such as compound enzyme hydrolysis, filtration, concentration and other steps may cause the loss of aroma components and changes in taste. This may be because although the three-stage temperature extraction has the advantage of being able to extract tea components more finely, due to the complexity of the process, improper control of temperature and time in each stage may lead to incomplete or over-extraction of certain components, and also cause the aroma and taste of the final tea powder to fail to achieve the best effect. At the same time, the temperature of the first extraction is 20-30°C, which is still high compared to the temperature of the present invention, and the time of the first extraction is 20-30min, which may lead to low extraction efficiency. In the subsequent operation, the second extract and the third extract need to be mixed, compound enzyme hydrolysis, filtration, concentration to obtain a concentrated solution, and then the concentrated solution is mixed with the first extract. These steps may introduce impurities or lose some effective ingredients, thereby affecting the quality of the tea powder.

[0024] Therefore, it can be seen that only when the "high-low temperature composite extraction method" of the present invention is adopted, can the tea powder obtained achieve a better balance in aroma, taste and ingredient content and have the best quality.

[0025] Furthermore, the preparation method of the rock tea freeze-dried powder also includes raw material processing, crushing and grinding of tea leaves after double roasting, disc centrifugation, ultrafiltration, Ro concentration and drying process after tea soup extraction, and the drying process adopts vacuum freeze drying.

[0026] In the traditional preparation method of rock tea freeze-dried powder, a high-temperature drying process is often used. This drying process has some defects. For example, high temperature may cause a large loss of aroma components in tea, making the final rock tea freeze-dried powder lack aroma; at the same time, high temperature may also destroy some effective ingredients in tea, such as tea polyphenols, affecting its nutritional value and taste.

[0027] In some embodiments of the present invention, it is also verified that the use of traditional high-temperature drying will lead to adverse effects after the medium-fire short-time double roasting process and the high-low temperature composite extraction process are adopted. Since the internal composition and structure of the tea leaves after double roasting and composite extraction have undergone certain changes, high-temperature drying will further aggravate the loss of aroma components, and may also change the properties of the effective ingredients in the tea leaves, affecting the aroma and nutritional quality of the final rock tea freeze-dried powder.

[0028] Only when the drying process of the present invention preferably uses vacuum freeze drying can the drying effect be significantly improved, so that the quality of the final rock tea freeze-dried powder can be optimized. This may be because vacuum freeze drying is carried out under low temperature and low pressure conditions, which can retain the aroma components in the tea leaves to the greatest extent and avoid the loss of aroma due to high temperature; at the same time, this drying method has less damage to the effective ingredients in the tea leaves, and can better maintain the nutritional quality and taste of the tea leaves. In addition, vacuum freeze drying can also keep the tea leaves in a better shape and structure, which is beneficial to improving the stability and solubility of the rock tea freeze-dried powder.

[0029] Furthermore, in the tea leaves short-time medium-fire re-roasting process, the thickness of the rock tea raw materials in the oven is 1-4 cm.

[0030] Furthermore, the particles of the crushed tea leaves are larger than 10 meshes.

[0031] In some embodiments, the preparation process of the rock tea freeze-dried powder of the present invention includes: raw material processing, short-time re-roasting of tea leaves at medium heat, crushing and grinding, high and low temperature composite extraction, disc centrifugation, ultrafiltration, Ro concentration and vacuum freeze drying. Among them, the tea leaves are crushed to more than 10 meshes, the centrifugal temperature of the disc centrifugation is 35°C, and the centrifugal flow rate is 5.0±0.5T / h. The appropriate centrifugal temperature and flow rate can effectively separate impurities in the tea soup, such as tea residues, macromolecular proteins, etc., making the tea soup clearer, because within this temperature and flow range, impurities can be fully precipitated or separated under the action of centrifugal force.

[0032] The pore size of the ultrafiltration membrane is ≤0.2μm. Within this pore size range, macromolecular substances in the tea soup, such as polysaccharides and proteins, can be effectively retained, while allowing small molecular effective components, such as tea polyphenols and caffeine, to pass through, thereby achieving the purpose of purifying and concentrating the tea soup. This is because small molecular substances smaller than the pore size can freely pass through the membrane pores, while macromolecular substances larger than the pore size are retained, making the effective components in the tea soup relatively enriched, improving the quality of the tea soup and the convenience of subsequent processing.

[0033] When Ro concentration is used, the concentration to the discharge concentration is 20+2brix, and the concentration temperature is ≤35℃. Within this concentration and temperature range, the volume of the tea soup can be effectively reduced, the content of the active ingredients can be increased, and the destruction of the active ingredients due to excessively high temperatures can be avoided. This is because at a suitable temperature, the water can be gradually removed, and the active ingredients can remain relatively stable within this concentration range. If the temperature is too high, such as exceeding 35℃, it may cause oxidative degradation of heat-sensitive ingredients such as tea polyphenols, affecting the quality of the tea powder. When concentrated to 20+2brix, it can not only ensure that the active ingredients are well concentrated, but also enable the tea soup to maintain good physical and chemical properties in subsequent vacuum freeze-drying processes, which is conducive to the preparation and quality maintenance of the final rock tea freeze-dried powder.

[0034] Relevant experiments were conducted in the present invention, and it was found that only when all these conditions acted synergistically, the best quality effect of rock tea freeze-dried powder could be achieved. Each condition is the best condition obtained after optimization and screening, and each condition works best under this condition. For example, crushing tea leaves to more than 10 meshes is beneficial to the subsequent extraction process, because the appropriate particle size can increase the contact area between tea leaves and solvents and improve the extraction efficiency; short-term re-baking at medium fire can remove moisture and stale taste and enhance the aroma, because baking at a temperature of 90-110°C for 10-20 minutes can adjust and optimize some volatile components in tea leaves; high-low temperature composite extraction combines the advantages of low-temperature extraction for fragrance preservation and high-temperature extraction for flavor enhancement, which can make the tea soup mellow and rich in aroma, because low-temperature extraction can retain the unique aroma of tea leaves, and high-temperature extraction can increase the thickness of the taste of tea soup; disc centrifugation, ultrafiltration and Ro concentration can further purify and concentrate tea soup, remove impurities, and increase the content of effective ingredients; vacuum freeze drying can retain the aroma and effective ingredients of tea leaves to the greatest extent, and avoid component loss caused by high-temperature drying and other methods, because vacuum freeze drying is carried out under low temperature and low pressure conditions.

[0035] On the other hand, the present invention provides a freeze-dried rock tea powder prepared by the preparation method described in any one of the above technical solutions.

[0036] The beneficial effects of the present invention are:

[0037] 1. The present invention provides a method for preparing a high-low temperature composite extraction rock tea freeze-dried powder and its application. A medium-fire short-time re-roasting process is added before the tea soup is extracted, which effectively removes the moisture and stale taste generated during the storage of tea leaves, while enhancing the aroma of rock tea, retaining the floral and fruity aroma to make the taste more mellow and smooth, showing the rock rhyme. At the same time, a high-low temperature composite extraction method is adopted to optimize the extraction temperature and extraction time of one extraction and two extractions, and maximize the combination of the advantages of low-temperature extraction and high-temperature extraction to make the taste mellow, solving the problem that rock tea powder is easy to be bitter and has a mixed taste. At the same time, a vacuum freeze-drying method is used to retain the aroma and effective ingredients of tea leaves to the greatest extent, avoiding the loss of components caused by high-temperature drying and other methods, and ensuring the quality of freeze-dried powder.

[0038] 2. The present invention provides a method for preparing a freeze-dried rock tea powder by high-low temperature composite extraction and its application, which adopts a high-low temperature combined extraction method, and the main extraction of tea soup is a combination of low temperature and high temperature. The low-temperature extraction saves the cost of tea. Because low-temperature extraction can better retain the aroma, if low-temperature extraction is used alone, in order to achieve a certain yield and concentration, more tea raw materials may be needed. The present invention reduces the amount of tea used while ensuring quality through high-low temperature composite extraction, thereby saving costs.

[0039] 3. The present invention provides a new process for producing rock tea powder, that is, the tea leaves are roasted for a short time at medium heat before extraction, the tea soup is extracted by a combination of low-temperature extraction and high-temperature short-time extraction, and the drying method is vacuum freeze drying. This process innovation provides new ideas and methods for the production of rock tea powder. Compared with traditional processes, it can better balance the extraction of aroma and flavor; at the same time, vacuum freeze drying can better retain the quality of tea leaves than traditional drying methods. It provides an efficient and high-quality solution for the production of rock tea powder, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a flow chart for preparing the freeze-dried rock tea powder by high and low temperature composite extraction. DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below in conjunction with the examples. It should be pointed out that the examples described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0042] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0043] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0044] Example 1 A method for preparing a freeze-dried rock tea powder by high and low temperature composite extraction

[0045] This embodiment provides a method for preparing a freeze-dried rock tea powder by high-low temperature composite extraction as the best method. The process is as follows: Figure 1 As shown, the steps are as follows:

[0046] 1. Raw material processing: The rock tea raw materials are initially picked and sieved to ensure that the raw tea leaves are uniform in size without obvious stems and yellow leaves;

[0047] 2. Tea baking: Spread the rock tea raw materials into a thickness of 1-4cm (specifically 2cm) and put them into a preheated oven at 90-110℃ (specifically 100℃) for 10-20 minutes (specifically 15 minutes);

[0048] 3. Tea leaves crushing: crush the tea leaves to a size of 10 mesh or more (specifically 10 mesh in this embodiment);

[0049] 4. Extraction: For the first extraction, the ratio of tea to water is 1:7-1:15 (specifically 1:8), and the ratio of tea to ice is 1:3-1:35 (specifically 1:4). The temperature is controlled at 0-15°C, and the extraction time is 30-120 minutes (specifically 60 minutes). The extraction needs to be stirred several times. After the extraction, the tea soup is filtered out and refrigerated for standby use, and the tea leaves are retained; for the second extraction, 85-100°C (specifically 85-95°C) hot water with a ratio of tea to water of 1:5-1:15 (specifically 1:10) is added to the original tea leaves. The extraction time is 5-10 minutes (specifically 10 minutes). After the extraction, it is quickly cooled to 0-5°C, and then mixed with the first extraction tea soup to obtain the final extract;

[0050] 5. Disc centrifuge: centrifugal temperature ≤35℃, centrifugal flow rate 5.0±0.5T / h;

[0051] 6. Ultrafiltration: Ultrafiltration membrane pore size ≤ 0.2 μm, temperature ≤ 35°C;

[0052] 7. Ro concentration: ≤35℃, discharge concentration 20±2brix;

[0053] 8. Vacuum freeze drying: Pre-freeze at a low temperature of -45°C, and enter the pre-vacuum stage after crystallization into a solid to remove most of the free water, and finally enter the analytical drying stage to remove the bound water, and finally obtain freeze-dried tea powder with a water content of less than 5%.

[0054] The invention provides a novel production process of rock tea powder: tea leaves are roasted for a short time at medium fire before extraction, tea soup is extracted by a combination of low-temperature extraction and high-temperature short-time extraction, and vacuum freeze drying is used for drying.

[0055] Compared with the traditional rock tea powder processing technology, the present invention adds a medium-fire short-time re-baking process before tea soup extraction, which can remove moisture and stale taste generated when tea leaves are stored. At the same time, medium-fire baking can enhance the aroma of rock tea, and moderate temperature can retain the floral and fruity aroma of rock tea, making its taste more mellow and smooth, showing rock rhyme. At the same time, the composite extraction tea soup of the present invention adopts a high-low temperature combined extraction method, which has the advantages of both extraction methods, one extraction is low-temperature extraction, and the other is high-temperature extraction. The main extraction tea soup is low temperature, and has the unique aroma of rock tea extracted at low temperature, and the high-temperature extraction tea soup is supplemented to increase its pyrotechnics and mellow taste, and the low-temperature drying method is used to retain the aroma of tea to the greatest extent, which not only improves the flavor quality of rock tea powder, but also saves tea costs compared to low-temperature extraction.

[0056] Example 2 Necessity of the medium-fire short-time re-baking process of the present invention

[0057] The processing of rock tea raw materials already includes a baking process, so the "re-baking" (i.e. "medium-fire short-time re-baking") of the present invention refers to the re-baking of the finished rock tea raw materials. Since the finished tea raw materials have been aged during transportation, storage, and reprocessing, the purpose of re-baking is to remove the moisture and stale taste generated during the storage of tea leaves. At the same time, medium-fire baking can enhance the aroma of rock tea again. The appropriate temperature and time can retain the floral and fruity aroma of rock tea, making its taste more mellow and smooth, showing the rock charm.

[0058] In the traditional processing technology of rock tea powder, due to the limitations of the cognition of traditional technology and the basic satisfaction of traditional technology with tea quality (for example, in the traditional technology, the understanding of the role of re-drying in significantly improving the aroma of rock tea, removing moisture and stale taste, and improving taste is not deep enough. Traditional concepts focus more on the impact of basic tea extraction methods (such as low-temperature or high-temperature extraction) on the quality of tea soup, and do not fully realize the importance of re-drying in improving overall quality), the "medium-fire short-time re-drying" process is not carried out. Therefore, in order to verify the necessity of the "medium-fire short-time re-drying" process of the present invention, in this embodiment, a comparative test is carried out, and the quality of the final rock tea powder is subjected to sensory evaluation and related component detection.

[0059] The specific steps are as follows:

[0060] 1. Not using the “medium-fire short-time re-roasting” process before tea soup extraction

[0061] 1. Raw material processing; 2. Crushing: crush the tea leaves into broken tea (about 10 mesh); 3. Extraction: extract the tea in the ratio of 1:8 to water and 1:4 to ice, control the temperature at 0-15℃, extract for 60 minutes, stir several times during extraction, filter the tea soup after extraction and refrigerate for later use, and keep the tea leaves; for the second extraction, add 85-95℃ hot water with a ratio of 1:10 to tea to the original tea leaves, extract for 10 minutes, quickly cool to 0-5℃ after extraction, and then mix with the tea soup in the first extraction to obtain the final extract; 4. Disc centrifugation 5. Ultrafiltration 6. Ro concentration 7. Vacuum freeze drying.

[0062] Three different rock tea raw materials were selected to repeat the above experiment.

[0063] 2. Add the "medium-fire short-time re-roasting" process before tea soup extraction

[0064] 1. Raw material processing; 2. Tea baking: spread the tea leaves into a thickness of 2-5cm and bake them in a preheated oven at 100℃ for 15 minutes; 3. Crushing: crush the tea leaves into broken tea (about 10 meshes) 4. Extraction: extract the tea leaves in a ratio of 1:8 to tea-water and 1:4 to tea-ice, control the temperature at 0-15℃, extract for 60 minutes, stir several times during extraction, filter the tea soup after extraction and refrigerate for later use, and keep the tea leaves; for the second extraction, add 85-95℃ hot water with a ratio of 1:10 to tea-water to the original tea leaves, extract for 10 minutes, quickly cool to 0-5℃ after extraction, and then mix with the tea soup to obtain the final extract; 5. Disc centrifugation; 6. Ultrafiltration; 7. Ro concentration; 8. Vacuum freeze drying.

[0065] Three different rock tea raw materials were selected to repeat the above experiment.

[0066] The comparative test results are shown in Table 1.

[0067] Table 1. Quality test results of rock tea powder obtained under different double roasting processes

[0068]

[0069] Three different types of rock tea were re-roasted and not re-roasted respectively, and the above steps were used to make freeze-dried powder. The six freeze-dried powders were subjected to sensory evaluation, and their soup color, aroma and taste were evaluated according to the sensory evaluation method of tea in accordance with GBT23776-2018. The results showed that the soup color of the freeze-dried powder made with the re-roasting process would become redder and brighter, and the aroma and taste were better than the non-re-roasted tea powder, which was mainly reflected in the increased roasting aroma, mellow or mild taste, and reduced bitterness and stale taste after re-roasting.

[0070] Therefore, it can be seen that in the processing technology of rock tea powder, the "medium fire short-time re-roasting" process is very necessary. This process can effectively remove the moisture and stale taste generated when the tea leaves are stored, significantly enhance the aroma of rock tea, retain the floral and fruity aroma of rock tea, make the taste more mellow and smooth, and show the rock rhyme, thereby improving the quality of rock tea powder. Traditional processes did not adopt this process due to insufficient understanding of the re-roasting effect and basic satisfaction with existing quality, but through the comparative test of this embodiment, the advantages brought by the re-roasting process can be clearly seen, which provides a strong basis for the improvement of the processing technology of rock tea powder.

[0071] Example 3 Necessity of high and low temperature composite extraction in the present invention

[0072] In the traditional processing technology of rock tea powder, a single low-temperature extraction or high-temperature extraction process is adopted, but each has its own disadvantages. Low-temperature extraction can well preserve the aroma of tea, but the tea soup extracted by low-temperature extraction has a low concentration and a weak taste, and the loss of tea substances is large; high-temperature extraction can extract most of the internal substances in tea, and the taste is strong, but the loss of tea aroma is large. Therefore, in order to verify the necessity of the "high and low temperature composite extraction" process adopted in the present invention, a comparative test is carried out in this embodiment, and the quality of the final rock tea powder is subjected to sensory evaluation and related component detection. The specific steps are as follows:

[0073] 1. Adopt the "high and low temperature composite extraction" of the present invention: first low temperature (0-15℃) and then high temperature (85-95℃) treatment

[0074] 1. Raw material processing; 2. Tea baking: spread the rock tea raw material into a thickness of 2cm and put it into a preheated 100℃ oven for re-baking for 15 minutes; 3. Crushing: crush the tea leaves into broken tea (about 10 mesh); 4. Extraction: extract the first tea according to the ratio of tea to water 1:8 and tea to ice 1:4, control the temperature at 0-15℃, extract for 60 minutes, stir several times during extraction, filter the tea soup after extraction and refrigerate for later use, and keep the tea leaves; second extraction: add 85-95℃ hot water with a ratio of tea to water 1:10 to the original tea leaves, extract for 10 minutes, quickly cool to 0-5℃ after extraction, and then mix with the first tea soup to obtain the final extract; 5. Disc centrifugation; 6. Ultrafiltration; 7. Ro concentration; 8. Vacuum freeze drying.

[0075] 2. High temperature extraction

[0076] 1. Raw material processing; 2. Tea baking: spread the rock tea raw material into a thickness of 2cm and put it into a preheated 100℃ oven for re-baking for 15 minutes; 3. Crushing: crush the tea leaves into broken tea (about 10 mesh); 4. Extraction: extract the first tea according to the ratio of tea to water of 1:12, control the temperature at 90-100℃, extract for 20 minutes, and stir several times during extraction; for the second tea, add 85-95℃ hot water with a ratio of tea to water of 1:10 to the original tea leaves, extract for 5 minutes, and then mix with the first tea soup to obtain the final extract; 5. Disc centrifugation; 6. Ultrafiltration; 7. Ro concentration; 8. Vacuum freeze drying.

[0077] 3. Low temperature extraction

[0078] 1. Raw material processing; 2. Tea baking: spread the rock tea raw material into a thickness of 2cm and put it into a preheated 100℃ oven for re-baking for 15 minutes; 3. Crushing: crush the tea leaves into broken tea (about 20 mesh); 4. Extraction: extract the first tea according to the ratio of tea to water of 1:12, control the temperature at 0-15℃, extract for 60 minutes, and stir several times during extraction; for the second tea, add 0-15℃ ice water with a ratio of tea to water of 1:10 to the original tea leaves, extract for 5 minutes, and then mix with the first tea soup to obtain the final extract; 5. Disc centrifugation; 6. Ultrafiltration; 7. Ro concentration; 8. Vacuum freeze drying.

[0079] 4. Use "high and low temperature composite extraction": high temperature (85-95℃) first and then low temperature (0-15℃) treatment

[0080] 1. Raw material processing; 2. Tea baking: spread the rock tea raw material into a thickness of 2cm and put it into a preheated 100℃ oven for re-baking for 15 minutes; 3. Crushing: crush the tea leaves into broken tea (about 10 mesh); 4. Extraction: add 85-95℃ hot water with a tea-water ratio of 1:10 to the original tea leaves, extract for 10 minutes, quickly cool to 0-5℃ after the extraction, filter the tea soup and refrigerate for later use, and keep the tea leaves; extract the second extraction at a ratio of tea-water ratio of 1:8 and tea-ice ratio of 1:4, control the temperature at 0-15℃, extract for 60 minutes, stir several times during extraction, filter the tea soup after the extraction, and mix it with the first extraction tea soup to obtain the final extract; 5. Disc centrifugation; 6. Ultrafiltration; 7. Ro concentration; 8. Vacuum freeze drying.

[0081] Four types of tea powders made by different processes were boiled at a concentration of 0.2 ppm, and their soup color, aroma and taste were evaluated according to the sensory evaluation method for tea of ​​GBT23776-2018. At the same time, the caffeine and tea polyphenols of the four types of tea powders were tested according to the national food safety standard GB 5009.139-2014 Determination of caffeine in beverages and the test method for the content of tea polyphenols and catechins in tea of ​​GB / T 8313-2018. The results are shown in Table 2.

[0082] Table 2. Quality test results of rock tea powder obtained under different extraction processes

[0083]

[0084] Tea polyphenols and caffeine are flavoring substances in tea leaves, and their contents are positively correlated with astringency and bitterness. Combined with the caffeine, tea polyphenols and sensory evaluation data in Table 2, the tea powder using the "mixed extraction" of the present invention is significantly superior to the tea powder using "high temperature extraction", "low temperature extraction" and "high temperature followed by low temperature extraction" in terms of aroma and taste. Although the tea soup of the tea powder using "high temperature extraction" is thicker, the aroma is weaker and more stuffy, and more bitter; the tea powder using "low temperature extraction" has too low an extraction rate, which causes the subsequent concentration and other processing processes to take too long and also causes aroma loss. Although the final tea powder has a better aroma, it has a thin and weak taste, and the cost is relatively high. For "extracting tea powder using "high temperature followed by low temperature", extracting at a higher temperature first may cause some aroma components in the tea leaves to be lost at high temperatures, making the aroma of the final tea powder have a roasted aroma but it is weak and has a miscellaneous taste. At the same time, high-temperature treatment first may cause changes in some components in the tea, affecting the extraction of effective ingredients in the tea during subsequent low-temperature extraction, resulting in a thicker taste but with bitterness and off-flavors, which also affects the quality of the final tea powder.

[0085] In summary, the "high and low temperature mixed extraction" method of the present invention can effectively improve the quality of traditional tea powder.

[0086] Meanwhile, in the Chinese invention patent with the authorization announcement number of "CN104106696B" and the invention name of "A tea beverage and its manufacturing method" (reference document 1), although the "high and low temperature composite extraction method" is also adopted: the extraction temperature of the first extraction is 50-85℃, the extraction time is 10-30min, and the tea-water ratio is 1:(50-80); the second extraction temperature conditions are complex (such as 75℃ at the top of the tower and 55℃ for the feed), and the overall temperature range is relatively high. However, it is completely different from the "high and low temperature composite extraction method" of the present invention.

[0087] In the Chinese invention patent with authorization announcement number "CN101164424B" and invention name "A method for preparing instant tea powder" (comparative document 2), a "three-stage extraction method" is adopted: the extraction temperature of the first extraction is 20-30°C, the extraction time is 20-30min, and the tea-to-water ratio is 1:(4-6); the extraction temperature of the second extraction is 40-70°C, the extraction time is 10-15min, and the tea-to-water ratio is 1:(10-15); the extraction temperature of the third extraction is 85-100°C, the extraction time is 5-10min, and the tea-to-water ratio is 1:(4-6); therefore, it is completely different from the "high and low temperature composite extraction method" of the present invention.

[0088] The conditions of the above two reference documents and the "high and low temperature composite extraction method" of the present invention are specifically shown in Table 3:

[0089] Table 3. Specific conditions of the “high and low temperature composite extraction method” in different comparative documents and this application

[0090]

[0091]

[0092] At the same time, in order to further verify that the "high and low temperature mixed extraction" method of the present invention can effectively improve the quality of the prepared tea powder, the "high and low temperature mixed extraction" method of the present invention, as well as the extraction methods in Comparative Documents 1 and 2 are respectively used in this embodiment to prepare three types of tea powders. Similarly, the three types of tea powders prepared by different processes are boiled at a concentration of 0.2 per thousand, and the soup color, aroma and taste are evaluated according to the GBT23776-2018 tea sensory evaluation method. At the same time, the three types of tea powders are tested for caffeine and tea polyphenols according to GB 5009.139-2014 National Food Safety Standard Determination of Caffeine in Beverages and GB / T 8313-2018 Detection Method for the Content of Tea Polyphenols and Catechins in Tea. The results are shown in Table 4.

[0093] Table 4. Quality test results of rock tea powder obtained under different extraction conditions in the present invention and the reference document

[0094]

[0095] As can be seen from Table 4, the tea powder prepared by the "mixed extraction" of the present invention is significantly superior to the tea powder prepared by the method of Comparative Document 1 or Comparative Document 2 in terms of soup color, aroma and taste. When the tea powder prepared by the method of Comparative Document 1 is in a relatively high temperature range as a whole, more internal substances can be extracted, but the aroma is also weak and dull, and the content of caffeine and tea polyphenols is also significantly high, resulting in a heavier bitter taste. This may be because the temperature of the first extraction is 50-85°C, which is relatively high and not conducive to the retention of aroma, and the extraction time is 10-20min, which is relatively short, and the aroma components in the tea leaves may not be fully extracted. The subsequent operation is to directly mix the first extract and the second extract after clarification (weight ratio: 350:1). This mixing method may not be able to well integrate the advantages of the two extracts, thereby affecting the quality of the tea powder. When the tea powder prepared by the method of comparative document 2 is extracted by three-stage temperature, different components of tea leaves can be extracted at different temperature stages, but the operation is complicated, and subsequent processing steps such as compound enzyme hydrolysis, filtration, concentration and other steps may cause the loss of aroma components and changes in taste. This may be because although the three-stage temperature extraction has the advantage of being able to extract tea components more finely, due to the complexity of the process, improper control of temperature and time in each stage may lead to incomplete or over-extraction of certain components, and also cause the aroma and taste of the final tea powder to fail to achieve the best effect. At the same time, the temperature of the first extraction is 20-30°C, which is still higher than the temperature of the first extraction of the present invention, and the time of the first extraction is 20-30min, which may lead to low extraction efficiency. In the subsequent operation, the second extract and the third extract need to be mixed, compound enzyme hydrolysis, filtration, concentration to obtain a concentrated solution, and then the concentrated solution is mixed with the first extract. These steps may introduce impurities or lose some effective ingredients, thereby affecting the quality of the tea powder.

[0096] Therefore, it can be seen that only when the "high-low temperature composite extraction method" of the present invention is adopted, can the tea powder obtained achieve a better balance in aroma, taste and ingredient content and have the best quality.

[0097] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing freeze-dried rock tea powder, characterized in that: The steps include: (1) before extracting tea soup, the tea leaves are roasted for a short time at medium heat; (2) obtaining the first extract and the second extract by high and low temperature composite extraction; (3) rapidly cooling the second extract tea soup, and mixing it with the first extract tea soup to obtain a final extract, which is used to prepare rock tea freeze-dried powder; In the medium-fire short-time re-roasting process adopted in step (1), the re-roasting temperature of the tea leaves is 90-110° C. and the re-roasting time is 10-20 minutes.

2. The preparation method according to claim 1, characterized in that In the step (2), the tea soup is extracted by combining low-temperature extraction and high-temperature short-time extraction. The first extraction is performed by low-temperature extraction, and the tea soup is filtered and refrigerated for later use, while the tea leaves are retained. The second extraction is performed by high-temperature extraction, and after the second extraction is completed, the tea soup is quickly cooled and mixed with the first extraction to obtain the final extract.

3. The preparation method according to claim 2, characterized in that: The extraction temperature is 0-15°C, and the extraction time is 30-120 minutes.

4. The preparation method according to claim 3, characterized in that: The secondary extraction temperature is 85-100° C., and the extraction time is 5-10 minutes.

5. The preparation method according to claim 4, characterized in that: The ratio of tea to water is 1:7-1:15, and the ratio of tea to ice is 1:3-1:

35.

6. The preparation method according to claim 5, characterized in that: The tea-water ratio of the two extractions is 1:5-1:

15.

7. The preparation method according to claim 6, characterized in that: After the second extraction, the tea soup is rapidly cooled to a temperature of 0-5°C.

8. The preparation method according to claim 1, characterized in that: The preparation method of the rock tea freeze-dried powder also includes raw material processing, crushing and grinding of tea leaves after double roasting, disc centrifugation, ultrafiltration, Ro concentration and drying process after tea soup extraction, and the drying process adopts vacuum freeze drying.

9. The preparation method according to claim 8, characterized in that: In the tea leaves short-time medium-fire re-roasting process, the thickness of the rock tea raw materials in the oven is 1-4 cm.

10. The preparation method according to claim 9, characterized in that: The particles of the tea leaves after crushing are larger than 10 mesh.

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