Manufacturing method of black tea using frost-damaged tea leaves

Abstract

The present invention is a method for making black tea using frost-damaged tea leaves, which can produce black tea with a smooth taste and excellent umami and aroma by utilizing first flush tea that is discarded due to low-temperature damage from frost that occurs repeatedly every year. It can be used as a future frost damage countermeasure for tea farmers whose income is reduced due to a decrease in the production volume of first flush tea, which is purchased at a high price, and a delay in the harvest season.

Description

Technology Field

[0001] The present invention relates to a method for making black tea using frost-damaged tea leaves, and specifically, to a method for making black tea using tea leaves that are discarded due to frost damage caused by climate change such as drought, low temperature, and high temperature that occurs every year. Background Technology

[0003] The tea tree (Camellia sinenisis O. Kuntze) is a subtropical crop that is a perennial evergreen broad-leaved tree belonging to the genus Camellia of the family Camelliaceae. Countries such as Korea, China, Japan, and Taiwan, where small-leaved varieties of tea trees are mainly produced, are primarily cultivated in regions around 30°N North latitude. Compared to other crops, tea trees have weak cold tolerance; when the minimum temperature drops below -2°C, new shoots (branches that have newly grown in the current year) suffer frost damage and die, and if the temperature drops below -10°C for more than one hour, wilting occurs. The rate of damage can vary depending not only on the minimum temperature but also on the duration of the low temperature.

[0004] The harvest season accounts for the largest share of factors determining tea quality and price; the earlier the harvest, the higher the profitability for the farm. In Korea, tea can be harvested three to four times a year and is classified into first flush, second flush, third flush, and fourth flush teas depending on when the leaves are harvested. It is generally known that tea harvested earlier has less astringency and a well-balanced umami flavor, resulting in higher quality. Conversely, as the harvest season is delayed, the tea leaves grow larger and become more bitter and astringent; however, since the yield increases, it has the advantage of being relatively cheaper.

[0005] First flush tea, made from tea leaves harvested in the spring, contains the most abundant nutrients because it is produced by continuously receiving photosynthesis and nutrients from the previous autumn through the winter. The tea contains a large amount of Vitamin C, and in particular, it has the advantage of having an excellent umami taste, as its amino acid content is about 1.7 to 2 times higher than that of second and third flush teas.

[0006] Abnormal temperature phenomena are frequently observed in April, which is primarily the harvest season for first flush tea, due to various factors. Among these, frost occurs when temperatures drop below the freezing point on clear, windless nights, and as water vapor in the atmosphere condenses on parts vulnerable to the cold, it causes physiological disorders. Major tea-producing regions, including Hadong and Boseong, are facing business difficulties as the harvest season for high-quality first flush tea is delayed and the yield of tea leaves decreases due to low-temperature damage, such as frost, that recurs every year.

[0007] Accordingly, the present invention aims to harvest first flush tea that is discarded due to frost damage, process it using the traditional black tea production method of the Hadong region, and verify the commercial value of the black tea to utilize it as a countermeasure against frost damage. Prior art literature

[0009] Republic of Korea Registered Patent No. 10-1125774 The problem to be solved

[0010] The present invention is intended to produce black tea from tea leaves that are discarded due to low-temperature damage caused by frost, and to identify the components of the black tea produced in this way to utilize as a countermeasure against future frost damage. means of solving the problem

[0012] The method for making black tea using frost-damaged tea leaves according to the present invention may include: (a) a step of collecting tea leaves that have withered and been discarded due to low-temperature damage including frost; (b) a step of spreading the collected tea leaves widely indoors and evaporating moisture to wither them; (c) a step of rolling the withered tea leaves using a rolling machine for 15 to 25 minutes, and then oxidizing them by partially blocking sunlight for 30 to 50 minutes; and (d) a step of spreading the rolled and oxidized tea leaves in the sun to dry them for 5 hours or more.

[0013] In step (a) above, the tea leaves are first flush tea harvested between late April and early May, and in step (b) above, the harvested tea leaves that have suffered cold damage may be processed for 20 to 40 minutes, shortening the wilting time compared to normal tea leaves that have not suffered cold damage.

[0014] The above step (c) may be repeated a total of three times, wherein the pressure of the kneading machine is set to low for the first kneading and oxidation, the pressure of the kneading machine is set to medium for the second kneading and oxidation, and additionally the pressure of the kneading machine is set to high for the third kneading and oxidation, and the tea leaves kneaded and oxidized in step (d) are dried so that their moisture content is 5% or less. Effects of the invention

[0016] This invention enables the production of black tea with a smooth taste, excellent umami flavor, and superior aroma by utilizing first flush tea that is discarded due to low-temperature damage from recurring frosts every year. It can also be utilized as a future frost damage countermeasure for tea farmers whose income is reduced due to decreased production of first flush tea, which is purchased at a high price, and delayed harvesting. Brief explanation of the drawing

[0018] FIG. 1 is a flowchart illustrating a method for making black tea using frost-damaged tea leaves according to the present invention. Figure 2 is a diagram showing the appearance of normal tea leaves and frost-damaged tea leaves. Figure 3 is a graph showing the catechin analysis results of the present invention. Figure 4 is a graph showing the caffeine analysis results of the present invention. Figure 5 is a graph showing the theaflavin analysis results of the present invention. Figure 6 is a graph showing the results of discriminant function analysis (DFA) using the electronic tongue of the present invention in two dimensions and three dimensions. Figure 7 is a graph showing the distance values ​​of sour, salty, and umami tastes using the electronic tongue of the present invention. Specific details for implementing the invention

[0019] The present invention is described more specifically below through specific details for implementing the invention, <Examples>, and <Experimental Examples>; however, since the embodiments of the present invention can be modified in various different forms, the scope of the present invention is not limited to the embodiments described below.

[0020] Throughout the specification of the present invention, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Throughout the specification of the present invention, when a step is described as being "on" or "before" another step, this may include not only cases where the step is in a direct chronological relationship with the other step, but also cases where the chronological order of the two steps may change, such as in an indirect chronological relationship, where the chronological order of the two steps may change, such as a mixing step following each step.

[0021] Throughout the specification of this invention, terms such as "approximately," "substantially," etc., are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding the invention. Throughout the specification, the terms "step of" or "step of" do not mean "step for."

[0023] The present invention relates to a method for making black tea using frost-damaged tea leaves, and the method for making black tea according to an embodiment of the present invention will be described with reference to the attached drawings.

[0025] Tea is a beverage made by steeping plant-based ingredients, including tea leaves, and is one of the three major non-alcoholic beverages enjoyed by all humanity, along with coffee and cocoa. It contains large amounts of caffeine, catechins, and theanine, and is enjoyed by many people for its distinctive, subtle taste and aroma. The most popular types include black tea, green tea, and herbal tea.

[0027] Black tea is made by fermenting and drying the young leaves of tea trees, primarily produced in regions such as China and Sri Lanka. During the fermentation process, tannins become insoluble, reducing the astringent taste and giving the tea a distinctive reddish color and aroma. Catechin, a type of polyphenol abundant in black tea, possesses powerful antioxidant properties. Therefore, consuming black tea regularly can help maintain health while preventing various age-related diseases; notably, it reduces the risk of heart disease, arteriosclerosis, stroke, and cancer. Additionally, the caffeine contained in black tea acts on the central nervous system to stimulate alertness and promote blood circulation, while also being effective for diuretic effects and fatigue recovery.

[0029] FIG. 1 is a flowchart illustrating a method for making black tea using frost-damaged tea leaves according to the present invention. Referring to FIG. 1, the method for making black tea using frost-damaged tea leaves (S100) includes a tea leaf harvesting step (S110), a wilting step (S120), a rolling and oxidation step (S130), and a drying step (S140).

[0031] (a) Tea leaf harvesting stage

[0033] Harvesting is the process of picking tea leaves using human hands or machines. Depending on the harvesting season, tea is also classified into first flush, second flush, third flush, and last (fourth) flush teas. In Korea, the first flush tea is generally harvested between late April and early May, the second flush tea between late May and early June, the third flush tea between late June and July, and the last flush tea between late August and early September.

[0035] Figure 2 is a diagram showing the appearance of normal tea leaves and frost-damaged tea leaves. In the case of first flush tea, which is made from the very first young tea leaves that emerge in early spring and is recognized as the highest quality in taste and aroma, the biggest problem during the harvest season is damage caused by frost, which often occurs, and frost-damaged tea leaves cannot be used as tea and are discarded as they turn brown.

[0037] In the present invention, tea leaves that are discarded after dying due to low-temperature damage including frost are collected as first flush tea, a high-quality tea harvested between late April and early May, and impurities are picked out from the collected tea leaves.

[0039] (b) Withering stage

[0041] Withering is a phenomenon in which a plant wilts and dries out due to a lack of moisture, and it involves wilting the fresh leaves of the tea plant. As part of the manufacturing process for black tea or partially fermented tea, tea leaves are withered to create a unique aroma and soften the texture of the leaves. It is the first step in the production process for fully fermented and semi-fermented teas, such as black tea and oolong tea, but it is not performed on unfermented teas such as green tea.

[0043] Cold damage to tea trees is divided into red wither, in which the tissue exceeds its freezing tolerance limit and ice crystals formed within the cells destroy the cell membrane, causing the damaged area to turn red, dry out, and die, and green wither, in which the roots and stems at the base of the tea tree freeze due to continuous low temperatures and lack of water, inhibiting water absorption, causing the leaves to dry out and turn a faded green color due to a lack of internal water before dying.

[0045] Since the harvested tea leaves that have suffered cold damage have a lower moisture content than normal tea leaves that have not suffered cold damage, the wilting time is shortened by about one hour compared to that of normal tea leaves that have not suffered cold damage, and is carried out for 20 to 40 minutes. The harvested tea leaves are spread out widely on a net or shelf laid out in a large room and withered by evaporating the moisture.

[0047] (c) Mindfulness and oxidation steps

[0049] Rolling is the process of rubbing withered tea leaves, after the wilting process is complete, using hands or machinery to reshape them into rod-like or needle-like forms, thereby crushing the leaf tissue. During this process, more than 80% of the tea leaf's cellular tissue is destroyed, and a sticky tea juice is produced.

[0051] If tea leaves are left as they are after rolling, the tea juice produced during the process combines with oxygen to generate oxidizing enzymes, leading to fermentation. As fermentation occurs, the leaves turn brown, and the unique flavor and color of black tea are determined at this stage. While fresh leaves typically emit a fishy odor, black tea that has undergone this process exhibits a variety of aromas, including sweet notes.

[0053] After rolling the above withered tea leaves using a rolling machine for 15 to 25 minutes, they are oxidized by partially blocking sunlight for 30 to 50 minutes.

[0055] If the above rolling step is performed with strong pressure from the beginning, the tea leaves will be damaged and tear frequently. Therefore, the process is carried out by gradually increasing the pressure intensity from low to medium, and from medium to high. The degree of oxidation can be increased by the heat generated while repeating the rolling step three times, compared to oxidation under sunlight.

[0057] More specifically, the pressure of the kneading machine is set to low for the first kneading for 15 to 25 minutes and oxidized for 30 to 50 minutes, then the pressure of the kneading machine is set to medium for the second kneading for 15 to 25 minutes and oxidized for 30 to 50 minutes, and then additionally the pressure of the kneading machine is set to high for the third kneading for 15 to 25 minutes and oxidized for 30 to 50 minutes.

[0059] (d) Drying step

[0061] Drying is a process that stops the oxidative fermentation of tea leaves at an appropriate state, preventing spoilage and fixing the flavor. During the drying stage, properly controlling the moisture content of the tea leaves is key.

[0063] The tea leaves are spread out in the sun for at least 5 hours to dry completely so that the moisture content of the above-mentioned and oxidized tea leaves is 5% or less, and then processed into black tea. The finished black tea can be divided into smaller portions and packaged into tea bags.

[0065] <Example> Black Tea Production

[0067] On May 3, 2022, about 20 kg of frost-damaged tea leaves (1 bud, 2 leaves to 3 leaves) were harvested from a cultivation farm at 1158-2, Buchun-ri, Hwagae-myeon, Hadong-gun, Gyeongsangnam-do and used for making black tea.

[0069] The harvested tea leaves were spread out widely on a shelf and withered for 30 minutes, and then rolled using a tea roller (Tea roller, 6CR-Z45, Zhejiang, China). The tea leaves were rolled once for 20 minutes with the pressure of the roller set to low, and then oxidized for 40 minutes by covering them with a mesh that partially blocked sunlight. Afterward, the tea leaves were rolled a second time for 20 minutes with the pressure of the roller set to medium and oxidized for 40 minutes. Finally, the tea leaves were rolled a third time for 20 minutes with the pressure of the roller set to high and oxidized for 40 minutes. Afterward, the tea leaves were spread out completely in the sun and dried for more than 5 hours until the moisture content was reduced to 5% or less, at which point black tea was produced.

[0071] During the wilting and rolling process, the moisture in the frost-damaged parts of the tea leaves evaporated rapidly and was naturally shredded, so the finished tea leaves did not retain their original form.

[0073] To confirm the value of the frost-damaged black tea (Stress) of the present invention for use as a tea bag, it was compared with regular black tea (KOR) made from normal tea leaves that were not damaged by low temperatures harvested at a similar time, Jaksal black tea (HD_JS) made using the same tea-making method, GABA black tea (GABA) made after anaerobic treatment before wilting, and Chinese Keemun black tea (CHN), which is called one of the world's top three black teas.

[0075] All analysis results were presented as mean values ​​and standard deviations measured in three repetitions using the SAS program (Ver. 9.3. Cary. NC. USA), and PROC ANOVA analysis of variance and Duncan's Multiple Range Test post-hoc analysis were performed to compare significance at the mean value p<0.05 significance level.

[0077] <Experimental Example 1> Analysis of Catechin, Caffeine, and Theaflavin

[0079] 1-1. Experimental Method

[0080] 0.5 g of ground tea leaves were extracted by adding 50 mL of 50% ethanol and ultrasonically treating for 1 hour and 30 minutes. An equal amount of ethyl acetate was added to the extract and mixed, followed by separation, extraction, and vacuum concentration. The vacuum concentrate was diluted to 20 mL of methanol and filtered through a PFFL 0.45 μm filter.

[0082] 1-2. Experimental Conditions

[0083] An HPLC equipped with a TSK-ODS 80™ column was used, and each standard was purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA). [Table 1] shows the experimental conditions for the analysis of catechin, caffeine, and theaflavin.

[0085] Instrument HPLC (Ultimate 3000, Dionex, USA) Column TSK-ODS 80™ column (4.5 x 250mm, 5μm, phenomenex, California, USA) Detector PDA-3000, Dionex, UV 240nm Mobile phase Time 0.2% H3PO4(on water) 100% acetonitrile 0 85 15 2 85 15 2.1 70 30 40 70 30 40.1 0 100 42 0 100 42.1 85 15 47 85 15 Flow rate 1.0 mL / min Retention time Time peak 5.2 (-)-epigallocatechin(EGC) 6.8 (-)-catechin(C) 7.9 caffeine 8.9 (-)-epicatechin(EC) 9.5 (-)-epigallocatechin gallate (EGCG) 16.4 (-)-epicatechin gallate(ECG) 35.6 theaflavin[theaflavin(TF'), theaflavin 3-gallate(TF3G), theaflavin 3'-gallate(TF3'G), theaflavin 3,3'-digallate(TF3,3'G)]

[0087] 1-3. Experimental Results

[0088] [Table 2] shows the results of catechin and caffeine analysis for frost-damaged black tea, regular black tea, Jaksal black tea, GABA black tea, and Keemun black tea. (a; ECG and EGCG, b; EGC, EC and C, c; EC and ECG, d; EGC and EGCG)

[0090] gallate type (a) non-gallate type (b) a / b de-hydroxylated (c) tri-hydroxylated (d) catechin ratio (c / d) Regular black tea 0.278 0.114 2.439 0.163 0.212 0.769 Jacksal black tea 0.162 0.082 1.976 0.128 0.104 1.231 Keemun black tea 0.216 0.135 1.600 0.155 0.178 0.871 GABA black tea 0.115 0.080 1.438 0.069 0.109 0.633 Frost-damaged black tea 0.151 0.906 0.167 0.124 0.122 1.016

[0092] Tea leaves are composed of approximately 75–80% water, with the remainder consisting of solids, which are known to make up about 20–30% of the total. These solids contain various components such as amino acids, catechins, caffeine, chlorophyll, fiber, and vitamins. Among these, catechins are one of the total phenolic compounds belonging to the flavan-3-ols of the flavonoid group and are classified into gallate-type (EGCG, ECG, GCG) catechins, which produce a bitter and astringent taste, and non-gallate-type (EC, EGC, C) catechins, which produce a sweet and bitter taste.

[0093] Figure 3 is a graph showing the catechin analysis results of the present invention. The gallate-type catechin content, including EGCG and ECG, was high in regular black tea at 0.278% and in Keemun black tea at 0.216%, while it was lowest in GABA black tea at 0.115%. The most distinctive feature of frost-damaged black tea was that the non-gallate-type catechin content was 0.906%, with the content of C being the highest at 0.811%, and the total catechin content was also 1.057%, which was higher than that of the other four types of black tea (0.196% to 0.392%).

[0094] This is consistent with the results showing that when tea trees are exposed to low temperatures, the catechin content temporarily increases rapidly between 1 and 3 hours, with C showing the largest increase of 4.2 times 3 hours after exposure compared to before exposure. In particular, non-gallate type catechins, which are involved in bitter and sweet flavors, are highly expressed under light conditions and their content decreases under shade conditions; this appears to be the result of inadequate photoprotection due to the necrosis of the tea leaf surface tissue after frost damage.

[0095] Meanwhile, according to the biosynthetic pathway of catechins, dihydroquercetin, a precursor of dehydroxylated catechins (EC, ECG), is produced by dihydrokaempferol via 3'-hydroxylase, while dihydromyricetin, a precursor of trihydroxylated catechins (EGC, EGCG), is produced by dihydrokaempferol via 3',5'-hydroxylase, showing genetic differences. When investigated using a method that utilizes catechin indicators (dehydroxylated catechins / trihydroxylated catechins) to confirm genetic origin relationships, the same Jaksal black tea and frost-damaged black tea yielded values ​​of 1.231 and 1.016, respectively, followed by Keemun black tea at 0.871, regular black tea at 0.769, and GABA black tea at 0.633.

[0096] Figure 4 is a graph showing the caffeine analysis results of the present invention. In Jaksal black tea, the caffeine content was 0.836%, which is 2.0 to 2.3 times lower than that of Keemun black tea (1.960%) and regular black tea (1.651%). It was also effective in reducing caffeine content in frost-damaged black tea, with a value of 0.420%. This is because caffeine, whose synthesis is inhibited under light conditions, showed a tendency to increase in the early stages of low temperature during the freezing test, but then showed a tendency to decrease rapidly at the stage where the leaves completely withered. This appears to be the result of low-temperature stress caused by frost destroying the tissues of the tea leaves and consequently preventing the photoprotective action of the leaf cells.

[0097] Figure 5 is a graph showing the results of the theaflavin analysis of the present invention. Although the theaflavin content was expected to be highest in frost-damaged black tea, which had already undergone significant oxidation before harvest, the total theaflavin content was actually the lowest at 0.127%, followed by regular black tea (0.130%), GABA black tea (0.132%), Keemun black tea (0.147%), and Jaksal black tea (0.241%).

[0099] <Experimental Example 2> Analysis of Free Amino Acids

[0101] 2-1. Experimental Method

[0102] 0.1g of crushed tea leaves were mixed with 10mL of distilled water and shaken for 3 hours. Then, 1mL of 10% 5-sulfosalicylic acid dihydrate was added, and the mixture was left at 5℃ for 12 hours to precipitate and remove proteins. After centrifugation at 4,000rpm for 15 minutes, the supernatant was collected and concentrated using a rotary evaporator (EYELAN-1100V-W, Japan). Next, 5mL of 0.2M, pH 2.2 lithium citrate loading buffer was added for dilution, followed by filtration through a 0.45μm membrane filter. The filtrate was analyzed using an amino acid analyzer (Skyam S7130, Amino acid reagent organize, Germany) with UV / VIS detectors at 400nm (1.0 AU) and 570nm (1.0 AU).

[0104] 2-2. Experimental Results

[0105] [Table 3] shows the results of the free amino acid analysis of frost-damaged black tea, regular black tea, Jaksal black tea, GABA black tea, and Keemun black tea.

[0107] Regular black tea Jacksal black tea Keemun black tea GABA black tea Frost-damaged black tea Asp 56.4 12.7 27.4 4.1 23.3 Thr 23.4 5.7 11.0 4.9 12.3 Ser 53.9 15.1 16.3 14.7 30.2 Asn 166.5 3.7 3.7 4.3 10.9 Glu 0.0 22.7 21.1 20.1 40.7 The 422.7 212.1 364.9 246.9 307.9 Pro 36.3 6.4 12.6 6.7 9.3 Ala 29.2 14.6 16.8 17.6 29.5 Leu 18.5 6.4 8.6 6.6 10.8 Tyr 0.0 10.2 15.9 10.7 15.7 Gaba 79.6 16.9 10.9 146.9 140.4 Lys 36.5 3.1 7.1 3.5 8.0 Arg 94.4 5.6 20.2 4.8 86.2 Urea 396.1 171.8 171.8 353.9 292.0 So on 262.4 207.0 250.1 192.5 205.1 Total 1575.9 713.3 958.3 1037.9 1122.1

[0109] Regular black tea contained the highest amount of free amino acids at 1,576 mg / 100g, followed by frost-damaged black tea at 1,122 mg / 100g, which showed a relatively high amino acid content. In particular, regarding the content of GABA (γ-aminobutyric acid), which is known to stimulate blood flow to the brain, increase oxygen supply to promote the metabolic function of brain cells, help lower blood pressure, and recently have a preventive effect against Parkinson's disease, Jaksal black tea made using the same tea processing method contained 16.9 mg / 100g, frost-damaged black tea contained 140.4 mg / 100g, and GABA black tea processed by anaerobically contained 146.9 mg / 100g.

[0110] This indicates that the low temperature caused by frost acted as a stress on the tea tree, increasing the GABA content of the tea leaves, and showed a level of GABA content similar to the effect of anaerobic treatment during the tea making process to artificially produce GABA tea.

[0112] <Experimental Example 3> Taste Analysis Using an Electronic Tongue

[0114] 3-1. Experimental Method

[0115] 150 mL of 100°C distilled water was added to 1.5 g of ground tea leaves and steeped for 3 minutes. The tea was then filtered using filter paper to prevent floating particles and foreign substances from adhering to the sensor, and 250 µL of the filtrate was diluted with 25 mL of purified water. Using an electronic tongue system (Electronic tongue, ASTREE, Alpha MOS, Toulouse, France) equipped with 7 sensors—3 calibrated sensors AHS (HCl, sour taste), NMS (MSG, umami taste), CTS (NaCl, salty taste), 2 sensors PKS and ANS involved in sweet and bitter tastes, and arbitrary sensor values ​​CPS and SCS—5 replicate measurements were taken, and the results were analyzed in 3 replicates after excluding the initial and final values.

[0117] 3-2. Experimental Results

[0118] [Table 4] shows the results of taste analysis of frost-damaged black tea, regular black tea, Jaksal black tea, GABA black tea, and Keemun black tea using an electronic tongue.

[0120] Sample names AHS PKS CTS NMS CPS ANS SCS Regular black tea 8.0 6.0 6.6 5.9 5.9 5.2 4.7 Jacksal black tea 5.9 4.8 4.7 4.0 5.8 5.3 5.7 Keemun black tea 4.6 7.1 6.8 8.3 7.8 8.0 7.4 GABA black tea 6.1 6.1 6.0 6.2 3.1 5.1 5.7 Frost-damaged black tea 4.7 4.9 5.1 5.4 5.0 5.8 6.6

[0122] In the past, the taste of tea relied on sensory evaluation, primarily using quantitative descriptive analysis (QDA) to rate sweet, nutty, bitter, astringent, and umami on a 9-point scale. However, recently, electronic tongue analysis has been used to visualize the tastes of coffee, juice, beer, and wine, serving as an indicator to determine consumers' purchasing decisions. The electronic tongue system from Alpha Mos of France analyzed the taste component patterns of black tea using seven sensors: standard solutions HCl (sour, AHS), NaCl (salty, CTS), and MSG (umami, NMS), as well as sweet (PKS), bitter (ANS), and other sensor values ​​corresponding to pain sensations such as astringent and spicy tastes.

[0123] Figure 6 is a graph showing the results of discriminant function analysis (DFA) using the electronic tongue of the present invention in two and three dimensions. On the DFA plot, DF1 (discriminant function first score) was 96.3% and DF2 was 2.9%. Regular black tea was located in the upper right corner, Keemun black tea in the lower right corner, Jaksal black tea and GABA black tea were located in the upper left center corner, and frost-damaged black tea was located in the leftmost corner.

[0124] Figure 7 is a graph showing the distance values ​​for sourness, saltiness, and umami using the electronic tongue of the present invention. Looking at the taste screening values ​​of the seven sensors, frost-damaged black tea generally showed a neutral taste trend without any particularly strong flavor, while Keemun black tea showed high sensor values ​​for umami (NMS) and saltiness (CTS), and also showed high values ​​for PKS, ANS, and SCS.

[0126] As previously mentioned, when black tea is made from frost-damaged tea leaves, it exhibits an overall mild taste and a catechin content similar to that of regular black tea, while also being highly valuable as a low-catechin black tea. Furthermore, it has high utility value in terms of functionality, such as exhibiting a high GABA content due to natural cold stress. Therefore, considering that the parts are discarded after dying due to frost damage, it is believed that it can be developed into a sufficiently competitive product by emphasizing low caffeine content and high GABA content.

[0128] Optimal embodiments have been disclosed in the specification as described above. Specific terms have been used herein, but they are used only for the purpose of describing the invention and are not intended to limit the meaning or the scope of the invention as described in the claims. Therefore, those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the invention should be determined by the technical spirit of the appended claims. Explanation of the symbols

[0130] S100: Black tea production method using frost-damaged tea leaves S110: Tea leaf harvesting stage S120: Withering stage S130: Mindfulness and oxidation step S140: Drying step

Claims

Claim 1 (a) a step of harvesting tea leaves that have withered and been discarded due to low-temperature damage including frost; (b) a step of spreading the harvested tea leaves widely indoors and wilting them by evaporating moisture; (c) a step of rolling the wilted tea leaves using a rolling machine for 15 to 25 minutes, and then oxidizing them by partially blocking sunlight for 30 to 50 minutes; and (d) a step of spreading the rolled and oxidized tea leaves in the sun to dry them for 5 hours or more; wherein, in step (b), the harvested tea leaves are wilted for 20 to 40 minutes, which is shorter than the wilting time of normal tea leaves that have not suffered low-temperature damage. Claim 2 A method for making black tea according to claim 1, characterized in that, in step (a), the tea leaves are first flush tea harvested between late April and early May. Claim 3 delete Claim 4 A method for making black tea according to claim 1, wherein the above step (c) is repeated a total of three times, wherein the pressure of the kneading machine is set to low for the first kneading and oxidation, the pressure of the kneading machine is set to medium for the second kneading and oxidation, and additionally the pressure of the kneading machine is set to high for the third kneading and oxidation. Claim 5 A method for making black tea according to claim 1, characterized in that, in step (d), the moisture content of the kneaded and oxidized tea leaves is dried to be 5% or less. Claim 6 Black tea characterized by being manufactured by the method of any one of claims 1, 2, 4, and 5.

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