Device for improving color of green tea leaves, method for improving color of green tea leaves, and method for producing green tea

Abstract

To provide an apparatus for improving the color of green tea leaves, a method for improving the color of green tea leaves and a method for producing green tea, capable of improving the color of the green tea leaves by performing a simple treatment without using an additive such as an electrolyte.SOLUTION: The tea leaf color improving apparatus includes a low-temperature treatment means for performing low-temperature steam treatment or low-temperature water immersion treatment on plucked raw tea leaves, in which the treatment temperature of the surface of the raw tea leaves is maintained at a predetermined temperature in the range of 30 to 50 °C for a predetermined set time and the treatment time is less than 60 minutes when the predetermined temperature exceeds 40 °C, and a parching treatment means for parching the tea leaves treated by the low-temperature treatment means.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus and a method for improving the color of green tea leaves, which can improve the color of green tea leaves to a bright dark green, and a method for producing green tea, which can improve the color of green tea leaves. [Background technology]

[0002] When producing green tea, fresh tea leaves are plucked from the tea plant and transported to the manufacturing factory, where the oxidizing enzymes are inactivated through a process known as steaming. However, due to limitations in the factory's capacity, it is sometimes not possible to inactivate the oxidizing enzymes immediately after plucking. Therefore, it is necessary to maintain the freshness of the leaves between plucking and the azolimus treatment to prevent deterioration. Fresh tea leaves continue to respire even after plucking. This respiration generates heat energy that breaks down carbohydrates and proteins, raising the surface temperature and promoting oxidation, causing the leaves to fade to a yellow-green and their quality to decline. Fresh tea leaves contain chlorophyll (chlorophyll a and b). However, after plucking, heat during storage and the temperature conditions of the tea manufacturing process can cause the magnesium in the chlorophyll molecule to detach, converting it to pheophytin, resulting in the tea leaf's faded yellow-green color.

[0003] As a conventional technique for preventing discoloration of green tea leaves, Patent Document 1 discloses a technique in which, as a pretreatment for the steaming step in the tea manufacturing process, fresh tea leaves before steaming are immersed in alkaline ionized water prepared by adding a small amount of an electrolyte consisting of one of sodium chloride, potassium chloride, and calcium lactate to water, or this alkaline ionized water is sprayed onto the surface of the fresh tea leaves or dropped into the steamer. Patent Document 1 states that by using this alkaline ionized water, discoloration of green tea leaves can be prevented and the hue can be improved to a vivid green. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-215768 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology disclosed in Patent Document 1 requires that fresh tea leaves be treated using alkaline ionized water to which electrolytes have been added, which has the problem that small amounts of additive salts such as sodium chloride may remain in the produced green tea leaves.

[0006] Therefore, an object of the present invention is to provide an apparatus for improving the color of green tea leaves, a method for improving the color of green tea leaves, and a method for producing green tea, which can improve the color of green tea leaves through simple processing without using additives such as electrolytes. [Means for solving the problem]

[0007] The green tea leaf color improving device of the present invention comprises a low-temperature treatment means for carrying out a low-temperature steam treatment or a low-temperature water immersion treatment on the surface of picked fresh tea leaves, maintaining the treatment temperature of the fresh tea leaves at a predetermined temperature in the range of 30 to 50°C (at or near the predetermined temperature) for a predetermined set time, and a blue-killing treatment means for carrying out a blue-killing treatment on the tea leaves treated by the low-temperature treatment means.

[0008] Before the harvested fresh tea leaves are subjected to a deactivation treatment (deactivation) by steaming or the like, they are subjected to a low-temperature treatment using low-temperature steam or low-temperature water immersion for a predetermined set time. This low-temperature treatment involves steam treatment or water immersion, which maintains the surface temperature of the fresh tea leaves at a predetermined temperature between 30 and 50°C. Because the fresh tea leaves are subjected to a low-temperature steam treatment or low-temperature water immersion treatment at 30 to 50°C before the deactivation treatment, the stomata on the surface of the fresh tea leaves open, allowing water to be reabsorbed into the cells, restoring freshness to the fresh tea leaves. As a result, the appearance of the green tea leaves can be improved to a vibrant, deep green. Generally, fine gases exist between the cells of plants, and the influence of these gases makes the green color of chlorophyll appear cloudy in the fresh leaves. However, although intracellular chlorophyll a converts to pheophytin a at temperatures above a certain level, in the present invention, chlorophyll a is not completely converted to pheophytin a during the steam treatment or water immersion treatment at 30-50°C. The intracellular gases expand thermally within the cells and are then expelled without dissolving the cell walls. This presumably explains why the appearance of tea leaves, which were previously cloudy when fresh, appears to be a more vibrant dark green than when fresh. That is, low-temperature treatment at 30-50°C allows fresh tea leaves to replenish intracellular water to reduce their surface temperature during transpiration. In subsequent processes after low-temperature treatment, the replenished water allows the tea leaves to lower their surface temperature through transpiration. As a result, heat-induced pheophytinization of chlorophyll is suppressed, improving the appearance of green tea leaves to a vibrant dark green. Thus, according to the present invention, the color of green tea leaves can be improved to a vibrant dark green by simply performing a simple low-temperature treatment before the blue-killing treatment, without the use of additives. Furthermore, by carrying out the blue-killing treatment immediately after the low-temperature treatment, the tea leaves can be treated while still sufficiently moist, thereby preventing discoloration of the tea leaves and reliably improving the appearance color of the tea leaves.The water used in the low-temperature steam treatment and low-temperature water soaking treatment in this invention is not alkaline ionized water containing electrolytes as described in the above-mentioned Patent Document 1 (JP-A-10-215768), but is simple water such as tap water or groundwater containing no additives.In the present invention, "green tea" refers to so-called non-fermented tea, and is a concept that includes sencha, tencha, gyokuro, kabusecha, kamairicha, and the like.

[0009] The low-temperature treatment means is preferably configured to limit the treatment time for low-temperature steam treatment or low-temperature water soaking treatment to less than 60 minutes when the predetermined temperature exceeds 40°C. Because fresh tea leaves are affected by the heat of the steam or soaking water at temperatures above 40°C, the treatment time for low-temperature treatment to improve the dark green color of green tea leaves is limited to less than 60 minutes (1 hour). The limit for this treatment time is approximately 60 minutes when the temperature is between 42 and 45°C.

[0010] It is also preferable that the low-temperature treatment means is configured so that the treatment time for the low-temperature steam treatment or low-temperature water soaking treatment is 30 minutes or less when the predetermined temperature is approximately 50°C. At a temperature range of approximately 50°C, fresh tea leaves are significantly affected by the heat from the steam or soaking water, so the treatment time for the low-temperature treatment to obtain the effect of improving the dark green color of green tea leaves is set to 30 minutes or less.

[0011] It is also preferable that the low-temperature treatment means is configured to perform low-temperature steam treatment or low-temperature water immersion treatment at a predetermined temperature in the range of 30 to 42°C (at or near the predetermined temperature). By performing low-temperature treatment in this temperature range, the content of glutamic acid in the tea leaves increases as a by-product. Glutamic acid is an amino acid essential for the metabolic synthesis of theanine and catechins, which are typical components of tea, in the tea leaves, and is the component that gives tea its umami flavor.

[0012] It is also preferable that the low-temperature treatment means is configured to perform low-temperature treatment on fresh tea leaves on a horizontal movement mechanism that transports the fresh tea leaves horizontally. By using a horizontal movement mechanism that transports the tea leaves horizontally, damage to the tea leaves is minimized, making it less likely for the leaves to break and resulting in tea leaves with an excellent appearance.

[0013] Furthermore, according to the method for improving the color of green tea leaves of the present invention, the picked fresh tea leaves are subjected to a low-temperature steam treatment or a low-temperature water immersion treatment in which the treatment temperature of the surface of the fresh tea leaves is maintained at a predetermined temperature in the range of 30 to 50°C (at or near the predetermined temperature) for a predetermined set time, and the low-temperature treated tea leaves are subjected to a blue-killing treatment.

[0014] This system is configured to subject freshly picked tea leaves to a low-temperature treatment using low-temperature steam or low-temperature water immersion for a predetermined period of time before undergoing a deactivation treatment such as steaming. This low-temperature treatment involves steaming or water immersion, with the surface temperature of the fresh tea leaves maintained at a predetermined temperature between 30 and 50°C. Because the low-temperature steam treatment or low-temperature water immersion treatment at 30 to 50°C is performed before the deactivation treatment, the pores on the surface of the fresh tea leaves open, allowing water to be reabsorbed into the cells, restoring freshness to the fresh tea leaves. As a result, the appearance of the green tea leaves can be improved to a vibrant, dark green. Specifically, the low-temperature treatment at 30 to 50°C allows the fresh tea leaves to replenish intracellular moisture, which lowers the surface temperature during transpiration. In the subsequent process after the low-temperature treatment, the replenished intracellular moisture allows the tea leaves to lower their surface temperature through transpiration. As a result, the pheophytinization of chlorophyll due to heat is suppressed, improving the appearance of green tea leaves to a vivid dark green. Thus, according to the present invention, the color of green tea leaves can be improved to a vivid dark green by simply performing a simple low-temperature treatment before the blue-killing treatment, without using any additives. Furthermore, by performing the blue-killing treatment immediately after the low-temperature treatment, tea leaves that are still sufficiently moist can be treated, thereby preventing discoloration of the tea leaves and reliably improving the appearance color of the tea leaves. The water used in the low-temperature steam treatment and low-temperature water soaking treatment in the present invention is simple water, such as tap water or groundwater, that does not contain any additives. Furthermore, in the present invention, "green tea" refers to so-called unfermented tea, and is a concept that includes sencha, tencha, gyokuro, kabusecha, kamairicha, etc.

[0015] When the predetermined temperature exceeds 40°C, the treatment time for low-temperature steam treatment or low-temperature water soaking treatment is preferably less than 60 minutes. At temperatures above 40°C, the fresh tea leaves are affected by the heat from the steam or soaking water, so the treatment time for low-temperature treatment to improve the dark green color of green tea leaves is set to less than 60 minutes (1 hour). The limit of this treatment time is approximately 60 minutes when the temperature is 42 to 45°C.

[0016] When the predetermined temperature is approximately 50°C, it is also preferable to set the treatment time of low-temperature steam treatment or low-temperature water soaking treatment to 30 minutes or less. At a temperature of approximately 50°C, fresh tea leaves are significantly affected by the heat from the steam or soaking water, so the treatment time of low-temperature treatment to obtain the effect of improving the dark green color of green tea leaves is set to 30 minutes or less.

[0017] It is also preferable to perform low-temperature steam treatment or low-temperature water immersion treatment at a predetermined temperature in the range of 30 to 42°C (at or near the predetermined temperature). By performing low-temperature treatment in this temperature range, the content of glutamic acid in the tea leaves increases as a by-product. Glutamic acid is an amino acid essential for the metabolic synthesis of theanine and catechins, which are typical components of tea, in the tea leaves, and is the component that gives tea its umami flavor.

[0018] It is also preferable to carry out the low-temperature treatment while transporting the fresh tea leaves horizontally. By using a horizontal transport mechanism that transports the fresh tea leaves horizontally, damage to the fresh tea leaves is minimized, resulting in tea leaves that are less likely to break and have an excellent appearance.

[0019] Furthermore, the method for producing green tea of ​​the present invention comprises a low-temperature treatment step in which the surface of the picked fresh tea leaves is subjected to a low-temperature steam treatment or low-temperature water immersion treatment, in which the treatment temperature of the surface of the fresh tea leaves is maintained at a predetermined temperature in the range of 30 to 50°C (at or near the predetermined temperature) for a predetermined set time, and a blue-killing treatment step in which the tea leaves that have been low-temperature treated in the low-temperature treatment step are subjected to a blue-killing treatment.

[0020] This system is configured to subject freshly picked tea leaves to a low-temperature treatment using low-temperature steam or low-temperature water immersion for a predetermined period of time before undergoing a deactivation treatment such as steaming. This low-temperature treatment involves steaming or water immersion, with the surface temperature of the fresh tea leaves maintained at a predetermined temperature between 30 and 50°C. Because the low-temperature steam treatment or low-temperature water immersion treatment at 30 to 50°C is performed before the deactivation treatment, the pores on the surface of the fresh tea leaves open, allowing water to be reabsorbed into the cells, restoring freshness to the fresh tea leaves. As a result, the appearance of the green tea leaves can be improved to a vibrant, dark green. Specifically, the low-temperature treatment at 30 to 50°C allows the fresh tea leaves to replenish intracellular moisture, which lowers the surface temperature during transpiration. In the subsequent process after the low-temperature treatment, the replenished intracellular moisture allows the tea leaves to lower their surface temperature through transpiration. As a result, the pheophytinization of chlorophyll due to heat is suppressed, improving the appearance of green tea leaves to a vivid dark green. Thus, according to the present invention, the color of green tea leaves can be improved to a vivid dark green by simply performing a simple low-temperature treatment before the blue-killing treatment, without using any additives. Furthermore, by performing the blue-killing treatment immediately after the low-temperature treatment, tea leaves that are still sufficiently moist can be treated, thereby preventing discoloration of the tea leaves and reliably improving the appearance color of the tea leaves. The water used in the low-temperature steam treatment and low-temperature water soaking treatment in this invention is simple water, such as tap water or groundwater, that does not contain additives. Furthermore, the "green tea" used in this invention refers to so-called unfermented tea, and is a concept that includes sencha, tencha, gyokuro, kabusecha, kamairicha, etc.

[0021] In the low-temperature treatment step, when the predetermined temperature exceeds 40°C, the treatment time for the low-temperature steam treatment or low-temperature water soaking treatment is preferably less than 60 minutes. At temperatures above 40°C, the fresh tea leaves are affected by the heat from the steam or soaking water, so the treatment time for the low-temperature treatment to obtain the effect of improving the dark green color of green tea leaves is set to less than 60 minutes (1 hour). The limit of this treatment time is approximately 60 minutes when the temperature is 42 to 45°C.

[0022] In the low-temperature treatment step, when the predetermined temperature is approximately 50°C, it is also preferable that the treatment time for the low-temperature steam treatment or low-temperature water soaking treatment is 30 minutes or less. At a temperature of approximately 50°C, fresh tea leaves are significantly affected by the heat from the steam or soaking water, so the treatment time for the low-temperature treatment to obtain the effect of improving the dark green color of green tea leaves is set to 30 minutes or less.

[0023] The low-temperature treatment step is preferably a low-temperature steam treatment or low-temperature water immersion treatment at a predetermined temperature in the range of 30 to 42°C (at or near the predetermined temperature). By performing low-temperature treatment in this temperature range, the content of glutamic acid in the tea leaves increases as a by-product. Glutamic acid is an amino acid essential for the metabolic synthesis of theanine and catechins, which are typical components of tea, in the tea leaves, and is the component that gives tea its umami flavor.

[0024] It is also preferable that the low-temperature treatment step is a step in which the low-temperature treatment is performed while the fresh tea leaves are transported horizontally. By using a horizontal transport mechanism for transporting the fresh tea leaves horizontally, damage to the fresh tea leaves is minimized, resulting in tea leaves that are less likely to break and have an excellent appearance. [Effects of the Invention]

[0025] According to the present invention, the color of green tea leaves can be improved to a vivid dark green by simply performing a simple low-temperature treatment before the blue-killing treatment, without using any additives, etc. Furthermore, by performing the blue-killing treatment immediately after the low-temperature treatment, the blue-killing treatment can be performed under high-temperature conditions on tea leaves that are still sufficiently moist, thereby preventing discoloration of the tea leaves and reliably improving the appearance color of the tea leaves. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a block diagram showing a schematic configuration of a tea leaf color improving device portion of a green tea production apparatus according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing an example of the hardware configuration of a low-temperature treatment means in the tea leaf color improving device of FIG. 1. [Figure 3] FIG. 2 is a block diagram showing an example of the mechanical configuration of the low-temperature treatment means in the tea leaf color improving device of FIG. 1; [Figure 4] 2 is a flow chart showing the outline of the flow of low-temperature steam treatment in the tea leaf color improving device of FIG. 1. [Figure 5] 4 is a flowchart showing a schematic flow of low-temperature steam treatment in the tea leaf color improving device according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] FIG. 1 shows a schematic configuration of a tea leaf color improving device in a green tea production apparatus according to a first embodiment of the present invention, and this tea leaf color improving device constitutes a part of the production apparatus for producing green tea.

[0028] In Figure 1, reference numeral 10 denotes a low-temperature treatment means for treating freshly picked tea leaves with low-temperature steam, and reference numeral 11 denotes a green-killing treatment means, such as a steamer, for inactivating the oxidases in the fresh tea leaves sent from the low-temperature treatment means 10. In this embodiment, since the temperature used to inactivate tea leaf oxidases with steam is typically 80°C or higher, the treatment of applying steam below 80°C to the surface of the tea leaves is referred to as "low-temperature treatment" or "low-temperature steam treatment" to clearly distinguish it from the green-killing treatment. The green-killing treatment means 11 can be a rotary steam treatment device, and the functions of the low-temperature treatment means 10 can be fulfilled by setting the treatment temperature below 80°C. In this case, the green-killing treatment means can be configured as a single device. Naturally, the low-temperature treatment means and the green-killing treatment means can be provided separately, or they can be provided as multiple devices to form a production line.

[0029] The low-temperature treatment means 10 performs low-temperature steam treatment so that the treatment temperature of the surface of the fresh tea leaves reaches a predetermined temperature in the range of 30 to 50°C (the predetermined temperature or a temperature close to the predetermined temperature), and controls the treatment time to be less than 60 minutes if the predetermined temperature exceeds 40°C. In other words, if the predetermined temperature exceeds 40°C, the low-temperature steam treatment is terminated when the treatment time reaches 60 minutes or more.

[0030] Although not shown, for example, a green tea (sencha) manufacturing device may include, following the blue killing treatment means 11, a cooling treatment means for quickly cooling the steamed leaves to about room temperature in order to maintain the color of the steamed leaves, a leaf beating treatment means for shaking the leaves by blowing dry hot air into them to maintain the color of the cooled tea leaves and shorten the time for the next rough rolling treatment, a rough rolling treatment means for blowing dry hot air into the tea leaves and applying moderate friction and pressure to the tea leaves in order to soften them and reduce their internal moisture, and a rolling treatment means for making up for insufficient rolling in the rough rolling treatment. The system comprises a rolling and twisting processing means for massing and rolling the tea leaves under pressure in order to break down the structure of the tea leaves and make it easier for the ingredients to leach out and for the moisture to be uniform, a medium rolling processing means for rolling and rolling the tea leaves by blowing in dry hot air to loosen the tea leaves and give them a twisted shape so that they can be easily shaped in the next fine rolling processing, a fine rolling processing means for rolling the tea leaves in only one direction while removing the moisture inside the tea leaves and drying them in order to give the tea leaves a thin, elongated shape, and a drying processing means for drying the tea leaves to reduce the moisture content to about 5%, all of which are connected in sequence.The equipment for carrying out the processes other than the low-temperature processing, such as the blue killing process, cooling process, leaf beating process, rough rolling process, rolling and twisting process, medium rolling process, fine rolling process and drying process, are all commercially available and well-known, so detailed explanations will be omitted. Furthermore, although the above description has been given of a manufacturing apparatus for sencha, in the case of a manufacturing apparatus for tencha, following the green tea killing means 11, a loose tea cooling means for quickly cooling the steamed leaves to about room temperature in order to maintain the color of the steamed leaves, and a drying means for drying the tea leaves to reduce the moisture content to about 5%, are provided, and these are connected in sequence. The equipment for realizing the green tea killing treatment, loose tea cooling treatment and drying treatment, other than the low-temperature treatment, are all commercially available and of known configuration, so detailed explanations will be omitted.

[0031] 2 shows a schematic diagram of an example of the hardware configuration of the low-temperature treatment means 10. The low-temperature treatment means 10 in this embodiment comprises a low-temperature steam treatment chamber 10a for performing low-temperature steam treatment on the transported fresh tea leaves, a temperature detection unit 10b for detecting a temperature corresponding to the treatment temperature on the surface of the fresh tea leaves in this low-temperature steam treatment chamber 10a, a humidity detection unit 10c for detecting the internal humidity, a time detection unit 10d for detecting the treatment time, and a control unit 10e for inputting the temperature detected by the temperature detection unit 10b, the humidity detected by the humidity detection unit 10c, and the treatment time detected by the time detection unit 10d, and controlling the steam temperature and the end of the low-temperature steam treatment.

[0032] The control unit 10e controls the steam in the low-temperature steam treatment chamber 10a using a built-in computer in accordance with the detected treatment temperature, humidity, and treatment time so as to maintain the treatment temperature of the surface of the fresh tea leaves at a predetermined temperature in the range of 30 to 50°C (at or near the predetermined temperature). In this case, the low-temperature steam treatment is continued until the steam treatment time reaches a predetermined set time, at which point the low-temperature steam treatment is terminated. The predetermined set time is preferably 5 to 20 minutes, but may be, for example, 5, 15, 30, 60, or 120 minutes. However, if the predetermined temperature exceeds 40°C, the control unit 10e controls the steam in the low-temperature steam treatment chamber 10a so that the treatment time is less than 60 minutes.

[0033] The low-temperature steam treatment chamber 10a may be a rotary steam treatment device, a low-temperature steamer, or a device with a net-structured transport belt installed inside the low-temperature steam treatment chamber 10a. For the soaking treatment, a device using a washer or a device using a horizontal movement mechanism (described later) combined with a conveyor may also be used. There are no particular limitations on the configuration of the device, as long as it can maintain the treatment temperature of the surface of the raw tea leaves at a predetermined temperature for a set period of time.

[0034] In this embodiment, as an example of using a low-temperature steamer, a small two-chamber independent dough conditioner SS5022 manufactured by NIPPO Corporation, which has a chamber capable of controlling temperature and humidity, is used. Also, an example of using a low-temperature steam treatment chamber 10a equipped with a net-structured transport belt will be described below.

[0035] Figure 3 shows three schematic configurations of the low-temperature steam treatment chamber. Figure 3(A) shows a low-temperature steam treatment chamber 10a equipped with a single-stage net-type transport belt 10f1. This low-temperature steam treatment chamber 10a is equipped with a single-stage net-type transport belt 10f1 that moves horizontally inside. Within the low-temperature steam treatment chamber 10a, the surfaces of the fresh tea leaves placed on the net of the transport belt 10f1 are subjected to low-temperature steam treatment by low-temperature steam at 30 to 50°C that is ventilated through the net. Because the transport belt 10f1 moves horizontally during steam treatment, damage to the fresh tea leaves can be reduced and the occurrence of broken leaves can be suppressed. From the perspective of mass production of tea leaves, a rotary steam treatment device can be used, but considering damage to the fresh tea leaves, it is preferable to use a horizontally moving type using a net. Furthermore, "horizontal" does not necessarily mean completely horizontal movement, but can also mean transportation at an angle.

[0036] The low-temperature steam treatment chamber may be a low-temperature steam treatment chamber 10a' equipped with serial single-stage net-type transport belts 10f1' and 10f2' as shown in Figure 3(B), or may be a low-temperature steam treatment chamber 10a" equipped with multi-stage net-type transport belts 10f1", 10f2", and 10f3" as shown in Figure 3(C).

[0037] FIG. 4 shows a schematic flow of control by the computer of the control unit 10e in the low-temperature treatment means 10.

[0038] First, the temperature detection unit 10b detects the processing temperature inside the low-temperature steam processing chamber 10a (corresponding to the processing temperature on the surface of the raw tea leaves) (step S1), and determines whether the detected processing temperature is a predetermined temperature in the range of 30 to 50°C (a predetermined temperature or a temperature close to it) (step S2).

[0039] If it is determined in step S2 that the processing temperature is not the predetermined temperature in the range of 30 to 50°C (the predetermined temperature or a temperature close to it) (NO), the control unit 10e adjusts the steam temperature in the low-temperature steam processing chamber 10a to this predetermined temperature (the predetermined temperature or a temperature close to it) (step S3), and then repeats the processing of steps S1 to S3.

[0040] If it is determined in step S2 that the processing temperature is a predetermined temperature in the range of 30 to 50° C. (predetermined temperature or a temperature close to it) (YES), it is determined whether the processing temperature exceeds 40° C. (step S4).

[0041] If it is determined in step S4 that the processing temperature exceeds 40° C. (YES), it is determined whether the processing time detected by the time detection unit 10d is less than 60 minutes (step S5).

[0042] If it is determined in step S4 that the processing temperature does not exceed 40°C (if NO), and if it is determined in step S5 that the processing time is less than 60 minutes (if YES), it is determined whether the processing time is equal to or longer than a predetermined set time (e.g., 5 to 20 minutes) (step S6).

[0043] In step S6, if it is determined that the treatment time is not equal to or longer than the predetermined setting time (NO), the process returns to step S1, and the above-described processes of steps S1 to S6 are repeated, thereby allowing the low-temperature treatment means 10 to continue the low-temperature steam treatment.

[0044] If it is determined in step S5 that the processing time is not less than 60 minutes (if NO), and if it is determined in step S6 that the processing time is equal to or longer than the set time (if YES), the low-temperature steam processing by the low-temperature processing means 10 is terminated (step S7).

[0045] According to the control shown in Figure 4, the steam treatment time is controlled to a predetermined set time, the treatment temperature of the fresh tea leaf surface is maintained at a predetermined temperature in the range of 30 to 50°C, and the steam in the low-temperature steam treatment chamber 10a is controlled so that the treatment time is less than 60 minutes when the predetermined temperature exceeds 40°C. After the above low-temperature treatment by the low-temperature treatment means 10, a deactivation treatment by the blue-killing treatment means 11 is carried out.

[0046] In this embodiment, the greening treatment means 11 is composed of a steamer that performs steaming treatment to inactivate oxidase in the tea leaves at a temperature of 80 to 100°C, but instead of steaming treatment, the oxidase may be inactivated by pan-frying treatment, hot air treatment, or microwave irradiation treatment.

[0047] In addition, in this embodiment, a low-temperature steam treatment is performed in which fresh tea leaves are exposed to low-temperature steam at 30 to 50°C. However, if a low-temperature water soaking treatment is performed in which the tea leaves are soaked in water at 30 to 50°C instead of the low-temperature steam treatment, the same effect can be obtained if the amount of tea leaves is small.

[0048] As described above in detail, according to this embodiment, prior to the deactivation (deactivation) treatment of harvested fresh tea leaves by steaming or other methods, low-temperature steam treatment is performed using steam, with the surface temperature of the fresh tea leaves set to a predetermined temperature in the range of 30 to 50°C. If this predetermined temperature exceeds 40°C, the treatment time is set to less than 60 minutes. Because the low-temperature steam treatment at 30 to 50°C is performed prior to the deactivation (deactivation) treatment, the pores on the surface of the fresh tea leaves open, allowing water to be reabsorbed into the cells, restoring freshness to the fresh tea leaves. As a result, the appearance color of the green tea leaves can be improved to a vivid dark green. Because the fresh tea leaves are affected by the heat of the steam or steeping water at temperatures above 40°C, the low-temperature treatment time to improve the dark green color of the tea leaves is set to less than 60 minutes. The treatment time limit is approximately 60 minutes when the temperature is 42 to 45°C. Thus, according to this embodiment, the color of green tea leaves can be improved to a vivid dark green by simply performing the simple low-temperature treatment prior to the deactivation treatment without the use of additives or other additives. Furthermore, the blue killing treatment step is the step in which pheophytinization of chlorophyll in fresh tea leaves is most pronounced, and by carrying out the blue killing treatment immediately after the low-temperature treatment, tea leaves that are sufficiently moist can be subjected to the blue killing treatment, thereby preventing the pheophytinization of chlorophyll in the blue killing treatment step and reliably improving the external color of the tea leaves.

[0049] As a modification of this embodiment, low-temperature steam treatment may be performed so that the surface temperature of the fresh tea leaves reaches a predetermined temperature (at or near the predetermined temperature) in the range of 30 to 42°C. This process involves determining whether the steam treatment temperature is at or near the predetermined temperature in the range of 30 to 42°C in step S2 of the low-temperature steam treatment flow shown in Figure 4 . If the temperature is not at or near the predetermined temperature (NO), the steam temperature is adjusted in step S3. This modification not only improves the color of green tea leaves to a vibrant dark green, but also increases the glutamic acid content in the tea leaves. Glutamic acid is an amino acid essential for the metabolic synthesis of theanine and catechins, which are typical components of tea, in the tea leaves, and is the umami component of tea. The other configurations and processes in this modification are the same as those in the first embodiment.

[0050] Next, a second embodiment of the present invention will be described. In the second embodiment, the flow of control by the computer of the control unit 10e in the low-temperature treatment means 10 is different from that in the first embodiment, but the other configurations of the low-temperature treatment means 10 are the same as those in the first embodiment. Therefore, only the different parts will be described below.

[0051] FIG. 5 shows a schematic flow of control by the computer of the control unit 10e in the low-temperature treatment means 10 in this embodiment.

[0052] First, the temperature detection unit 10b detects the processing temperature inside the low-temperature steam processing chamber 10a (corresponding to the processing temperature on the surface of the raw tea leaves) (step S11), and determines whether the detected processing temperature is a predetermined temperature in the range of 30 to 50°C (a predetermined temperature or a temperature close to it) (step S12).

[0053] If it is determined in step S12 that the processing temperature is not the predetermined temperature in the range of 30 to 50°C (the predetermined temperature or a temperature close to it) (NO), the control unit 10e adjusts the steam temperature in the low-temperature steam processing chamber 10a to this predetermined temperature (the predetermined temperature or a temperature close to it) (step S13), and then repeats the processing of steps S11 to S13.

[0054] If it is determined in step S12 that the processing temperature is a predetermined temperature in the range of 30 to 50° C. (predetermined temperature or a temperature close to it) (YES), it is determined whether the processing temperature exceeds 40° C. (step S14).

[0055] If it is determined in step S14 that the processing temperature exceeds 40° C. (YES), it is determined whether the processing time detected by the time detection unit 10d is less than 60 minutes (step S15).

[0056] If it is determined in step S15 that the processing time is less than 60 minutes (YES), it is determined whether the processing temperature is approximately 50° C. (step S16).

[0057] If it is determined in step S16 that the processing temperature is approximately 50° C. (YES), it is determined whether the processing time is 30 minutes or less (step S17).

[0058] If it is determined in step S14 that the processing temperature does not exceed 40°C (if NO), if it is determined in step S16 that the processing temperature is not approximately 50°C (if NO), or if it is determined in step S17 that the processing time is 30 minutes or less (if YES), it is determined whether the processing time is equal to or longer than a predetermined set time (e.g., 5 to 20 minutes) (step S18).

[0059] In step S18, if it is determined that the processing time is not equal to or longer than the predetermined setting time (if NO), the process returns to step S11, and the processes of steps S11 to S18 described above are repeated.

[0060] If it is determined in step S15 that the processing time is not less than 60 minutes (if NO), if it is determined in step S17 that the processing time is not less than 30 minutes (if NO), or if it is determined in step S18 that the processing time is greater than or equal to the set time (if YES), the low-temperature steam processing by the low-temperature processing means 10 is terminated (step S19).

[0061] According to the control shown in Figure 5, the steam treatment time is controlled to be a predetermined set time, the treatment temperature of the tea leaf surface is maintained at a predetermined temperature in the range of 30 to 50°C (the predetermined temperature or a temperature close to that), and the steam in the low-temperature steam treatment chamber 10a is controlled so that the treatment time is less than 60 minutes when the predetermined temperature exceeds 40°C, and further so that the treatment time is 30 minutes or less when the predetermined temperature is approximately 50°C.

[0062] In this embodiment, the greening treatment means 11 is composed of a steamer that performs steaming treatment to inactivate oxidase in the tea leaves at a temperature of 80 to 100°C, but instead of steaming treatment, the oxidase may be inactivated by pan-frying treatment, hot air treatment, or microwave irradiation treatment.

[0063] In addition, in this embodiment, a low-temperature steam treatment is performed in which the fresh tea leaves are exposed to low-temperature steam at 30 to 50°C. However, if a low-temperature water soaking treatment is performed in which the fresh tea leaves are soaked in low-temperature water at 30 to 50°C instead of the low-temperature steam treatment, the same effect can be obtained if a small amount of fresh tea leaves is used.

[0064] As described above in detail, according to this embodiment, prior to the deactivation (deactivation) treatment of harvested fresh tea leaves by steaming or other methods, the fresh tea leaves are subjected to a low-temperature steam treatment using steam, where the surface temperature of the fresh tea leaves is set at a predetermined temperature (at or near the predetermined temperature) in the range of 30 to 50°C. If the predetermined temperature exceeds 40°C, the treatment time is set to less than 60 minutes, and if the predetermined temperature is approximately 50°C, the treatment time is set to 30 minutes or less. Because the fresh tea leaves are subjected to a low-temperature steam treatment at 30 to 50°C prior to the deactivation (deactivation) treatment, the pores on the surface of the fresh tea leaves open, allowing water to be reabsorbed into the cells, restoring freshness to the fresh tea leaves. As a result, the appearance of the green tea leaves can be improved to a vibrant dark green. Because the fresh tea leaves are affected by the heat of the steam or steeping water at temperatures above 40°C, the low-temperature treatment time to improve the dark green color of the tea leaves is set to less than 60 minutes. The treatment time limit is approximately 60 minutes when the temperature is 42 to 45°C. Furthermore, because tea leaves are significantly affected by the heat of steam or steeping water at temperatures above 50°C, the low-temperature treatment time required to improve the dark green color of tea leaves is set to 30 minutes or less. Thus, according to this embodiment, the color of green tea leaves can be improved to a vivid dark green by simply performing the simple low-temperature treatment before the blue-killing treatment, without using any additives. Furthermore, by performing the blue-killing treatment immediately after the low-temperature treatment, tea leaves that are still sufficiently moist can be treated with the blue-killing treatment, preventing the conversion of chlorophyll to pheophytin during the blue-killing treatment step and reliably improving the appearance color of the tea leaves.

[0065] As a modification of this embodiment, low-temperature steam treatment may be performed so that the treatment temperature of the surface of the fresh tea leaves reaches a predetermined temperature (at or near the predetermined temperature) in the range of 30 to 42°C. This treatment is carried out by determining whether the steam treatment temperature is at or near the predetermined temperature in the range of 30 to 42°C in step S12 of the low-temperature steam treatment flow shown in Figure 5, and if it is not at or near the predetermined temperature (NO), performing a steam temperature adjustment process in step S13. This modification increases the glutamic acid content in the tea leaves. Glutamic acid is an amino acid essential for the metabolic synthesis of theanine and catechins, which are typical components found in tea, in the tea leaves, and is the component that gives tea its umami flavor. Note that the other configurations and processes in this modification are the same as those in this embodiment. [Example]

[0066] Fresh tea leaves of the "Yabukita" variety and "Yutaka Midori" variety, harvested the day before or the day of the test, were subjected to low-temperature treatments using low-temperature steam or low-temperature water immersion, followed by a desiccation treatment using steaming. Low-temperature steaming was performed using a low-temperature steamer QTS-23HTA manufactured by Fukushima Garirei Co., Ltd., and low-temperature water immersion was performed using a pot filled with warm water at the specified temperature. Steaming treatment was performed by placing 200 g of tea leaves per sample in a laundry bag and using a household steamer. The desiccation treatment (steaming treatment) was performed at 100°C for 180 seconds. After the desiccation treatment, the desiccation-treated tea leaves were placed in a constant-temperature drying chamber and dried at 105°C for 60 minutes and 85°C for 90 minutes to produce tencha-type green tea.

[0067] The treatment conditions for each sample (samples 1a to 6a, 1b to 4b, 1c to 2c, and 4c) in the low-temperature steam treatment were a treatment temperature of 30 to 50°C, a treatment time of 15 to 120 minutes, and a treatment humidity of 60 to 100%. Furthermore, the treatment conditions for sample 7a in the low-temperature water soaking treatment were a treatment temperature of 30°C and a treatment time of 30 minutes. A comparative control sample of green tea was produced by subjecting fresh tea leaves from the same lot (fresh tea leaves picked on the same day from the same tea plant) used in each sample to a de-icing treatment and drying treatment without low-temperature treatment. The 14 green tea samples and the seven control green tea samples obtained by the tea processing described above were analyzed for L in the tea leaves. * C * hue angle h and lightness L in h color space * The glutamic acid content was measured. * C * When the hue angle h in the h color space approaches 90°, it indicates yellow, and when it approaches 180°, it indicates green. Therefore, a larger hue angle h than the control sample indicates that the green color of the tea leaves has improved, and a smaller hue angle h than the control sample indicates that the color of the tea leaves has faded to yellow. Regarding the hue angle h and glutamic acid content of the tea leaves, the increase in the hue angle h and the increase in the amount of glutamic acid were calculated by subtracting the measured value of the control sample from the measured value of each sample that had been subjected to low-temperature treatment. Hue angle h and lightness L * was measured using a color difference meter SE7700 manufactured by Nippon Denshoku Industries Co., Ltd. The glutamic acid content was measured using a tea component analyzer GTN-9 manufactured by Shizuoka Seiki Co., Ltd. and sold by Kawasaki Kiko Co., Ltd. The unit of hue angle h is (°), and the unit of glutamic acid content is (g / 100g).

[0068] The treatment conditions for each sample, as well as the measured hue angle, brightness, and glutamic acid content, are shown in Tables 1 to 3 below.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] As shown in Table 1, for samples 1a-1c, 2a, 2b, 3a, 4a, 4b, 5a, 6a, and 7a, the hue angle of the green tea leaves obtained by low-temperature treatment increased relative to the hue angle of the tea leaves of the control sample. An increase in the hue angle (h) near 90° indicates that the hue of the sample has shifted toward greener, while a change or decrease in the hue angle indicates that the hue of the sample has remained unchanged or shifted toward yellow. Therefore, for samples 1a-1c, 2a, 2b, 3a, 4a, 4b, 5a, 6a, and 7a, the color of the tea leaves changed to dark green, and the evaluation of the color improvement of the tea leaves was good (◯). On the other hand, for samples 2c, 3b, and 4c, the hue angle (h) remained unchanged or decreased after low-temperature treatment, and the evaluation of the color improvement of the tea leaves was poor (×). Therefore, it was found that the color of the tea leaves can be improved to a vivid dark green by setting the treatment temperature in the range of 30 to 50°C as the treatment condition, and by setting the treatment time to less than 60 minutes when the treatment temperature exceeds 40°C. Furthermore, as shown in samples 5a and 6a, it was found that the color of the tea leaves can be improved to a vivid dark green by setting the treatment time to 30 minutes or less when the treatment temperature is approximately 50°C. Furthermore, it was found that not only low-temperature steam treatment (samples 1a to 6a) but also low-temperature water immersion treatment (sample 7a) is an effective low-temperature treatment method.

[0073] Furthermore, comparing Samples 2a, 2c, and 3b with Sample 4c in Table 1 reveals that, for the same low-temperature treatment time, a treatment temperature of 30-42°C results in a greater increase in glutamic acid content in green tea than a treatment temperature of greater than 42°C but less than 50°C. Similarly, comparing Samples 3a and 4b reveals that, for the same low-temperature treatment time, a treatment temperature of 30-42°C results in a greater increase in glutamic acid content than a treatment temperature of greater than 42°C but less than 50°C. Therefore, low-temperature treatment so that the treatment temperature on the tea leaf surface is within the range of 30-42°C increases the glutamic acid content in the tea leaves. Furthermore, it was revealed that a low-temperature treatment time of 15-30 minutes at a temperature of 30-42°C improves the color of the tea leaves and increases the glutamic acid content in the tea leaves by more than 1.5 times compared to a control sample that was not low-temperature treated.

[0074] The above-described embodiments and examples are merely illustrative of the present invention and are not limiting, and the present invention can be embodied in various other modified and altered forms. Therefore, the scope of the present invention is defined only by the claims and their equivalents. [Explanation of symbols]

[0075] 10 Low-temperature processing methods 10a, 10a', 10a" Low temperature steam treatment chamber 10b Temperature detection unit 10c Humidity detection unit 10d Time detection section 10e Control Unit 10f1, 10f1′, 10f1″, 10f2′, 10f2″, 10f3″ transport belt 11 Blue killing means

Claims

1. The color improving device for green tea leaves is characterized by comprising: a low-temperature treatment means for subjecting picked fresh tea leaves to low-temperature steam treatment or low-temperature water immersion treatment, which maintains the treatment temperature of the surface of the fresh tea leaves at a predetermined temperature in the range of 30 to 50°C for a predetermined set time; and a blue-killing treatment means for subjecting the tea leaves treated by the low-temperature treatment means to a blue-killing treatment.

2. 2. The apparatus for improving the color of green tea leaves according to claim 1, wherein the low-temperature treatment means is configured to set the treatment time of the low-temperature steam treatment or the low-temperature water immersion treatment to less than 60 minutes when the predetermined temperature exceeds 40°C.

3. 3. The apparatus for improving the color of green tea leaves according to claim 2, wherein the low-temperature treatment means is configured to set the treatment time of the low-temperature steam treatment or the low-temperature water immersion treatment to 30 minutes or less when the predetermined temperature is 50°C.

4. The color improving device for green tea leaves according to any one of claims 1 to 3, characterized in that the low-temperature treatment means is configured to perform the low-temperature steam treatment or the low-temperature water immersion treatment at the predetermined temperature in the range of 30 to 42°C.

5. 4. The apparatus for improving the color of green tea leaves according to claim 1, wherein the low-temperature treatment means is configured to perform low-temperature treatment on fresh tea leaves on a horizontal movement mechanism that transports the fresh tea leaves horizontally.

6. The method for improving the color of green tea leaves comprises subjecting picked fresh tea leaves to a low-temperature steam treatment or a low-temperature water immersion treatment in which the treatment temperature of the surface of the fresh tea leaves is maintained at a predetermined temperature in the range of 30 to 50°C for a predetermined set time, and subjecting the low-temperature treated tea leaves to a blue-killing treatment.

7. 7. The method for improving the color of green tea leaves according to claim 6, wherein when the predetermined temperature exceeds 40°C, the treatment time for the low-temperature steam treatment or the low-temperature water soaking treatment is less than 60 minutes.

8. 8. The method for improving the color of green tea leaves according to claim 7, wherein when the predetermined temperature is 50°C, the treatment time of the low-temperature steam treatment or the low-temperature water immersion treatment is 30 minutes or less.

9. 9. The method for improving the color of green tea leaves according to any one of claims 6 to 8, wherein the low-temperature steam treatment or the low-temperature water soaking treatment is carried out at the predetermined temperature in the range of 30 to 42°C.

10. 9. The method for improving the color of green tea leaves according to claim 6, wherein the low-temperature treatment is performed while the fresh tea leaves are transported horizontally.

11. This method for producing green tea is characterized by comprising a low-temperature treatment step in which picked fresh tea leaves are subjected to low-temperature steam treatment or low-temperature water immersion treatment, in which the treatment temperature of the surface of the fresh tea leaves is maintained at a predetermined temperature in the range of 30 to 50°C for a predetermined set time, and a blue-killing treatment step in which the tea leaves treated in the low-temperature treatment step are subjected to a blue-killing treatment.

12. 12. The method for producing green tea according to claim 11, wherein the low-temperature treatment step is a step in which, when the predetermined temperature exceeds 40°C, the treatment time of the low-temperature steam treatment or the low-temperature water immersion treatment is set to less than 60 minutes.

13. 13. The method for producing green tea according to claim 12, wherein the low-temperature treatment step is a step in which the treatment time of the low-temperature steam treatment or the low-temperature water immersion treatment is 30 minutes or less when the predetermined temperature is 50°C.

14. The method for producing green tea according to any one of claims 11 to 13, characterized in that the low-temperature treatment step is a step of performing the low-temperature steam treatment or the low-temperature water immersion treatment at the predetermined temperature in the range of 30 to 42°C.

15. 14. The method for producing green tea according to claim 11, wherein the low-temperature treatment step is a step of performing the low-temperature treatment while transporting the fresh tea leaves horizontally.

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