Microwave aging method and microwave aging apparatus

Abstract

To provide a microwave aging method and a microwave aging device which enable aging foods sufficiently while keeping them from excessive drying even in the case of drying and aging easy-to-dry foods and foods with low water contents by radiating microwave.MEANS FOR SOLVING THE PROBLEM: A microwave aging method has a dry aging process in which the surface of food M is dried and aged by radiating microwave on food M while blowing air in an aging chamber 40. In the dry aging process, the microwave radiating amount, the temperature in the aging chamber 40 and / or the air blowing amount are adjusted so that the internal temperature of the food M becomes higher than the surface temperature. And, at the same time, a breathable and moisture-permeable sheet S is put over the food M so that the water-evaporation is suppressed from the food M.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a microwave aging method and a microwave aging apparatus for aging food by irradiating microwaves.

Background Art

[0002] In recent years, so-called aged meat, in which the umami of beef is increased by aging beef for a certain period, has become widely known, and its demand is increasing. When aging beef, dry aging in which air is directly applied to the beef to dry it and aging is performed in a dry state, and wet aging in which it is vacuum-packed and aged are known. For example, the inventor has disclosed a technique for performing dry aging in a short aging period by irradiating microwaves while directly applying cold air to the food stored in the aging chamber (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In dry aging, air is applied to the food to dry the food and lower the water content of the food, so that aging can be performed while preventing the food from spoiling. However, when the food to be aged is not a relatively large lump like meat, but a relatively small slice like seafood that is easy to dry, or when the water content is low like dry tea leaves, there is a problem that aging progresses difficultly and a sufficiently aged food cannot be obtained. In particular, when performing dry aging while irradiating microwaves as in Patent Document 1, since the temperature inside the food can be increased by the microwaves, the moisture inside the food also tends to evaporate easily, and it is particularly desired to solve the above problems.

[0005] The present invention aims to provide a microwave aging method and a microwave aging apparatus capable of sufficiently aging food by suppressing excessive drying of the food even when performing dry aging by irradiating food that is easy to dry or has a low moisture content with microwaves.

Means for Solving the Problems

[0006] In order to achieve the above problems, the present inventors have conducted intensive research, and even when performing dry aging on foods that are relatively easy to dry or originally have a low moisture content, it is possible to suppress moisture evaporation in the food and create a microwave aging method capable of sufficiently aging the food, leading to the completion of the present invention. That is, the present invention relates to the microwave aging methods of the following (1) to (6). (1) A microwave aging method having a dry aging step of blowing air while irradiating food accommodated in an aging chamber with microwaves. In the dry aging step, after spraying water or water vapor on the surface of the food, or while spraying water or water vapor on the surface of the food, irradiate the food with microwaves so that the internal temperature is higher than the surface temperature of the food. In the dry aging step, covering the food with a sheet having air permeability and moisture permeability, a microwave aging method characterized by this. (2) A microwave aging method having a dry aging step of blowing air while irradiating food accommodated in an aging chamber with microwaves. The food is food in which the internal temperature of the food cannot be directly measured by contacting the food. In the dry aging step, measuring the temperature of water placed in a container accommodated in the aging chamber together with the food, and the measured temperature is regarded as the internal temperature of the food, and the internal temperature is made higher than the surface temperature of the food , controlling the irradiation amount of the microwaves, the temperature of the aging chamber, and / or the air volume. In the dry aging step, covering the food with a sheet having air permeability and moisture permeability, a microwave aging method characterized by this. (3) The microwave aging method according to the above (1) or (2), wherein the sheet has a cut. (4) In the dry aging process, in order to suppress the moisture evaporation of the food, (1) the air volume is set to less than 0.5 m / s, and / or (2) the irradiation amount of the microwave, the temperature of the aging chamber, and / or the air volume are controlled so that the temperature difference between the surface temperature and the internal temperature of the food is within 8°C. The microwave aging method according to any one of (1) to (3) above. (5) The microwave aging method according to any one of (1) to (4) above, wherein the food is dry tea leaves, fish fillets, or fish roe.

Effects of the Invention

[0008] According to the present invention, even when performing dry aging by irradiating a food that is prone to drying or has a low moisture content with microwaves, it is possible to suppress excessive drying of the food and sufficiently age the food, and a microwave aging method and a microwave aging apparatus can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

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Figure 7

Embodiments for Carrying Out the Invention

[0010] The microwave aging device 1 according to this embodiment irradiates food M with microwaves while blowing cold air, thereby cooling the surface of the food M to which microorganisms adhere to suppress spoilage, and increasing the temperature inside the food by microwaves to promote aging. In this embodiment, dry aging (dry aging) using such a microwave aging device 1 will be described. In particular, in the microwave aging method according to this embodiment, in order to suppress excessive drying of the food M in dry aging, (1) a sheet S having air permeability and moisture permeability such as a cooking sheet or an aging sheet employed in wet aging is placed on the food M for dry aging, (2) dry aging is performed with the air volume of the fan 43 being less than 0.5 m / second, and (3) dry aging is performed by controlling the irradiation amount of microwaves, the temperature of the aging chamber, and the air volume so that the temperature difference between the surface temperature and the internal temperature of the food M is within 8°C. By these methods, even in the dry aging of food M that is not easily dried, such as a meat block of beef, but is easily dried, such as small slices of seafood, or food M with a low moisture content, such as dried tea leaves, it is possible to suppress the evaporation of moisture from the food M and sufficiently age the food M. Note that the above three methods are methods aimed at sufficiently aging even easily dried foods or foods M with a low moisture content by dry aging, and any one of the methods may be used, or two or more methods may be combined. In the following, first, the microwave aging device 1 according to this embodiment will be described.

[0011] (Microwave Aging Device) FIG. 1 is a configuration diagram of a microwave aging device 1 according to the present embodiment. The microwave aging device 1 according to the present embodiment is a device capable of dry aging and wet aging, and can age various foods M such as meats (including processed meat foods such as ham), seafood, dairy products such as cheese, beans such as coffee beans, vegetables, fruits, noodles, breads, alcoholic beverages such as wine, and fermented foods (including fermented seasonings such as miso and soy sauce). However, as described above, in the microwave aging method according to the present embodiment, it is particularly useful for dry aging of foods M that are prone to drying, such as small slices of seafood, and foods M with a low moisture content, such as dried tea leaves.

[0012] As shown in FIG. 1, the microwave aging device 1 includes a cooler 10, a refrigerant flow path 20, a microwave oscillation unit 30, an aging chamber 40, a heat insulation unit 50, an internal temperature sensor 60, a control unit 70, a UV lamp 80, and an operation unit 90.

[0013] As shown in FIG. 1, the cooler 10 is connected to the refrigerant flow path 20 and cools the refrigerant circulating in the refrigerant flow path 20. As the cooler 10, for example, a known device having a compressor, a condenser, etc. and capable of cooling the refrigerant by heat exchange with the outside can be used.

[0014] The refrigerant flow path 20 is connected to the cooler 10, and the refrigerant for cooling the air in the internal space of the aging chamber 40 circulates. The refrigerant flow path 20 is in direct contact with the wall portion 41 of the aging chamber 40. The refrigerant circulating in the refrigerant flow path 20 exchanges heat with the wall portion 41 of the aging chamber 40, so that the wall portion 41 of the aging chamber 40 is cooled, and the air in the aging chamber 40 in contact with the wall portion 41 is cooled. Then, the refrigerant that has been heated by the heat exchange returns to the cooler 10 again and is cooled by the cooler 10. The refrigerant is not particularly limited, and for example, HFC (hydrofluorocarbon) or HC (hydrocarbon) can be used.

[0015] The microwave oscillation unit 30 oscillates microwaves for irradiating the food M. In the present embodiment, a solid-state semiconductor oscillator using a semiconductor element is used as the microwave oscillation unit 30. Compared with a magnetron, the semiconductor oscillator can obtain a high frequency and output stability, and can precisely control the output value and frequency in units of several microseconds. The microwaves oscillated by the microwave oscillation unit 30 are irradiated into the aging chamber 40 from the irradiation port 42 of the aging chamber 40 via the cable 31.

[0016] The food M for aging is placed in the aging chamber 40. The microwaves oscillated by the microwave oscillation unit 30 are irradiated into the aging chamber 40 from the irradiation port 42 via the cable 31, and uniformly heat the food M placed in the aging chamber 40. In the present embodiment, a small and high-gain patch antenna (planar antenna) is attached to the irradiation port 42, whereby the microwaves oscillated by the microwave oscillation unit 30 are irradiated into the aging chamber 40. Further, the refrigerant flow path 20 is in direct contact with the wall portion 41 of the aging chamber 40 without a gap, and the refrigerant flowing through the refrigerant flow path 20 cools the wall portion 41 of the aging chamber 40, and the wall portion 41 cools the air in the aging chamber 40 that contacts the wall portion 41, so that the food M can be cooled from the surface. Thereby, it becomes possible to make the internal temperature of the food M higher than the surface temperature of the food M.

[0017] In addition, as shown in FIG. 1, the aging chamber 40 is provided with a fan 43 and a door (not shown). The fan 43 can blow air at an air volume suitable for general aging of the food M (for example, 0.5 to 10.0 m / sec). Also, in the present embodiment, the fan 43 can also blow air at an air volume of less than 0.5 m / sec. By causing the air in the aging chamber 40 to convect, the fan 43 can direct the cold air cooled by the refrigerant onto the food M, thereby efficiently cooling the surface of the food M. Further, the door has a choke structure to prevent microwaves from leaking to the outside and can be opened and closed from the outside. Note that the choke structure can be a known structure. The user can open and close the door to take the food M to be aged in and out of the aging chamber 40. Further, on all surfaces of the inner surface (inner wall) of the wall portion 41 of the aging chamber 40, reflectors for reflecting microwaves are installed. In the aging chamber 40, shelves of any shape made of a microwave-permeable material such as Teflon (registered trademark) or polypropylene may be installed. Also, when using a metal material such as stainless steel, a lattice-shaped shelf with a spacing of 20 mm or more or a punching metal-shaped shelf with an opening of 20 mm or more in diameter may be installed.

[0018] The heat insulation part 50 is a member for suppressing the refrigerant flowing through the refrigerant flow path 20 from exchanging heat with the outside air before reaching the aging chamber 40. As shown in FIG. 1, the heat insulation part 50 is in direct contact with the refrigerant flow path 20 without a gap and sandwiches the refrigerant flow path 20 together with the wall portion 41 of the aging chamber 40. The material of the heat insulation part 50 is not particularly limited, and for example, expanded polystyrene or urethane can be used.

[0019] The internal temperature sensor 60 measures the internal temperature of the food M. Here, FIG. 2 is a diagram showing the configuration of the internal temperature sensor 60 according to the present embodiment. As shown in FIG. 2, the internal temperature sensor 60 includes a sheath portion 61, a sleeve portion 62, a lead wire portion 63, and an internal connector 64. Further, as shown in FIG. 1, the internal temperature sensor 60 is connected to a receiving meter 68 outside the aging chamber 40 via the internal connector 64, the internal adapter 65, the external adapter 66, and the external connector 67, and the temperature is measured by the receiving meter 68.

[0020] Also, in the present embodiment, the microwave aging apparatus 1 has an external temperature sensor (not shown) that measures the surface temperature of the food M. As the external temperature sensor, for example, a radiation type temperature sensor that measures the intensity of infrared rays or visible light non - contact can be used, or a configuration without an external temperature sensor can also be adopted.

[0021] The internal temperature of the food M measured by the internal temperature sensor 60 and the surface temperature of the food M measured by the external temperature sensor are output to the control unit 70. Then, as will be described later, based on the internal temperature of the food M measured by the internal temperature sensor 60 and / or the external temperature of the food M measured by the external temperature sensor, the control unit 70 performs temperature control and air volume control.

[0022] The control unit 70 incorporates a program for temperature control so that the surface temperature and the internal temperature of the food M to be aged reach predetermined temperatures respectively. Specifically, based on the internal temperature of the food M measured by the internal temperature sensor 60 and / or the external temperature of the food M measured by the external temperature sensor, the control unit 70 controls the operations of the cooler 10, the microwave oscillation unit 30, and the fan 43, thereby controlling the temperature of the cold air from the cooler 10, the output of the microwave from the microwave oscillation unit 30, and the air volume of the fan 43 to perform temperature control. For example, the control unit 70 can increase the internal temperature of the food M by increasing the output of the microwave from the microwave oscillation unit 30, and can lower the surface temperature and / or the internal temperature of the food M by lowering the temperature of the cold air from the cooler 10 or increasing the air volume of the fan 43.

[0023] In addition, the control unit 70 can control the oscillation of the microwave by the microwave oscillation unit 30. In particular, in this embodiment, the microwave oscillation unit 30 is a semiconductor oscillator, and the oscillation of the microwave can be controlled with high precision. Then, the control unit 70 irradiates the food M with microwaves by controlling the oscillation of the microwave by the microwave oscillation unit 30.

[0024] When aging the food M by irradiating it with microwaves in this way, since the microwaves heat up to the inside of the food by dielectric heating, it is possible to heat not only the surface but also the inside of the food M. Usually, warming the inside of the food M can promote the aging of the food M, but warming the surface of the food M will promote the growth of bacteria adhering to the surface of the food M. In contrast, in the microwave aging apparatus 1 according to this embodiment, the growth of bacteria adhering to the surface of the food M can be suppressed by cooling the surface of the food M by the operation of the cooling mechanism, that is, the cooler 10 and the fan 43.

[0025] In particular, in the microwave aging device 1 according to the present embodiment, under the control of the control unit 70, heating of the food M by the heating mechanism (microwave oscillation unit 30) and cooling of the surface of the food M by the cooling mechanism (cooler 10 and fan 43) are performed simultaneously, so that the operation of the heating mechanism and the cooling mechanism is controlled such that the surface temperature of the food M becomes lower than the internal temperature. Specifically, the control unit 70 controls the temperature of the cold air by the cooler 10, the output of the microwave oscillation unit 30, and the air volume by the fan 43 so that the surface temperature of the food M becomes lower than the internal temperature. Note that it is not necessary to continuously irradiate the food M with microwaves during the aging process, and the configuration can be such that the food M is irradiated with microwaves for at least 1 hour or more (preferably 3 hours or more, more preferably 5 hours or more).

[0026] Also, in the present embodiment, the microwave aging device 1 includes an operation unit 90 for the user to operate, and the user can cause the microwave aging device 1 to execute a dry aging mode in which temperature control and air volume control suitable for dry aging of the food M are performed by operating the operation unit 90. Further, in the microwave aging device 1 according to the present embodiment, in addition to the normal dry aging mode for dry aging meat chunks such as beef, a specific dry aging mode for appropriately dry aging the food M such as seafood with small slices that are easy to dry or the food M with a low water content such as dried tea leaves can be selected by the operation unit 90. When the specific dry aging mode is selected, temperature control and air volume control suitable for the food M that is easy to dry or the food M with a low water content can also be performed. Note that the temperature control and air volume control in the normal dry aging mode and the specific dry aging mode will be described later.

[0027] The UV lamp 80 is a device that generates ultraviolet rays. In this embodiment, by directly installing the UV lamp inside the aging chamber 40, during the aging of the food M, the ultraviolet rays generated by the UV lamp 80 can be irradiated onto the surface of the food M placed inside the aging chamber 40. In this way, by directly irradiating the surface of the food M with ultraviolet rays during aging, the growth of bacteria present on the surface of the food M can be further suppressed. Note that the control unit 70 can also control the operation of the UV lamp 80. For example, the control unit 70 can control to irradiate the UV lamp 80 with ultraviolet rays for a certain period of time (for example, several hours) starting from the timing when aging starts or the timing when the door of the aging chamber 40 is closed (after being opened).

[0028] (Dry aging) Next, the dry aging of the food M according to this embodiment will be described. Dry aging is a method of aging the food M while suppressing spoilage by aging the food M while directly blowing air on it without wrapping it in a vacuum pack or the like. In the normal dry aging mode for aging meat chunks or the like, in order to suppress spoilage, the meat M is arranged so that it is directly exposed to the air, and aging is performed at an air volume suitable for general aging (for example, 0.5 to 10.0 m / second). Also, in this embodiment, in the normal dry aging mode, by controlling the temperature of the cold air by the cooler 10, the output of the microwave by the microwave oscillation unit 30, and the air volume of the fan 43 so that the difference between the surface temperature and the internal temperature of the food M exceeds 8°C, while suppressing the growth of bacteria adhering to the surface of the food M, the aging inside the food M is promoted.

[0029] On the one hand, for foods M such as sliced seafood that are small and prone to drying, or foods M with a low moisture content such as dried tea leaves, when dry-aging is performed in the normal dry-aging mode, there has been a problem that the food M dries out immediately and a sufficient aging period cannot be obtained. Therefore, in this embodiment, for foods M that are prone to drying or have a low moisture content, in order to suppress the evaporation of moisture from the food M and obtain a sufficient aging period, dry-aging is performed by the microwave aging methods (1) to (3) below. Note that the microwave aging method of (1) below can be performed in both the normal dry-aging mode and the specific dry-aging mode described above, and the microwave aging methods of (2) and (3) are performed in the specific dry-aging mode.

[0030] (1) A method of performing microwave aging by covering the food M with a sheet S Figure 3 is a diagram for explaining an example of the microwave aging method according to this embodiment. In this embodiment, as shown in Figure 3, the food M is placed in a container C such as a colander or a bowl, and the upper surface of the container C containing the food M is covered with a sheet S. By covering the food M with the sheet S in this way, it is possible to suppress the direct hitting of cold air on the food M, so that the diffusion of the water vapor generated by the irradiation of the microwave to the food M to the outside of the container C is suppressed, and the humidity inside the container C can be maintained in a high state, effectively preventing the moisture in the food M from evaporating excessively and the food M from drying beyond the range suitable for aging. Note that in the diagram shown in Figure 3, a configuration in which the sheet S is covered so as not to contact the food M is illustrated, but a configuration in which the sheet S is covered on the food M so that the food M and the sheet S are in contact may also be used. Also, as shown in Figure 3, it is not limited to a configuration in which only one side of the food M is covered with the sheet S, and a configuration in which the entire food M is wrapped with the sheet S may also be used.

[0031] Further, the sheet S is made of a material that is resistant to microwaves and has air permeability and moisture permeability. Since the sheet S has air permeability, the air cooled by the cooler 10 can pass through the sheet S to cool the surface of the food M. Since the sheet S has moisture permeability, it is possible to prevent the water vapor evaporated from the food M from condensing on the sheet S and dripping onto the food M. As such a sheet S, a commercially available cooking sheet or aging sheet can be used. Also, if it has the above characteristics, tissue paper, kitchen paper, etc. can also be used. Cuts N are made in the sheet S, and the moisture evaporation of the food M can be adjusted according to the size and / or amount of the cuts N. For example, for a food M such as dry tea leaves with a low moisture content, the amount of moisture evaporation of the food M can be reduced by making the size of the cuts N smaller or reducing the amount of the cuts N. Also, for a food M such as seafood that can be gradually dried, the amount of moisture evaporation of the food M can be increased by making the cuts N relatively large or increasing the amount of the cuts N relatively.

[0032] (2) A method of performing microwave aging with the air volume of the fan 43 less than 0.5 m / s Also, when the specific dry aging mode is selected, the microwave aging apparatus 1 according to the present embodiment controls the operation of the fan 43 by the control unit 70 in order to suppress the moisture evaporation of the food M and obtain a sufficient aging period, so that the air volume of the fan 43, which is 0.5 to 10.0 m / s in the normal dry aging mode, can be controlled to less than 0.5 m / s. Thereby, it is possible to suppress the food M from being overdried by the cold air blown from the fan 43 and promote the aging of the food M.

[0033] (3) A method of performing microwave aging with the difference between the external temperature and the internal temperature of the food M within 8°C Further, when the specific dry-aging mode is selected, the microwave aging device 1 according to the present embodiment adjusts the irradiation amount of microwaves, the temperature of the aging chamber 40, and the air volume of the fan 43 by the control unit 70 so that the difference between the surface temperature and the internal temperature of the food M is within 8°C. By setting the difference between the surface temperature and the internal temperature of the food M to within 8°C in this way, it is possible to suppress the drying of the food M and ensure a sufficient aging period.

[0034] (4) Others Also, for foods M such as dried tea leaves that have a low water content from the beginning and are difficult to age, before performing dry-aging by the microwave aging method of (1) to (3) above, water is sprayed onto the surface of the food M by spraying or the like to wet the food M, thereby promoting the aging of the food M. Also, for foods M such as seafood that are prone to drying, by spraying water onto the food M by spraying or the like during dry-aging, it is possible to maintain a water content suitable for aging. By spraying water onto the food M by spraying or the like in this way and maintaining a water content suitable for aging, a sufficient aging period can be ensured and the food M can be sufficiently aged. For example, in the case of dried tea leaves, just spraying water at first causes drying in about 4 days and aging does not progress, but by additionally spraying water during dry-aging, it becomes possible to age for 20 days. Note that instead of a configuration in which water is sprayed onto the food M by spraying or the like, a configuration in which water vapor (not superheated steam) is sprayed onto the food M may be used. Also, the microwave aging device 1 may be configured to be provided with a mechanism for automatically spraying water or water vapor onto the food M.

[0035] Furthermore, in the microwave aging device 1 of this embodiment, in dry aging such as a beef chunk, the sheath portion 61 of the internal temperature sensor 60 is directly inserted into the food M to measure the internal temperature of the food M, and temperature control and air volume control are performed based on the measured internal temperature of the food M. However, there are cases where the internal temperature of the food M to be aged cannot be directly measured by inserting the sheath portion 61 of the internal temperature sensor 60, such as in tea leaves and fish roe. In this embodiment, for such a food M, as shown in FIG. 3, water W is put into a container such as a beaker B, and the temperature of this water W is measured by the internal temperature sensor 60, so that the measured temperature of the water W is regarded as the internal temperature of the food M, and temperature control and air volume control can be performed. Also, in the configuration shown in FIG. 3, it is also possible to adopt a configuration in which the food M is aged by irradiating the food M with microwaves of a constant output without performing control based on the temperature measured by the internal temperature sensor 60. In this case, it is preferable to adopt a configuration in which the beaker B with the internal temperature sensor 60 inserted is placed still under the shelf 44 with a mesh having a predetermined pitch width (for example, within 2 cm), on the side opposite to the irradiation port 42 through the shelf 44. Thereby, the microwaves irradiated from the irradiation port 42 to the beaker B can be attenuated, the internal temperature sensor 60 can be protected, the absorption of microwaves by the water W can be suppressed, and the food M can be irradiated with sufficient microwaves.

[0036] Next, a test example of dry aging according to this embodiment will be described.

[0037] (Dry aging of dry tea leaves) A dry-aging test was conducted using commercially available dried tea leaves for black tea (summer-harvested dried tea leaves from Nepal) as raw materials. Specifically, 60 g of dried black tea leaves were spread out in a polypropylene vat, and after spraying 12 g of distilled water, as shown in Fig. 3, the upper surface of the vat was covered with a cooking sheet with several cuts and set in the aging chamber 40. Also, a beaker containing 50 ml of distilled water was placed stationary in the aging chamber 40 for temperature control, and the temperature of the distilled water W in the beaker was measured with the internal temperature sensor 60. Then, while cooling the indoor temperature to 0°C, the temperature of the cold air from the cooler 10 and the output of the microwave from the microwave oscillation unit 30 were controlled by the control unit 70 so that the temperature of the distilled water W in the beaker would reach 5°C by continuously irradiating microwaves for 9 days. Also, during the microwave irradiation, the air was blown by the fan 43 at a maximum air velocity of 1 m / s to circulate the air in the aging chamber 40. Then, the weight of the dried tea leaves was measured once a day, and dry-aging was performed until the day when the weight no longer changed (the 9th day). As a comparative example, the same dried tea leaves were put into a bag with a zipper and refrigerated at 0°C for 9 days without being irradiated with microwaves.

[0038] For the dried tea leaves of black tea aged for 9 days by the above dry-aging method (Example 1) and the dried tea leaves of black tea aged for 9 days with the surface temperature and internal temperature set to 0°C without irradiating microwaves (Comparative Example 1), a sensory test was conducted by two external experts (food analysts). Specifically, for each dried tea leaf, hot black tea (1.5 g of tea leaves extracted with 120 ml of hot water for 3 minutes) and iced black tea (4 g of tea leaves extracted with 400 ml of water for about 6 hours) were brewed and tasted to conduct the sensory test.

[0039] As a result of the sensory test, it was evaluated that for hot black tea, it was difficult to distinguish between the dried tea leaves of Example 1 and those of Comparative Example 1. On the other hand, for iced black tea, it was evaluated that the black tea made from the dried tea leaves of Example 1 was clearly tasted better. Such an evaluation is presumably because in the iced black tea brewed with the dried tea leaves of Example 1, the aging of the dried tea leaves was promoted and the components changed, resulting in a better sharpness of astringency (the astringency disappears quickly in the mouth without lingering), and also because the unpleasant taste no longer remained, thus emphasizing the original fruity and honey-like sweetness and making it more distinguishable.

[0040] (Dry aging of fresh tea leaves) Next, a dry aging test was conducted using fresh tea leaves of Yabukita tea as raw materials. Specifically, 250 g of fresh tea leaves were spread out on a polypropylene colander and set in the aging chamber 40. Also, a beaker B containing 50 ml of distilled water was placed in the aging chamber 40 for temperature control and left standing, and the distilled water W in the beaker B was measured with the internal temperature sensor 60. Then, while cooling the temperature inside the chamber to 0°C by the control unit 70, microwave was continuously irradiated for 13 days, and the temperature of the cold air by the cooler 10 and the output of the microwave by the microwave oscillation unit 30 were controlled so that the temperature of the beaker B would become 5°C. Also, during the microwave irradiation, the air was blown by the fan 43 at an air volume with a maximum wind speed of 1 m / s to circulate the air inside the aging chamber 40. Then, the weight of the fresh tea leaves was measured once a day, and dry aging was performed until the day when the weight no longer changed (the 13th day). As a comparative example, 170 g of the same fresh tea leaves were spread out on a polypropylene colander and dried at 30°C for 2 days without irradiating with microwave.

[0041] Through the above dry-aging, the amino acid content was measured for the dried tea leaves obtained by aging the fresh tea leaves of Yabukita for 13 days (Example 2) and the dried tea leaves obtained by drying the fresh tea leaves of Yabukita at 30°C for 2 days without irradiating with microwaves (Comparative Example 2). Fig. 4 shows the measurement results of the amino acid content. In Fig. 4, the gray bar line indicates the amino acid content of the dried tea leaves of Example 2, and the white bar line indicates the amino acid content of the dried tea leaves of Comparative Example 2. The analysis was carried out by the Japan Food Analysis Center, a general incorporated foundation, and the free amino acids were measured by an automatic amino acid analysis method. As shown in Fig. 4, although the total amino acid content is higher in the dried tea leaves of Comparative Example 2, it was found that only glutamic acid and aspartic acid, which have two carboxyl groups in the molecule, increased in the fresh tea leaves of Example 2 compared to the dried tea leaves of Comparative Example 2. From this, it was found that by aging fresh tea leaves at a low temperature as in Example 2, glutamic acid, a umami component, selectively increases.

[0042] Furthermore, in the above dry-aging test, a sensory test was carried out by one external expert (a food analyst) on the dried tea leaves obtained by aging the fresh tea leaves of Yabugata for 13 days (Example 2) and the dried tea leaves obtained by drying the fresh tea leaves of Yabugata at 30°C for 2 days without irradiating with microwaves (Comparative Example 2). Specifically, for each dried tea leaf, extraction was carried out at room temperature (1 g of tea leaves extracted with 100 ml of water for 3 hours), with boiling water (1 g of tea leaves extracted with 65 ml of boiling water for 1 minute), and at 70°C (second infusion, 1 g of tea leaves extracted with 65 ml of boiling water for 1 minute), and the sensory test was conducted by tasting the extracted tea. As a result, although the tea leaves obtained by aging or drying fresh tea leaves had a remaining green odor, a fruity flavor was recognized only in the second infusion of the tea leaves of Example 2 at 70°C. Although the fresh tea leaves could not be processed to the level of commercially available tea, it was confirmed that the microwave aging method according to this embodiment reduced astringency and increased umami.

[0043] (Dry-aging of Suzuko) A dry-aging test was conducted using commercially available sujiko as a raw material. Specifically, approximately 800 g of sujiko was placed in a polypropylene vat, and the top of the vat was covered with a cooking sheet with several cuts, and then set in an aging chamber 40. Also, a beaker B containing 50 ml of distilled water was placed in the aging chamber 40 for temperature control and left standing. While cooling the indoor temperature to -2°C, microwave was continuously irradiated to set the internal temperature of sujiko to 6°C, and aging was carried out for 6 days. Also, during the microwave irradiation, the fan 43 was made to blow air at a maximum wind speed of 1 m / s to circulate the air in the aging chamber 40. Sampling was carried out on the 3rd day in the middle, and sujiko aged for 3 days (Example 3) and sujiko aged for 6 days (Example 4) were obtained. Then, for the sujiko of Examples 3 and 4, and the sujiko frozen and stored without microwave irradiation (Comparative Example 3), after storing at freezing (-30°C), it was transferred to a refrigerator (5°C) and left standing for 24 hours to thaw. Then, each sujiko was prepared into pickled ikura using warm water of about 40°C by a chef at a Japanese restaurant and subjected to a sensory test.

[0044] The sensory test was conducted by 10 panelists with rich food experience at the General Incorporated Foundation Research Institute for Taste Science. Also, in this sensory test, the ikura derived from the sujiko of Comparative Example 3 frozen and stored without microwave irradiation was used as a control, and the "flavor" and "intensity of the unique taste of ikura" of the ikura derived from the sujiko of Example 3 and Example 4 were comparatively evaluated. Also, each panelist was asked to freely comment on each ikura.

[0045] Figure 5 shows the results of sensory evaluations of "umami" and "intensity of the unique taste of ikura" of ikura derived from suziko of Examples 3 and 4 aged for 3 days and 6 days with microwave irradiation, using the evaluation of ikura derived from suziko of Comparative Example 3 stored frozen without microwave irradiation as a control. In addition, in Figure 5, for "umami" and "intensity of the unique taste of ikura", the evaluation in Comparative Example 3 was set as 3 points of the reference point, and when it was "strong" compared to Comparative Example 3, it was evaluated as 5 points, when it was "somewhat strong" as 4 points, when it was "the same as Comparative Example 3" as 3 points, when it was "somewhat weak" as 2 points, and when it was "weak" as 1 point on a 5-point scale, and the average value of the evaluation values of each panel was obtained. As shown in Figure 5, for the ikura derived from suziko of Example 3 aged for 3 days by dry aging according to the present embodiment, the proportion of people who felt that "umami" and "intensity of the unique taste of ikura" were stronger than those in Comparative Example 3 was large. In addition, as a comment on the ikura derived from suziko of Example 3 irradiated with microwave continuously for 3 days, the impression of "both color and taste are the best, and it seems to have a wide range of applications (the moist feeling is suitable for onigiri)" was obtained. Incidentally, the ikura derived from suziko of Example 4 aged for 6 days with microwave irradiation had an overlong aging period, and "umami" and "intensity of the unique taste of ikura" decreased compared to Comparative Example 3.

[0046] (Dry aging of red sea bream) A dry aging test was conducted using commercially available red sea bream (raw fish) as a raw material. Specifically, one red sea bream (raw fish) was sliced into 3 pieces, one half body was stored frozen as it was, and the other half body (about 500 g of red sea bream fillet) was put into the aging chamber 40, and a thermocouple was inserted. The temperature of the cold air by the cooler 10 and the output of the microwave by the microwave oscillation unit 30 were controlled so that the temperature inside the aging chamber 40 was 0°C and the internal temperature of the red sea bream was 8°C. In addition, during the microwave irradiation, the fan 43 was made to blow air at an air volume with a maximum wind speed of 0.3 m / s to circulate the air inside the aging chamber 40. Then, the red sea bream fillet was aged for 3 days by continuously irradiating it with microwave.

[0047] For the slices of sea bream aged for 3 days by the above dry aging (Example 5) and the slices of sea bream frozen and stored without being irradiated with microwaves (Comparative Example 4), the contents of glutamic acid and free amino acids, as well as the contents of nucleic acid components of inosine and inosinic acid, were measured. Glutamic acid is an amino acid related to umami, and inosinic acid is a nucleic acid component related to the umami of fish. Both of them are indicators showing the umami of fish. This analysis was carried out by the Food Science and Technology Research Institute, a general incorporated foundation. Free amino acids were measured by an automatic amino acid analysis method, and inosinic acid was measured by high performance liquid chromatography. The measurement results of free amino acids and the analysis results of nucleic acid components are shown in FIG. 6 and Table 1 below. Also, the measurement results of glutamic acid, total free amino acids, inosine, and inosinic acid are shown in FIG. 7.

Table 1

[0048] As shown in FIG. 7, in the slices of sea bream of Example 5 irradiated with microwaves, the contents of glutamic acid and inosinic acid increased compared with the slices of sea bream of Comparative Example 4 not irradiated with microwaves. Specifically, in the microwave aging method (Example 5) according to this embodiment, compared with frozen storage without microwave irradiation (Comparative Example 4), in the 3-day dry aging, the content of glutamic acid increased by 63% and the content of inosinic acid increased by 7%. Also, generally in fish, glutamic acid increases as the aging period passes, while inosinic acid tends to decrease. However, it was found that by shortening the aging period with microwaves, it is possible to provide aged fish containing a large amount of glutamic acid without decreasing inosinic acid.

[0049] In this test example, slices of sea bream of about 500 g were directly put into the aging chamber 40 for aging, but it is also effective to put the slices of sea bream in a vat and cover the slices of sea bream with an aging sheet for aging. In this case, since the evaporation of moisture from the slices of sea bream is suppressed, the optimal aging period becomes as long as 7 days, and accordingly, it becomes possible to carry out aging for a longer time.

[0050] (Dry aging of bluefin tuna) A dry aging test was conducted using bluefin tuna slices as raw materials. Specifically, the bluefin tuna slices were placed in a polypropylene vat, and the upper surface of the vat was covered with a cooking sheet with several cuts, and then set in the aging chamber 40. While cooling the indoor temperature to 0°C, microwave was continuously irradiated to set the internal temperature of the bluefin tuna to 8°C, and aging was carried out for 7 days. During the microwave irradiation, the fan 43 was made to blow air at a maximum air velocity of 1 m / s to circulate the air in the aging chamber 40.

[0051] The contents of glutamic acid and inosinic acid were measured for the bluefin tuna slices aged for 7 days by the above dry aging (Example 6) and the bluefin tuna slices frozen and stored without microwave irradiation (Comparative Example 5). As a result, it was found that for the bluefin tuna slices of Comparative Example 5, in the bluefin tuna slices of Example 6, glutamic acid increased by 1.3 times and inosinic acid increased by 1.1 times.

[0052] As described above, in the dry aging process of aging food M by drying the surface of food M by blowing air while irradiating food M with microwave, in the dry aging process, (1) covering food M with sheet S, (2) setting the air volume of fan 43 to less than 0.5 m / s, (3) making the difference between the external temperature and the internal temperature of food M within 8°C, by any of these methods, the moisture evaporation of food M due to microwave irradiation can be suppressed, and the moisture content of food M can be maintained within a range suitable for aging for a long time. Even for food M such as dried tea leaves with a low moisture content and food M such as seafood that is easy to dry, a sufficient aging period can be obtained, and food M can be sufficiently aged.

[0053] In addition, in foods M such as dried tea leaves, since the water content is low, aging hardly progresses during dry aging. However, after spraying water by means of mist spraying or the like and covering with the sheet S to suppress water evaporation, aging can be promoted. Further, in foods such as tea leaves and fish roe where the internal temperature sensor 60 cannot be inserted into the food M to measure the internal temperature of the food M, water W is placed in a beaker B housed in the aging chamber 40 in the same manner as the food M, the temperature of the water W in the beaker B is measured by the internal temperature sensor 60, and by estimating the measured temperature of the water W as the internal temperature of the food M, appropriate temperature control can be performed for foods M such as tea leaves and fish roe, and appropriate aging can be performed.

Explanation of Signs

[0054] 1…Microwave aging device 10…Cooler 20…Refrigerant flow path 30…Microwave oscillation unit 31…Cable 40…Aging chamber 41…Wall portion 42…Irradiation port 43…Fan 50…Heat insulation portion 60…Internal temperature sensor 70…Control unit 80…UV lamp 90…Operation unit

Claims

1. A microwave aging method having a dry aging process of blowing air while irradiating food stored in an aging chamber with microwaves, wherein: In the dry aging process, after spraying water or water vapor onto the surface of the food, or while spraying water or water vapor onto the surface of the food, irradiate the food with microwaves so that the internal temperature is higher than the surface temperature of the food; In the dry aging process, a method of microwave aging, characterized in that a sheet having air permeability and moisture permeability is covered on the food.

2. A microwave aging method having a dry aging process of blowing air while irradiating food stored in an aging chamber with microwaves, wherein: The food is food that cannot directly measure the internal temperature of the food in contact with the food; In the dry aging process, measure the temperature of the water placed in the container stored in the aging chamber together with the food, regard the measured temperature as the internal temperature of the food, and irradiate the microwave so that the internal temperature is higher than the surface temperature of the food. Control the amount, the temperature of the aging chamber, and / or the air volume; In the dry aging process, a method of microwave aging, characterized in that a sheet having air permeability and moisture permeability is covered on the food.

3. The method of microwave aging according to claim 1 or 2, wherein the sheet has a cut.

4. In the dry aging process, in order to suppress the moisture evaporation of the food, (1) The air volume is less than 0.5 m / sec, and / or (2) The method of microwave aging according to any one of claims 1 to 3, characterized in that the irradiation amount of the microwave, the temperature of the aging chamber, and / or the air volume are controlled so that the temperature difference between the surface temperature and the internal temperature of the food is within 8°C.

5. The method of microwave aging according to any one of claims 1 to 4, wherein the food is dry tea leaves, sliced fish, or fish roe.

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