rice cooker

Abstract

To provide a rice cooker that can maintain the warmth of freshly cooked rice and its aesthetic appearance, even after several hours have passed between cooking and eating. [Solution] The rice cooker 1 comprises a pot 5 capable of containing the food to be cooked, a heating coil 11 capable of heating the inside of the pot 5, a pressure regulating valve 47 capable of adjusting the pressure inside the pot 5 by allowing or blocking airflow between the inside and outside of the pot 5, a heating control circuit board 22 as a control unit capable of performing a first warming step in which the heating coil 11 is controlled to keep the rice warm, and a second warming step in which the pressure regulating valve 47 is controlled to block airflow between the inside and outside of the pot 5, and the heating coil 11 is controlled to keep the rice warm at a higher warming temperature than the first warming step until a predetermined high-temperature maintenance time has elapsed from the start, and an operation unit 56 capable of selectively selecting between the first warming step and the second warming step.

Description

【Technical Field】 【0001】 Embodiments according to the present invention relate to a rice cooker. 【Background Art】 【0002】 There is known a rice cooker having a function of shifting from a rice cooking process to a warming process and a function of starting the warming process when a warming switch is operated. When shifting from the rice cooking process to the warming process, the rice cooker performs normal warming including low-temperature warming or high-temperature warming. When starting the warming process by operating the warming switch, the rice cooker performs over-high-temperature warming in which temperature adjustment is performed at a predetermined temperature higher than high-temperature warming for a predetermined time, and then shifts to normal warming. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2004-267381 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 In recent years, with the diversification of lifestyles, the meal timing may be different for each person constituting a family, or may be different between holidays and weekdays. Therefore, if the rice is cooked in advance to suit those who eat early, when there is a gap of several hours between those who eat early and those who eat late, those who eat late will eat the rice being warmed instead of freshly cooked rice. That is, those who eat the rice being warmed late cannot eat warm rice like freshly cooked rice. Thus, a solution of providing warm rice like freshly cooked rice even during warming by raising the warming temperature can be considered. 【0005】 However, if rice is kept warm at a high temperature for an extended period after cooking, the Maillard reaction will progress in the rice during this time. Rice that has undergone the Maillard reaction will turn yellow or brown, and its appearance will deteriorate. 【0006】 Therefore, rice cookers are required to maintain both the warmth of freshly cooked rice and its aesthetic appeal, even after several hours have passed between cooking and eating. 【0007】 Therefore, the present invention aims to provide a rice cooker that can maintain both the warmth of freshly cooked rice and the aesthetic appearance of freshly cooked rice, even after a gap of several hours has passed between cooking the rice and eating it. [Means for solving the problem] 【0008】 To solve the aforementioned problems, an embodiment of the present invention provides a rice cooker comprising: a pot capable of containing food to be cooked and cooked rice; a heating unit capable of heating the inside of the pot; a pressure regulating unit capable of adjusting the pressure inside the pot by allowing or blocking airflow between the inside and outside of the pot; a control unit capable of performing a first warming step of keeping the rice warm by controlling at least the heating unit; a second warming step of blocking airflow between the inside and outside of the pot by controlling the pressure regulating unit, and controlling the heating unit to keep the rice warm at a high warming temperature higher than the warming temperature in the first warming step until a predetermined high-temperature maintenance time has elapsed from the start; and an operation unit capable of selectively selecting the first warming step and the second warming step. [Brief explanation of the drawing] 【0009】 [Figure 1] A perspective view of a rice cooker, which is an example of a heating appliance according to an embodiment of the present invention. [Figure 2] A longitudinal cross-sectional view of a rice cooker, which is an example of a heating appliance according to an embodiment of the present invention. [Figure 3] A cross-sectional view of the inner frame and heating coil of a rice cooker according to an embodiment of the present invention. [Figure 4] A bottom view of the inner frame and heating coil of a rice cooker according to an embodiment of the present invention. [Figure 5] A control block diagram of a rice cooker, which is an example of a heating appliance according to an embodiment of the present invention. [Figure 6] A diagram illustrating the time changes in the temperature inside the pot, the output of the heating coil, and the operation of the pressure reducing unit during the first warming process of a rice cooker according to an embodiment of the present invention. [Figure 7] This figure illustrates the time-dependent changes in the temperature inside the pot, the output of the heating coil, and the operation of the depressurization unit during the second warming process of a rice cooker according to an embodiment of the present invention. [Figure 8] This figure shows a first example of the first screen displayed by the display unit of a rice cooker according to an embodiment of the present invention. [Figure 9] This figure shows an example of a screen for selecting a warming method displayed on the display unit of a rice cooker according to an embodiment of the present invention. [Figure 10] This figure shows an example of a display when a rice cooker according to an embodiment of the present invention is performing the rice cooking process. [Figure 11] This figure shows an example of a display when a rice cooker according to an embodiment of the present invention transitions from the rice cooking process to the first warming process. [Figure 12] This figure shows an example of a display when a rice cooker according to an embodiment of the present invention continues the first warming process. [Figure 13] This figure shows an example of a display when a rice cooker according to an embodiment of the present invention is performing the rice cooking process. [Figure 14] This figure shows an example of a display when a rice cooker according to an embodiment of the present invention transitions from the rice cooking process to the second warming process. [Figure 15] This figure shows an example of a display when a rice cooker according to an embodiment of the present invention continues the second warming process. [Figure 16] This figure shows an example of a display when the rice cooker according to an embodiment of the present invention continues the second warming process. 【0010】 Hereinafter, embodiments of the rice cooker according to the present invention will be described with reference to Figures 1 to 16. Note that identical or corresponding components are denoted by the same reference numerals in multiple drawings. 【0011】 FIG. 1 is a perspective view of a rice cooker which is an example of a cooking appliance according to an embodiment of the present invention. 【0012】 FIG. 2 is a longitudinal sectional view of a rice cooker which is an example of a cooking appliance according to an embodiment of the present invention. 【0013】 Note that FIG. 1 is a perspective view of the rice cooker 1 which is an example of the cooking appliance according to the present embodiment, as seen from the upper front right of the rice cooker 1. That is, in FIG. 1, the front, right side, and upper surface of the rice cooker 1 are visible, and the back, left side, and bottom surface of the rice cooker 1 are hidden. 【0014】 As shown in FIGS. 1 and 2, the rice cooker 1 according to the present embodiment includes a rectangular main body 3 having a pot accommodating portion 2 opened upward, a pot 5 accommodated in the pot accommodating portion 2, a lid 6 covering the upper surface of the main body 3 to open and close the pot accommodating portion 2, a hinge mechanism 7 for supporting the lid 6 to be openable and closable with respect to the main body 3, and a power line 8 connectable to an external power source, for example, a socket of a commercial AC power source. When the lid 6 is opened upward from the main body 3, the pot 5 can be taken out from the pot accommodating portion 2. 【0015】 The rice cooker 1 heats water and rice, which are the objects to be cooked in the pot 5, to cook rice, and heats and keeps warm the cooked rice (cooked rice) with a heating coil 11. The rice cooker 1 cooks the objects to be cooked in a rice cooking course selectively selected from a plurality of rice cooking courses. 【0016】 Each rice cooking course pressurizes and heats the objects to be cooked in the pot 5 at a predetermined pressure. Each rice cooking course has steps set according to the brand of rice and the degree of milling. Each step includes, for example, a soaking step for promoting the absorption of water by the rice put into the pot 5, a boiling heating step for raising the temperature of the objects to be cooked to the boiling point in a short time, a boiling continuation step for continuing the boiling of the objects to be cooked, and a uniform heating step for maintaining the temperature at a high temperature so as not to burn the rice. The rice cooker 1 can also execute a warming step for keeping the rice in the pot 5 at a predetermined warming temperature independently of or continuously with the rice cooking course. 【0017】 Rice cooker 1 can also execute a cooking course that heats items other than the rice to be cooked in pot 5 using a predetermined heating pattern. Unless otherwise specified, items to be cooked include the rice to be cooked. 【0018】 The pot 5 is a container with a bottom that holds water and rice to be cooked. The pot 5 has a main material 5a made of aluminum with high thermal conductivity and a heating element 5b that is joined to the bottom surface from the lower outer surface of the main material. The material of the heating element is, for example, a magnetic metal plate made of ferritic stainless steel. 【0019】 The pot 5 is equipped with a flange portion 12 that protrudes radially outward and encircles the entire circumference of its outer surface. 【0020】 The main body 3 has a rectangular shape in plan view. The main body 3 defines the front, back, left side, right side, and bottom of the rice cooker 1 below the lid 6. The main body 3 comprises a bottom plate 15 that defines the bottom of the main body 3, an upper frame 16 that covers the top of the bottom plate 15 and defines part of the top surface and side of the main body 3, a bowl-shaped inner frame 17 integrally molded with the upper frame 16, and an outer frame 18 that defines the remaining part of the top surface of the main body 3. 【0021】 The base plate 15, the upper frame 16, and the outer frame 18 form the outer casing of the main body 3. The base plate 15 and the upper frame 16 are molded products of synthetic resin, such as polypropylene (PP). The outer frame 18 is a molded product of metal material, such as stainless steel. 【0022】 The upper frame 16 and the inner frame 17 define the pot storage section 2. The inner frame 17 corresponds to the bottom plate of the pot storage section 2. The inner frame 17 is a molded product of synthetic resin, such as polyethylene terephthalate (PET). 【0023】 Furthermore, the main body 3 has a control unit housing chamber 19 partitioned between the outer casing and the pot housing section 2. The outer casing of the main body 3 has a ventilation opening 21 that guides outside air into the control unit housing chamber 19. The ventilation opening 21 is preferably located on the bottom or side surface of the main body 3. 【0024】 The main unit 3 includes a heating control circuit board 22 housed in a control unit housing 19. The heating control circuit board 22 includes a microprocessor and a memory device that stores various calculation programs executed by the microprocessor, parameters, and other digital information. The memory device stores various settings (arguments) related to multiple pre-set rice cooking modes. The main unit 3 also includes a heat sink 23 attached to the microprocessor of the heating control circuit board 22 and a cooling fan 25 that blows air onto the heat sink 23. 【0025】 The heat sink 23 is made of a material with good thermal conductivity, such as aluminum. The cooling fan 25 is positioned below or to the side of the heat sink 23. The combined cooling performance of the heat sink 23 and the cooling fan 25 is set to keep the microprocessor temperature within the operating temperature range. It is preferable that the cooling fan 25 and the vent 21 of the main body 3 are positioned so as to sandwich the pot 5. Such a configuration contributes to miniaturization of the product. 【0026】 Furthermore, the main body 3 includes a heating coil 11 provided on the outer surface of the inner frame 17, and a pot temperature sensor 26 provided in the center of the bottom surface of the inner frame 17 for detecting the temperature of the bottom of the pot 5. 【0027】 The heating coil 11 is positioned so as to face the bottom surface from the lower outer surface of the pot 5 housed in the pot housing section 2. The heating coil 11 generates an alternating magnetic field to electromagnetically induce heating of the heating element in the pot 5. 【0028】 The pot temperature sensor 26 has a thermistor that detects the temperature of the bottom of the pot 5. The temperature of the bottom of the pot 5 will also be referred to as the "pot bottom temperature" below. The pot temperature sensor 26 is pressed against the bottom surface of the pot 5 by spring force. The pot bottom temperature detected by the pot temperature sensor 26 is used exclusively for controlling the heating temperature of the pot 5 by the heating coil 11. 【0029】 The hinge mechanism 7 includes a hinge shaft 31 that pivotably connects the main body 3 and the lid 6, and a hinge spring 32 that applies spring force to the lid 6 so that the lid 6, which closes the pot storage section 2, opens upward toward the main body 3 around the hinge shaft 31. The hinge shaft 31 is located near the upper rear of the main body 3. 【0030】 The planar shape of the lid 6 is rectangular, covering the main body 3. The lid 6 defines the front, back, left side, right side, and top surface of the rice cooker 1 above the main body 3. The lid 6 comprises an outer lid 35 positioned on top of the rice cooker 1, an outer lid cover 36 positioned between the outer lid 35 and the main body 3, a metal heat dissipation plate 37 provided on the outer lid cover 36, a lid heater 38 provided on the heat dissipation plate 37, and an inner lid unit 39 that is detachably attached to the outer lid cover 36 and detachably mounted below the heat dissipation plate 37. 【0031】 The inner cover unit 39 includes a metal inner cover 41 positioned below the heat sink 37 and in contact with the heat sink 37, a cover packing 42 provided on the outer circumference of the inner cover 41, and a packing base 43 that integrates the inner cover 41 and the cover packing 42. 【0032】 The heat sink 37 and the inner lid 41 are molded products of anodized aluminum or stainless steel sheets. The inner lid 41 makes up the majority of the bottom surface of the lid 6. The inner lid 41 has a disc shape that is substantially the same diameter as the upper opening of the pot 5. 【0033】 The lid gasket 42 is, for example, a molded product of silicone rubber or fluororubber. The lid gasket 42 is a sealing material that closes the gap between the pot 5 and the inner lid 41 when the lid 6 is closed. The lid gasket 42 contacts the upper surface of the flange portion 12 of the pot 5 when the lid 6 is closed. 【0034】 When the lid 6 with the inner lid unit 39 attached is closed, the lid packing 42 is pressed against the upper surface of the flange portion 12 of the pot 5, and the inner lid unit 39 completely covers the upper opening of the pot 5, sealing in the steam generated when the pot 5 is heated. 【0035】 The lid heater 38 is, for example, a cord heater. The lid heater 38 heats the inner lid 41, which is in contact with the heat sink 37, by heating the heat sink 37. 【0036】 Furthermore, the lid 6 is equipped with a steam vent 45 that is detachably attached to the rear half of the upper surface of the lid 6 and discharges steam generated from the food being cooked in the pot 5 to the outside of the rice cooker 1, a steam discharge passage 46 that guides the steam in the pot 5 to the steam vent 45, and a pressure regulating valve 47 that allows or blocks the flow of gas in the steam discharge passage 46. The outside of the rice cooker 1 will hereafter also be referred to as the "outside of the machine". 【0037】 The steam discharge passage 46 connects the steam outlet 45 and the pressure regulating valve 47. 【0038】 The pressure regulating valve 47 is, for example, a solenoid valve. When the pressure regulating valve 47 is opened, the inside of the pot 5 is connected to the outside of the machine. At this time, the pressure regulating valve 47 opens the inside of the pot 5 to the atmosphere. The steam generated inside the pot 5 is released to the outside of the rice cooker 1. When the pressure regulating valve 47 is closed, the connection between the inside of the pot 5 and the outside of the machine is severed, and the inflow and outflow of gas through the steam discharge passage 46 is restricted. At this time, the pressure regulating valve 47 seals the inside of the pot 5. The steam generated inside the pot 5 raises the internal pressure of the pot 5 above atmospheric pressure. It is also possible to reduce the internal pressure of the pot 5 below atmospheric pressure by drawing out the gas inside the pot 5 with the pressure regulating valve 47 closed. It is also possible to reduce the internal pressure of the pot 5 below atmospheric pressure by lowering the temperature inside the pot 5 with the pressure regulating valve 47 closed, as the temperature inside the pot 5 decreases and the steam condenses and liquefies as a result of this temperature decrease. For the sake of explanation, the action of closing the pressure regulating valve 47 and reducing the internal pressure of the pot 5 by lowering the temperature inside the pot 5 is called "sealed depressurization." 【0039】 The pressure regulating valve 47 includes a ball-shaped valve body 47a that allows or blocks the flow of gas in the steam discharge passage 46, and a solenoid 47b that drives the valve body 47a to open and close. When releasing steam from the pot 5 to the outside of the rice cooker 1, the solenoid 47b moves the valve body 47a in one direction so that it moves away from the valve seat, opening the steam discharge passage 46. When increasing or decreasing the internal pressure of the pot 5, the solenoid 47b moves the valve body 47a in the other direction so that it fits into the valve seat, closing the steam discharge passage 46. When the food being cooked in the pot 5 boils and generates steam, and this steam fills the pot 5, causing the internal pressure of the pot 5 to exceed a predetermined value, the valve body 47a moves away from the valve seat against its own weight, opening the steam discharge passage 46. Then, when the internal pressure of the pot 5 drops below a predetermined value, the valve body 47a settles into the valve seat by its own weight and closes the steam discharge passage 46. Through this operation of the valve body 47a, the pressure inside the pot 5 is maintained at or above atmospheric pressure. 【0040】 Furthermore, the lid 6 is equipped with a pressure reducing pump 48 that reduces the pressure inside the pot 5 when the lid 6 is closed. 【0041】 The suction side of the pressure reducing pump 48 is connected to the pressure reducing port 49 of the inner lid 41. The pressure reducing pump 48 reduces the internal pressure of the pot 5 by discharging the gas inside the pot 5 to the outside of the rice cooker 1 through the pressure reducing port 49. When reducing the internal pressure of the pot 5, the pot 5 is placed in the pot housing 2, the lid 6 is closed, and the pressure regulating valve 47 is closed. When restoring the internal pressure of the pot 5 from a reduced pressure state to atmospheric pressure, the pressure reducing pump 48 is stopped and the pressure regulating valve 47 is opened. This connects the inside of the pot 5 to the outside of the rice cooker 1, allowing outside air to flow into the pot 5. The passage connecting the pressure reducing pump 48 and the pressure reducing port 49 may be equipped with an on / off valve to allow or block the flow of gas. 【0042】 In other words, the pressure reducing pump 48 and the pressure regulating valve 47 function as a pressure reducing unit capable of reducing the internal pressure of the pot 5 to a reduced state below atmospheric pressure, and the pressure regulating valve 47 also functions as a pressure increasing unit capable of increasing the internal pressure of the pot 5 to a higher state than atmospheric pressure. Furthermore, the internal pressure of the pot 5 can also be reduced to a reduced state below atmospheric pressure by closing the pressure regulating valve 47 while the internal pressure of the pot 5 is pressurized to a state below atmospheric pressure by closed pressure reduction, which condenses the steam inside the pot 5 due to the decrease in temperature inside the pot 5 over time. 【0043】 Furthermore, the lid 6 includes a lid open operation button 50 provided on the front half of the upper surface of the lid 6, a lid lock mechanism 51 that locks the opening and closing of the lid 6, an operation panel 52 that serves as an input / output device, and an input / output control circuit board 53 that controls the operation of the operation panel 52. 【0044】 When the lid opening button 50 is pressed, the lock between the lid 6, which closes the pot storage compartment 2, and the main body 3 is released. Once the lock between the lid 6 and the main body 3 is released, the spring force of the hinge spring 32 opens the lid 6 around the hinge shaft 31 as the pivot point. 【0045】 The lid locking mechanism 51 locks the lid 6 when the main body 3 is closed. The lid locking mechanism 51 releases the lock on the lid 6 in conjunction with the operation of the lid open button 50. The lid locking mechanism 51 restricts the opening of the lid 6 even if the lid open button 50 is operated once when the internal pressure of the pot 5 is pressurized or depressurized. If the lid open button 50 is operated again within a predetermined time, the lid locking mechanism 51 operates the pressure regulating valve 47 and the depressurizing pump 48 to restore the internal pressure of the pot 5 to atmospheric pressure, and then releases the restriction on opening the lid 6. The lid locking operation of this lid locking mechanism 51 is controlled by the heating control circuit board 22. The detailed structure and control contents of the lid locking mechanism 51 may be based on known technology, such as that described in Japanese Patent Application Publication No. 2015-171545. The lid locking operation of the lid locking mechanism 51 is not performed at all times. When the lid locking operation is not performed, the lid 6 can be opened with a single operation of the lid open button 50. 【0046】 The control panel 52 includes a display unit 55 that displays various information and an operation unit 56 that accepts various operations. 【0047】 The display unit 55 is an output device that displays the current status of the rice cooker 1 in a visually recognizable manner. The display unit 55 is, for example, a display and a light-emitting diode (LED). The display is a liquid crystal display (LCD) or an organic electro-luminescence (organic light-emitting diode) panel. 【0048】 The display unit 55 includes multiple light-emitting diodes (LEDs), including one that lights up the string "Reservation" (Figure 1) when a reservation has been set and the rice cooking operation is waiting to be scheduled, one that lights up the string "Keep Warm" (Figure 1) when the food being cooked in the pot 5 is being kept warm, one that lights up the string "Pressure" (Figure 1) when the rice cooking operation is being performed and the internal pressure of the pot 5 is higher than atmospheric pressure, and one that lights up the string "Vacuum" (Figure 1) when the internal pressure of the pot 5 is lower than atmospheric pressure. Therefore, even in a dimmed state with reduced brightness on the display, the user can easily recognize the current status of the rice cooker 1. The light-emitting colors of the multiple LEDs may be uniform or different from each other. The user can more easily recognize the current status of the rice cooker 1 by the difference in light-emitting colors. The display and the LEDs may be installed close together or far apart. The displays from these LEDs may also be shown on the display. 【0049】 The operation unit 56 is an input device, specifically a touch sensor. The operation unit 56 is positioned directly above the display unit 55, overlapping it. The touch sensor comprises multiple key elements arranged on a plane. Each key element includes, for example, a transparent electrode made of a conductive polymer, a contact portion connected to the input / output control circuit board 53, and a patterned wiring connecting the transparent electrode portion and the contact portion. By pressing, touching, or bringing a fingertip close to any of the display elements displayed by the display unit 55, the key element positioned directly above that display element is operated. The operation received by this key element is output to the input / output control circuit board 53 as a selection of a display element on the display unit 55 displayed directly below it. 【0050】 The input / output control circuit board 53 is housed in the cover 6 and positioned directly below the operation panel 52. The input / output control circuit board 53 includes a microprocessor, a memory device that stores various calculation programs executed by the microprocessor, digital information such as parameters, and a real-time clock (RTC) with a timing function. The memory device stores various settings (arguments) related to multiple pre-set rice cooking modes. The real-time clock has the function of a clock that marks the current time of the rice cooker 1, and also has a timing function. The real-time clock can be located in either the heating control circuit board 22 or the input / output control circuit board 53. 【0051】 Incidentally, it is presumed that the user of the rice cooker 1 will stand facing the front of the rice cooker 1 and operate the control panel 52. Therefore, the rice cooker 1 according to this embodiment is equipped with a lid open operation button 50 located on the front half of the upper surface, close to the user facing the front of the rice cooker 1, and a steam vent 45 located on the rear half of the upper surface, farther from the user facing the front of the rice cooker 1. As a result, the rice cooker 1 according to this embodiment can easily secure a large space for positioning the display unit 55 between the lid open operation button 50 and the steam vent 45, and the size of the control unit 56, which is positioned directly above the display unit 55, can be set to be as large as possible. Thus, the rice cooker 1 can achieve high visibility of the display unit 55, high operability of the control unit 56, and high safety from steam discharged from the steam vent 45. 【0052】 Furthermore, the rice cooker 1 according to this embodiment does not have physical operation keys, such as a cooking key and an off key, which are provided in conventional rice cookers, and can be operated solely by the operation unit 56. Therefore, the rice cooker 1 according to this embodiment eliminates the trouble of searching for operation keys and provides intuitive operability. In addition, the rice cooker 1, which does not have physical operation keys, improves space utilization efficiency by combining the display unit 55 and the operation unit 56, and it is easier to design an extremely smart appearance compared to conventional rice cookers in which input and output devices are dispersed. Moreover, the top surface of the rice cooker 1, which does not have physical operation keys, can be a flat surface with almost no irregularities or a gently curved surface. The shape of the top surface of the rice cooker 1 makes cleaning, such as wiping, easy. 【0053】 Figure 3 is a cross-sectional view of the inner frame and heating coil of a rice cooker according to an embodiment of the present invention. 【0054】 Figure 4 is a bottom view of the inner frame and heating coil of a rice cooker according to an embodiment of the present invention. 【0055】 As shown in Figures 3 and 4, the heating coil 11 of the rice cooker 1 according to this embodiment includes a plurality of coils 11u and 11d. 【0056】 The first coil 11u is provided on the outer surface of the inner frame 17, and the second coil 11d is provided on the bottom outer surface of the inner frame 17. The first coil 11u faces the lower outer surface of the pot 5, with the inner frame 17 in between. The second coil 11d faces the bottom outer surface of the pot 5, with the inner frame 17 in between. 【0057】 The heat transfer that occurs when current is applied to the heating coil 11 will be explained. 【0058】 When the first coil 11u is energized, the lower outer surface of the pot 5 heats up first. The heat from this area is conducted to the main material 5a of the pot 5 and then transferred to the water contained in the food being cooked, which is in contact with the lower inner surface of the pot 5. Heat transfer within the food being cooked mainly occurs through the movement of water, i.e., convection. Where rice is present in the food being cooked, the movement of water is restricted to the narrow gaps between the rice grains, slowing down the movement of water and heat. In contrast, where there is no rice, the movement of water and heat, i.e., convection, becomes more active. Therefore, after the water in contact with the lower inner surface, the water in the upper part of the food being cooked heats up. Because the rice grains sink to the bottom of the pot 5 due to their own weight, the upper part of the food being cooked contains almost no rice grains and is essentially only water. Subsequently, in the central part of the food being cooked, the water and heat from the high-temperature upper part move to the still-low-temperature middle part of the food being cooked, and then to the lower part of the food being cooked. This phenomenon is what is known as thermal convection, and is called "external convection" by the first coil 11u. 【0059】 Furthermore, when the second coil 11d is energized, the outer surface of the bottom of the pot 5 heats up first, and the heat from this part is conducted to the main material 5a of the pot 5 and then moves to the inner surface of the bottom of the pot 5, the water contained in the lower layer of the food being cooked that is in contact with the bottom of the pot. Because the rice grains sink to the bottom of the pot 5 due to their own weight, the bottom of the pot is covered with the rice and water contained in the lower layer of the food being cooked. Therefore, the heat from the bottom of the pot increases the temperature and pressure of the water covering the bottom of the pot. Subsequently, the water at the bottom of the pot, whose temperature and pressure have increased, moves upward through the gaps between the rice grains contained in the food being cooked. In other words, the water heated in the lower layer of the food being cooked, i.e., the hot water, moves with the heat to the middle layer of the food being cooked, and then to the upper layer of the food being cooked. This phenomenon is called "blowing up" and is called "internal convection" by the second coil 11d. 【0060】 When the first coil 11u and the second coil 11d are energized alternately, external and internal convection occurs alternately around the food being cooked in the pot 5. In other words, when the first coil 11u and the second coil 11d are energized alternately, the agitation of the water contained in the food being cooked in the pot 5 is promoted, reducing uneven heating of the food. 【0061】 The heating control circuit board 22 of the rice cooker 1 according to this embodiment operates the heating coil 11 with a plurality of energization types, which are various combinations of the energization time of the first coil 11u, the energization time of the second coil 11d, the output of the first coil 11u, and the output of the second coil 11d. These plurality of energization types are stored in the memory unit. 【0062】 In one of the energizing types, the first coil 11u is energized with a first output W1 and a first energizing time T1, and then the second coil 11d is energized with a second output W2 and a second energizing time T2. Preferably, the energizing times T1 and T2 are several seconds or longer. By doing so, the rice cooker 1 can generate alternating external and internal convection around the food being cooked in the pot 5 for a predetermined period of time or longer. This alternating generation of external and internal convection promotes the stirring of the water in the food being cooked in the pot 5 and reduces uneven heating. 【0063】 It is preferable that the first energizing time T1 and the second energizing time T2 are different. In other words, it is preferable to make the time during which external convection occurs and the time during which internal convection occurs different for a given type of energizing. 【0064】 The energizing type may include one in which either the energizing time or output of the heating coil 11 is varied, while the other remains constant. The energizing time of each coil 11 and 11d may be constant, while the output of each coil 11 and 11d may be different. Alternatively, the output of each coil 11 and 11d may be constant, while the energizing time of each coil 11 and 11d may be different. 【0065】 Multiple energizing types may include one that has a period of no energizing time during which the energizing of all heating coils 11 is cut off. That is, in an energizing type, one of the two coils 11 and 11d is energized for a predetermined time and output, and after the first period of no energizing time has elapsed, the other of the two coils 11 and 11d is energized for a predetermined time and output, and then the system waits for the second period of no energizing time to elapse. The first period of no energizing time and the second period of no energizing time may be the same or different. 【0066】 Furthermore, the energizing type may include one in which only one of the two coils 11 and 11d is intermittently energized, and the other coil 11 and 11d is not energized (no energizing). In such an energizing type, one of the two coils 11 and 11d is energized for a predetermined energizing time and a predetermined energizing output, and neither coil 11 nor 11d is energized for a predetermined energizing time. Such an energizing type is suitable for the heat retention process. 【0067】 These types of electrical stimulation are performed repeatedly for a predetermined time or a predetermined number of times. 【0068】 When the energization type is switched, the system switches from the first energization type, which energizes the first coil 11u with a first output W1 and a first energization time T1, to the second energization type, which energizes the second coil 11d with a second output W2 and a second energization time T2, to the second energization type, which energizes the first coil 11u with a third output W3 and a third energization time T3, to the fourth energization type, which energizes the second coil 11d with a fourth output W4 and a fourth energization time T4. Each energization type is repeated for a predetermined time or a predetermined number of times before and after the switch. 【0069】 The content of each power supply type, and the combinations of multiple power supply types, are suitably set for each step included in the rice cooking course and the cooking course. 【0070】 In the energized type, the output adjustment of the first coil 11u and the output adjustment of the second coil 11d are performed, for example, by PWM control (Pulse Width Modulation). 【0071】 Figure 5 is a control block diagram of a rice cooker, which is an example of a heating appliance according to an embodiment of the present invention. 【0072】 As shown in Figures 1 to 4, and also in Figure 5, the rice cooker 1 according to this embodiment operates by coordinating the input / output control circuit board 53 and the heating control circuit board 22. The input / output control circuit board 53 and the heating control circuit board 22 input and output control signals in both directions. The input / output control circuit board 53 outputs a heating control signal to the heating control circuit board 22, and the heating control circuit board 22 outputs a display control signal to the input / output control circuit board 53. 【0073】 Furthermore, the rice cooker 1 includes a coil drive circuit 61 that energizes the heating coil 11, a lid heater drive circuit 63 that energizes the lid heater 38, a lid temperature sensor 65 that detects the temperature of the inner lid 41, a lid opening / closing sensor 66 that is provided inside the lid 6 to detect the opening and closing of the lid 6, a pressure sensor 67 that detects the internal pressure of the pot 5, and a notification unit 68. 【0074】 The coil drive circuit 61 includes a first drive circuit 61u that energizes a first coil 11u based on a first heating control signal output by the heating control circuit board 22, and a second drive circuit 61d that energizes a second coil 11d based on a second heating control signal output by the heating control circuit board 22. The two coil drive circuits 61u and 61d are, for example, at least one of a power supply circuit, an inverter, an IH (Induction Heating) drive circuit, and a switching element. The coil drive circuit 61 increases or decreases the output of the two coils 11u and 11d by changing at least one of the period of the high-frequency current energized to the two coils 11u and 11d, and the duty cycle of the energizing time. 【0075】 For the sake of explanation, it is assumed that rice cooker 1 is equipped with a switching element that selectively selects whether to energize the two coils 11u and 11d. Rice cooker 1 may also be able to energize the two coils 11u and 11d simultaneously. In other words, there may be periods when the two coils 11u and 11d are energized at the same time. 【0076】 The lid heater drive circuit 63 supplies a DC or AC current to the lid heater 38 based on the lid heating control signal output by the heating control circuit board 22. 【0077】 The lid temperature sensor 65 is a thermistor. The lid temperature sensor 65 detects the temperature of the heat sink 37. The temperature detected by the lid temperature sensor 65, that is, the temperature of the heat sink 37, correlates with the temperature of the inner lid 41. In other words, the temperature of the inner lid 41 can be estimated from the temperature detected by the lid temperature sensor 65. The temperature of the inner lid 41 estimated from the temperature detected by the lid temperature sensor 65 will hereafter be referred to as the "lid temperature". The lid temperature detected by the lid temperature sensor 65 is used primarily for controlling the heating temperature of the inner lid 41 by the lid heater 38. 【0078】 The lid opening / closing sensor 66 is preferably located near the hinge mechanism 7. The lid opening / closing sensor 66 can be any type of sensor, such as optical, mechanical, or magnetic, as long as it can output a detection signal based on the opening and closing of the lid 6 to the input / output control circuit board 53. 【0079】 The pressure sensor 67 is located inside the lid 6 and detects the pressure on the side of the pot 5 that is above the pressure regulating valve 47 in the steam discharge passage 46, and outputs it to the heating control circuit board 22. 【0080】 The notification unit 68 is at least one of the following: a light source that lights up or flashes, such as a lamp or a light-emitting diode (LED), which appeals to the user's sight; a sound generator that emits electrically synthesized sounds or buzzer sounds, which appeals to the user's hearing; or a vibrator, which appeals to the user's touch. 【0081】 The inputs to the input / output control circuit board 53 are the operation signals output by each key element of the operation unit 56 and the display control signals output by the heating control circuit board 22. Based on these inputs, the input / output control circuit board 53 controls the display operation of the display unit 55, controls the operation of the notification unit 68, and outputs a heating control signal to the heating control circuit board 22. 【0082】 The microprocessor on the input / output control circuit board 53 functions as an input signal generation unit 72 that generates control signals corresponding to the operation signals output by each key element by executing a predetermined program, a display control unit 73 that controls the display operation of the display unit 55, and a condition setting unit 75 that works in conjunction with the input signal generation unit 72 and the display control unit 73 to enable the presentation, selection, and setting of various conditions that can be selected by the key elements. 【0083】 The condition setting unit 75 sequentially presents multiple courses, including, for example, a cooking course and a rice cooking course, enabling the selection and setting of the desired course. 【0084】 The memory device of the input / output control circuit board 53 stores rice cooking courses corresponding to various conditions that can be selected using key elements, such as rice brand, cooking method, and hardness. The display unit 55 displays the various conditions of the rice cooking courses stored in the memory device, and accepts the operation of the operation unit 56 to select these conditions, thereby appropriately selecting and setting the rice cooking course and cooking course. 【0085】 The heating control circuit board 22 of the main unit 3 controls the temperature of the pot 5 and the inner lid 41 by heating and adjusting the heating coil 11 and the lid heater 38 during cooking and warming, based on the pot bottom temperature detected by the pot temperature sensor 26 and the lid temperature detected by the lid temperature sensor 65. 【0086】 The inputs to the heating control circuit board 22 are the temperature detection signal output by the pot temperature sensor 26, the temperature detection signal output by the lid temperature sensor 65, the internal pressure detection signal output by the pressure sensor 67, the lid opening / closing detection signal output by the lid opening / closing sensor 66, and the heating control signal output by the input / output control circuit board 53. 【0087】 Based on these inputs, the heating control circuit board 22 controls the heating coil 11 that heats the pot 5 during cooking and keeping warm, and the lid heater 38 that heats the inner lid 41, respectively. The heating control circuit board 22 mainly controls the heating coil 11 based on the temperature detection signal output by the pot temperature sensor 26 to manage the temperature of the bottom of the pot 5. The heating control circuit board 22 mainly controls the lid heater 38 based on the temperature detection signal output by the lid temperature sensor 65 to manage the temperature of the inner lid 41. 【0088】 Furthermore, the heating control circuit board 22 controls the opening and closing operation of the pressure regulating valve 47 of the steam discharge passage 46, the depressurization operation of the depressurizing pump 48, and the lid locking operation of the lid locking mechanism 51, respectively, based on the internal pressure detection signal output by the pressure sensor 67. 【0089】 The microprocessor on the heating control circuit board 22 functions as a rice cooking control unit 77 and a heat retention control unit 78 by executing a predetermined program. 【0090】 When the operation unit 56 receives a command to start cooking, the rice cooking control unit 77 sequentially executes the soaking process, the boiling process, the boiling continuation process, and the steaming process to cook the rice. In addition, when the operation unit 56 receives a command to start cooking, the rice cooking control unit 77 sequentially executes the cooking process. 【0091】 The heat retention control unit 78 performs a heat retention process. The heat retention process consists of a simple heat retention process, which maintains the rice in the pot 5 at a predetermined heat retention temperature, and a reheating heat retention process, which reheats the rice in the pot 5 that is below the predetermined heat retention temperature to the predetermined heat retention temperature. 【0092】 The memory device of the heating control circuit board 22 stores various combinations of the drive timings of the pressure regulating valve 47 and the pressure reducing pump 48, the energization types of the first coil 11u and the second coil 11d, and combinations of their execution timings in the rice cooking course and the cooking course. 【0093】 An example of the rice cooking operation using rice cooker 1 will be explained. 【0094】 The food to be cooked is placed inside the pot 5. Then, the pot 5 containing the food to be cooked is placed inside the pot storage section 2 of the main body 3, and the lid 6 is closed. 【0095】 When the power plug of the rice cooker 1 is plugged into a commercial AC power outlet, the rice cooker 1 starts up in an initial state where it is not performing cooking or keeping rice warm. This initial state is also called the standby state or the stopped state. Each time a key element of the operation unit 56 is operated in the standby state, an operation signal corresponding to the operated key element is input to the input signal generation unit 72. The condition setting unit 75 works in conjunction with the input signal generation unit 72 to change the course settings and works in conjunction with the display control unit 73 to display the changed settings on the display unit 55. The display unit 55 visually presents the current course settings corresponding to the operated key element to the user of the rice cooker 1. 【0096】 When a key element corresponding to course selection is operated, an operation signal corresponding to course selection is input to the input signal generation unit 72. The condition setting unit 75 stores the course displayed on the display unit 55 in the memory device and outputs a heating pattern corresponding to the selected course to the heating control circuit board 22. The rice cooking control unit 77 of the heating control circuit board 22 executes a soaking process, a boiling heating process, a boiling continuation process, and a steaming process according to the input heating pattern. 【0097】 During the soaking and cooking process, the rice cooking control unit 77 controls the pressure regulating valve 47 and the pressure reducing pump 48 to reduce the internal pressure of the pot 5. When the soaking and cooking process begins, the display control unit 73 lights up the light-emitting diode located directly below the word "vacuum". 【0098】 The rice cooking control unit 77 closes the pressure regulating valve 47 to block the flow of gas in the steam exhaust passage 46 and operates the pressure reducing pump 48 to exhaust the gas inside the pot 5 to the outside of the rice cooker 1. The rice cooking control unit 77 operates the pressure reducing pump 48 to perform vacuuming, which removes the air inside the sealed pot 5. Based on the internal pressure detection signal of the pot 5 output by the pressure sensor 67, the rice cooking control unit 77 controls the pressure reducing pump 48 so that the internal pressure inside the pot 5 is maintained below a predetermined value. In other words, throughout the entire soaking and cooking process, the internal pressure of the pot 5 is kept in a reduced state lower than atmospheric pressure. 【0099】 The rice cooking control unit 77 switches the power supply to the heating coil 11 based on the temperature detection signal output by the pot temperature sensor 26 to heat the pot 5 and promote water absorption of the rice. At this time, it estimates the amount of rice to be cooked from the time required for the temperature of the pot 5 to reach a predetermined temperature and the amount of heating. The soaking and cooking process ends when a predetermined time has elapsed. 【0100】 During the boiling heating process, the rice cooking control unit 77 energizes the heating coil 11 until it detects that the rice to be cooked is boiling. The rice to be cooked in the pot 5 is heated more strongly than in the soaking process, and the temperature of the rice to be cooked rises to the boiling point in a short time. The rice cooking control unit 77 stops the pressure reducing pump 48 and opens the pressure regulating valve 47. As a result, the internal pressure of the pot 5 immediately recovers to atmospheric pressure. The display control unit 73 turns off the light-emitting diode located directly below the word "vacuum". 【0101】 Subsequently, when the temperature of the bottom of the pot 5 reaches a predetermined temperature, for example, 90 degrees Celsius or higher, and the temperature of the inner lid 41 also reaches a predetermined temperature, for example, 90 degrees Celsius or higher, the rice cooking control unit 77 opens the pressure regulating valve 47 and starts detecting boiling of the food being cooked under atmospheric pressure. The display control unit 73 lights up the light-emitting diode located directly below the word "Pressurized" based on the internal pressure of the pot 5 detected by the pressure sensor 67. The rice cooking control unit 77 monitors the rate of temperature rise per unit time at the bottom of the pot 5 or the rate of temperature rise per unit time at the inner lid 41, and determines that the food being cooked has boiled when these rate of temperature rise falls below a predetermined rate. 【0102】 During the boiling continuation process, the rice cooking control unit 77 switches the power supply to the heating coil 11 to maintain the temperature of the bottom of the pot 5 at or above a predetermined temperature, for example, 98 degrees Celsius or higher, and continuously powers the lid heater 38 to maintain the temperature of the inner lid 41 at or above a predetermined temperature, for example, 98 degrees Celsius or higher. 【0103】 The rice cooking control unit 77 determines that the rice is cooked and terminates the boiling process when the rate of temperature rise at the bottom of the pot 5 exceeds a predetermined rate, or when the excess moisture in the pot 5 reaches a dry-up temperature, for example, 120 degrees Celsius. 【0104】 During the steaming process, the rice cooking control unit 77 switches the power supply to the lid heater 38 based on the temperature of the inner lid 41 to prevent condensation from forming on the inner lid 41. The rice cooking control unit 77 also switches the power supply to the heating coil 11 based on the temperature of the bottom of the pot 5 to manage the temperature of the food being cooked. The steaming process continues for a predetermined time. When the steaming process is complete, the rice cooking control unit 77 completes the rice cooking operation, and the warming control unit 78 starts the warming process. 【0105】 After completing the rice cooking operation, the heating control circuit board 22 outputs a display control signal corresponding to the completion of the rice cooking operation. The input / output control circuit board 53, upon receiving this display control signal, controls the display operation of the display unit 55 and the notification operation of the notification unit 68 to inform the user of the completion of the rice cooking process. 【0106】 The heat retention control unit 78 generates heat in the heating coil 11 until the temperature of the rice drops from the freshly cooked temperature, effectively 100 degrees Celsius, to the warming temperature, effectively 70 degrees Celsius, and continues to generate heat in the heating coil 11 even after the warming temperature stabilizes at 70 degrees Celsius. The heat retention control unit 78 adjusts the output of the heating coil 11 so that the temperature at the bottom of the pot 5 remains constant. 【0107】 Rice cooker 1 can also reheat the rice in pot 5. 【0108】 Next, the warming process performed by the rice cooker 1 according to this embodiment will be described in detail. The simple warming process performed by the rice cooker 1 according to this embodiment includes a first warming process for keeping the rice warm and a second warming process for keeping the rice warm at a higher warming temperature than that of the first warming process. The warming control unit 78 can selectively perform the first warming process and the second warming process. 【0109】 Figure 6 illustrates the time changes in the temperature inside the pot, the output of the heating coil, and the operation of the depressurization unit during the first warming process of a rice cooker according to an embodiment of the present invention. 【0110】 Figure 7 illustrates the time changes in the temperature inside the pot, the output of the heating coil, and the operation of the depressurization unit during the second warming process of a rice cooker according to an embodiment of the present invention. 【0111】 As illustrated in Figure 6, the first heat retention process performed by the heat retention control unit 78 controls at least the heating coil 11 to keep the rice warm. The target value Tkw1 of the heat retention temperature in the first heat retention process is set to, for example, 70 degrees Celsius. For the sake of explanation, the target value Tkw1 of the heat retention temperature in the first heat retention process will also be called the reference heat retention target temperature Tkw1. 【0112】 The heat retention control unit 78 controls the heating coil 11 to keep the rice warm so that the bottom temperature of the pot detected by the pot temperature sensor 26 maintains the standard heat retention target temperature Tkw1. Alternatively, the heat retention control unit 78 may also keep the rice warm by controlling the heating coil 11 so that the temperature inside the pot, estimated from the bottom temperature of the pot detected by the pot temperature sensor 26 and the lid temperature detected by the lid temperature sensor 65, maintains the standard heat retention target temperature Tkw1. For the sake of explanation, the temperature of the rice estimated from the bottom temperature of the pot and the temperature inside the pot will be referred to as the "temperature of the rice" below. 【0113】 At the start of the first heat retention process, the temperature of the rice cooked in the rice cooking process is significantly higher than the standard heat retention target temperature Tkw1, for example, reaching 100 degrees Celsius. Therefore, the heat retention control unit 78 stops the heating coil 11 and waits until the temperature of the rice drops (cools down) to the standard heat retention target temperature Tkw1. In the example in Figure 6, the time it takes for the temperature of the rice to drop to the standard heat retention target temperature Tkw1 is shown as approximately 1 hour and 30 minutes. Once the temperature of the rice reaches the standard heat retention target temperature Tkw1, the heat retention control unit 78 controls the heating coil 11 to maintain the temperature of the rice at the standard heat retention target temperature Tkw1. 【0114】 Furthermore, after the rice reaches the standard target temperature Tkw1, the heat retention control unit 78 reduces the pressure inside the pot 5 to a level lower than atmospheric pressure to suppress deterioration of the rice's appearance, primarily discoloration. After the rice reaches the standard target temperature Tkw1, the heat retention control unit 78 controls the pressure regulating valve 47 to block airflow between the inside and outside of the pot 5, and intermittently operates the pressure reducing pump 48 to reduce the pressure inside the pot 5. For example, the heat retention control unit 78 keeps the pressure regulating valve 47 closed and operates the pressure reducing pump 48 for a few minutes at a predetermined first time interval Wi1, for example, every 3 hours, to maintain a state where the pressure inside the pot 5 is lower than atmospheric pressure. 【0115】 Furthermore, the discoloration of rice can be evaluated by measuring the color of freshly cooked rice and rice that has been kept warm, for example, using a colorimeter. 【0116】 As described above, the first warming process does not reduce the pressure inside the pot 5 immediately after it starts, but maintains atmospheric pressure inside the pot 5. In this way, the rice cooker 1 performing the first warming process can easily and quickly open the lid 6 without having to restore the internal pressure of the pot 5 to atmospheric pressure for a predetermined time, for example, about 2 hours, after the cooking operation. Therefore, for a predetermined time, for example, about 2 hours, after the cooking operation, the user can quickly and easily eat the cooked rice. Furthermore, after a predetermined time, for example, about 2 hours, has elapsed since the cooking operation, the rice cooker 1 performing the first warming process reduces the pressure inside the pot 5 to suppress deterioration of the appearance of the rice during warming. 【0117】 The heat retention control unit 78 can perform the first heat retention process immediately following the rice cooking operation, or it can perform a reheating heat retention process independently of the rice cooking operation. As illustrated by the dashed line in Figure 6, the reheating heat retention process heats rice that is at a temperature lower than the reference heat retention target temperature Tkw1 and then retains the heat of the rice heated to the reference heat retention target temperature Tkw1. The time required to heat the rice at a temperature lower than the reference heat retention target temperature Tkw1 depends on the initial temperature of the rice, but for illustrative purposes, it is assumed that the rice reaches the reference heat retention target temperature Tkw1 in about 1 hour and 30 minutes. When the rice reaches the reference heat retention target temperature Tkw1, the heat retention control unit 78 retains the heat of the rice with the same settings as in the first heat retention process. 【0118】 Next, as illustrated in Figure 7, the second heat retention process performed by the heat retention control unit 78 involves controlling the pressure regulating valve 47 to block airflow between the inside and outside of the pot 5, and controlling the heating coil 11 until a predetermined high-temperature maintenance time has elapsed from the start, thereby keeping the rice warm at a high heat retention temperature TkwH that is higher than the standard heat retention target temperature Tkw1 of the first heat retention process. The high heat retention temperature TkwH, which is the target value of the heat retention temperature in the second heat retention process, is set to, for example, 80 degrees Celsius. 【0119】 At the start of the second warming process, the temperature of the rice cooked in the cooking process has reached a temperature above the high warming temperature TkwH, for example, 100 degrees Celsius. Therefore, the warming control unit 78 stops the heating coil 11 and waits until the temperature of the rice drops (cools down) to the high warming temperature TkwH. In the example in Figure 7, the time it takes for the temperature of the rice to drop to the high warming temperature TkwH is shown as approximately 1 hour. 【0120】 Furthermore, the heat retention control unit 78 controls the pressure regulating valve 47 at the same time as the start of the second heat retention process to block the airflow between the inside and outside of the pot 5. As the airflow is blocked, the steam inside the pot 5 gradually condenses into liquid (water) as the temperature decreases. At this time, the volume of steam filling the pot 5 decreases, so the pressure inside the pot 5 becomes lower than atmospheric pressure. In other words, when the rice cooker 1 starts the second heat retention process, it performs a sealed depressurization. By doing so, the rice cooker 1 reduces the pressure inside the pot 5 immediately after the cooking operation, suppressing the deterioration of the appearance of the rice during heat retention, mainly discoloration. 【0121】 However, simply blocking the airflow between the inside and outside of the pot 5 to reduce the pressure inside the pot 5 does not significantly reduce the pressure inside the pot 5 from atmospheric pressure, and does not greatly affect how easy it is to open the lid 6. In other words, the rice cooker 1, which performs the second warming process, achieves both ease of opening the lid 6 and suppression of the deterioration of the rice's appearance due to warming immediately after the cooking operation. 【0122】 Next, after a predetermined waiting time W2, for example 1 hour, the heat retention control unit 78 keeps the pressure regulating valve 47 closed and intermittently operates the pressure reducing pump 48 to reduce the pressure inside the pot 5. The heat retention control unit 78, for example, keeps the pressure regulating valve 47 closed and operates the pressure reducing pump 48 for a few minutes at a predetermined second time interval Wi2, for example every 3 hours, to maintain a state where the pressure inside the pot 5 is lower than atmospheric pressure. In this way, the rice cooker 1 keeps the rice warm at a high heat retention temperature TkwH that is higher than the standard heat retention target temperature Tkw1 in the first heat retention process, while suppressing deterioration of the appearance of the rice. In other words, the rice cooker 1 can provide rice at a temperature range closer to freshly cooked rice for a longer period of time after the end of the cooking operation. 【0123】 The second time interval Wi2 may be the same as or different from the first time interval Wi1 in the first heat retention process. 【0124】 By the way, if you keep cooked rice warm for several hours after it has been cooked, it may turn yellow or brown, potentially degrading its appearance. This tendency to deteriorate is exacerbated the higher the warming temperature. 【0125】 Therefore, in this embodiment, the rice cooker 1 controls the heating coil 11 from the start of the second warming process until a predetermined high-temperature maintenance time, for example 3 hours, has elapsed, to keep the rice warm at a high warming temperature TkwH that is higher than that of the first warming process. After the high-temperature maintenance time has elapsed, the heating coil 11 is stopped and the system waits until the temperature of the rice drops (cools down) to the standard warming target temperature Tkw1. In the example in Figure 7, the time it takes for the temperature of the rice to drop to the standard warming target temperature Tkw1 is shown as approximately 30 minutes. When the temperature of the rice drops to the standard warming target temperature Tkw1, the warming control unit 78 controls the heating coil 11 to maintain the temperature of the rice at the standard warming target temperature Tkw1. In other words, it can also be described that the rice cooker 1, after the predetermined high-temperature maintenance time has elapsed, lowers the temperature of the rice to the standard warming target temperature Tkw1 and transitions to the first warming process. In other words, after the rice temperature drops to the standard target temperature Tkw1, the heat retention control unit 78 maintains a reduced pressure inside the pot 5, lower than atmospheric pressure, to suppress deterioration of the rice's appearance. 【0126】 As described above, the second warming process maintains a pressure below atmospheric pressure inside the pot 5 from the moment it starts. By doing so, the rice cooker 1 performing the second warming process maintains the temperature of the rice within the temperature range of the first warming process within one hour of the start of warming, i.e., a temperature range close to that of freshly cooked rice, for a predetermined high-temperature maintenance time, for example, about 3 hours, after the cooking operation, and suppresses deterioration of the appearance of the rice by maintaining a pressure below atmospheric pressure inside the pot 5. Furthermore, after the predetermined high-temperature maintenance time has elapsed, the rice cooker 1 performing the second warming process lowers the temperature of the rice during warming, effectively transitioning to the first warming process and suppressing deterioration of the appearance of the rice during warming for a longer period of time. 【0127】 Furthermore, by setting the predetermined high-temperature maintenance time to approximately 3 hours, the rice cooker 1 can, for example, provide freshly cooked rice to a family member who eats between 6 PM and 7 PM, while also providing rice at a temperature close to freshly cooked to another family member who eats later, between 9 PM and 10 PM, and to yet another family member who eats at an intermediate time. 【0128】 In the example shown in Figure 7, the high-temperature retention temperature TkwH remains constant during the predetermined high-temperature maintenance period, but may be set to decrease towards the retention temperature in the first retention process, i.e., the standard retention target temperature Tkw1, as time progresses. The high-temperature retention temperature TkwH may be set to decrease to the standard retention target temperature Tkw1 at a constant rate, or it may be set to decrease to the standard retention target temperature Tkw1 in stages. In the example of a staged decrease, the high-temperature retention temperature TkwH may be set to be maintained at 75 degrees Celsius, an intermediate temperature between the high-temperature retention temperature TkwH and the standard retention target temperature Tkw1, for a predetermined time, for example, about 45 minutes. Compared to keeping the high-temperature retention temperature TkwH constant during the predetermined high-temperature maintenance period, the second retention process can perform a longer high-temperature maintenance period by decreasing the high-temperature retention temperature TkwH during the predetermined high-temperature maintenance period. Furthermore, the second heat retention process can further prevent deterioration of the rice's appearance by lowering the heat retention temperature while maintaining the predetermined high-temperature maintenance time. 【0129】 Furthermore, the rice cooking process preceding the first warming process and the rice cooking process preceding the second warming process may be the same or different. The high warming temperature TkwH of the second warming process is higher than the standard warming target temperature Tkw1 of the first warming process, and it is thought that the amount of steam filling the pot 5 will relatively increase. Since the large amount of steam in the second warming process may soften the rice, it is assumed that the rice will be cooked slightly firmer in the rice cooking process preceding the second warming process. The firmness of the cooked rice can be adjusted by shortening the soaking time or the steaming time. Furthermore, the predetermined high-temperature maintenance time may be adjustable. The high-temperature retention temperature TkwH can be set to a higher temperature the shorter the predetermined high-temperature maintenance time, within the adjustable range of the predetermined high-temperature maintenance time. In this embodiment, the rice cooker 1 was described assuming that the predetermined high-temperature maintenance time was, for example, 3 hours and the high-temperature retention temperature TkwH was set to, for example, 80 degrees Celsius. If the predetermined high-temperature maintenance time was, for example, 2 hours, the high-temperature retention temperature TkwH may be set to, for example, 85 degrees Celsius. If the predetermined high-temperature maintenance time was, for example, 1 hour, the high-temperature retention temperature TkwH may be set to, for example, 90 degrees Celsius. The shorter the predetermined high-temperature maintenance time, the less the aesthetic deterioration of the rice. Therefore, by setting the high-temperature retention temperature TkwH higher the shorter the predetermined high-temperature maintenance time, the rice cooker 1 can provide the user with rice at a temperature close to that of freshly cooked rice the shorter the time elapsed from the start of the second warming process. 【0130】 Next, we will describe the screen display related to the warming process performed by the rice cooker 1 according to this embodiment. 【0131】 Figure 8 shows a first example of the first screen displayed by the display unit of a rice cooker according to an embodiment of the present invention. 【0132】 The first screen SS1 shown in Figure 8 is an example of the so-called top screen of the rice cooker 1. When the power line 8 is plugged into the outlet, the input / output control circuit board 53 and the heating control circuit board 22 are activated. At that point, the display control unit 73 displays the first screen SS1 as the initial screen on the display unit 55. 【0133】 As shown in Figure 8, the first screen SS1 of the rice cooker 1 according to this embodiment displays a plurality of display elements 91. 【0134】 Furthermore, pressing, touching, or bringing a fingertip close to any of the display elements 91 will operate the key elements of the operation unit 56 located directly above that display element 91. For the sake of clarity, the explanation of how to operate the key elements will be replaced with an explanation of how to operate the display elements 91. 【0135】 The first screen SS1 is divided into four display areas A1, A2, A3, and A4, which are arranged sequentially from the top edge to the bottom edge of the first screen SS1. 【0136】 The uppermost display area A1 is the area that displays the menu keys. Display area A1 contains four display elements 91a to 91d, arranged from left to right. The rightmost display element 91a displays the text "Rice" and a downward-pointing triangle "▽" shape below it. The display element 91b to its right displays the text "Cooking Instructions" and a downward-pointing triangle "▽" shape below it. The third display element from the left, 91c, displays the text "Texture" and a downward-pointing triangle "▽" shape below it. The rightmost display element 91d displays the text "Keep Warm" and a downward-pointing triangle "▽" shape below it. 【0137】 The second display area from the top, A2, is the area that displays the settings applied to the rice cooking operation. Display area A2 contains four display elements 91e through 91h, arranged from left to right. The rightmost display element 91e is directly below the display element 91a, which is labeled "Rice," and displays information about the selected rice, such as the text "White Rice, Brand Selected." The display element 91f to its right is directly below the display element 91b, which is labeled "Cooking Method," and displays information about the selected cooking method, such as the text "Kamado Master." The third display element from the left, 91g, is directly below the display element 91c, which is labeled "Texture," and displays information about the selected firmness adjustment, such as the text "Recommended." The rightmost display element 91h is directly below the display element 91d, which is labeled "Keep Warm," and displays information about the selected keep-warm process, such as the text "Standard." The text "Standard" indicates that the first heat retention process is selected as the heat retention process to be executed by the heat retention control unit 78. 【0138】 When the display element 91a, which displays "rice," is operated, the display unit 55 transitions to a screen for selecting the type of rice. When a type of rice, for example, "white rice, random brand," is selected on the destination screen, the display on the display unit 55 returns to the first screen SS1, and at this time, the display element 91e directly below the display element 91a displays the text "white rice, random brand." 【0139】 When the display element 91b, which displays "Cooking Method," is operated, the display unit 55 transitions to a screen where the cooking method is selected. When a cooking method, such as "Kamado Meijin," is selected on the destination screen, the display on the display unit 55 returns to the first screen SS1, and at this time, the display element 91f directly below the display element 91b displays the text "Kamado Meijin." 【0140】 When the display element 91c labeled "Texture" is operated, the display unit 55 transitions to a screen where the user can select the texture, or firmness, of the rice to be cooked. When the user selects the texture of the rice to be cooked, for example "Recommended," on the subsequent screen, the display on the display unit 55 returns to the first screen SS1, and at this time, the display element 91g directly below the display element 91c displays the text "Recommended." 【0141】 When the display element 91d, which displays "Insulate," is operated, the display unit 55 transitions to an insulating method selection screen where an insulating process is selected. When an insulating process, for example "Standard," is selected on the destination insulating method selection screen, the display on the display unit 55 returns to the first screen SS1, and at this time, the display element 91h directly below the display element 91d displays the text "Standard." 【0142】 The second display area from the bottom, A3, contains three display elements 91i through 91k, arranged from left to right. The rightmost display element 91i displays the text "Hitashi Plus". The central display element 91j displays time information such as the cooking time, the estimated remaining time until cooking is complete, and the estimated completion time, for example, the text "Approximately 21 minutes", and the text "Cooking Time" to remind that the time information is the cooking time. The rightmost display element 91k displays the text "Start Cooking". 【0143】 When the display element 91i, which displays "Soaking Plus," is operated, the display unit 55 transitions to an additional time setting screen that allows the user to add an extension of the soaking time to the cooking process, so that the rice can absorb water for the desired amount of time. The display element 91i functions as a soaking extension key, which is a soaking extension instruction unit that accepts an operation to add an extension of the soaking time to the cooking process. 【0144】 For the sake of clarity, we will refer to the act of extending the soaking time as "extending the soaking time," the initial soaking time without extension as "initial soaking time," and the soaking time with extension as "extended soaking time." The initial soaking time is shorter than the minimum selectable extended soaking time. 【0145】 Furthermore, soaking the rice in water for the initial soaking time is called "standard soaking," and soaking the rice in water for the extended soaking time is called "additional soaking." 【0146】 In other words, the additional time setting screen is an operation screen for extending the soaking time, changing the initial soaking time to an extended soaking time. Figure 8 shows an example of the display element 91i, "Soaking Plus," when the rice cooking operation is performed with standard soaking. When the rice cooking operation is performed with additional soaking, the display element 91i will display, for example, "Soaking +30 minutes." 【0147】 When the display element 91p, which displays "Start Cooking," is operated, the rice cooker 1 applies the rice settings, cooking method settings, hardness settings, keep-warm settings, and soaking settings displayed in display area A2 and starts the cooking operation. The display element 91p functions as a start key, acting as a start instruction unit that accepts the start of the cooking operation, which involves soaking the rice in water to promote water absorption and then cooking the rice using the heating operation of the heating coil 11. 【0148】 The bottommost display area A4 contains five display elements 91l through 91p, arranged from left to right. The rightmost display element 91l displays a gear-shaped icon. Display element 91m displays the text "Keep Warm". Display element 91n displays the text "Reservation". Display element 91o displays the current time. Display element 91p displays the text "Off". 【0149】 When the display element 91l, which displays a gear-shaped icon, is operated, the display unit 55 transitions to a settings screen where the current time, key lock, screen brightness, screen design, and settings can be initialized can be set. 【0150】 When the display element 91m, which displays "Keep Warm," is operated, the rice cooker 1 starts the keep-warm process. The keep-warm process started in this case is a reheat keep-warm process. The display element 91m is operated when the rice cooker 1 is used to reheat and keep warm already cooked rice without reducing the cooking process or cooking operation. In other words, the rice cooker 1 can perform the second keep-warm process immediately after the cooking process in which the food to be cooked is cooked, but it is restricted from performing the second keep-warm process without continuing from the cooking process. Furthermore, the rice cooker 1 can perform the first keep-warm process immediately after the cooking process in which the food to be cooked is cooked, and it can also perform the first keep-warm process without continuing from the cooking process. 【0151】 When the display element 91n, which displays "Reservation," is operated, the display unit 55 transitions to the reservation setting screen. The display element 91n functions as a reservation key, acting as a reservation instruction unit that accepts a reservation cooking operation in which the rice is soaked in water to allow it to absorb water, and then cooked at the reserved time by the heating operation of the heating coil 11. The reservation setting screen provides a reservation operation key for setting the time when the rice will be cooked, and a reservation start key for accepting the start of the reservation cooking operation. When the display element 91p, which is marked "Off," is operated, the rice cooker 1 stops any ongoing operations such as rice cooking or the keep-warm process. 【0152】 Figure 9 shows an example of a warming method selection screen displayed on the display unit of a rice cooker according to an embodiment of the present invention. 【0153】 As shown in Figure 9, the heat retention method selection screen SS2 displays multiple display elements 93. 【0154】 Furthermore, pressing, touching, or bringing a fingertip close to any of the display elements 93 activates a key element of the operation unit 56 located directly above that display element 93. For the sake of clarity, the explanation of the operation of the key elements will be replaced with the explanation of the operation of the display elements 93. In other words, the heat retention method selection screen SS2 functions as an operation unit 56 that allows the user to selectively choose between the first heat retention process and the second heat retention process. 【0155】 The multiple display elements 93 include a current setting display element 93a, which is positioned near the upper edge of the heating method selection screen SS2 and displays the text "It is set to "Standard Heating". Do you want to change the heating method?", and a display element 93b, which is positioned near the left edge of the lower edge of the heating method selection screen SS2 and displays the text "Back" enclosed in a frame. 【0156】 When the display element 93b, which displays "Back," is operated, the display unit 55 returns to the first screen SS1. At this time, the display element 91h of the first screen SS1 maintains the display that was displayed when transitioning from the first screen SS1 to the heat retention method selection screen SS2, for example, the display of "Standard." 【0157】 Furthermore, the multiple display elements 93 include multiple display elements 93c to 93f, which are displayed in the central area between the upper display element 93a and the lower display element 93b of the heat retention method selection screen SS2. Multiple display elements 93c and 93d display the options for the simple heat retention process included in the heat retention process. For example, the two display elements 93c and 93d are positioned in the center of the heat retention method selection screen SS2, side by side. The two display elements 93c and 93d display text that suggests the content of the options. 【0158】 The text in display element 93c, namely "Standard Insulation," and the text in display element 93d, namely "Freshly Made Insulation," are examples of options for the simple insulation process included in the insulation process. "Standard Insulation" is a name intended to present the first insulation process of the simple insulation process in a way that is easy for the user to understand, and "Freshly Made Insulation" is a name intended to present the second insulation process of the simple insulation process in a way that is easy for the user to understand. 【0159】 Display element 93e is located directly below display element 91d, which displays "Freshly Made Warm," and displays information related to freshly made warming, such as text that reads "Warming temperature set 3 hours higher than 'Standard Warm'." The "3 hours" in the text indicates the high-temperature maintenance time in the second warming process, and is based on the set value for the high-temperature maintenance time. 【0160】 The border 93f of the display element 93f surrounds the selected option, either "Standard Warming" or "Freshly Made Warming," visually indicating that the selected option is chosen. The currently selected warming process, i.e., the display element 93c that displays "Standard Warming," is surrounded by a border 93f with a vivid hue, while the currently unselected warming process, i.e., the display element 93d that displays "Freshly Made Warming," is not surrounded by a border. 【0161】 Each of the display elements 93, excluding display elements 93a and 93e, is associated with the respective key elements of the operation unit 56. 【0162】 If the border line 93f is absent and the display element 93d that displays "Freshly Made, Keep Warm" is operated, the display unit 55 changes the display content of the currently set display element 93a to "It is set to 'Freshly Made, Keep Warm'. Do you want to change the warming setting?", surrounds the display element 93d that displays "Freshly Made, Keep Warm" with a border line 93f, and removes the border line 93f of the display element 93c that displays "Standard Warming". In this case, the simple warming process executed by the warming control unit 78 is set to the second warming process. 【0163】 Furthermore, if the border line 93f is not present and the display element 93d that displays "Keep Warm Freshly Made" is operated, the simple warming process executed by the warming control unit 78 may be set to the second warming process, and the screen displayed by the display unit 55 may immediately transition from the warming method selection screen SS2 to the first screen SS1. 【0164】 On the other hand, if the display element 93c that displays "Standard Warming" is operated without the border line 93f, the display unit 55 changes the display content of the currently set display element 93a to "It is set to "Standard Warming". Do you want to change the warming setting?", surrounds the display element 93c that displays "Standard Warming" with a border line 93f, and removes the border line 93f of the display element 93d that displays "Freshly Made Warming". In this case, the simple warming process executed by the warming control unit 78 is set to the first warming process. 【0165】 Furthermore, if the border line 93f is absent and the display element 93d that displays "Standard Insulation" is operated, the simple insulation process executed by the insulation control unit 78 is set to the first insulation process, and the screen displayed by the display unit 55 may immediately transition from the insulation method selection screen SS2 to the first screen SS1. 【0166】 The initial value of the simple heat retention process may be the first heat retention process or the second heat retention process. 【0167】 In addition, a rice cooker 1 without a display showing the warming method selection screen SS2 as illustrated in Figure 9 may have, for example, a touch key that allows switching whether or not to perform the warming process after the cooking process. In such cases, it would be sufficient to specify the execution of the first warming process by briefly touching the touch key for the warming process, specify the execution of the second warming process by long-pressing the touch key for the warming process, and to cancel the execution of the warming process or not perform the warming process by touching the touch key while the execution of the first and second warming processes is specified. 【0168】 Next, we will explain the transition of the display when moving from the rice cooking process to the first warming process. 【0169】 Figure 10 shows an example of a display when a rice cooker according to an embodiment of the present invention is performing the rice cooking process. 【0170】 Figure 11 shows an example of the display when a rice cooker according to an embodiment of the present invention transitions from the rice cooking process to the first warming process. 【0171】 Figure 12 shows an example of the display when the rice cooker according to an embodiment of the present invention continues the first warming process. 【0172】 As shown in Figures 10 to 12, the display unit 55 has a display that shows a process execution screen SS3 having a plurality of display elements 95, and a display element 96a that illuminates "Reservation", a display element 96b that illuminates "Keep Warm", and a display element 96c that illuminates "Pressure". 【0173】 The process execution screen SS3 shown in Figures 10 to 12 is a modified version of the first screen SS1, which is an example of the so-called top screen of the rice cooker 1, and shares display areas A2 and A4. The process execution screen SS3 has a display area B between display area A2 and display area A4 that displays the status of the process currently being executed. Display area B is a modified version of the first screen SS1 where display area A1 is hidden, with display area A3 expanding its display range vertically and changing its display content. 【0174】 Furthermore, to ensure that it is clear that the first warming process is performed after the rice cooking process illustrated in Figure 10, the display element 91h in display area A2 displays the text "Standard Warming". 【0175】 Display area A4 hides all display elements except for the display element 91o that displays the current time. For the sake of explanation, the current time of display element 91o in Figures 10 to 12 is fixed to "20:00". 【0176】 Display area B, illustrated in Figure 10, is an example of a display when the rice cooking process and operation are being performed. Display area B includes a display element 95a that displays the text "Cooking" to indicate that the rice cooking process is in progress, and a display element 95b that displays the text "1 minute remaining" to indicate the remaining time of the rice cooking process. The remaining time displayed by display element 95b changes and decreases moment by moment, reflecting the estimated amount of rice to be cooked and the progress of the rice cooking process. 【0177】 Furthermore, the process execution screen SS3 spans display area B and display area A4 and includes a display element 97 that displays the text "Off (long press)" surrounded by a border, reminiscent of a force stop button that can be long-pressed to forcibly stop the process being executed by the rice cooker 1. 【0178】 At the timing illustrated in Figure 10, the pressure inside the pot 5 is increased, so the display element 96c that illuminates to indicate "pressure" is lit. 【0179】 Display area B, illustrated in Figure 11, is an example of the display when the rice cooking process is completed and the process transitions to the first warming process. Display area B includes a display element 95e that displays the text "Please loosen the rice" to prompt the user to loosen the freshly cooked rice, and a display element 95f that displays the text "Warming elapsed: 0 minutes" which represents the elapsed time since the start of the first warming process. The warming elapsed time displayed by display element 95f changes moment by moment and increases in accordance with the measurement results for the duration of the warming process. 【0180】 It is preferable that the display element 95e that displays "Please loosen it" is hidden after a predetermined time, for example, 1 hour, has elapsed since the start of the first heat retention process. 【0181】 At the timing illustrated in Figure 11, the rice is being kept warm, so the display element 96b that illuminates to indicate "Keep Warm" is lit. 【0182】 In this embodiment, the display unit 55 of the rice cooker 1, when executing the reheating and keeping warm process without continuing the rice cooking process to cook the food to be cooked into rice, displays the same screen as the first keeping warm process, that is, the process execution screen SS3 illustrated in Figure 11. 【0183】 Display area B, illustrated in Figure 12, is an example of the display after a predetermined time, for example, 2 hours, has elapsed since the start of the first heat retention process. Display area B hides the display element 95e that displays "Please loosen," and includes a display element 95f that displays the text "Heat retention elapsed: 2 hours," which represents the elapsed time measured from the start of the first heat retention process. The heat retention elapsed time displayed by display element 95f changes moment by moment and increases, reflecting the measurement result over the duration of the heat retention process. 【0184】 Furthermore, the display area B shown in Figure 12 includes a display element 95g that displays the text "vacuum" to indicate that the inside of the pot 5 is under reduced pressure to prevent deterioration of the appearance of the rice due to heat retention. The display unit 55 may also light up a light-emitting diode to display "vacuum". 【0185】 Next, we will explain the transition of the display when moving from the rice cooking process to the second warming process. 【0186】 Figure 13 shows an example of a display when a rice cooker according to an embodiment of the present invention is performing the rice cooking process. 【0187】 Figure 14 shows an example of the display when a rice cooker according to an embodiment of the present invention transitions from the rice cooking process to the second warming process. 【0188】 Figure 15 shows an example of the display when the rice cooker according to an embodiment of the present invention continues the second warming process. 【0189】 Figure 16 shows an example of the display when the rice cooker according to an embodiment of the present invention continues the second warming process. 【0190】 Figures 13 to 16 show examples of displays when rice cooker 1 performs the rice cooking process, followed by the second warming process. Therefore, the same reference numerals are used for components identical to those shown in the display examples in Figures 10 to 12, and redundant explanations are omitted. 【0191】 Display area B, illustrated in Figure 13, is an example of the display when the rice cooking process and operation are being performed. To ensure that it is clear that the second warming process is performed after the rice cooking process illustrated in Figure 13, display element 91h in display area A2 displays the text "Keep warm freshly cooked." 【0192】 Display area B, illustrated in Figure 14, is an example of the display when the rice cooking process is completed and the process transitions to the second warming process. Display area B includes a display element 95e that displays the text "Please loosen the rice" to prompt the user to loosen the freshly cooked rice, and a display element 95f that displays the text "Warming elapsed: 0 minutes" which represents the elapsed time since the start of the second warming process. The warming elapsed time displayed by display element 95f changes and increases moment by moment, reflecting the measurement result over the duration of the warming process. 【0193】 Furthermore, the display area B illustrated in Figure 14 includes a display element 95g that displays the text "vacuum" to indicate that the inside of the pot 5 is under reduced pressure to prevent deterioration of the appearance of the rice due to the warming process. The display unit 55 may also light up a light-emitting diode to display "vacuum". As can be seen by comparing the process execution screen SS3 in Figure 14, which is the screen display when transitioning to the second warming process, with the process execution screen SS3 in Figure 11, which is the screen display when transitioning to the first warming process, in the second warming process, the inside of the pot 5 is under reduced pressure immediately after transitioning from the cooking process to the warming process, and the display element 95g of "vacuum" is displayed. 【0194】 At the timing illustrated in Figure 14, the rice is being kept warm, so the display element 96b that illuminates to indicate "Keep Warm" is lit. 【0195】 Display area B illustrated in Figure 15 is an example of the display after a predetermined time, for example, 2 hours, has elapsed since the start of the second heat retention process. Display area B hides the display element 95e that displays "Please loosen," and includes a display element 95f that displays the text "Heat retention elapsed: 2 hours," which represents the elapsed time measured from the start of the second heat retention process. The heat retention elapsed time displayed by display element 95f changes and increases moment by moment, reflecting the measurement result over the duration of the heat retention process. Display area B illustrated in Figure 15 also includes a display element 95g that displays the text "Vacuum," indicating that the inside of the pot 5 is under reduced pressure to prevent deterioration of the appearance of the rice due to heat retention. The display unit 55 may also light up a light-emitting diode to display "Vacuum." 【0196】 The rice cooker 1 according to this embodiment, configured as described above, performs at least a first warming step in which the heating coil 11 is controlled to keep the cooked rice warm at a standard warming target temperature Tkw1, and a second warming step in which the pressure regulating valve 47 is controlled to block airflow between the inside and outside of the pot 5, and the heating coil 11 is controlled from the start until a predetermined high-temperature maintenance time has elapsed, keeping the cooked rice warm at a high warming temperature TkwH that is higher than the standard warming target temperature Tkw1 of the first warming step. Therefore, after the cooking step, the rice cooker 1 can maintain the temperature of the rice in the temperature range within one hour from the start of warming in the first warming step, that is, in a temperature range close to that of freshly cooked rice, for a predetermined high-temperature maintenance time, for example, about 3 hours, and can suppress the Maillard reaction due to sealed pressure reduction, that is, the deterioration of the appearance of the rice. 【0197】 Incidentally, the temperature of freshly cooked rice is close to 100 degrees Celsius, which gives rise to steam and volatile aerobic odors. In addition, the moisture retained on the surface of the rice creates gloss and transparency, as well as stickiness, sweetness, and umami. These factors contribute to the deliciousness of freshly cooked rice. (See "Kitaoji Rosanjin's Egg Rice - Objective Evaluation of Deliciousness -"). In other words, rice cooker 1, which performs the second warming process, can maintain the deliciousness of rice that is close to that of freshly cooked rice for a longer period than when the first warming process is performed, by keeping the rice warm at a temperature range closer to that of freshly cooked rice. 【0198】 Furthermore, the rice cooker 1 according to this embodiment is equipped with an operation unit 56 that allows the user to selectively select between a first warming process and a second warming process. Therefore, the rice cooker 1 can switch between a first warming process, which performs standard warming, and a second warming process, which performs warming at a temperature range closer to freshly cooked rice than the standard, very easily and simply. 【0199】 Furthermore, the rice cooker 1 according to this embodiment is equipped with a pressure reducing pump 48, which is a pressure reducing unit capable of intermittently exhausting the gas inside the pot 5 to the outside of the machine during the first and second heat retention processes, thereby reducing the pressure inside the pot 5 to a state lower than atmospheric pressure. Therefore, even when the amount of steam inside the pot 5 drops to a level where suppression of the Maillard reaction by sealed pressure reduction cannot be expected, that is, when the temperature inside the pot drops, the rice cooker 1 can actively reduce the pressure inside the pot 5 to a pressure lower than atmospheric pressure to suppress deterioration of the appearance of the rice, mainly discoloration. 【0200】 Furthermore, the rice cooker 1 according to this embodiment can perform the second warming process immediately after the cooking process, but it is restricted from performing the second warming process without continuing from the cooking process. Therefore, the rice cooker 1 can prevent the deterioration of the appearance of the rice from accelerating due to the user intentionally or unintentionally repeating the second warming process. If, as exemplified in this embodiment, the user repeats the second warming process, which is set to maintain a high temperature for 3 hours, every 3 hours, and keeps the rice warm at a high warming temperature TkwH for a total of 6 hours, it will be difficult to prevent the deterioration of the appearance of the rice. The rice cooker 1 can reliably avoid such a situation. 【0201】 Furthermore, the high-temperature retention temperature TkwH of the rice cooker 1 according to this embodiment can be lowered over time to approach the standard-temperature retention target temperature Tkw1 of the first-temperature retention process. As a result, the rice cooker 1 can extend the high-temperature maintenance time or further suppress the deterioration of the appearance of the rice while keeping the high-temperature maintenance time constant. 【0202】 Furthermore, the high-temperature retention temperature TkwH of the rice cooker 1 according to this embodiment can be set to a higher temperature the shorter the predetermined high-temperature retention time, within a range where the predetermined high-temperature retention time can be changed. In this way, the rice cooker 1 can provide rice that is even closer to freshly cooked to family members whose meal times are not far apart, while also providing rice that is close to freshly cooked to family members whose meal times are several hours apart, without compromising the appearance of the rice. 【0203】 Furthermore, the rice cooker 1 according to this embodiment is equipped with a display unit 55 that displays the same screen as the first warming process when the reheating and warming process is executed without continuing to the cooking process. Therefore, the rice cooker 1 can easily recognize that the reheating and warming process is performed at the standard warming target temperature Tkw1 of the first warming process, rather than as the second warming process. 【0204】 Therefore, according to the rice cooker 1 of the present invention, even after a gap of several hours between cooking the rice and eating it, it is possible to maintain both the warmth of freshly cooked rice and the aesthetic appearance of freshly cooked rice. 【0205】 While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols] 【0206】 1...Rice cooker, 2...Pot storage compartment, 3...Main body, 5...Pot, 5a...Main material, 5b...Heating element, 6...Lid, 7...Hinge mechanism, 8...Power line, 11...Heating coil, 11u...First coil, 11d...Second coil, 12...Flange section, 15...Bottom plate, 16...Upper frame, 17...Inner frame, 18...Outer frame, 19...Control unit housing, 21...Ventilation opening, 22...Heating control circuit board, 23...Burning Heater, 25...Cooling fan, 26...Pot temperature sensor, 31...Hinge shaft, 32...Hinge spring, 35...Outer lid, 36...Outer lid cover, 37...Heat sink, 38...Lid heater, 39...Inner lid unit, 41...Inner lid, 42...Lid gasket, 43...Gasket base, 45...Steam vent, 46...Steam exhaust passage, 47...Pressure regulating valve, 47a...Valve body, 47b...Solenoy D, 48...Depressurizing pump, 49...Depressurizing port, 50...Lid open operation button, 51...Lid lock mechanism, 52...Operation panel, 53...Input / output control circuit board, 55...Display unit, 56...Operation unit, 61...Coil drive circuit, 61u...First drive circuit, 61d...Second drive circuit, 63...Lid heater drive circuit, 65...Lid temperature sensor, 66...Lid open / close sensor, 67...Pressure sensor, 68...Notification unit, 72...Input signal generation unit, 73...Display control unit, 75...Condition setting unit, 77...Rice cooking control unit, 78...Keep warm control unit, 91, 91a to 91p...Display elements, 93, 93a to 93f...Display elements, 93a...Current setting display element, 93f...Frame line, 95, 95a to 95g...Display elements, 96a to 96c...Display elements, 97...Display elements.

Claims

[Claim 1] A pot capable of containing the food to be cooked and the cooked rice, A heating unit capable of heating the inside of the pot, A pressure regulating unit capable of adjusting the pressure inside the pot by allowing or blocking airflow between the inside and outside of the pot, A control unit capable of performing at least the following: a first warming step of controlling the heating unit to keep the rice warm; and a second warming step of controlling the pressure regulating unit to block airflow between the inside and outside of the pot, and controlling the heating unit from the start until a predetermined high-temperature maintenance time has elapsed to keep the rice warm at a high warming temperature higher than the warming temperature in the first warming step. A rice cooker comprising an operating unit that allows the user to selectively select between the first warming step and the second warming step. [Claim 2] The rice cooker according to claim 1, further comprising a pressure reduction unit capable of intermittently exhausting the gas inside the pot to the outside of the machine during the first and second heat retention processes to reduce the pressure inside the pot to a state lower than atmospheric pressure. [Claim 3] The rice cooker according to claim 1 or 2, wherein the control unit can perform the second warming step continuously from the rice cooking step of cooking the food to be cooked into rice, but restricts the performance of the second warming step without continuing from the rice cooking step. [Claim 4] The rice cooker according to claim 1 or 2, wherein the high heat retention temperature decreases over time to approach the heat retention temperature of the first heat retention step. [Claim 5] The predetermined high-temperature maintenance time is changeable, The rice cooker according to claim 1 or 2, wherein the high-temperature retention temperature is set to a higher temperature as the predetermined high-temperature retention time decreases, within a range in which the predetermined high-temperature retention time can be changed. [Claim 6] The rice cooker according to claim 1 or 2, further comprising a display unit that performs the same screen display as the first warming step when the warming step is performed without continuing to the rice cooking step in which the food to be cooked is cooked into rice.

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