JPH1057235A - Rice cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a time required for a water intake process without any need of adding complicated equipment by heating water preliminarily contained in a pot to the prescribed preheating temperature with a heating means before the supply of rice to the pot. SOLUTION: A control part 5 stores procedures for programming and controlling the temperature and the time required respectively at preheating, water intake, boiling and steaming processes. A preheating key 9 is first pressed, with water contained in a pot, and the control part 5 is thereby made to start the preheating process. Thereafter, the control part 5 proceeds to each process subsequent to the water intake process, when a boiling key 10 is pressed after the preheating process is over and rice is fed. In this case, a reporting means 11 informs a user of the fact that water temperature is at a preheating level at the preheating process. According to this construction, temperature for the rice and hot water to reach a thermal equilibrium after the supply of the rice, quickly arrives at the level required for the boiling process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rice cooker for reducing the cooking time.

[0002]

2. Description of the Related Art As a conventional rice cooker, the time required for a water absorption process in which rice and water are heated to a predetermined temperature during rice cooking to absorb water into rice is shortened, and thus, from water absorption to the end of rice cooking. The aim of shortening the time is disclosed in Japanese Patent Laid-Open Publication No. H5-253053.

[0003] The overall configuration of the rice cooker will be described with reference to FIG. In FIG. 6, reference numeral 113 denotes a rice cooker main body, in which a pot storage unit 115 for storing a pot 114 is provided. Pot 11
A lid 118 that can be opened and closed is disposed on the upper part of the cover 4, and the inner lid 120 is heated by a lid heater 119 disposed inside the lid 118. Further, a doughnut-shaped first heating coil 121 is arranged outside the protective frame 116 so that the bottom of the pot 114 is induction-heated.

Further, a detachable water tank 126 is arranged in the rice cooker main body 113, and an outlet 127 is provided at a lower portion of the water tank 126. The outlet 127 is connected to the inlet of a pump 128 driven by a motor 129. A water supply pipe 130 is connected to the outlet of the pump 128, and a switching valve 131 is provided in the middle of the water supply pipe 130. The flow of water is switched to the pan outlet 133 side channel facing the inside 114.

[0005] A water purifier 134 is attached to an inflow port 132 of the water tank 126 so as to purify water from the inflow port 132. A heating element 135 made of a magnetic material is disposed on the inner bottom of the water tank 126, and the heating element 135 is induction-heated by a second heating coil 136 disposed below the water tank 126. The second heating coil 136 and the first heating coil 121 are supplied with a high-frequency current from an inverter circuit to generate a high-frequency magnetic field.

With the above configuration, the water in the water tank 126 is heated by the second heating coil 136, and the hot water heated by the heating is supplied to the pot 114 by driving the motor 129.
After hot water is supplied into the pan 114, the first heating coil 1
21 is operated to heat the pot 114, and the inside of the pot 114 is maintained at the water absorption temperature. If there is a large amount of rice in the pot, hot water from the water tank 126 is supplied to the pot 114.
Supplied to

[0007] The rice cooker includes a rice amount detecting means for detecting the weight of the rice put into the pot 114 and a water supply amount detecting means. The amount of water is detected by the amount detecting means, and a corresponding amount of hot water is supplied into the pot 114 by the motor 129, and it takes only a short time to raise the temperature in the pot 114 to the water absorption temperature, thereby shortening the water absorption time. ing.

[0008] The above-mentioned water absorption process is to maintain the rice and water put in the pot 114 at a water absorption temperature slightly lower than the gelatinization temperature of rice (about 45 to 65 ° C), When the temperature of the rice becomes higher than the gelatinization temperature during the water absorption process, the rice taste deteriorates, so rapid heating was not possible, and the rice had to be heated slowly.

[0009]

In the above-described conventional rice cooker, the water supply amount detecting means detects a change in water level in the water tank 126 as a change in capacitance, or detects a change in the pot 114 from the water tank 126. The amount of water supply is detected from the driving time of the pump 128 for supplying water to the water tank 1.
The water in 26 is different from the first heating coil 121 in the second
Induction heating using a heating coil 136 of
The heater is wound around a water supply pipe for supplying water from the water tank 126 to the pot 114, and it is necessary to attach a new device as described above to a conventional rice cooker and control them.

[0010] In order to shorten the time required to raise the temperature inside the pot 114 to the water absorption temperature in the water absorption process at the beginning of cooking rice, heated water is supplied after the rice is charged. The temperature of hot water supplied to 114 is also controlled to be higher as the amount of rice is larger, but is at most about 60 ° C., and even if the heat capacity of the rice being washed with cold water and the hot pot is cold, hot water of 60 ° C. is supplied. Even so, the initial temperature in the pot was lower than that, making it difficult to control the temperature appropriately.

[0011] Therefore, an object of the present invention is to reduce the time required for the water absorption process without providing complicated equipment.

[0012]

Means for Solving the Problems In order to solve the above problems, a rice cooker according to the present invention is characterized in that a rice cooker main body and a heating means for heating the pan are provided. A rice cooker comprising: a temperature detecting means for detecting the temperature of the pan; and a control means for controlling the heating means based on the temperature detected by the temperature detecting means to perform a rice cooking process. Before the rice is put into the pot, a preheating step of heating water previously put in the pot to a predetermined preheating temperature by the heating means is performed.

According to a second aspect of the present invention, in the rice cooker according to the first aspect, the temperature of the water in the pan is detected by the temperature detecting means during the preheating step, and the detected temperature is the preheating temperature. Is provided with a notifying means for notifying that the time has been reached.

According to a third aspect of the present invention, in the rice cooker according to the first aspect, the control means is configured such that, after the water temperature in the pan reaches the preheating temperature in the preheating step, the control means sets the temperature in the pan at the preheating temperature. And the addition of rice into the pot is detected when the temperature detected by the temperature detecting means drops from the preheating temperature, and the rice cooking process is started.

According to a fourth aspect of the present invention, in the rice cooker according to the first aspect, the preheating temperature is such that water is added to the water in the pot that has reached the preheating temperature. Is a temperature at which the temperature reaches a temperature below the gelatinization temperature of rice by thermal equilibrium.

According to a fifth aspect of the present invention, in the rice cooker according to the first aspect, room temperature detecting means for detecting a room temperature is provided,
The control means determines the preheating temperature using the temperature detected by the room temperature detecting means as the temperature of the rice put into the inner pot after the preheating step. The invention according to claim 6 is
The rice cooker according to claim 1, wherein a scale is provided on an inner surface of the pan to indicate a water level of water to be preheated in the preheating step.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a conventional rice cooker in which rice is cooked by controlling the heating temperature and heating time of a rice cooking process (consisting of a water absorption process, a cooking process, and a steaming process). The rice cooker is provided with a new preheating process prior to the water absorption process.

Here, the preheating process is a process in which only water is first poured into a pot, and then the water and the pot are rapidly heated to a predetermined preheating temperature and maintained at that temperature. further,
When the temperature reaches the preheating temperature, an alarm sound is generated by a buzzer or the like, or displayed on the display unit to prompt the user to put rice into the pot. In addition, since this preheating temperature is set higher than the temperature necessary for normal rice water absorption, when you hear the notification sound prompting the introduction of rice and put the washed rice,
To set the preheating temperature high in consideration of the room temperature and the amount of rice so that the hot water, the pot and the rice reach the thermal equilibrium without dropping the temperature of the pot significantly, and almost reach the temperature required for the water absorption process. This is to shorten the time required for raising the temperature to the temperature required for the water absorption process.

FIG. 1 shows an embodiment of a rice cooker according to the present invention.
This will be described with reference to FIGS.

A sectional view of the rice cooker according to the present invention will be described with reference to FIG. In FIG. 1, 1 is a rice cooker main body, 2 is a lid body that covers an upper opening of the rice cooker main body 1, 3 is a pot that is removably stored in the rice cooker main body 1, and 4 is a pan that is attached to the lid 2 and is attached to the lid 2. An inner lid for covering the upper surface opening, a control unit for performing heating control based on an input from an operation unit (not shown), a temperature sensor for contacting the pan 3 and detecting the temperature, and a heating unit for heating the pan 3 The halogen heater 8 is a light-transmissive protection plate that is disposed in the space between the halogen heater 7 and the pot 3 and protects the halogen heater 7.

A block diagram of the rice cooker will be described with reference to FIG. In FIG. 2, reference numeral 5 denotes a control unit composed of a microcomputer or the like, and the control unit 5 determines the temperature and time required in each of the preheating step, the water absorption step, the cooking step, and the steaming step. The program control procedure is stored. Reference numeral 9 denotes a preheating key provided on the operation unit of the rice cooker, and the control unit 5 starts a preheating process by pressing the preheating key 9 with water being put in the pot first. Reference numeral 10 denotes a rice cooking key. After the preheating step is completed and rice is input, the rice cooking key 10 is pressed to advance to each step after the water absorption step. Reference numeral 11 denotes a notification unit that notifies the user that the water temperature has reached the preheating temperature during the preheating process. In addition, as the notification means 11, notification may be performed using a buzzer, or the display unit may be flashed or lit to notify.

Reference numeral 12 denotes a room temperature sensor. The room temperature sensor 12 is disposed near the bottom of the periphery of the rice cooker, which is not easily affected by heat during cooking and keeping heat, or near the operation unit of the rice cooker. The control unit 5 is disposed on a printed circuit board. The control unit 5 controls the energization of the halogen heater 7, which is a heating unit for heating the pan 3, based on the detection values from the temperature sensor 6 and the room temperature sensor 12. In addition,
As a heating unit other than the halogen heater 7, any of a sheath heater, electromagnetic induction heating, and the like may be used.

FIG. 3 shows a pot used in the rice cooker described above. In FIG. 3, a scale 3a indicating the amount of water to be supplied in the preheating process is formed on the inner surface of the pan 3 by engraving or printing. The scale 3a indicates a water level of a water supply amount required when a user puts water into the pot 3 and then puts rice in washing and cooks rice before the preheating process,
The required water level is indicated by a number corresponding to the amount of rice to be introduced later. Further, the scale 3b is conventionally formed in a pot, and indicates a water level necessary when rice is poured into the pot 3 and then water is supplied to cook rice.

Further, the scales 3a and 3b shown in FIG.
Indicates that white rice is formed in order to indicate the type of rice cooked above, and is used when rice is cooked. In addition, above the scale 3a, "high speed"
Is formed. This may be displayed by a mark or the like. As described above, the scale 3a and the scale 3b are formed at different positions and have different displays.
Further, in order to facilitate the distinction between the scales 3a and 3b, the scales 3a and 3b may be formed in different colors or with different marks.

In addition, since the types of cooked rice include cooked rice, rice cooked rice, etc., a scale with these characters may be formed. In addition, in addition to the above-mentioned "high speed", characters such as "espresso" and "pilot guide" and a mark or the like corresponding thereto can be attached. These are distinguished from the scale of the water level of the conventional rice cooker, etc., and are stamped at different positions, or printed with different colors, or provided with different marks such as high speed, or both. Either one may be adopted.

FIG. 4 is a flowchart showing the program control of the rice cooker according to the present invention.

First, the user supplies water to the pot 3 (step G).
1) When the preheating key 9 is pressed (step G2), the preheating process starts, and the water in the pot 3 is rapidly heated to a predetermined preheating temperature and maintained at the preheating temperature (step G3). When the temperature reaches the preheating temperature, the user is notified by the notification means 11 to urge the user to insert rice (step G4), and waits for the user to insert rice (step G5). When the rice is put into the pot 3 and the user presses the rice cooker key 10 (step G6), the water absorption process starts, and the rice and water in the pot 3 are kept at the water absorption temperature for a predetermined time to absorb water. (Step G7).

In the present invention, since the pot and water are preheated so that the water absorption temperature becomes a predetermined value when the rice is charged,
It is not necessary to heat rice and water slowly as in the conventional case when heating rice at the same time from a low temperature. Since the rice is at a predetermined temperature when the rice is put in, the time required for the water absorption process is about 5 minutes. , Is greatly reduced as compared with the related art.

When the water absorption process is completed, the process proceeds to the cooking process (step G8), and after the steaming process (step G9).
Finish cooking rice.

FIG. 5 is a flow chart showing the procedure of the main part of the program control of the rice cooker according to the present invention.

In FIG. 5, the user puts water into the pot 3 up to the water level graduation 3a corresponding to the amount of rice initially marked with high speed (step S1).

Next, when the lid 2 of the rice cooker is closed and the preheating key 9 is pressed (step S2), the control unit 5 drives the halogen heater 7 (step S3), and the water in the pot 3 reaches the preheating temperature Ty. (Step S4). When the control unit 5 detects the signal of the temperature sensor 6 and the water temperature reaches the preheating temperature Ty, the power supply to the halogen heater 7 is cut off (step S5).
The notification means 11 prompts the user to put rice into the pot 3 (step S6). In the procedure up to this point, the lid 2 was closed at the time of heating, but the time for heating the water to the preheating temperature Ty depends on the amount of water, but is within 5 minutes, so it is programmed so that the preheating can be performed even when the lid 2 is opened. You may.

Here, a method of detecting the input of rice will be described. The controller 5 detects the water temperature T _t after t seconds from the end of the preheating process by the temperature sensor 6 (step S7), and detects the water temperature T _{(t + 2)} two seconds after taking the sampling time as 2 seconds. (Step S8). If the value T _(t) -T _{(t + 2)} of the temperature drop during this period exceeds 0.2 (.degree. C.) (step S9), 10 seconds after this (ie, (t + 12) seconds after the end of the preheating process). detecting the temperature _{T (t + 12) (step} S10), and the value _{T (t + 2)} during this period of temperature drop -T
_When it is detected that _{(t + 12)} has dropped to 2 (° C.) or more and rapidly dropped, it is determined that rice has been put into the pot 3 by the user (step S11).

If the sampling time is 2 (seconds) and the temperature is falling, the temperature is updated if it does not exceed 0.2 (° C.) (step S12), and the halogen heater 7 is set so that the water temperature is maintained at the preheating temperature. Is driven (step S3). This 0.2 (° C.) is set to a value that allows a temperature drift caused by driving or shutting off the halogen heater 7 when the water temperature of the pot 3 is mainly maintained at the preheating temperature Ty. .

Then, when rice is input by the user, the process shifts to a water absorption process. The user closes the lid 2 (step S1)
3) When the cooked rice key 3 is pressed (step S14), the water absorption time t 'is counted (step S15), and the halogen heater 7 is driven (step S16). If t 'does not exceed 5 (minutes) (step S17), the water temperature T (t) of the pot 3
Is detected (step S18), and when the water temperature T (t) of the pot 3 exceeds the set temperature 60 (° C.) of the water absorption process (step S1).
9), energization of the halogen heater 7 is cut off to 60 (° C.)
(Step S20). When the water absorption time t ′ is maintained at 60 ° C. and the water absorption time t ′ exceeds 5 (minutes), the water absorption process is terminated (step S17), and the rice cooking is terminated by program control from the cooking process to the steaming process.

Here, the above-described preheating temperature Ty will be described.

First, water is supplied to the pot 3 by the user,
By pressing the preheating key 9, the process shifts to the preheating process, and after reaching the preheating temperature Ty, the temperature of the pot 3 and the water in the pot 3 are both set to the temperature T.
It is held in y. Here, it is assumed that when the user throws in the rice at the temperature Ta and mixes the rice and the hot water, the pot 3 and the hot water and the rice are thermally equilibrated to reach the temperature Tk. Assuming that the weight of the supplied water is Gw, the weight of the pot is Gn, the specific heat of the pot is α, the volume of the rice to be charged is V, the specific gravity of the rice is r, and the specific heat of the rice is β, Holds.

(Gw + αGn) Ty + βrVTa = (Gw + αGn + βrV) Tk (Equation 1) By transforming (Equation 1), the following is obtained. Dividing by (Gw + αGn) gives (Equation 2).

Ty = Tk + βrV / (Gw + αGn) · (Tk−Ta) (Equation 2) There is a specific ratio between the amount of rice in rice cooking and the amount of water supply.
For example, when white rice is cooked, the relationship of (Equation 3) holds.

Gw = 1.4 rV (Equation 3) Further, as an example when the capacity of the rice cooker is 1 liter, the weight of the pan 3 is 509 (g), made of an aluminum alloy, and its specific heat β is 0.26 ( cal / g ° C) and specific heat α of rice
Is 0.45 (cal / g ° C.), (Equation 2) becomes (Equation 4) from the relationship between these conditions and (Equation 3).

Ty = Tk + 0.26 rV / (1.4 rV + 229) · (Tk−Ta) (Equation 4) Next, the user puts rice into the pot 3 held at the preheating temperature and is preheated. The temperature Tk when the hot water and rice are mixed and thermally equilibrated is 60 (° C.) below the gelatinization temperature of rice.
Set to.

From equation (4), the highest preheating temperature Ty can be obtained by setting the high speed scale 8a to 5.5 (the scale formed above the scale shown in FIG. 3 and below the "high speed"). Case), that is, the weight of rice required for one scale is 150 (g), so if the high-speed scale 3a is 5.5, the rice weight V is 825.
(G), at which time the preheating temperature Ty is given by (Equation 5)
It is represented as

Ty = 69.3−0.16Ta (Equation 5) Further, when the preheating temperature Ty must be minimized, when the weight of rice to be introduced is the smallest, that is, when the high-speed scale 3a is If the rice weight V is 15
0 (g), and at this time, Ty = 65.3-0.09Ta (Equation 6) Therefore, when the amount of rice is not taken into account, a lower (Equation 6) is adopted instead of a higher (Equation 5). There is a need to.

If the initial temperature Ta of the rice is set to the normal temperature of 20 (° C.), the preheating temperature Ty becomes 63.5 (° C.), and the temperature of the water when the water is poured into the pot is detected by the temperature sensor 5. Assuming that the temperature is Ta, seasonal variations can be reflected.

The rice cooker of the present invention is provided near the bottom of the periphery of the rice cooker, which is not easily affected by heat generated during the heating or keeping the temperature when the halogen heater 7 is driven, or near the operation unit of the rice cooker. The room temperature sensor 12 is provided on the printed circuit board of the control unit 5, and when the preheating key 9 is pressed, the room temperature is measured by the room temperature sensor 12 and the measured value is set to Ta in (Equation 6). Preheating temperature can be determined with high accuracy. For example, when the room temperature is 0 (° C.) in winter, it is assumed that the initial temperature Ta of rice is also 0 (° C.), so the preheating temperature Ty is 65.3 from (Equation 6).
(° C.).

As described above, if the preheating temperature Ty is controlled with high accuracy by taking into account the rice initial temperature Ta, the next water absorption process can be completed with a minimum water absorption time. If the preheating temperature Ty is set lower, the initial temperature of the water absorption process, that is, the thermal equilibrium temperature Tk decreases in parallel with the preheating temperature Ty and becomes lower than 60 (° C.) as shown in (Equation 4). Would. At this time, the rice stays at the bottom of the pot during the water absorption process, and if the heating is rapidly performed to raise the temperature to the predetermined water absorption process temperature, the rice in contact with the pot 3 is heated to a temperature higher than the gelatinization temperature. It is gelatinized. It is necessary to reduce the rate of temperature rise in the water absorption process, and as a result, the water absorption time must be extended, and the time required for cooking rice cannot be reduced.

In the conventional rice cooking method, when rice and water are almost simultaneously put into the pot 3 and heating is started, the time required for the water absorption process is as follows. It took about 20 minutes to heat the resin slowly at a low temperature rise rate so as not to cause the water absorption. However, by providing the preheating step of the present invention, the time required for the water absorption step was about 5 minutes.
Minutes, and it is possible to move on to the next cooking process. The time required for preheating is about 3 minutes because only water can be heated with the maximum power, so the time until the next cooking process is almost halved, greatly contributing to shortening of rice cooking time can do.

Further, in the present invention, when rice cooking is started without performing the preheating process as in the conventional case, the control unit 5 has a built-in program for determining which of the preheating key 9 and the rice cooking key 10 has been input first. Thus, after rice is introduced according to the scale of the conventional method, water is supplied to the pot and the rice cooking key 10
By pressing, the water absorption process can be started while slowly heating the rice and water put into the pot 3 as in the conventional method.

[0049]

According to the first aspect of the present invention, a pot provided in the rice cooker main body, a heating means for heating the pot, In a rice cooker comprising a temperature detecting means for detecting a temperature, and a control means for controlling the heating means based on the detected temperature of the temperature detecting means and performing a rice cooking process, the control means comprises: Prior to charging, by providing a preheating step of performing a preheating step of heating the water previously placed in the pan to a predetermined preheating temperature by the heating means, the water previously placed in the pan can be heated to a predetermined preheating temperature, Since the pot and the surroundings of the pot are also heated to the preheating temperature and heated, the temperature at which the rice and hot water reach thermal equilibrium reaches the temperature required for the rice cooking process in a short time after the rice is put into the pot. It is not necessary to raise the temperature of rice and hot water slowly. It is possible to shorten the time to.

According to the second aspect of the present invention, the temperature of the water in the pan is detected by the temperature detecting means during the preheating step, and the fact that the detected temperature has reached the preheating temperature is notified. Since the notification means is provided, the user can be quickly notified that the preheating process has been completed.

According to the third aspect of the present invention, after the water temperature in the pot reaches the preheating temperature in the preheating step, the control means holds the water in the pot at the preheating temperature,
It is possible to automatically switch from the preheating process to the rice cooking process in order to detect the introduction of rice into the pot from the fact that the temperature detected by the temperature detecting means drops from the preheating temperature and start the water absorption process. Becomes

According to the fourth aspect of the present invention, the preheating temperature is such that the rice and the water reach thermal equilibrium in a state where the rice is poured into the water in the pot that has reached the preheating temperature. The temperature required to cook rice is below the gelatinization temperature of rice, so there is no need to slowly heat the rice and water in the pot to the rice's water absorption temperature and raise the temperature. Can be shortened.

According to a fifth aspect of the present invention, there is provided a room temperature detecting means for detecting a room temperature, wherein the control means feeds the temperature detected by the room temperature detecting means into the inner pot after the preheating step. Since the preheating temperature is determined as the temperature of the rice, the preheating temperature can be accurately set by estimating the installation condition of the rice cooker and the seasonal rice temperature.

According to the sixth aspect of the present invention, the scale is provided on the inner surface of the pot to indicate the level of water to be preheated in the preheating step, so that the user can easily supply water into the pot. In addition, at the end of the preheating process, the water level can be reconfirmed and the amount of rice to be input can be determined without error.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an embodiment of a rice cooker according to the present invention.

FIG. 2 is a block diagram showing an embodiment of the rice cooker according to the present invention.

FIG. 3 is a perspective view showing a pot of the rice cooker according to the embodiment of the present invention.

FIG. 4 is a flowchart showing control of the rice cooker according to the embodiment of the present invention.

FIG. 5 is a flowchart showing control of a preheating step and a water absorption step of the rice cooker according to the embodiment of the present invention.

FIG. 6 is a side sectional view showing a conventional rice cooker.

[Explanation of symbols]

 3 Pot 5 Control unit 6 Temperature sensor 7 Halogen heater 9 Preheating key 10 Cooking rice key 11 Notification means 12 Room temperature sensor

Claims (6)

[Claims] 1. A pot provided in a rice cooker main body, a heating means for heating the pot, a temperature detecting means for detecting a temperature of the pot, and the heating means based on a temperature detected by the temperature detecting means. And a control means for performing a rice cooking process by controlling the rice cooker, the control means, before putting the rice into the pot, the water previously put in the pot to a predetermined preheating temperature by the heating means. A rice cooker characterized by performing a preheating step of heating. 2. The rice cooker according to claim 1, wherein a temperature of the water in the pan is detected by the temperature detecting means during the preheating process, and a notification is given that the detected temperature has reached the preheating temperature. A rice cooker comprising a notification unit. 3. The rice cooker according to claim 1, wherein the control means holds the water in the pot at the preheating temperature after the water temperature in the pot reaches the preheating temperature in the preheating step, A rice cooker characterized by detecting the introduction of rice into the pot from the fact that the temperature detected by the temperature detecting means drops from the preheating temperature and starting the rice cooking process. 4. The rice cooker according to claim 1, wherein the preheating temperature is such that when the rice is put into the water in the pot that has reached the preheating temperature, the water and the rice reach thermal equilibrium. A rice cooker characterized in that the temperature is below the gelatinization temperature of rice. 5. The rice cooker according to claim 1, further comprising a room temperature detecting means for detecting a room temperature, wherein the control means inputs the temperature detected by the room temperature detecting means into the inner pot after the preheating step. A rice cooker characterized by determining a preheating temperature as a temperature of the rice cooker. 6. The rice cooker according to claim 1, wherein a scale is provided on an inner surface of the pan to indicate a water level of water to be preheated in the preheating step.