JP2023062552A - Fryer - Google Patents

Abstract

To appropriately cook an object to be cooked by preventing overshooting of the temperature of cooking oil.SOLUTION: A storage part of a burner controller of a fryer stores a cooking temperature zone V composed of a permissible upper limit temperature T1 and a permissible lower limit temperature T2 for each elapsed time set beforehand, and predetermined control lines L1-L3 set by variables of the time elapsed from the start of cooking and a predetermined target temperature on the basis of the cooking temperature zone V. The control lines L1-L3 are set in a first control region E1 lower than the permissible lower limit temperature T2 in an initial stage of the cooking, set in a second control region E2 in the cooking temperature zone V and in the lower half of the cooking temperature zone V in the intermediate stage of the cooking, and set in a third control region E3 in the cooking temperature zone V and in the upper half of the cooking temperature zone V in the ending stage of the cooking.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present disclosure relates to a fryer for commercial use that heats cooking oil in an oil tank, puts food into the oil tank, and heats and cooks the food.

As disclosed in Patent Document 1, the fryer has an oil tank containing cooking oil, heating means such as a burner or pulse combustor for heating the cooking oil, and control means for controlling the heating means. The control means controls the heating means to perform heat cooking when an object to be cooked, such as potatoes, is put into the oil bath.
The control means includes a control line in which the detected temperature of the cooking oil obtained from a temperature detecting means such as a thermistor changes in a continuous line or an intermittent stepped line depending on the variables of the elapsed time from the start of cooking and the target temperature. is set. This control line is determined based on a cooking temperature zone surrounded by an allowable upper limit temperature and an allowable lower limit temperature for each elapsed time set in advance for cooking the food.
When cooking is started, the control means controls the heating means (for example, ON/OFF control of the pulse combustor) so that the detected temperature of the cooking oil changes along the control line within the cooking temperature range.

Japanese Patent No. 5340962

However, in such a fryer, if you cook with less cooking oil, the amount of heat stored in the cooking oil will decrease accordingly. shows a tendency to change more sensitively and with a larger amplitude.
In addition, the cooking temperature range is based on the value measured by inserting a thermometer into the center of the cooking oil where the food is directly cooked, that is, the value affected by the heat of vaporization of the food. On the other hand, the detected temperature is the temperature detected by a thermistor or the like provided on the wall surface of the oil tank, which is not easily affected by the food to be cooked, and varies depending on the detection position and the detection environment. Therefore, it is unavoidable that a deviation occurs between the cooking temperature zone and the detected temperature, and simply performing ON/OFF control so that the detected temperature does not exceed the cooking temperature zone causes a deviation between the actual temperature and the cooking temperature zone. becomes larger.

Then, when cooking, for example, frozen potatoes at about -20°C as the food to be cooked, immediately after the food to be cooked is added, the food to be cooked deprives the cooking oil of a large amount of heat and the amount of water retained by the food to be cooked. Since the heat of vaporization is generated with the evaporation of the food, an undershoot in which the temperature of the food to be cooked falls significantly below the cooking temperature range is likely to occur.
On the other hand, if the control line is carelessly set to a relatively high temperature at the beginning of cooking so that the heating means is likely to be turned on, the temperature around the food may tend to rise. However, there is a certain time lag until the situation is transmitted to the thermistor or the like provided on the wall. Therefore, there is a possibility that the amount of heat is applied unnecessarily for a long period of time, and that an excessive amount of heat is applied to the food to be cooked, resulting in a poor finish.

Therefore, the present disclosure prevents the measured temperature of the food from deviating from the cooking temperature range even when the food is cooked with a small amount of cooking oil, and maintains the finish of the food in good condition. The purpose is to provide a fryer that can

To achieve the above object, the present disclosure provides an oil tank capable of containing cooking oil;
temperature detection means for detecting the temperature of the cooking oil;
a heating means provided in the oil tank for heating the cooking oil by ON/OFF operation;
a control means for controlling the heating means, comprising a timer and a storage unit;
The storage unit stores a cooking temperature range composed of an allowable upper limit temperature and an allowable lower limit temperature for each preset elapsed time, and an elapsed time from the start of cooking and a predetermined target temperature based on the cooking temperature range. and a predetermined control line set by a variable of
The control means is a fryer that controls ON/OFF of the heating means so that the temperature detected by the temperature detection means changes along the control line,
The control line is set within a first control region below the allowable lower limit temperature in the early stage of cooking, and within a second control region within the cooking temperature zone and the lower half of the cooking temperature zone during the middle stage of cooking. It is characterized in that, at the end of cooking, it is set within the cooking temperature range and within a third control range which is the upper half of the cooking temperature range.
It should be noted that the control lines in the early stage of cooking include not only those set entirely within the first control area, but also some lines set within the second control area at late timing leading to the middle stage of cooking.
Similarly, the control line for the final stage of cooking includes not only those set entirely within the third control region, but also those set partially within the second control region.
In another aspect of the present disclosure, in the above configuration, the allowable lower limit temperature is defined as a curve with a minimum temperature that shows a downward trend and then an upward trend over time,
The temperature of the control line in the first control region is set to a value below the allowable lower limit temperature and above the minimum temperature.
Another aspect of the present disclosure is that, in the above configuration, the control line in the second control region, when the allowable lower limit temperature exceeds the minimum allowable temperature and exhibits a rising tendency, changes the allowable upper limit temperature and the allowable lower limit temperature over time. It is characterized in that it is set so as to approach the median of the temperature.

According to the present disclosure, even when the food is cooked with a small amount of cooking oil, the measured temperature of the food is prevented from deviating from the cooking temperature range, and the finish of the food is maintained well. can do.
According to another aspect of the present disclosure, in addition to the above effects, the allowable lower limit temperature is defined as a curve with a minimum temperature showing a downward trend followed by an upward trend over time, and the first control Since the temperature of the control line in the region is set to a value lower than the allowable lower limit temperature and higher than the minimum temperature, it is possible to prevent undershoot due to excessive suppression of heating by the heating means.
According to another aspect of the present disclosure, in addition to the above effects, the control line in the second control region, when the allowable lower limit temperature exceeds the minimum temperature and shows a rising tendency, the allowable upper limit temperature and the allowable lower limit temperature Since it approaches the median of , a rapid rise in the measured temperature can be suppressed.

1 is a perspective view of a fryer; FIG. 1 is a schematic diagram of a fryer; FIG. FIG. 4 is an explanatory diagram of an operation panel; FIG. 4 is an explanatory diagram of cooking temperature zones and control lines;

Embodiments of the present disclosure will be described below with reference to the drawings.
FIG. 1 is a perspective view showing an example of a fryer, and FIG. 2 is a schematic diagram of the fryer. This fryer 1 has a pair of left and right oil tanks 3, 3 in the upper part of the body 2. - 特許庁A pair of left and right pulse combustors 4, 4 as heating means are provided at the bottom of each oil tank 3, respectively. Each pulse combustor 4 has a combustion chamber 5 provided on the front inner wall of the oil tank 3 and a tail pipe 6 connected to the combustion chamber 5 and routed in a meandering manner within the oil tank 3 .
Since the configurations of the oil tanks 3 and their combustion systems and exhaust systems are the same on the left and right sides, the oil tank 3 on the left side of FIG. 1 will be mainly described below.

The oil tank 3 has a first cooking section 7 and a second cooking section 8 . The first cooking section 7 is formed above the pulse combustor 4 and has a rectangular tubular shape with an opening area that does not change in the vertical direction. The second cooking portion 8 is positioned above the first cooking portion 7 and is formed in an inverse tapered shape that widens in the front, rear, left, and right directions as it goes upward from the upper end of the first cooking portion 7 . The portion up to the upper end of the second cooking portion 8 serves as a storage portion for the cooking oil. A basket 9 containing food to be cooked such as potatoes can be put into the oil tank 3. - 特許庁Above the pulse combustors 4,4 there is a net 10 for receiving a basket 9. FIG.
A first oil surface temperature sensor 11 is provided near the upper end surface of the first cooking section 7 . A second oil surface temperature sensor 12 is provided near the upper end surface of the second cooking section 8 . A cooking temperature sensor 13 is provided near the tail pipe 6 of the pulse combustor 4 in the oil tank 3 . An electric heater 33 is provided on the lower outer peripheral surface of the oil tank 3 .

Behind the oil tank 3 and above the vessel body 2, an oil increase tank 14 for containing cooking oil is provided. An oil increase pipe 15 connected to the second cooking section 8 at the rear surface of the oil tank 3 is connected to the lower surface of the oil increase tank 14 . The oil increase pipe 15 is provided with an oil increase valve 16 that is manually opened and closed. An oil-increasing temperature sensor 17 is provided in the oil-increasing tank 14 to detect the temperature of the stored cooking oil.
An overflow portion 18 is provided on the front surface of the oil increase tank 14 . The overflow portion 18 is formed by a pipe connected to the front surface of the oil increase tank 14, a flow path formed in the front surface of the oil increase tank 14 in the vertical direction, and the like. The upper end of the overflow part 18 is connected to an opening formed in the upper front part of the oil tank 14 and hangs down, and the lower end of the overflow part 18 is connected to the rear inner surface of the oil tank 3 via the outlet 19. Therefore, when the cooking oil in the oil increase tank 14 exceeds the lower edge of the opening, the overflowing cooking oil flows down into the oil tank 3 from the outlet 19 along the rear inner surface of the oil tank 3 .

An air chamber 20 is provided outside the front side of the oil tank 3 . A mixing chamber (not shown) communicating with the combustion chamber 5 is provided in the air chamber 20 . A gas conduit 21 equipped with a gas solenoid valve 22 is connected to the mixing chamber to supply fuel gas. An air supply pipe 23 is connected to the mixing chamber. The air supply pipe 23 is connected to a fan 24 provided at the bottom of the body 2 to supply combustion air.
The tail pipes 6 , 6 of the pulse combustors 4 , 4 are connected to exhaust pipes 25 , 25 drawn out from the air chamber 20 after being arranged in a meandering manner under the oil tank 3 . The exhaust pipes 25 , 25 have mufflers 26 , 26 arranged at the rear part of the body 2 . The mufflers 26, 26 are disposed facing upward while being in contact with the rear surface of the fuel tank 14 so that combustion exhaust can be discharged.
The increased oil tank 14 and the mufflers 26 , 26 are covered with an exhaust pipe cover 27 provided on the body 2 . Protective covers 28 are provided on the front surfaces of the left and right exhaust pipe covers 27 , 27 . Basket hangers 29 , 29 for suspending and supporting the baskets 9 , 9 are fixed to the protective cover 28 . The outlet 19 of the overflow portion 18 is provided below the basket hanger 29 .

A filtering tank 30 having a filter at the bottom is provided at the bottom of the vessel 2 . An oil drain pipe 31 is connected to the bottom of the oil tank 3 so that the cooking oil in the oil tank 3 can be discharged to the filtering tank 30 through the oil drain pipe 31 . The oil drain pipe 31 is provided with an oil drain valve 32 that is manually opened.
A filtering pump 35 is provided at the bottom of the vessel 2 . The suction side of filtering pump 35 is connected to the bottom of filtering tank 30 via suction pipe 36 . A discharge side of the filtering pump 35 branches into a first oil supply pipe 37 and a second oil supply pipe 38 . The first oil supply pipe 37 is connected to the oil increase pipe 15 on the upstream side of the oil increase valve 16 . The first oil supply pipe 37 is provided with a first oil supply valve 39 that is manually opened and closed.
The second oil supply pipe 38 is connected to the lower portion of the oil tank 3 . The second oil supply pipe 38 is provided with a second oil supply valve 40 that is manually opened and closed.

Below the oil tank 3, an additional oil tank 45 using a 18-liter can is provided. The supplementary oil tank 45 is installed on a stand 46 provided on the vessel body 2 . The stand 46 is provided with a heat retaining heater 47 for heating the supplementary oil tank 45 and a tank temperature sensor 48 for detecting the temperature of the supplementary oil tank 45 .
A lower end of a supplementary oil pipe 49 is inserted into the supplementary oil tank 45 . The upper end of the additional oil pipe 49 is connected to the oil tank 3 above the second cooking section 8 . A supplementary oil pump 50 and a supplementary oil solenoid valve 51 are provided in the supplementary oil pipe 49 from the upstream side.

A fly controller 60 is provided on the front upper portion of the body 2 . The fly controller 60 has an operation panel 61 . As shown in FIG. 3, the operation panel 61 includes a power switch 62, a plurality of cooking buttons 63, 63, . There are provided a mode selection button 65 for selecting the rated quantity, and rated quantity display lamps 66A and 66B for displaying the rated quantity. The rated quantity display lamp 66A corresponds to the first rated quantity, and the rated quantity display lamp 66B corresponds to the second rated quantity.
A burner controller 70 is provided at the bottom of the vessel 2 . The burner controller 70 has a timer 71 and a storage unit 72, and performs ON/OFF control of the pulse burner 4 according to the cooking mode instructed by the fry controller 60 to cook the food such as potatoes. Detection signals from the first and second oil surface temperature sensors 11 and 12, the cooking temperature sensor 13, the oil increase temperature sensor 17, the tank temperature sensor 48, and the like are input to the burner controller 70. FIG. Based on these detection signals and instructions from the operation panel 61, the burner controller 70 operates the pulse combustor 4, the gas solenoid valve 22, the fan 24, the electric heater 33, the filtering pump 35, the heat retaining heater 47, the additional oil pump 50, It controls the addition oil electromagnetic valve 51 and the like.

In the fryer 1 configured as described above, the amount of food to be cooked at one time is specified in two types, a predetermined first rated amount and a second rated amount, which is larger than the first rated amount. Cooking is possible in the first cooking mode corresponding to the amount and the second cooking mode corresponding to the second rated amount. The increased oil tank 14 contains a full (increased amount) of cooking oil.
When the cook turns on the power switch 62 of the operation panel 61 , the burner controller 70 rotates the fan 24 for a predetermined time to supply air, and then intermittently burns the mixed gas in the combustion chamber 5 to ON/OFF. That is, the mixed gas is ignited in the combustion chamber 5 to be explosively burned in the combustion chamber 5, and the combustion exhaust gas is forcibly discharged to the tail pipe 6 due to the pressure increase in the combustion chamber 5 accompanying the combustion. Then, fuel gas and combustion air are sucked into the combustion chamber 5, which has a negative pressure due to the discharge of the combustion exhaust. By repeating this ON/OFF operation, the cooking oil stored in the oil tank 3 is heated.

Before starting cooking, the burner controller 70 monitors the detected temperature obtained from the cooking temperature sensor 13, and turns on the pulse combustor 4 so that the detected temperature maintains a predetermined standby temperature (for example, 160°C). Execute the standby mode with /OFF control.
While the standby mode is being executed, the fry controller 60 notifies by outputting a display indicating that cooking is OK on the display section 64 of the operation panel 61, for example.
Then, the cook selects either the first or second cooking mode with the mode selection button 65, puts the basket containing the corresponding rated amount of food into the oil tank 3, and presses the cooking start button (here Then, the cooking button 63) at the left end is pressed and operated. Then, the burner controller 70 heats and cooks the food using the cooking time and the heat amount of the pulse burner 4 that are set in advance corresponding to the rated amounts.

In the storage unit 72 of the burner controller 70, a cooking temperature range V surrounded by an allowable upper limit temperature T1 and an allowable lower limit temperature T2, which change with time, is set as indicated by a dashed line in FIG. This cooking temperature zone V shows a downward trend and then an upward trend as time elapses, and the allowable lower limit temperature T2 has a minimum temperature Tmin at the reversal position of the downward trend and the upward trend. Based on this cooking temperature range V, the target temperature at the start of cooking corresponding to each cooking mode is stored in the storage unit 72 intermittently, in which the target temperature changes stepwise according to the variables of the elapsed time from the start of cooking and the target temperature. Control lines L1 to L3 (indicated by solid lines) are respectively set.
However, in each cooking mode, the control line L1 at the beginning of cooking from the cooking start time t0 to the first elapsed time t1 is set within the first control region E1 below the allowable lower limit temperature T2 of the cooking temperature range V. However, the control line L1 is set so that it exceeds the minimum temperature Tmin and is partly within the second control region E2, which is the lower half of the cooking temperature zone V, immediately before the first elapsed time t1. .
Next, the control lines L2, L2, . is set within The control line L2 after the allowable lower limit temperature T2 exceeds the minimum allowable temperature Tmin and exhibits an upward tendency is set so as to gradually approach the median value Tmid between the allowable upper limit temperature T1 and the allowable lower limit temperature T2 over time. ing.
The control line L3 for the end of cooking from the second elapsed time t2 to the third elapsed time t3 at which cooking ends is within the cooking temperature range V and within the third control region E3, which is the upper half of the cooking temperature range V. is set. However, the control line L3 is set so that a part of it lies within the second control region E2 immediately before the third elapsed time t3.

The burner controller 70 ON/OFF-controls the pulse combustor 4 so that the detected temperature is maintained along the control lines L1, L2, L3 corresponding to the selected cooking mode from the cooking start time t0.
Therefore, in the early stage of cooking, the ON/OFF control is performed based on the control line L1 in the first control area E1, so that the cooking oil is not excessively heated, and overshoot can be suppressed. In the early stage of cooking, air bubbles are generated from the food to be cooked, and the heat of vaporization of the air bubbles cools the cooking oil, making it difficult for the temperature of the cooking oil to rise.
However, as the cooking progresses, the number of air bubbles generated decreases, so the temperature of the cooking oil tends to rise.
Therefore, in the middle stage of cooking, the control line L2 is set to the second control area E2, which is the lower half of the cooking temperature zone V, so that the sudden rise of the cooking oil can be suppressed and overshoot in the middle stage of cooking can be prevented. be able to.

At the end of cooking, the control line L3 is set to the third control region E3, which is the upper half of the cooking temperature zone V, so that the temperature of the cooking oil at the end of cooking can be close to the temperature at the start of cooking. Therefore, it becomes possible to rapidly prepare the next food to be cooked. At the end of cooking, the cooking of the food has progressed considerably, and the number of air bubbles generated has decreased. is close. Therefore, even if the control line L3 is set to the third control region E3, which is the upper half of the cooking temperature zone V, the possibility that the temperature of the cooking oil suddenly exceeds the cooking temperature zone V is small.
By ON/OFF controlling the pulse burner 4 along each of the control lines L1 to L3, the actual cooking oil temperature (measured temperature) T changes within the cooking temperature zone V as indicated by the dotted line. will do.
When the time expires at the third elapsed time t3, the frying controller 60 sounds an alarm to notify the end of cooking. Therefore, the cook pulls up the basket 9 from the oil tank 3. When cooking is continued, the same control is repeated by putting in the food to be cooked and pressing the cooking start button.

On the other hand, the burner controller 70 monitors the detected temperature obtained from the tank temperature sensor 48 during operation in each cooking mode, and turns on the heat retaining heater 47 so that the additional oil tank 45 maintains a predetermined heat retaining temperature. /OFF control.
When the first and second oil surface temperature sensors 11 and 12 detect a decrease in the required amount of cooking oil in one of the cooking modes, or when a predetermined number of times of cooking is reached, the additional oil pump 50 is driven. to open the oil solenoid valve 51. Then, the cooking oil liquefied in the additional oil tank 45 is directly supplied to the oil tank 3 through the additional oil pipe 49 .

As described above, the fryer 1 of the above configuration is provided with an oil tank 3 capable of containing cooking oil, a cooking temperature sensor 13 (temperature detecting means) for detecting the temperature of the cooking oil, and the oil tank 3, which can be operated ON/OFF. a pulse combustor 4 (heating means) for heating the cooking oil by heating, and a burner controller 70 (control means) for controlling the pulse combustor 4 having a timer 71 and a storage unit 72 . The storage unit 72 also stores a cooking temperature range V composed of a permissible upper limit temperature T1 and a permissible lower limit temperature T2 for each preset elapsed time, and the elapsed time from the start of cooking based on the cooking temperature range V. and a predetermined target temperature are stored. Further, the burner controller 70 ON/OFF-controls the pulse combustor 4 so that the temperature detected by the cooking temperature sensor 13 changes along the control lines L1 to L3.
The control lines L1 to L3 are set within the first control region E1 below the permissible lower limit temperature T2 in the early stage of cooking, and within the cooking temperature zone V and the lower half of the cooking temperature zone V in the middle stage of cooking. It is set within the second control region E2, and is set within the third control region E3 which is within the cooking temperature zone V and the upper half of the cooking temperature zone V at the end of cooking.
According to this configuration, even when the food is cooked with a small amount of cooking oil, the actually measured temperature T of the food is prevented from deviating from the cooking temperature range V, and the food is finished well. can be held.

In particular, the allowable lower limit temperature T2 is defined as a curve with a minimum temperature Tmin showing a downward trend and then an upward trend over time. It is set to a value below the lower limit temperature T2 and above the minimum temperature Tmin.
Therefore, it is possible to prevent the occurrence of undershoot due to excessive suppression of heating by the pulse combustor 4 .
Further, the control line L2 in the second control region E2 is arranged so that when the allowable lower limit temperature T2 exceeds the minimum allowable temperature Tmin and exhibits an upward tendency, the median value Tmid between the allowable upper limit temperature T1 and the allowable lower limit temperature T2 is approached as time elapses. is set to
Therefore, a rapid rise in the measured temperature T can be suppressed.

Modified examples will be described below.
The cooking temperature zone and control line are not limited to the above-described forms, and can be changed as appropriate. For example, the cooking temperature zone may be linear, and the control line is not limited to the above-described intermittent linear shape, but may be intermittent curved, continuous curved, or linear. . The lengths of the initial stage of cooking, the middle stage of cooking, and the final stage of cooking are not limited to the above forms.
In the above embodiment, part of the control lines at the beginning of cooking are set within the second control area, but all of the control lines may be set within the first control area. Similarly, in the above embodiment, part of the control line for the end of cooking is set within the second control region, but the entire control line may be set within the third control region.
In the above embodiment, the first and second cooking modes are executable, but the number of cooking modes may be single, or three or more cooking modes may be executable. In either case, the control line settings of the present disclosure are possible.

The fryer is not limited to having separate frying controller and burner controller, and may have one controller that functions as both a frying controller and a burner controller.
The heating means may be formed only by a pulse combustor or may be formed only by an electric heater. Also, the heating means may be formed only by a gas burner provided outside the oil tank. Furthermore, the heating means may be formed by combinations other than the combination of a pulse combustor and an electric heater.
In the above embodiment, a pair of left and right oil tanks are provided, but the number of oil tanks may be one, or conversely, three or more.
The present disclosure is applicable even to a pressure fryer that closes the opening of the oil tank with a lid.

DESCRIPTION OF SYMBOLS 1... Fryer, 2... Body, 3... Oil tank, 4... Pulse combustor, 5... Combustion chamber, 6... Tail pipe, 7... 1st cooking part, 8... 2nd cooking part , 9... Basket 11... First oil surface temperature sensor 12... Second oil surface temperature sensor 13... Cooking temperature sensor 14... Oil increase tank 15... Oil increase pipe 16... Oil increase valve 18 Overflow portion 22 Gas solenoid valve 30 Filtering tank 35 Filtering pump 37 First oil supply pipe 38 Second oil supply pipe 39 Second 1 refueling valve 40 second refueling valve 60 fry controller 61 operation panel 62 power switch 63 cooking button 64 display unit 65 mode selection button 66A , 66B... Rated amount display lamp, 70... Burner controller, 71... Timer, 72... Storage unit, V... Cooking temperature range, T1... Allowable upper limit temperature, T2... Allowable lower limit temperature, Tmid... median value, Tmin... minimum temperature, L1 to L3... control line, E1... first control area, E2... second control area, E3... third control area.

Claims (3)

an oil tank capable of containing cooking oil;
temperature detection means for detecting the temperature of the cooking oil;
a heating means provided in the oil tank for heating the cooking oil by ON/OFF operation;
a control means for controlling the heating means, comprising a timer and a storage unit;
The storage unit stores a cooking temperature range composed of an allowable upper limit temperature and an allowable lower limit temperature for each preset elapsed time, and an elapsed time from the start of cooking and a predetermined target temperature based on the cooking temperature range. and a predetermined control line set by a variable of
The control means is a fryer that controls ON/OFF of the heating means so that the temperature detected by the temperature detection means changes along the control line,
The control line is set within a first control region below the allowable lower limit temperature in the early stage of cooking, and within a second control region within the cooking temperature zone and the lower half of the cooking temperature zone during the middle stage of cooking. set, and in the final stage of cooking, set within the cooking temperature range and within a third control range that is the upper half of the cooking temperature range. The lower allowable temperature limit is defined as a curve with a minimum temperature showing a downward trend followed by an upward trend over time,
2. The fryer according to claim 1, wherein the temperature of said control line in said first control region is set to a value below said lower limit temperature and above said minimum temperature. The control line in the second control region is set so as to approach the median value between the allowable upper limit temperature and the allowable lower limit temperature over time when the allowable lower limit temperature exceeds the minimum allowable temperature and shows an upward trend. 3. The fryer of claim 2, wherein the fryer comprises:

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