Control method for operating a cooking oven in a frying program configured for a predetermined set temperature

Abstract

A control method for operating a cooking oven in a frying program configured for a predetermined set temperature, wherein the cooking oven has an oven cavity, a tray arranged within the oven cavity, a bottom heating element for heating the bottom of the oven cavity, a fan located at a rear wall of the oven cavity, and an annular heating element surrounding the fan. The method comprises the following phases: (a) a heating phase, wherein the annular heating element is continuously operated and the bottom heating element is intermittently operated, the heating phase being carried out until a temperature of the oven cavity is reached, which corresponds to the set temperature plus a predetermined first hysteresis; (b) a subsequent holding phase, wherein the bottom heating element and the annular heating element are non-operated; and (c) a frying phase, which is carried out after a temperature within the oven cavity is reached, which corresponds to the set temperature minus a predetermined second hysteresis, the frying phase comprising continuously or intermittently operating the annular heating element and intermittently operating the bottom heating element in order to raise the temperature within the oven cavity to a temperature corresponding to the set temperature plus a predetermined third hysteresis.

Description

[0001] The present invention relates to a method for operating a cooking oven, in particular to a method for operating a cooking oven in a frying program configured for a predetermined set temperature, wherein the cooking oven has an oven cavity, a tray arranged within the oven cavity, a bottom heating element for heating the bottom of the oven cavity, a fan located at a rear wall of the oven cavity, and an annular heating element surrounding the fan. BACKGROUND

[0002] The present invention therefore relates to a control method for operating a convection oven in a frying program, which program aims at simulating the frying of frozen convenience food in a substantially fat-free manner, i.e. without submerging the food product in hot fat such as oil, but wherein similar cooking results as in standard frying are to be achieved.

[0003] In EP 2704526 a microwave oven is disclosed which comprises, in addition to a microwave unit, a grill element and a convection heating element. The oven can be operated in a pan-frying cooking mode in which the food is not only heated by microwaves, but is further heated by the grill and / or convection heating element in order to both heat the core of the food product and at the same time pan-fry the surface of the food product.

[0004] While EP 2704526 is limited to using a microwave unit to provide heat to the food product, such that the control scheme presented therein seems not to be directly transferable to other oven types such as convection ovens, the pan-frying cooking mode presented in this document is further considered to be disadvantageous because microwave heating leads to an uneven evaporation of water, especially in the first phase of the cooking process. That is, especially when the food product being processed has a small cross-section, such as in thin French fries, the microwaves fully penetrate the food product, which leads to the interior of the food product drying out before sufficient browning is achieved at the outer surface of the food product.

[0005] Attempts to simulate frying in a conventional convection oven by heating the food product with a grill element provided at the top of the oven cavity are problematic, because this simulation leads to an uneven browning. Thus, considering that more heat is transferred to the top side of the food product, the top side browns much faster than the bottom, such that in order to achieve an even browning, the food product needs to be flipped over during the cooking process.

[0006] In view of the above-mentioned disadvantages of the prior art methods, it is an object of the present invention to provide a control method for operating a convection cooking oven in a frying program which allows to achieve better cooking results than the known methods.

[0007] The present application solves the above-mentioned objects by providing a control method for operating a cooking oven in a frying program configured for a predetermined set temperature, which control method is defined in claim 1.

[0008] The method is configured to be applied to a cooking oven having an oven cavity, a tray arranged within the oven cavity, a bottom heating element for heating the bottom of the oven cavity, a fan located at a rear wall of the oven cavity, and an annular heating element surrounding the fan. The method is thus configured for a convection oven or for a cooking oven having a convection heating function, such as a so-called combination cooking oven, which can be heated not only by convection heating, but also by at least one further heating method, such as radiant heating, induction heating, steam heating and microwave heating.

[0009] The method is for operating a cooking oven in a deep-frying program, which method comprises several phases, including a heating phase, a subsequent holding phase and a frying phase.

[0010] In the heating phase, the annular heating element is continuously operated and the bottom heating element is intermittently operated. That is, the annular heating element is continuously operated, while the bottom heating element is operated in a cyclical manner, wherein the bottom heating element is either turned on and off, or operated at a repeatedly varying power level. In this way, a rapid heating of the food products to be processed is achieved, while the heat transfer from the bottom is limited, in order to achieve a uniform browning on all sides of the food products without having to turn the food products during the heating. The heating phase provides a faster heating of the food products in the heating regime employed in the method compared to other standard cooking programs.

[0011] The heating phase is carried out until a temperature of the oven cavity is reached, which temperature corresponds to the set temperature plus a predetermined first hysteresis. This overshoot in terms of the set temperature provides a faster heat transfer on the outside of the food, which faster heat transfer causes the water on the surface to evaporate faster, thus providing a crisper texture.

[0012] In the holding phase, which follows the heating phase, both the bottom heating element and the annular heating element are non-operational. During the holding phase, the heat energy that has been transferred to the surface of the food products is allowed to penetrate into the food products, in order to propagate to the center of the food products. The holding phase is carried out until a temperature within the oven cavity is reached, which temperature corresponds to the set temperature minus a predetermined second hysteresis.

[0013] Upon reaching this latter temperature, the frying phase is initiated, during which the annular heating element is continuously or intermittently operated and the bottom heating element is intermittently operated, in order to raise the temperature within the oven cavity to a temperature corresponding to the set temperature plus a predetermined third hysteresis. During the frying phase, the oven temperature can thus be gradually raised to the desired set temperature plus the set third hysteresis.

[0014] The frying phase can be terminated after a certain time has elapsed, after a predetermined overall cooking time has been reached, or after a certain degree of browning has been reached, manually by the user, or automatically under the control of the oven controller.

[0015] The method has been successfully tested in various different convenience food products, such as French fries, potato pancakes, fish sticks, breaded and deep-fried fish, chicken nuggets, spring rolls, potato wedges, puff pastry, etc., and has the advantage over existing solutions of allowing to achieve good frying results comparable to conventional deep-frying methods, but in a fat-free, oil-free or low-oil manner, without the need to provide a deep-frying fat bath for submerging the food products, nor the need to repeatedly flip the food products by the user to achieve uniform browning.

[0016] The preferred embodiments of the present invention are defined in the dependent claims.

[0017] Preferably, the fan located at the back wall of the oven cavity is operable during all phases in order to distribute air throughout the oven cavity, and the air to be heated by the annular element surrounding the fan is fed to the trays supporting the food products to be processed.

[0018] During the heating phase and / or the frying phase, the bottom heating element is preferably operated intermittently, so as to be operable during 50% to 70% of the respective phase.

[0019] The intermittent operation of the bottom heating element during the heating phase, and the similar intermittent operation of the bottom heating element and optionally the annular heating element during the frying phase, can comprise periodically switching the respective heating element so that it can be alternately operated at a first power level and a second power level, or periodically switching on and off. Thus, for example, in an oven comprising an annular element with a power intake of 2.3 kW and a bottom heating element with a power intake of 1.0 kW, by continuously operating the annular heating element during the heating phase, and by intermittently operating the bottom heating element by periodically switching it on and off so as to be operable during 50% to 70% of the heating phase, the overall power intake of the oven is cycled between 2.3 kW and 3.3 kW, wherein the overall average power intake of the oven during the heating phase is limited to a value below 3 kW.

[0020] The predetermined first hysteresis, i.e. the overshoot of the temperature to which the oven cavity is heated during the heating phase above the set temperature, can correspond to 5% to 15%, preferably about 10%, of the set temperature. That is, while the preferred set temperature is in the range of 180°C to 220°C, the value of the first hysteresis is preferably 10°C to 30°C, preferably about 20°C, when the method is performed with a set temperature of e.g. 200°C.

[0021] That is, while in a conventional deep-frying method, a temperature of about 170-180°C is considered to be optimal, the above-mentioned set temperature takes into account that the present method does not use an oil bath to immerse these foodstuffs to be deep-fried, but uses a heated air stream, which has a lower heat transfer compared to an oil bath.

[0022] While in the preferred embodiment the ring-shaped heating element has a power intake of 1.8 kW to 2.5 kW, preferably 2.0 kW to 2.4 kW, such as, for example, about 2.3 kW, the bottom heating element preferably has a power intake of 0.8 kW to 1.5 kW, wherein the preferred power intake of the bottom heating element is about 1 kW.

[0023] In the preferred embodiment of the present application, the ring-shaped heating element is operated during the heating phase with a power intake corresponding to 180% to 250% of the power intake of the bottom heating element. By providing the major part of the heat via the ring-shaped heating element, the heat transfer from the bottom is limited in order to achieve a uniform browning on all sides of the food products without having to turn these food products during the heating.

[0024] In the preferred embodiment of the method presented herein, the predetermined second hysteresis, i.e. the temperature difference value by which the temperature within the oven cavity can drop during the holding phase, and which triggers the start of the deep-frying phase when reached, is preferably in the range of 5 K to 20 K, and most preferably about 10 K.

[0025] The predetermined third hysteresis, i.e. the temperature overshoot to which the oven cavity is heated to during the deep-frying phase, is preferably in the range of 5 K to 20 K, and most preferably about 10 K.

[0026] In order to achieve the best deep-frying results, both the ring-shaped heating element and the bottom heating element are operated with maximum power intake during the deep-frying phase. As mentioned above, taking into account that the bottom heating element is operated intermittently during the deep-frying phase, such as being operable during 50% to 70% of the deep-frying phase, the total power intake of the deep-frying phase can be kept below 3 kW in order to provide sufficient safety margins for operating the cooking oven in private households with only a few individual fused power circuits, and thus the maximum power intake of individual devices should be limited in these households.

[0027] While heating elements configured to be operated at different power levels can be employed, taking into account that in the various steps of the present method, the ring-shaped heating element is either continuously operated or not operable at all, the construction of the cooking oven can thus be simplified by employing a ring-shaped heating element configured with a constant power intake.

[0028] In case larger food items are to be processed which require a longer preparation time to be fully cooked, the method can comprise an additional step after the frying stage in which only the ring-shaped heating element is operated while the bottom heating element is switched off. While this additional heating step serves to provide heat to properly cook the interior of the larger food items where it takes more time for the heat to reach the interior of these food items, in this additional step only the ring-shaped heating element is operated in order to avoid overheating of the bottom side of the food items.

[0029] In an additional step which can be applied when processing larger food items, the temperature of the oven cavity can be reduced to a temperature in the range of 120°C to 170°C, preferably 130°C to 160°C, by limiting the heat provided by the ring-shaped heating element accordingly, in order to allow sufficient time to also cook the interior of these larger food items, but at the same time only cause a small amount of additional browning.

[0030] In a preferred embodiment, the method of the present application is performed using a tray having a discontinuous surface for placing food products, such as a plurality of holes or perforations distributed over the surface of the tray on which the food products can be placed. In order to provide for a uniform heating of these food products, the perforated tray is preferably arranged within the cooking cavity so as to be centered with respect to the ring-shaped element and the fan, i.e. most of the oven will be at the center level of the oven cavity.

[0031] In order to avoid soiling the bottom of the oven cavity during the use of a perforated tray, such as due to the dripping of the oil component of the food products which is released from these food products after heating, the perforated tray is preferably used together with an oil drip tray which is inserted into the oven cavity at the lowest level so as not to affect the supply of cooking heat.

[0032] An example of a particularly preferred perforated tray is disclosed in EP 3 113 576 B1 which can advantageously be used in the method presented herein.

[0033] When using a tray having a discontinuous surface for placing food products, particularly good cooking results can be achieved where the discontinuous surface for placing food products has a plurality of holes which account for at least 45% of the surface.

[0034] As pointed out above, the present method provides a control method for operating a cooking oven in a deep-frying procedure which allows for deep-frying food products in an "oil-free frying" mode, wherein the frying is not performed in a pool of frying oil in which the food products are submerged, but wherein the frying is achieved by placing the food products to be processed on a cooking tray which is placed within the oven cavity and then operating the heating means of the cooking oven in a certain way.

[0035] Compared to conventional oil-free frying or air-frying methods, such as the one set forth in the above cited EP 2 704 526, the present method achieves a higher heat transfer in the first phase of the method, and without the need to use microwaves. In case the oven cavity is heated to a temperature higher than the set temperature during the heating phase, this heating phase provides a faster heat transfer on the outside of the food, which serves to increase the water evaporation on the surface of the food products, which allows to achieve a crispy texture at the surface of the processed food products.

[0036] In each of the separate phases of the present method, by operating the bottom heating element intermittently or by turning it off completely, the present method effectively avoids overheating of the bottom side of the food products, and therefore does not require a manual turning of the food products during the cooking process. Therefore, the present control method allows to carry out the food preparation process in a fully automated manner, with no need for user intervention. Therefore, the frying function can be provided as a pre-programmed control scheme, which the user can select by simply selecting the "fry" function, and optionally additionally selecting the food category to be cooked, such as French fries, potato pieces, potato nuggets, potato strips or potato balls, fish sticks, breaded fish, fish and fries, chicken nuggets, breaded chicken, spring rolls, egg rolls, etc., in order to adjust the operating parameters of the cooking oven to further improve the cooking results. BRIEF DESCRIPTION OF DRAWINGS

[0037] The present application will be described in further detail with reference to the accompanying drawings, wherein further features, embodiments and advantages will be derived from the drawings, in which:

[0038] Figure 1 is a graphical representation of the temperature, voltage and total power consumption of a cooking oven operated according to the method set forth herein; and

[0039] Figure 2 A conventional control method is illustrated. DETAILED DESCRIPTION

[0040] As Figure 1 illustrated, as shown in the operating graph of a cooking oven operated according to the method set forth herein, upon selection of the slim fry function, the oven performs a heating phase, in which the oven cavity is heated from room temperature to a temperature corresponding to the set temperature plus a first hysteresis.

[0041] Both the set temperature and the first hysteresis are preferably set automatically by the device after the user has initiated an oil-free frying operation, such as by selecting an "oil-free frying" option from a list of available cooking programs, the function preferably being further specified by the user selecting the specific food product he or she wishes to process from a list, such as a drop-down menu. Based on the user selection, the program control selects the appropriate program parameters, such as the set temperature, the value of the first hysteresis, the value of the second hysteresis and the value of the third hysteresis, the duration of the individual program phases, the power level of the ring heating element and optionally the bottom heating element, the on-off cycle of the bottom heating element, etc.

[0042] Figure 1 An exemplary graph of a cooking stove with a 1 kW bottom heating element and a 2.3 kW ring element is shown, both elements being operated in an on-off mode in the exemplary embodiment shown, i.e. either at their full power level or being switched off.

[0043] Figure 1 An embodiment employing a set temperature of 200 °C is shown. With a first hysteresis of 10% of the set temperature employed in the initial heating phase, in the heating phase the stove cavity is heated to a temperature of 220 °C by continuously operating the 2.3 kW ring element and by simultaneously operating the 1.0 kW bottom heating element in an intermittent manner. To this end, in the example shown the bottom heating element is repeatedly switched on and off in a certain fixed cycle, in the example shown the fixed cycle comprising equal on and off phases of 48 s.

[0044] Upon reaching the temperature of 220 °C, the heating phase is terminated and the cooking stove switches to a holding phase in which both the bottom heating element and the ring heating element are non-operational.

[0045] In view of the fact that the graph shows the overall power consumption of the stove, including in addition to the heating elements also the fan, the interior lighting and the device control, during the holding phase the power curve does not drop to zero, but to a small value, which is indicative of the power consumption of such additional device components.

[0046] Without providing heat to the stove cavity during the holding phase, the temperature gradually drops until a temperature in the stove cavity is reached which corresponds to the set temperature of 200 °C minus a second hysteresis, in the embodiment shown the second hysteresis being set to a value of 5% of the set temperature. Upon the temperature in the stove cavity dropping from 200 °C to 190 °C during the holding phase, the stove control initiates a frying phase. In the embodiment shown, both the bottom heating element and the ring heating element are operated intermittently, i.e. being switched on and off simultaneously in a cycle similar to the cycle of the bottom heating element during the heating phase. Thus, during the frying phase the temperature within the stove cavity gradually increases until a temperature in the stove cavity is reached which corresponds to the set temperature plus a predetermined third hysteresis.Figure 1 An example is shown where this third hysteresis value is 5% of the set temperature. Therefore, the frying stage terminates when the temperature inside the oven cavity reaches 210°C.

[0047] Although Figure 1 In the illustration shown, the frying process ends at this stage, but the oven door remains closed for a certain period of time (about 3 minutes here), thus providing an additional holding period until the oven door is opened and the temperature inside the oven cavity drops rapidly.

[0048] In the case of processing larger foods, such as breaded fried fish or large stuffed rolls, a subsequent additional heating stage can be provided, in which the bottom heating element is turned off and heat is supplied to the oven cavity through the annular heating element. Preferably, this additional heating is performed at a temperature much lower than the set temperature, for example, 40K lower than the set temperature. This can be implemented by continuously operating the annular heating element at a lower power level, by intermittently operating the annular heating element in a corresponding cycle, or by a combination of both.

[0049] Figure 2 A conventional heating method for a radiant heating source, such as a heater or furnace heater for a glass-ceramic kitchen stove, is shown, which is described in further detail in EP 2 887 763A1. Figure 2 The demonstration shows the standard operation, in which, in the first stage 145, when the corresponding heating zone is turned on, the heater operates at a maximum or high power level to provide rapid heating to the heating zone, and where the power level is reduced to a lower level after a certain temperature level is reached.

[0050] Therefore, such as Figure 2 As depicted, during the first phase 145, the heater operates at full load, causing the heater's pulse-width modulated power curve 112 to exhibit a continuous maximum value 120. During the first phase 145, the temperature of the heating zone increases with a maximum gradient 110, depending on the thermal inertia of the heat source. Once the set temperature allocated for the power level selected by the user is reached, the power supply operates at a lower power level during the second phase 150, where the heater operates intermittently to provide less heat to the heating zone. Therefore, during this low-power phase, the pulse-width modulated power signal exhibits a peak value 125 at the full power level and a valley value 130 at the zero power level.

[0051] like Figure 2 As further shown, when switching from a high power level to a low power level, after reaching the set temperature of 170, the temperature curve can rise above the set temperature due to thermal inertia until a certain transition period is reached to achieve the final temperature of 180, which corresponds to the power level selected for the second stage 150.

[0052] As set out in EP 2 887 763 Al, when switching from a higher power level to a lower power level, the overshoot in temperature can be mitigated by reducing the ratio of on / off operations at the beginning of the second phase, such that the pulse width modulated power profile 112 shows shorter peaks and longer valleys until the required temperature level 180 is reached.

Claims

1. A control method for operating a cooking oven in a frying program configured for a predetermined set temperature, the cooking oven having an oven cavity, a tray arranged within the oven cavity, a bottom heating element for heating the bottom of the oven cavity, a fan located at a rear wall of the oven cavity, and an annular heating element surrounding the fan, the method comprising the following phases: (a) a heating stage, wherein, the annular heating element is continuously operated and the bottom heating element is intermittently operated, the heating phase being carried out until a temperature of the oven cavity is reached, the temperature corresponding to the set temperature plus a predetermined first hysteresis; (b) a subsequent holding phase in which the bottom heating element and the annular heating element are non-operational; and (c) a frying phase carried out after a temperature within the oven cavity is reached, the temperature corresponding to the set temperature minus a predetermined second hysteresis, the frying phase comprising continuously or intermittently operating the annular heating element and intermittently operating the bottom heating element in order to raise the temperature within the oven cavity to a temperature corresponding to the set temperature plus a predetermined third hysteresis.

2. The method of claim 1, wherein, the fan is operational during all phases.

3. The method of claim 1 or 2, wherein, the intermittent operation of the heating elements comprises intermittently operating the respective heating element so as to be operational during 50% to 70% of the respective phase, during the heating phase and / or during the frying phase.

4. The method of claim 3, wherein, the intermittent operation comprises periodically switching the heating element so as to be alternately operated at a first power level and a second power level, or periodically turned on and off.

5. The method of claim 1 or 2, wherein, the predetermined first hysteresis corresponds to 5% to 15% of the set temperature.

6. The method of claim 5, wherein, the predetermined first hysteresis corresponds to 10% of the set temperature.

7. The method of claim 1 or 2, wherein, the set temperature is in the range of 180°C to 220°C.

8. The method of claim 7, wherein, the set temperature is 200°C.

9. The method of claim 1 or 2, wherein, during the heating phase, the annular heating element is operated at a power intake corresponding to 180% to 250% of the power intake of the bottom heating element.

10. The method of claim 1 or 2, wherein, the predetermined second hysteresis is in the range of 5K to 20K.

11. The method of claim 10, wherein, the predetermined second hysteresis is 10K.

12. The method of claim 1 or 2, wherein, the predetermined third hysteresis is in the range of 5K to 20K.

13. The method of claim 12, wherein, the predetermined third hysteresis is 10K.

14. The method of claim 1 or 2, wherein, during the frying phase, both the annular heating element and the bottom heating element are operated at maximum power intake.

15. The method of claim 1 or 2, wherein, the annular heating element is configured for constant power intake.

16. The method of claim 1 or 2, further comprising: an additional step after the frying phase in which only the annular heating element is operational while the bottom heating element is turned off.

17. The method of claim 16, wherein, in the additional step, the temperature of the oven cavity is lowered to a temperature in the range of 120°C to 170°C.

18. The method of claim 17, wherein, in the additional step, the temperature of the oven cavity is lowered to a temperature in the range of 130°C to 160°C.

19. The method of claim 1 or 2, the method being terminated after a predetermined cooking time is reached.

20. The method of claim 1 or 2, the method being carried out using a tray having a discontinuous surface for placing food products.

21. The method of claim 20, wherein, the discontinuous surface for placing food products has a plurality of holes, the holes occupying at least 45% of the surface. the discontinuous surface for placing food products has a plurality of holes, the holes occupying at least 45% of the surface.

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