CN114514404A - Method for operating a cooking oven - Google Patents

Abstract

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

Description

Method for operating a cooking oven

The present invention relates to a method for operating a cooking oven, in particular 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 a bottom of the oven cavity, a fan located at a rear wall of the oven cavity, and a ring-shaped heating element surrounding the fan.

Background

The present invention therefore relates to a control method for operating a convection oven in a frying program intended to simulate the frying of frozen convenience food in a substantially fat-free manner, i.e. without immersing the food product in hot fat, such as oil, but wherein a similar cooking result as in standard frying is to be achieved.

In EP 2704526, a microwave oven is disclosed, which comprises a grill element and a convection heating element in addition to a microwave unit. The oven may be operated in a frying cooking mode, wherein the food is not only heated by microwaves, but is further heated by the grill and/or the convection heating element to both heat the core of the food product and simultaneously fry the surface of the food product.

Although EP 2704526 is limited to ovens that use microwave units to provide heat to food products, such that the control scheme proposed therein does not seem to be directly transferable to other oven types, such as convection ovens, the frying cooking mode proposed in this document is further considered disadvantageous, since microwave heating leads to uneven water evaporation, especially in the first stage of the cooking process. That is, particularly when the food product being processed has a small cross-sectional area, such as in thin french fries, the microwaves penetrate the food product completely, which results in the interior of the food product drying out before the outer surface of the food product reaches a sufficient degree of browning.

Attempting to simulate frying in a conventional convection oven by heating the food product with grill elements disposed at the top of the oven cavity is problematic because the simulation results in uneven browning. Thus, considering that more heat is transferred to the top side of the food product, browning is much faster on the top side than on the bottom side, so that to achieve uniform browning, it is necessary to turn the food product over during the cooking process.

In view of the above-mentioned drawbacks 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 procedure, which method allows to achieve better cooking results than the known methods.

The present application solves the above object by providing a control method for operating a cooking oven in a frying program configured for a predetermined set temperature, the control method being as defined in claim 1.

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 a bottom of the oven cavity, a fan located at a rear wall of the oven cavity, and a ring-shaped heating element surrounding the fan. The method is therefore configured for a convection oven or for a cooking oven with convection heating, such as a so-called combined cooking oven, which can be heated not only by convection heating but also by at least one further heating method, such as radiation heating, induction heating, steam heating and microwave heating.

The method for operating a cooking oven in a frying program comprises several phases including a heating phase, a subsequent holding phase and a frying phase.

In the heating phase, the ring-shaped heating element is operated continuously and the bottom heating element is operated intermittently. That is, the ring-shaped heating element operates continuously, while the bottom heating element operates in a cyclic manner, wherein the bottom heating element is turned on and off, or operates at repeatedly varying power levels. In this way, a rapid heating of these food products to be processed is achieved, wherein, however, 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 over these food products during heating. In the heating protocol employed in the present method, the heating phase provides for faster heating of the food product as compared to other standard cooking procedures.

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 provides faster heat transfer on the exterior of the food, in terms of set temperature, which causes the moisture on the surface to evaporate faster, providing a more crispy texture.

In the hold phase after the heating phase, both the bottom heating element and the ring-shaped heating element are non-operational. During the holding phase, the thermal energy that has been transferred to the surface of the food products is allowed to penetrate into these food products, so as to propagate towards the centre of these food products. The holding phase is carried out until the temperature inside the oven cavity is reached, which corresponds to the set temperature minus a predetermined second hysteresis.

After such a later temperature is reached, a frying phase is initiated, during which the ring-shaped heating element is operated continuously or intermittently and the bottom heating element is operated intermittently in order to raise the temperature inside the oven cavity to a temperature corresponding to the set temperature plus a predetermined third hysteresis. During this frying phase, the oven temperature may thus be stepped up to the desired set temperature plus a set third hysteresis.

The frying stage may terminate after a period of 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.

The present method has been successfully tested in a variety of different instant food products (such as french fries, potato cakes, fish strips, fried fish breaded with breading, chicken nuggets, spring rolls, potato nuggets, crunchy rolls, etc.) and has the advantage over existing solutions of allowing good frying results comparable to conventional frying methods to be achieved, but in fat-free, oil-free frying or oil-less frying without the need to provide a frying fat bath for submerging the food products and without the need for the user to repeatedly turn the food products over to achieve uniform browning.

Preferred embodiments of the invention are defined in the dependent claims.

Preferably, the fan located at the rear wall of the oven cavity is operable during all phases to distribute air throughout the oven cavity and to feed air heated by the annular element surrounding the fan to the trays supporting the food products to be processed.

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.

The intermittent operation of the bottom heating element during this heating phase, and the similar intermittent operation of the bottom heating element and the optional ring-shaped heating element during the frying phase, may comprise periodically switching the respective heating element so that it may be operated alternately at a first power level and a second power level, or periodically switched on and off. Thus, for example, in a furnace comprising an annular element with a power intake of 2.3kW and a bottom heating element with a power intake of 1.0kW, the overall power intake of the furnace is cycled between 2.3kW and 3.3kW by operating the annular heating element continuously during a heating phase and operating the bottom heating element intermittently by periodically turning the bottom heating element on and off so as to be operable during 50% to 70% of the heating phase, wherein the overall average power intake of the furnace during the heating phase is limited to values below 3 kW.

The predetermined first hysteresis, i.e. the temperature overshoot above the set temperature to which the oven cavity is heated during the heating phase, may correspond to 5% to 15%, preferably about 10%, of the set temperature. That is, while it is preferred that the set temperature be in the range of 180 ℃ to 220 ℃, when the process is carried out at a set temperature of, for example, 200 ℃, the first hysteresis preferably has a value of 10 ℃ to 30 ℃, preferably about 20 ℃.

That is, although a temperature of about 170 ℃ to 180 ℃ is considered to be optimal in the conventional frying method, the above-mentioned setting temperature takes into consideration that the method does not use an oil bath to immerse the foods to be fried, but uses a heated gas flow, which has a lower heat transfer than the oil bath.

While in a preferred embodiment the annular heating element has a power intake of 1.8kW to 2.5kW, preferably 2.0kW to 2.4kW, such as e.g. about 2.3kW, the bottom heating element preferably has a power intake of 0.8kW to 1.5kW, wherein the preferred power intake of the bottom heating element is about 1 kW.

In a preferred embodiment of the invention, 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 a substantial portion of the heat via the annular heating element, heat transfer from the base is limited to achieve uniform browning on all sides of the food product without having to invert the food product during heating.

In a preferred embodiment of the method proposed herein, a predetermined second hysteresis, i.e. a temperature difference value by which the temperature in the oven cavity may fall during the holding phase, and the start of the frying phase is triggered when this temperature difference value is reached, preferably in the range of 5K to 20K, preferably about 10K.

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

In order to achieve an optimal frying effect, both the ring-shaped heating element and the bottom heating element are operated with a maximum power intake during the frying phase. As mentioned above, considering that the bottom heating element is operated intermittently during the frying phase, such as being operable during 50% to 70% of the frying phase, the total power intake of the frying phase may be kept below 3kW in order to provide a sufficient safety margin for operating the cooking oven in private homes having only a small number of individually blown power supply circuits, and thus in these homes the maximum power intake of the individual devices should be limited.

Although heating elements configured to operate at different power levels may be employed, by employing an annular heating element configured with a constant power intake, the construction of the cooking oven may be simplified, considering that in various steps of the method, the annular heating element is either continuously operated or not operable at all.

In case larger food products are to be processed which require a longer preparation time to be fully cooked, the method may 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. Although this additional heating step serves to provide heat for proper cooking of the interior of larger food products, wherein more time is required for the heat to reach the interior of the food products, in this additional step only the annular heating element is operated in order to avoid overheating of the bottom side of the food products.

In an additional step that may be applied when processing larger food products, the temperature of the oven cavity may be reduced to a temperature in the range of 120 ℃ to 170 ℃, preferably 130 ℃ to 160 ℃, by limiting the heat provided by the annular heating element accordingly, in order to allow sufficient time to also cook the interior of these larger food products, but at the same time cause only a small amount of additional browning.

In a preferred embodiment, the method of the invention is carried out using a tray having a discontinuous surface for placing the food product, such as a plurality of holes or perforations distributed over the surface of the tray on which the food product can be placed. In order to provide an even 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 ovens will be at the central level of the oven cavity.

In order to avoid soiling of the oven cavity bottom during use of the perforated tray, for example due to dripping of fatty components of the food products released from the food products after heating, the perforated tray is preferably used with a drip tray which is inserted into the oven cavity at a minimum level so as not to interfere with the supply of cooking heat.

An example of a particularly preferred perforated tray, which may advantageously be used in the method proposed herein, is disclosed in EP 3113576B 1.

Particularly good cooking results can be achieved when using a tray having a discontinuous surface for placing food products, wherein the discontinuous surface has a plurality of holes, which holes account for at least 45% of the surface.

As indicated above, the present method provides a control method for operating a cooking oven in a frying program, which allows frying food products in an "oil free frying" mode, wherein frying is not performed in a frying fat bath 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 placed in the oven cavity and then operating the heating means of the cooking oven in some way.

The present process achieves higher heat transfer in the first stage of the process compared to conventional oil-free or air-fried processes, such as the process proposed in EP 2704526 acknowledged above, and does not require the use of microwaves. In case the oven cavity is heated to a temperature above the set temperature during the heating phase, the heating phase provides a faster heat transfer on the outside of the food products, which heat transfer serves to increase the evaporation of moisture on the surface of the food products, which allows to achieve a crispy texture at the surface of the processed food products.

By intermittently operating the bottom heating element or by completely switching off the bottom heating element to limit the heat provided from the bottom heating element at each of the separate stages of the method, the method effectively avoids overheating of the bottom side of the food products and thus does not require manual turning of the food products during the cooking process. Thus, the present control method allows to perform the food preparation process in a fully automated manner, wherein no user intervention is required. Thus, the frying function may be provided as a preprogrammed control scheme that the user may select by simply selecting the "fry" function, and optionally additionally selecting the type of food to be cooked, such as french fries, potato pieces, potato balls, potato strips or balls, fish strips, breaded fish, fish and french fries, chicken pieces, chicken breads, spring rolls, crisped rolls, and the like, in order to adjust the operating parameters of the cooking oven to further improve the cooking result.

Drawings

The invention will be described in additional detail with reference to the drawings, from which additional features, embodiments and advantages are derived, wherein:

fig. 1 is a graphical representation of temperature, voltage and total power consumption of a cooking oven operating according to the method presented herein; and

fig. 2 shows a conventional control method.

Detailed Description

As shown in fig. 1, as demonstrated by the operational diagram of the cooking oven operating according to the method proposed herein, when the oil-free frying (slim) function is selected, the oven performs a heating phase in which, starting from room temperature, the oven cavity is heated to a temperature corresponding to the set temperature plus a first hysteresis.

Both the set temperature and the first hysteresis are preferably set by the apparatus control automatically upon the user initiating an oil-free frying operation, such as by selecting an "oil-free frying" option from a list of available cooking programs, which function is preferably further specified by the user selecting a particular food product from a list, such as a pull-down menu, that he or she wishes to process. Based on the user selection, the program control selects 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 respective program phase, the power level of the ring-shaped heating element and optionally of the bottom heating element, the switching cycle of the bottom heating element, etc.

Fig. 1 shows an exemplary diagram of a cooking oven with a 1kW bottom heating element and a 2.3kW ring element, both elements being operated in switched mode, i.e. either at their full power level or being switched off, in the exemplary embodiment shown.

Fig. 1 shows an example using a set temperature of 200 c. In case of a first hysteresis of 10% of the set temperature in the initial heating phase, the furnace chamber was heated to a temperature of 220 ℃ in the heating phase by continuously operating the 2.3kW ring elements and by simultaneously operating the 1.0kW bottom heating elements 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, which in the example shown comprises an equal length switching phase of 48 s.

After reaching a temperature of 220 ℃, the heating phase is terminated and the cooking oven switches to a holding phase in which both the bottom heating element and the ring-shaped heating element are non-operational.

Considering that the figure shows the overall power consumption of the oven, and therefore in addition to the hearing element, 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 indicating the power consumption of such further device components.

In case no heat is provided to the oven cavity during the holding phase, the temperature is gradually decreased until a temperature in the oven cavity is reached, which corresponds to a set temperature of 200 ℃ minus a second hysteresis, which in the illustrated embodiment is set to a value of 5% of the set temperature. Thus, after the temperature in the oven cavity has decreased from 200 ℃ to 190 ℃ during the holding phase, the oven control initiates the frying phase. In the illustrated embodiment, both the bottom heating element and the ring-shaped heating element are operated intermittently, i.e. are turned 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 in the oven cavity is gradually increased until a temperature in the oven cavity is reached which corresponds to the set temperature plus a predetermined third hysteresis. Fig. 1 illustrates an example in which the value of this third hysteresis is 5% of the set temperature. Thus, the frying phase is terminated when the temperature in the oven cavity reaches 210 ℃.

Although in the illustration shown in fig. 1 the frying process is terminated at this stage, the oven door remains closed for a certain duration (here about 3 minutes), providing an additional holding stage until the oven door is opened and the temperature in the oven cavity therefore drops rapidly.

In case larger food products, such as fried fish or larger rolls of filling material, which are breaded on, are to be processed, a subsequent additional heating phase may be provided, in which the bottom heating element is switched off and heat is provided to the oven cavity by means of the ring-shaped heating element. Preferably, this additional heating is performed at a temperature much lower than the set temperature, such as 40K lower than the set temperature, which may be performed by continuously operating the annular heating element at a lower power level, by intermittently operating the annular heating element in corresponding cycles, or by a combination of both measures.

Fig. 2 shows a conventional heating method for a radiant heating source, such as a heater of a glass ceramic kitchen range or a furnace heater, which method is described in further detail in EP 2887763 a 1. Fig. 2 illustrates a conventional operation wherein, in a first phase 145, after opening the respective heating zone, the heater is operated at a maximum or high power level to provide rapid heating of the heating zone, and wherein after a certain temperature level is reached, the power level is reduced to a lower level.

To this end, as depicted in fig. 2, during the first phase 145, the heater is operated at full load, such that the pulse width modulated power curve 112 of the heater shows a continuous maximum 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. After reaching the set temperature assigned to the power level selected by the user, the power supply operates at a lower power level during the second phase 150, wherein the heater operates intermittently in order to provide less heat to the heating zone. Thus, during such a low power phase, the pulse width modulated power signal shows a peak 125 at full power level and a valley 130 at zero power level.

As further shown in fig. 2, when switching from a high power level to a low power level, after reaching the set temperature 170, the temperature profile may rise above the set temperature due to thermal inertia until after a certain transition period, a final temperature 180 is achieved, which corresponds to the power level selected for the second stage 150.

As proposed in EP 2887763 a1, 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 operation at the beginning of the second phase, so that the pulse width modulated power curve 112 shows shorter peaks and longer troughs until the desired temperature level 180 is reached.

Claims (16)

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 a bottom of the oven cavity, a fan located at a rear wall of the oven cavity, and a ring-shaped heating element surrounding the fan, the method comprising the following phases:

(a) a heating phase, in which the annular heating element is operated continuously and the bottom heating element is operated intermittently, the heating phase being carried out until a temperature of the oven chamber is reached, the temperature corresponding to the set temperature plus a predetermined first hysteresis;

(b) a subsequent holding phase, wherein the bottom heating element and the ring-shaped heating element are non-operational; and

(c) a frying phase performed after reaching a temperature inside the oven cavity, which temperature corresponds to the set temperature minus a predetermined second hysteresis, the frying phase comprising operating the ring-shaped heating element continuously or intermittently, and operating the bottom heating element intermittently, so as to raise the temperature inside 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, during the heating phase and/or during the frying phase, the intermittent operation of the heating elements comprises intermittently operating the respective heating elements so as to be operational during 50% to 70% of the respective phase.

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

5. The method of any one of the preceding claims, wherein the predetermined first hysteresis corresponds to 5-15%, preferably about 10%, of the set temperature.

6. The method of any one of the preceding claims, wherein the set temperature is in the range of 180 ℃ to 220 ℃, preferably about 200 ℃.

7. The method of any one of the preceding claims, wherein during the heating phase, the annular heating element is operated at a power intake corresponding to 180-250% of the power intake of the bottom heating element.

8. The method of any one of the preceding claims, wherein the predetermined second hysteresis is in the range of 5K to 20K, preferably about 10K.

9. The method of any one of the preceding claims, wherein the predetermined third hysteresis is in the range of 5K to 20K, and preferably about 10K.

10. The method of any one of the preceding claims, wherein during the frying phase both the annular heating element and the bottom heating element are operated at maximum power intake.

11. The method of any one of the preceding claims, wherein the annular heating element is configured for constant power intake.

12. The method of any of the preceding claims, further comprising: an additional step after the frying phase, wherein only the ring-shaped heating element is operated, while the bottom heating element is switched off.

13. The method of claim 12, wherein in the additional step the temperature of the furnace chamber is reduced to a temperature in the range of 120 ℃ to 170 ℃, preferably 130 ℃ to 160 ℃.

14. The method of any preceding claim, which terminates after a predetermined cooking time is reached.

15. The method of any one of the preceding claims, which is carried out using a tray having a discontinuous surface for placement of a food product.

16. The method of claim 15, wherein the discontinuous surface for placement of food products has a plurality of holes that comprise at least 45% of the surface.

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