EP1767860B1

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Info

Publication number: EP1767860B1
Application number: EP05108734A
Authority: EP
Inventors: Tamara Distaso; Stefania Fraccon; Ricardo Garcia-Padron; Ingrid Johnson
Original assignee: Whirlpool Corp
Current assignee: Whirlpool Corp
Priority date: 2005-09-21
Filing date: 2005-09-21
Publication date: 2011-09-21
Anticipated expiration: 2025-09-21
Also published as: PL1767860T3; EP1767860A1; ES2371757T3

Description

The present invention relates to a method for controlling the operation of a combination food cooking oven adapted to perform cooking process by conventional electric elements, by means of microwave heating and by means of the introduction of steam.

Background of the Invention

The process of cooking food in an oven is commonly known to be carried out according to widely differing conditions and manners depending on the results and effects that have to be reached. One of the most common methods of cooking food is through electric or gas burner heating elements wherein there occurs radiant, conduction and convection heat transfer.
Microwave cooking is also a common method of cooking food. Many modem kitchens are equipped with a microwave oven.
The benefits of cooking food with steam are well recognized and include accelerating the cooking process, moisturizing the food during the cooking process and preserving flavor, vitamins, and nutrients. Additionally, cooking with steam results in more homogeneously cooked food item having an appearance that appeals to the senses.
In order to be able to aggregate the advantageous features of these different cooking methods, various types of combination ovens have been disclosed.
U.S. Pat. Appl.US 2003/0230569 discloses a cooking oven having a steam generating part 15, a convection heater 19, and a magnetron 13. The steam generating part is controlled to heat based on temperature information of the temperature detecting part.
EP 0 698 768 B1 discloses a combined gas-microwave cooking oven with steam cooking facility. In this patent, an oven construction is described and claimed but there is no teaching regarding the method of optimizing the combination of the different heating methods.
US2004/232140 A1 discloses a high frequency heating apparatus with a steam generation function.
While the above described prior proposed oven systems include the use of conventional heat, microwave energy and steam, these solutions do not address adequately the problem of controlling the input of conventional heat, microwave energy and steam to a cook food in an optimal way and the benefits of cooking with a combination of conventional heat, microwave energy and steam are not fully realized.

Summary of the Invention:

According to the invention, a method of operating an oven (10) and controlling the introduction of conventional heat, microwave energy and steam to achieve optimal cooking results. The present invention is responsive to food type and food size to provide the ideal input of steam and microwave energy, where food size can be input directly or inferred from input cooking time.
The oven (10) includes a heating system (35), a microwave system (46) and a steam system (50). Acontrol panel 28 is provided for inputting data to acontroller 30. The oven operates according to a method which includes first inputting information regarding food type and at least one additional parameter. The duration of a first cooking step (74) and a second cooking step (78) are then calculated. Steam is introduced into the oven cavity (14) during the first cooking step while operating the heating system (35) to heat the oven cavity (14) to an oven set point temperature (TEMP₂). After the first cooking step, the microwave system (46) is energized for a first portion of the second cooking step while maintaining the oven cavity (14) at the oven set point temperature. The heating system (35) is de-energized at the end of the second cooking step. The one additional parameter is preferably a data input corresponding to the weight and/or size of the food item. The controller (30) determines an overall cooking period (80) and the duration of the first cooking step (76) is a fraction or percentage of the overall cooking period where the fraction or percentage of the overall cooking period is controlled according to the input food type and other data such as cooking time or weight.

Brief Description Of The Drawings

The present invention will be more apparent from the accompanying drawings, which are provided by way of non-limiting example and in which:

FIG. 1 is a perspective view of a oven embodying the principles of the present invention.
FIG. 2 is a schematic view of the oven embodying the principles of the present invention, and showing the heating system, microwave system and steam system.
FIG. 3 is a schematic illustration of the control unit and elements of the present invention.
FIG. 4 is a schematic diagram illustrating a method of cooking fish and vegetables with steam according to one embodiment of the present inventions.
FIG. 5 is a graph showing the input of conventional heat, microwave energy and steam over time during the operation of the oven of the present invention.
FIG. 6 is a flow chart illustrating the operation and control of the oven of the present invention.

Detailed Description Of The Preferred Embodiments

Referring now to the figures,Fig. 1 illustrates an exemplaryautomatic household oven 10 that can be used to implement a method for cooking food using a combination of conventional heating, high frequency or microwave heating, and steam generation according to the invention. Theoven 10 comprises acabinet 12 with an open-face cooking cavity 14 defined by cooking cavity walls: a pair of spacedside walls 16, 18 joined by atop wall 20, abottom wall 22, and a rear wall 23 (Fig. 2). Adoor 24 pivotable at a hinge selectively closes thecavity 14. When thedoor 24 is in the open position, a user can access thecavity 14, while thedoor 24 in the closed position prevents access to thecavity 14 and seals thecavity 14 from the external environment. Theoven 10 is shown as a cooker or cooking range having surface heating elements, however, theoven 10 may be of any known configuration including a countertop type oven.
Theoven 10 further comprises acontrol panel 28 accessible to the user for inputting desired cooking parameters, such as temperature and time, of manual cooking programs or for selecting automated cooking programs or functions and microwave use. Thecontrol panel 28 communicates with acontroller 30 located in thecabinet 12, as shown inFig. 2. Thecontroller 30 can be a proportional-integral-derivative (PID) controller or any other suitable controller, as is well-known in the automatic oven art. Thecontroller 30 stores data, such as default cooking parameters, the manually input cooking parameters, and the automated cooking programs, receives input from thecontrol panel 28, and sends output to thecontrol panel 28 for displaying a status of theoven 10 or otherwise communicating with the baker. Additionally, thecontroller 30 includes atimer 32 for tracking time during the manual and automated cooking programs and acooling fan 34 located in thecabinet 12 for drawing cooling air into thecabinet 12 and directing the air toward thecontroller 30 to avoid overheating of thecontroller 30 by heat conducted from thecavity 14. The cooling air flows around the outside of thecooking cavity walls 16, 18, 20, 22, 23.
With continued reference toFig. 2, theoven 10 further comprises aconventional heating system 35 having anupper heating element 36, commonly referred to as a broiler, and alower heating element 38. The schematic illustration of theFig. 2 shows thelower heating element 38 as being hidden or mounted beneath the cookingcavity bottom wall 22 in aheating element housing 40. Heat from thelower heating element 38 conducts through thebottom wall 22 and into thecavity 14. Alternatively, thelower heating element 38 can be mounted inside thecavity 14, as is well-known in the oven art. Further, the upper andlower heating elements 36, 38 can be mounted at theside walls 16, 18 of thecavity 14, as disclosed inU.S. Patent No. 6,545,251 to Allera et al. Theheating system 35 according to the illustrated embodiment further comprises aconvection fan 42 that circulates air and steam, when present, within thecavity 14. Theconvection fan 42 can be any suitable fan and can be mounted in any suitable location of thecavity 14, such as in therear wall 23. A ring shapedconvection heater 45 may be positioned about thefan 42.
Theoven 10 used in the method of the present invention also includes amicrowave heating system 46 including magnetron 47 as a high frequency generating part or microwave heating means. Themagnetron 46 may be disposed in any convenient or common location such as the space under theoven chamber 14 or along the top or side of theoven chamber 14. Awave guide 48 is provided for directing high frequency energy into theoven chamber 14. A stirrer (not shown) may be disposed at a position receiving the high frequency generated from the magnetron.
In addition to theconventional heating system 35 and themicrowave heating system 46 described above, theoven 10 comprises asteam system 50 preferably mounted within thecabinet 12 and configured to introduce steam into thecavity 14. Thesteam system 50 in the illustrated embodiment comprises aboiler 52 that heats water stored in thesteam system 50. However, thesteam system 50 can be any suitable system that is capable of introducing steam directly into thecavity 14 and varying the rate of steam generation. This may be accomplished by varying the duty cycle of aboiler 52 to increase or decrease the amount of steam generated. Alternatively, the steam system may include introducing water that is turned into steam in thecavity 14 and is not limited to the system shown schematically inFig. 2.
FIG. 3 is a block diagram that schematically illustrates a control system for the present invention. This system comprises the controller ormicroprocessor 30 which operably communicates with thecontrol panel 28 as described havinginput device 62 anddisplay device 68. Thecontroller 30 instructs theheating system 35 to activate or deactivate theupper heating element 36, thelower heating element 38, and theconvection fan 42, either all together, individually, or in groups, and provides instructions regarding the desired temperature of thecavity 14 and the rate at which theheating system 35 heats thecavity 14. Thecontrol unit 30 operates themicrowave system 46 and it can be understood that there may be control relay drive units selectively energizing and controlling a high voltage transformer (not shown) for driving the magnetron microwave element 47. Similarly, thecontroller 30 instructs thesteam system 50 to activate or deactivate theboiler 46 and provides instructions regarding the desired temperature of the water in thesteam system 50 in order to achieve the desired relative humidity in the cavity. Atemperature sensor 64 is provided for sensing the temperature of theoven cavity 14 and providing this input to thecontroller 30. A power supply (not shown) may also be provided.
As stated above, theexemplary oven 10 can be used to implement amethod 70, shown inFIG. 4, of cooking a food item with convention heat, microwave energy and with steam according to one embodiment of the invention. Themethod 70 comprises several steps during which theconventional heating system 35 andmicrowave heating system 46 operates to control a temperature of the food andcavity 14 and thesteam system 50 operates to control a relative humidity of thecavity 14. Before the first stage of themethod 70, the user prepares the food item as desired and places the food item and a corresponding food support, such as a cooking tray, if used, into thecavity 14step 72. The method is characterized as having adry preheating step 74 followed by afirst cooking step 76 and asecond cooking step 78. The first and second cooking steps form part of thetotal cooking period 80. Although it can be understood that some cooking occurs during thedry preheating step 74. The steps are defined by the operations of theheating system 35, themicrowave system 46 and thesteam system 50, as will be described in more detail below.
Steps of themethod 70 are shown in the corresponding graphFIG. 5. Fig. 5 is not intended to report actual behavior of the temperature and the relative humidity during themethod 70; rather,Fig. 5 represents a general behavior of these properties. It will be apparent to one of ordinary skill in the oven art that, in reality, the actual temperature and the actual relative humidity fluctuate about a target temperature and a target relative humidity during the operation of an oven.
Referring particularly toFig. 5, during thedry preheating step 74, theheating system 35 heats thecavity 14 to a first temperature at a first heating rate r₁, and thesteam system 50 is off or not activated so that thecavity 14 is relatively dry. According to one embodiment of the invention, the first temperature is the boiling point of water or 100 C. During thedry preheating step 74, the temperature of thecavity 14 is raised to at least the boiling point of water so that steam can be introduced into thecavity 14 during the subsequent steps. Preferably, the first heating rate is relatively fast so that thecavity 14 reaches the first temperature in a relatively short period of time. For example, a fast heating rate can correspond to operating theheating system 35 at substantially maximum capacity.
After the temperature of thecavity 14 reaches the first temperature or after a predetermined period of time, theheating system 35 continues to heat thecavity 14 to a second temperature at a second heating rate r₂, which occurs during the first cooking period. According to one embodiment of the invention, the second temperature is a cooking temperature, which can be entered manually by the user through theuser interface 28 or set by thecontroller 30 according to an automatic cooking cycle. The cooking temperature is selected or set, at least in part, based on the desired doneness of the food. Additionally, while the second heating rate can have any suitable value, the second heating rate is preferably less than the first heating rate. Once the cooking temperature is reached, theconventional heating system 35 maintains the temperature of thecavity 14 at the cooking temperature for the rest of the cooking cycle.
During thefirst cooking step 76, thesteam system 50 is operated to raise humidity of theoven cavity 14 but themicrowave system 46 is not energized. The duration of thefirst cooking step 76 is established from input by a user through thecontrol panel 28. The user inputs or selects the food type (FOOD TYPE) and at least one other parameter which corresponds to the food size or weight. The food size can be input directly by weight or through a scaled system such as selecting between "small", "medium" or "large". Alternatively, the food size can be inferred by thecontroller 30 from the user directly inputting the duration of theoverall cooking period 80 depending on the food type that is being cooked. Alternatively, the weight or size of the food item can be sensed through any known method for use in establishing the correct duration of the cooking steps. Where the user inputs food type and size/weight, thecontroller 30 establishes a duration for theoverall cooking period 80 according to an automatic program or pre-established lookup table which forms part of thecontroller 30. According to one embodiment of the invention, the duration of thefirst cooking step 76 is equal to a fraction or percentage (%) of the overall cooking period. The fraction or percentage of theoverall cooking period 80 is controlled according to an automatic program or pre-established lookup table which forms part of thecontroller 30.
Thesteam system 50 begins to introduce steam into the cavity during thefirst cooking step 76. Theboiler 52 can begin to preheat the water in thesteam system 50 prior to thefirst cooking step 76 so that the steam can be introduced into thecavity 14 at the beginning of thefirst cooking step 76, if desired. Introducing steam into thecavity 14 as soon as possible during thefirst cooking step 74 helps to ensure that the steam is present early in the cooking cycle for facilitating the cooking process. Thefirst cooking step 76 ensures that the food is not exposed to dry, high temperature environment, which can cause the food to dry out. Thus, the benefits of cooking with steam can be fully realized when the steam is introduced fairly quickly. Additionally, waiting until the temperature reaches at least the first temperature, which is preferably the boiling point of water, to introduce the steam into thecavity 14 ensures that the temperature of thecavity 14 is high enough to sustain steam in a vaporized state. As a result, the vapor will not condense in thecavity 14 and form water droplets on thewalls 16, 18, 20, 22, 23, or other items in thecavity 14. Formation of water droplets on porcelain, which is a material found on thecavity walls 16, 18, 20, 22, 23 of many ovens, can undesirably damage the material.
An important aspect of the present invention is that themicrowave heating system 46 remains de-energized during thefirst cooking step 76. This is to ensure that during the initial introduction of steam, the surface temperature of the food does rise to quickly or become to hot. The inventors have discovered that if the surface temperature of the food becomes to hot during this phase, the beneficial effects of the steam, noted above, are not achieved. The beneficial effects of a higher humidity environment are greatly enhanced when the food item is allowed to heat more slowly and when the surface temperature of the food item remain at or below the ambient temperature of thecooking cavity 14.
Following thefirst cooking step 76, thesecond cooking step 78 provides an opportunity for the food item to complete cooking. The duration of this period is the remainder or difference between theoverall cooking period 80 and thefirst cooking period 76. During the second cooking period, themicrowave system 46 may be energized to accelerate the cooking process. Additionally, there can optionally be an operation of thesteam system 50 for a limited period of time at the start of the second cooking period, andextra steam operation 82. Themicrowave system 46 may be de-energized near the end portion of the second cooking step to allow the food item being cooked to brown or crisp if desired.
Referring toFIG. 6, an implementation of themethod 50 with theoven 10 is presented. The cooking cycle is started, either before or after food is loaded into thecavity 14, by the user inputting a food type (FOOD TYPE) selection and either a food size (FOOD WEIGHT/SIZE) or cooking duration value, as shown instep 81 and described above. As shown insteps 82, theheating system 35 heats theoven cavity 14 and food items placed within theoven cavity 14. Optionally, depending on the type of food selected, themicrowave system 46 may be used during thedry preheat step 74, as shown instep 84. This occurs normally when cooking frozen items. It is also possible to include a microwave operation only step prior to thedry preheating step 74 dedicated to defrosting frozen food. When theoven cavity 14 reaches a first predetermined temperature TEMP₁, as shown atstep 86, the drypre-heat step 74 is completed. In the case themicrowave system 46 was energized, it is then de-energized,step 88.Steps 82, 84 and 86 form the drypre-heat step 74.
Entering into thefirst cooking step 76, thesteam system 50 is energized,step 90. The duration (T₁) of thefirst cooking step 76 is determined as described above, and is equal to a fraction or percentage (%) of theoverall cooking period 80. Steam is usually injected when the cavity temperature reaches about 100°C (TEMP₁ = 100°C) as shown inFIG. 4, with a first steam rate (SR₁) which is a relatively high duty cycle level. Steam is injected into the oven cavity for the first cooking step (T₁), shown atstep 82, which may be different for different food categories and it is related to the desired result, as discussed above.
After thefirst cooking step 76, the oven operates in thesecond cooking step 78 for the remainder of theoverall cooking period 80. In one embodiment, steam continues to be injected into theoven cavity 14 for a period of time where the steam injection rate is changed to second steam rate (SR₂) which is less than SR₁, shown atstep 94. This period of reduced steam input is shown insteps 96 and 98. During this initial portion of thesecond cooking step 78, themicrowave system 46 may be operated at a first duty cycle level (MW_DC2).
After a predetermined period of time, thesteam system 50 is de-energized, shown atstep 98, and the second cooking step is completed. During the remaining portion of thesecond step 76, theoven controller 30 may de-energize themicrowave system 46, as shown instep 100 and 102 such the final portion of the second cooking step is operated with just theheating system 35 to achieve good food browning, as shown at steps 104-106.
Throughout the entire cooking cycle, it can be understood that theheating elements 45 are energized to raise theoven cavity 14 to the desired temperature set point (TEMP_SETPOINT)· Theheating elements 45 may be energized in any particular combination in response to thetemperature sensor 64. This operation of theheating elements 45 occurs as a parallel operation, shown asstep 108, during the first, second and third cooking periods.
The steam injection scheme defined above improves the food quality due to the use of different steam rates. In the first cooking period, a higher level of relative humidity decreases the evaporation rate of the food being cooked, preserving the tenderness and the juiciness (meat, poultry) until the surface temperature reaches about 212°F (100°C) when a crust begins to form itself although normally 212 F (100°C) is not reached during the first cooking period. In the second cooking period, the steam rate is lowered and the surface of the food can continue to crisp while the food item cooks. During this step, the internal food temperature is allowed to increase giving a more homogeneous cooking.
The microwave energy contribution is also optimized in the present invention. Prior to the first cooking period, before the oven cavity reaches 100°C of the temperature cavity, microwave energy can be injected into the oven cavity to accelerate the initial heating. This microwave heating may not be activated for some food categories. In the first cooking step, microwave energy is not injected into the oven cavity as discussed above. In the second cooking step, the microwave element is energized at relatively low duty cycle MW_DC1, to accelerate the cooking rate. Finally, in the last portion of the second cooking step, where the steam duty cycle is stopped to help the formation of a food crust or browning, the microwave element can be activated or not in relation to the desired browning level and desired cooking speed.
It is possible to vary or otherwise alter certain aspects of themethod 50 without departing from the scope of the invention. For example, the dry preheating step can comprise multiple heating rates rather than a single heating rate, whereby the temperature of thecavity 14 is raised to a first preheat temperature at a first preheating rate and thereafter raised to a second preheat temperature at a second preheating rate different than the first preheating rate. An illustration of this example is heating thecavity 14 to about 90 °C in about 4 minutes and then heating the cavity to about 100 °C in about 2 minutes. By slowing down the heating of thecavity 14 before reaching the boiling point of water, theheating system 35 can more effectively heat thecavity 14 so that theentire cavity 14, including any spaces and items in thecavity 14, is uniformly heated to the boiling point of water. Furthermore, the cooking steps have been described above and shown inFig. 5 as maintaining the temperature of thecavity 14 at a constant second temperature. However, it is within the scope of the invention to vary the second or cooking temperature and, therefore, the temperature of thecavity 14 during the cooking step; thus, the term "maintain" is intended to include keeping the temperature of thecavity 14 substantially constant and varying the temperature of thecavity 14 according to the second or cooking temperature.

Claims

Method of cooking food using steam, conventional heat and microwave energy during a cooking cycle in an oven (10) with an oven cavity (14), a heating system (35), a microwave system (46) and a steam system (50), and a control panel 28 for inputting data to a controller 30, which method ischaracterized by the steps of:
loading food into the oven cavity (14) before a dry pre-heating step;
inputting information regarding food type and at least one additional parameter;
energizing the heating system (35) during the dry pre-heating step (74) to heat the oven cavity (14) to a first temperature (TEMP₁) before starting the first cooking step (76), said first temperature (TEMP₁) being sufficient to prevent condensation of steam on surfaces within the oven cavity (14);
calculating a duration of the first cooking step (76);
introducing steam into the oven cavity (14) during the first cooking step while operating the heating system (35) to heat the oven cavity (14) to an oven set point temperature (TEMP₂);
after the first cooking step, energizing the microwave system (46) for a first portion of a second cooking step (78) while maintaining the oven cavity (14) at the oven set point temperature;
de-energizing the heating system (35) at the end of the second cooking step.
The method of cooking food using steam, conventional heat and microwave energy according to claim 1, wherein the one additional parameter is a data input corresponding to the weight and/or size of the food item.
The method of cooking food using steam, conventional heat and microwave energy according to claim 1, wherein the one additional parameter is an input of the duration of the overall cooking period (80).
The method of cooking food using steam, conventional heat and microwave energy according to claim 1, wherein the controller (30) determines an overall cooking period (80) and the first cooking step (76) is a fraction or percentage of the overall cooking period and the second cooking step (78) is the remainder of the overall cooking period.
The method of cooking food using steam, conventional heat and microwave energy according to claim 4, wherein the fraction or percentage of the overall cooking period used to determine the duration of the first cooking step is controlled according to the input food type.
The method of cooking food using steam, conventional heat and microwave energy according to claim 1, wherein the first temperature (TEMP₁) is about the boiling point of water.
The method of cooking food using steam, conventional heat and microwave energy according to claim 1, further comprising the step of energizing only the microwave system (46) prior to the dry pre-heating step for defrosting frozen food.
The method of cooking food using steam, conventional heat and microwave energy according to claim 1, wherein the method is furthercharacterized by the steps of:
energizing the steam system (50) at a first steam rate (SR₁) for a first period of time, which defines the first cooking step, after the first temperature (TEMP₁) is reached in the oven cavity (14).
The method of cooking food using steam, conventional heat and microwave energy according to claim 4, wherein the first steam rate (SR₁) is determined according to the food type selection input by the user.
The method of cooking food using steam, conventional heat and microwave energy according to claim 1, wherein the method is furthercharacterized by the steps of:
energizing the steam system (50) at a second steam rate (SR₂), less than the first steam rate (SR₁) and energizing the microwave system (46) at a first duty cycle (MW_DC1) for a second period of time, after the first cooking step.
The method of cooking food using steam, conventional heat and microwave energy according to claim 7, wherein the method is furthercharacterized by the steps of:
de-energizing the steam system (50) and the microwave system (46), after the second period of time, and continuing to heat the oven cavity for the remainder of the second cooking step using the heating system (35).
The method of cooking food using steam, conventional heat and microwave energy according to claim 4, wherein the microwave system (46) is energized during the period of time prior to reaching the limit temperature (TEMP₁).