EP1767860A1

EP1767860A1 - Method of operating an oven having heating system, microwave system and steam system

Info

Publication number: EP1767860A1
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: 2007-03-28
Anticipated expiration: 2025-09-21
Also published as: ES2371757T3; EP1767860B1; PL1767860T3

Abstract

A method of operating an oven (10) and controlling the introduction of conventional heat, microwave energy and steam to achieve optimal cooking results. The oven (10) includes a heating system (35), a microwave system (46) and a steam system (50). A control panel 28 is provide for inputting data to a controller 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.

Description

The present invention relates to 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, and in particular, the method for controlling the operation of such an oven.

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.
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). A control panel 28 is provided for inputting data to a controller 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 exemplary automatic 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. The oven 10 comprises a cabinet 12 with an open-face cooking cavity 14 defined by cooking cavity walls: a pair of spaced side walls 16, 18 joined by a top wall 20, a bottom wall 22, and a rear wall 23 (Fig. 2). A door 24 pivotable at a hinge selectively closes the cavity 14. When the door 24 is in the open position, a user can access the cavity 14, while the door 24 in the closed position prevents access to the cavity 14 and seals the cavity 14 from the external environment. The oven 10 is shown as a cooker or cooking range having surface heating elements, however, the oven 10 may be of any known configuration including a countertop type oven.
The oven 10 further comprises a control 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. The control panel 28 communicates with a controller 30 located in the cabinet 12, as shown in Fig. 2. The controller 30 can be a proportional-integral-derivative (PID) controller or any other suitable controller, as is well-known in the automatic oven art. The controller 30 stores data, such as default cooking parameters, the manually input cooking parameters, and the automated cooking programs, receives input from the control panel 28, and sends output to the control panel 28 for displaying a status of the oven 10 or otherwise communicating with the baker. Additionally, the controller 30 includes a timer 32 for tracking time during the manual and automated cooking programs and a cooling fan 34 located in the cabinet 12 for drawing cooling air into the cabinet 12 and directing the air toward the controller 30 to avoid overheating of the controller 30 by heat conducted from the cavity 14. The cooling air flows around the outside of the cooking cavity walls 16, 18, 20, 22, 23.
With continued reference to Fig. 2, the oven 10 further comprises a conventional heating system 35 having an upper heating element 36, commonly referred to as a broiler, and a lower heating element 38. The schematic illustration of the Fig. 2 shows the lower heating element 38 as being hidden or mounted beneath the cooking cavity bottom wall 22 in a heating element housing 40. Heat from the lower heating element 38 conducts through the bottom wall 22 and into the cavity 14. Alternatively, the lower heating element 38 can be mounted inside the cavity 14, as is well-known in the oven art. Further, the upper and lower heating elements 36, 38 can be mounted at the side walls 16, 18 of the cavity 14, as disclosed in U.S. Patent No. 6,545,251 to Allera et al . The heating system 35 according to the illustrated embodiment further comprises a convection fan 42 that circulates air and steam, when present, within the cavity 14. The convection fan 42 can be any suitable fan and can be mounted in any suitable location of the cavity 14, such as in the rear wall 23. A ring shaped convection heater 45 may be positioned about the fan 42.
The oven 10 of the present invention also includes a microwave heating system 46 including magnetron 47 as a high frequency generating part or microwave heating means. The magnetron 46 may be disposed in any convenient or common location such as the space under the oven chamber 14 or along the top or side of the oven chamber 14. A wave guide 48 is provided for directing high frequency energy into the oven chamber 14. A stirrer (not shown) may be disposed at a position receiving the high frequency generated from the magnetron.
In addition to the conventional heating system 35 and the microwave heating system 46 described above, the oven 10 comprises a steam system 50 preferably mounted within the cabinet 12 and configured to introduce steam into the cavity 14. The steam system 50 in the illustrated embodiment comprises a boiler 52 that heats water stored in the steam system 50. However, the steam system 50 can be any suitable system that is capable of introducing steam directly into the cavity 14 and varying the rate of steam generation. This may be accomplished by varying the duty cycle of a boiler 52 to increase or decrease the amount of steam generated. Alternatively, the steam system may include introducing water that is turned into steam in the cavity 14 and is not limited to the system shown schematically in Fig. 2.
FIG. 3 is a block diagram that schematically illustrates a control system for the present invention. This system comprises the controller or microprocessor 30 which operably communicates with the control panel 28 as described having input device 62 and display device 68. The controller 30 instructs the heating system 35 to activate or deactivate the upper heating element 36, the lower heating element 38, and the convection fan 42, either all together, individually, or in groups, and provides instructions regarding the desired temperature of the cavity 14 and the rate at which the heating system 35 heats the cavity 14. The control unit 30 operates the microwave 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, the controller 30 instructs the steam system 50 to activate or deactivate the boiler 46 and provides instructions regarding the desired temperature of the water in the steam system 50 in order to achieve the desired relative humidity in the cavity. A temperature sensor 64 is provided for sensing the temperature of the oven cavity 14 and providing this input to the controller 30. A power supply (not shown) may also be provided.
As stated above, the exemplary oven 10 can be used to implement a method 70, shown in FIG. 4, of cooking a food item with convention heat, microwave energy and with steam according to one embodiment of the invention. The method 70 comprises several steps during which the conventional heating system 35 and microwave heating system 46 operates to control a temperature of the food and cavity 14 and the steam system 50 operates to control a relative humidity of the cavity 14. Before the first stage of the method 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 the cavity 14 step 72. The method can be characterized as having a dry preheating step 74 followed by a first cooking step 76 and a second cooking step 78. The first and second cooking steps form part of the total cooking period 80. Although it can be understood that some cooking occurs during the dry preheating step 74. The steps are defined by the operations of the heating system 35, the microwave system 46 and the steam system 50, as will be described in more detail below.
Steps of the method 70 are shown in the corresponding graph FIG. 5. Fig. 5 is not intended to report actual behavior of the temperature and the relative humidity during the method 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 to Fig. 5, during the dry preheating step 74, the heating system 35 heats the cavity 14 to a first temperature at a first heating rate r₁, and the steam system 50 is off or not activated so that the cavity 14 is relatively dry. According to one embodiment of the invention, the first temperature is the boiling point of water or 100 C. During the dry preheating step 74, the temperature of the cavity 14 is raised to at least the boiling point of water so that steam can be introduced into the cavity 14 during the subsequent steps. Preferably, the first heating rate is relatively fast so that the cavity 14 reaches the first temperature in a relatively short period of time. For example, a fast heating rate can correspond to operating the heating system 35 at substantially maximum capacity.
After the temperature of the cavity 14 reaches the first temperature or after a predetermined period of time, the heating system 35 continues to heat the cavity 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 the user interface 28 or set by the controller 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, the conventional heating system 35 maintains the temperature of the cavity 14 at the cooking temperature for the rest of the cooking cycle.
During the first cooking step 76, the steam system 50 is operated to raise humidity of the oven cavity 14 but the microwave system 46 is not energized. The duration of the first cooking step 76 is established from input by a user through the control 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 the controller 30 from the user directly inputting the duration of the overall 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, the controller 30 establishes a duration for the overall cooking period 80 according to an automatic program or pre-established lookup table which forms part of the controller 30. According to one embodiment of the invention, the duration of the first cooking step 76 is equal to a fraction or percentage (%) of the overall cooking period. The fraction or percentage of the overall cooking period 80 is controlled according to an automatic program or pre-established lookup table which forms part of the controller 30.
The steam system 50 begins to introduce steam into the cavity during the first cooking step 76. The boiler 52 can begin to preheat the water in the steam system 50 prior to the first cooking step 76 so that the steam can be introduced into the cavity 14 at the beginning of the first cooking step 76, if desired. Introducing steam into the cavity 14 as soon as possible during the first cooking step 74 helps to ensure that the steam is present early in the cooking cycle for facilitating the cooking process. The first 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 the cavity 14 ensures that the temperature of the cavity 14 is high enough to sustain steam in a vaporized state. As a result, the vapor will not condense in the cavity 14 and form water droplets on the walls 16, 18, 20, 22, 23, or other items in the cavity 14. Formation of water droplets on porcelain, which is a material found on the cavity walls 16, 18, 20, 22, 23 of many ovens, can undesirably damage the material.
An important aspect of the present invention is that the microwave heating system 46 remains de-energized during the first 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 the cooking cavity 14.
Following the first cooking step 76, the second cooking step 78 provides an opportunity for the food item to complete cooking. The duration of this period is the remainder or difference between the overall cooking period 80 and the first cooking period 76. During the second cooking period, the microwave system 46 may be energized to accelerate the cooking process. Additionally, there can optionally be an operation of the steam system 50 for a limited period of time at the start of the second cooking period, and extra steam operation 82. The microwave 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 to FIG. 6, an implementation of the method 50 with the oven 10 is presented. The cooking cycle is started, either before or after food is loaded into the cavity 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 in step 81 and described above. As shown in steps 82, the heating system 35 heats the oven cavity 14 and food items placed within the oven cavity 14. Optionally, depending on the type of food selected, the microwave system 46 may be used during the dry preheat step 74, as shown in step 84. This occurs normally when cooking frozen items. It is also possible to include a microwave operation only step prior to the dry preheating step 74 dedicated to defrosting frozen food. When the oven cavity 14 reaches a first predetermined temperature TEMP₁, as shown at step 86, the dry pre-heat step 74 is completed. In the case the microwave system 46 was energized, it is then de-energized, step 88. Steps 82, 84 and 86 form the dry pre-heat step 74.
Entering into the first cooking step 76, the steam system 50 is energized, step 90. The duration (T₁) of the first cooking step 76 is determined as described above, and is equal to a fraction or percentage (%) of the overall cooking period 80. Steam is usually injected when the cavity temperature reaches about 100°C (TEMP₁ = 100°C) as shown in FIG. 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 at step 82, which may be different for different food categories and it is related to the desired result, as discussed above.
After the first cooking step 76, the oven operates in the second cooking step 78 for the remainder of the overall cooking period 80. In one embodiment, steam continues to be injected into the oven 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 at step 94. This period of reduced steam input is shown in steps 96 and 98. During this initial portion of the second cooking step 78, the microwave system 46 may be operated at a first duty cycle level (MW_DC2).
After a predetermined period of time, the steam system 50 is de-energized, shown at step 98, and the second cooking step is completed. During the remaining portion of the second step 76, the oven controller 30 may de-energize the microwave system 46, as shown in step 100 and 102 such the final portion of the second cooking step is operated with just the heating system 35 to achieve good food browning, as shown at steps 104-106.
Throughout the entire cooking cycle, it can be understood that the heating elements 45 are energized to raise the oven cavity 14 to the desired temperature set point (TEMP_SETPOINT)· The heating elements 45 may be energized in any particular combination in response to the temperature sensor 64. This operation of the heating elements 45 occurs as a parallel operation, shown as step 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 the method 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 the cavity 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 the cavity 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 the cavity 14 before reaching the boiling point of water, the heating system 35 can more effectively heat the cavity 14 so that the entire cavity 14, including any spaces and items in the cavity 14, is uniformly heated to the boiling point of water. Furthermore, the cooking steps have been described above and shown in Fig. 5 as maintaining the temperature of the cavity 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 the cavity 14 during the cooking step; thus, the term "maintain" is intended to include keeping the temperature of the cavity 14 substantially constant and varying the temperature of the cavity 14 according to the second or cooking temperature.
As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.

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 is characterized by the steps of:
inputting information regarding food type and at least one additional parameter;

calculating a duration of a first cooking step (74);

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 method is further characterized by the steps of:
energizing the heating system (35) during a dry pre-heating step to heat the oven cavity (14) to a first temperature (TEMP₁) before starting the first cooking step.
The method of cooking food using steam, conventional heat and microwave energy according to claim 6, wherein the limit temperature (TEMP₁) is sufficient to prevent condensation of steam on surfaces within the oven cavity (14).
The method of cooking food using steam, conventional heat and microwave energy according to claim 6, 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 6, 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 further characterized 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 7, wherein the method is further characterized 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 9, wherein the method is further characterized 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).