EP3971481A1

EP3971481A1 - Slow cooking of a food product

Info

Publication number: EP3971481A1
Application number: EP20197266.8A
Authority: EP
Inventors: Thomas OTTI
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2020-09-21
Filing date: 2020-09-21
Publication date: 2022-03-23

Abstract

A kitchen appliance (10) is disclosed comprising a food preparation chamber (20), a fan (30) for circulating air through the food preparation chamber (20), a steam generator (40) arranged to introduce steam into the circulating air and a controller (50) adapted to control the steam generator. The kitchen appliance comprises a slow cooking mode in which the controller is adapted to control the steam generator such that a temperature in the food preparation chamber is maintained within a range of 50 - 90° C. Also disclosed is a slow cooking method with such a kitchen appliance.

Description

FIELD OF THE INVENTION

The present invention relates to a kitchen appliance comprising a food preparation chamber including a fan, a steam generator arranged to introduce steam into the food preparation chamber; and a controller arranged to control the fan and the steam generator.
The present invention further relates to a slow cooking method of a food product using such a kitchen appliance.

BACKGROUND OF THE INVENTION

In a slow cooking process, a food product is cooked at a relatively low temperature, e.g. 55 - 60°C, for a long time such that the food product is evenly cooked throughout to avoid the outside of the food product being more cooked than its inside. This furthermore can preserve nutrients such as proteins, and moisture levels within the food product, in particular when a cooking method such as sous vide cooking is used, when the food product is placed in a waterproof bag and placed in a water bath kept at the aforementioned temperature. This therefore is a particularly healthy way of preparing food, e.g. because no oils or fats are used to prepare the food product, and provides a cooked food product having an appealing texture that is difficult to achieve with higher temperature cooking methods.
There are several known kitchen appliances that focus on the preparation of a food product in a healthy manner, by avoiding the need to use significant amounts of oils or fats for the preparation of the food product. A particular class of such kitchen appliances uses steam for the cooking of the food product. For example, European patent application EP3653090A1 discloses a cooking apparatus comprising a food chamber and a steam supply for supplying steam to the food chamber. A control arrangement controls the steam supply to maintain a steam concentration in air inside the food chamber which is below saturation whilst maintaining a temperature of 100 - 120°C within the food chamber. Steaming the food under such conditions makes it difficult to achieve an evenly cooked food product, e.g. comparable to slow cooking methods such as sous vide cooking.

SUMMARY OF THE INVENTION

The present invention seeks to provide a kitchen appliance comprising a food preparation chamber including a fan, a steam generator arranged to introduce steam into the food preparation chamber and a controller arranged to control the fan and the steam generator that can implement a slow cooking method.
The present invention further seeks to provide a slow cooking method of a food product using such a kitchen appliance.
According to an aspect, there is provided a kitchen appliance comprising a food preparation chamber, a fan for circulating air through the food preparation chamber, a steam generator arranged to introduce steam into the circulating air and a controller adapted to control the steam generator, wherein the kitchen appliance comprises a slow cooking mode in which the controller is adapted to control the steam generator such that a temperature in the food preparation chamber is maintained within a range of 50 - 90° C . The invention is based on the surprising insight that effective slow cooking of a food product may be achieved using steam when keeping the temperature in the food preparation chamber within a temperature range of 50-90°C, thereby achieving results comparable to sous vide cooking without requiring a water bath and waterproof bag holding the food product, thus providing more straightforward slow cooking of such a food product.
Advantageously, such a slow cooking mode may be integrated into kitchen appliances capable of providing several cooking modes, including heating modes. For example, the kitchen appliance may further comprise a primary heater arranged to heat the circulating air under control of said controller. The controller may be adapted to disable said primary heater during at least part of said slow cooking mode, for instance where the desired temperature within the food preparation chamber is controlled with the steam from the steam generator. In some embodiments, the primary heater may be disabled for the full duration of the slow cooking mode.
To achieve the desired cooking results, it is important to maintain the temperature within the food preparation chamber in this temperature range. This may be achieved in a number of ways. In a first set of embodiments, the controller is adapted to control a rate at which steam is introduced into the food preparation chamber by the steam generator based on a transfer function linking said rate to the temperature in the food preparation chamber during said slow cooking mode. This has the advantage that no additional hardware is required to implement the slow cooking mode, thereby limiting the cost of the kitchen appliance.
In an alternative set of embodiments, the kitchen appliance further comprises a temperature sensor within the food preparation chamber, said temperature sensor being communicatively coupled to the controller, wherein the controller is adapted to control the steam generator in response to temperature data provided by said temperature sensor during said slow cooking mode in order to maintain the temperature within the food preparation chamber within the desired temperature range of 50-90°C, e.g. by switching off the steam generator when the temperature within the food preparation chamber as sensed by the temperature sensor approaches the upper limit of the temperature range and switching on the steam generator when the temperature within the food preparation chamber as sensed by the temperature sensor approaches the lower limit of the temperature range. Alternatively, the controller may control the steam generation rate of the steam generator based on the data provided by the temperature sensor. This for instance has the advantage that the temperature within the food preparation chamber may be maintained despite the occurrence of unexpected events such as a user opening the food preparation chamber during the slow cooking mode.
The temperature sensor may be located proximal to said primary heater in order to provide an accurate temperature reading. Preferably, the temperature sensor is located near the top of the food preparation chamber for this reason.
In some embodiments, the kitchen appliance further comprises a pressure releasing element fluidly coupled to the food preparation chamber for releasing pressure from the food preparation chamber such as to prevent the build-up of overpressure within the food preparation chamber during said slow cooking mode. Such a pressure releasing element may simply be a conduit through the wall of food preparation chamber connecting the food preparation chamber to the environment of the kitchen appliance, or alternatively may be a pressure release valve, such that some overpressure may be allowed within the food preparation chamber to assist the cooking of the food product.
The fan may be a centrifugal fan having an air inlet for receiving the steam from the steam generator and an air outlet for introducing the air carrying the steam into the food preparation chamber, wherein the air outlet is located in a position closer to a ceiling of the food preparation chamber compared to the air inlet. This configuration promotes a particularly effective circulation of the air/steam mixture through the food preparation chamber.
The steam generator may comprise a water evaporation surface, a surface heater arranged to heat said water evaporation surface and a water reservoir including an outlet arranged to release water onto said water evaporation surface, wherein said surface heater is controlled by the controller during said slow cooking mode such as to control an evaporation rate of water released onto said water evaporation surface. By controlling the operation of the surface heater, the amount of steam generated by the steam generator and consequently the temperature within the food preparation chamber may be accurately controlled.
Furthermore, the outlet may comprise a flow control element controlled by the controller such as to control a water flow rate onto said water evaporation surface during said slow cooking mode to further control the generation of the amount of steam by the steam generator. Preferably, said water flow rate is in a range of 0.2 - 2 g/min for appropriate control of the amount of steam generated during said slow cooking mode.
The steam generator may comprise a steam pan including the water evaporation surface, such that the steam may be generated in a simple and straightforward manner.
In an embodiment, the controller is adapted to control the respective duty cycles of the primary heater and the surface heater such as to maintain the temperature within the food preparation chamber in said range of 50 - 90°C. The periodic use of the primary heater in addition to the steam heater during the slow cooking mode provides additional control over the temperature within the food preparation chamber, should such additional control be desirable, as well as fast heating up of the food preparation chamber, e.g. during a preheating operation.
During the slow cooking mode, the humidity level in said food preparation chamber preferably is in excess of 50g/m³ to ensure the desired cooking of the food product within the food preparation chamber.
The kitchen appliance may take any suitable shape. In example embodiments, the kitchen appliance is an oven, an air fryer or a steamer.
According to another aspect, there is provided a method of slow cooking a food product in a food preparation chamber of a kitchen appliance of any of the herein described embodiments, the method comprising introducing steam into the food preparation chamber with the steam generator such that the temperature within the food preparation chamber is maintained within a range of 50 - 90 °C during said slow cooking. This allows for the slow cooking of a food product in a manner comparable to sous vide cooking.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in more detail and by way of non-limiting examples with reference to the accompanying drawings, wherein:

FIG. 1 schematically depicts a kitchen appliance according to an embodiment;
FIG. 2 depicts a transfer function for controlling the steam generator of the kitchen appliance according to an embodiment;
FIG. 3 depicts temperature and humidity levels within the food preparation chamber of such a kitchen appliance as a function of steam generator operation;
FIG. 4 schematically depicts a kitchen appliance according to another embodiment;
FIG. 5 schematically depicts a kitchen appliance according to yet another embodiment; and
FIG. 6 depicts a flowchart of a slow cooking method according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.
FIG. 1 schematically depicts a kitchen appliance 10 comprising a food preparation chamber 20. The food preparation chamber 20 may be accessible in any suitable manner, e.g. through a door (not shown) or a lid (not shown), which access may be at least partially transparent in order for a user to look into the food preparation chamber 20 of the kitchen appliance 10. A fan 30 is present within the food preparation chamber 20, and is arranged to circulate air through the food preparation chamber 20. The fan 30 may be any suitable type of fan, such as a centrifugal fan. A primary heater 32 may be arranged proximal to the fan 30 to heat the air circulated by the fan 30 through the food preparation chamber 20 in order to cook a food product 1 placed within the food preparation chamber 20, e.g. in a cooking basket or the like. The kitchen appliance 10 further comprises a steam generator 40 arranged to introduce steam into the food preparation chamber 20. The steam generator 40 preferably is arranged such that the generated steam is introduced into (mixed with) the air circulation generated by the fan 30 such that the air circulation contains the generated steam.
The kitchen appliance 10 further comprises a controller 50 arranged to control the fan 30, the primary heater 32 and the steam generator 40. In accordance with the present invention, the controller 50 is configured to implement a slow cooking mode for the food product 1 within the food preparation chamber 20, during which the controller 50 operates the steam generator 40 in such a manner that the temperature within the food preparation chamber 20 is maintained within a range of 50 to 90°C and preferably within a range of 60 to 90°C.This will be explained in further detail below. The controller 50 may invoke the slow cooking mode in response to a user input provided through a user interface 60, e.g. a touchscreen, knob, dial, button or the like. Alternatively, the user interface 60 may be a data communication module for wirelessly communicating with a client device such as a portable electronic device, e.g. smart phone, tablet or the like, in which case the user may select the slow cooking mode through an app running on the client device, with the client device communicating the selected mode of operation of the kitchen appliance 10 to the controller 50 through the data communication module.
The food preparation chamber 20 may be hermetically sealed, in which case the introduction of steam into the food preparation chamber 20 by the steam generator 40 may lead to the build-up of pressure within the food preparation chamber 20. In order to prevent steam from forcibly exiting the food preparation chamber 20 upon a user opening the food preparation chamber 20 exhibiting such overpressure conditions, a pressure releasing element 22 may be present that fluidly connects the food preparation chamber 20 to the environment of the kitchen appliance 10. The pressure releasing element 22 may simply be a channel or conduit extending through a wall delimiting the food preparation chamber 20. Alternatively, the pressure releasing element 22 may comprise a pressure release valve. Such a pressure release valve may be configured to maintain the pressure within the food preparation chamber 20 at atmospheric pressure or alternatively may be configured to control the degree of overpressure within the food preparation chamber 20, e.g. to allow a small degree of overpressure within the food preparation chamber 20 in order to assist the cooking process of the food product 1. The pressure release valve may be controlled by the controller 50, e.g. with the controller 50 being responsive to a pressure sensor (not shown) in the food preparation chamber 20.
In a first set of embodiments, the controller 50 is adapted to control the steam generator 40 during the slow cooking mode based on a transfer function as schematically depicted in FIG. 2, in which the flow rate F (g/min) of water onto a water evaporation surface heated by a surface heater is shown as a function of temperature T (°C). In an embodiment, the surface heater is kept continually on during the slow cooking process, with the water flow rate onto the water evaporation surface in a range of 0.2 to 2 g/min resulting in the temperature within the food preparation chamber 20 being kept within a range of 50 to 90°C. Of course, different flow rates may be required depending on the volume of the food preparation chamber 20 and the (air) tightness of the food preparation chamber 20. During an example embodiment of the slow cooking mode, the humidity level within the food preparation chamber 20 preferably is kept in excess of 50g/m3 in order to ensure an efficient heat transfer to the food product 1 by steam condensing thereon. A humidity sensor (not shown) may be present within the food preparation chamber 20 to measure the humidity level within the food preparation chamber 20, with the controller 50 adapted to control the steam generator in response to the humidity level data provided by the humidity sensor. Alternatively, the humidity may be the direct consequence of the temperature controlled steam generation. FIG. 3 is a graph depicting the temperature (right-hand Y-axis in °C and curve A) and humidity (left-hand Y-axis in g/m³ and curve B) as a function of the water flow rate (X-axis) onto the water evaporation surface of the steam generator 40 expressed as a duty cycle (on) percentage of a water pump delivering water to the water evaporation surface. The 20% duty cycle value equates to a water flow rate of about 2 g/min, at which a temperature of 90°C was achieved within the food preparation chamber 20 in the absence of a food product 1 therein, and a humidity in excess of 50g/m³ was achieved within the food preparation chamber 20 at a temperature of 50°C therein, which humidity quickly increased with increasing temperature, as can be seen from FIG. 3.
The steam generation rate of the steam generator 40 alternatively may be further controlled by controlling the duty cycle of its surface heater. Rather than keeping the surface heater permanently switched on during the slow cooking mode, this heater in this embodiment may be periodically switched off to control the temperature of the water evaporation surface of the steam generator 40, and the water evaporation rate as a consequence. In yet a further refinement, the primary heater 32 may be periodically switched on during the slow cooking mode to maintain the temperature within the food preparation chamber 20 within the desired temperature range. In a particular embodiment, the controller 50 is adapted to control the respective duty cycles of the primary heater 32 and the surface heater such as to maintain the temperature within the food preparation chamber 20 in the range of 50 - 90°C. However, it should be understood that the primary heater 32 may remain switched off for the duration of the slow cooking mode in an alternative set of embodiments, although the primary heater 32 may be engaged during pre-heating of the food preparation chamber 20 to prepare the food preparation chamber for the slow cooking mode of the kitchen appliance 10.
A particular embodiment of the kitchen appliance 10 is schematically depicted in further detail in FIG. 4. In this embodiment, the food preparation chamber 20 comprises a transparent lid 21 through which a user can access the food processing chamber 20 and view the progress of the cooking process of the food product 1 within the food preparation chamber 20, e.g. during the slow cooking mode of the kitchen appliance 10. The food product 1 may be placed in a basket 3 or a similar vessel comprising a plurality of openings to allow the circulating air flow 35 (curved arrows) generated by the fan 30, e.g. a centrifugal fan, under control of the motor 31 to effectively flow around the food product 1 to maximize the surface area of the food product 1 exposed to the steam containing air flow 35 such as to promote effective heat transfer into the food product 1 by steam condensing thereon. The fan 30 may be arranged to generate an air flow 35 at a flow rate of at least 2 L/sec, and preferably of at least 7L/sec to ensure an effective heat transfer into the food product 1.
The steam generator 40 may comprise a water reservoir 41, a water outlet 42, a flow control element 43, a water evaporation surface 44 and a surface heater 45 arranged to heat the water evaporation surface 44 for the generation of steam 46 into the food preparation chamber 20. The water outlet 42 is fluidly connected to the water reservoir 41 through the flow control element 43 and arranged to deposit water released from the water reservoir 41 onto the water evaporation surface 44 in order to generate steam by evaporation of water from the water evaporation surface 44 heated by this surface heater 45. The water evaporation surface 44 may form part of any suitable vessel for steam generation, such as a steam pan or the like. In a preferred embodiment, the flow control element 43 is a water pump under control of the controller 50, which water pump is controlled such that the amount of water released onto the water evaporation surface 44 is in a range of 0.2 to 2 g/min, depending on the (air) tightness of the food preparation chamber 20. Such an amount of water may be released from the water reservoir 41 as a continuous stream or trickle of water by the water pump, although it may not be straightforward to produce such a relatively small stream of water.
Therefore, the water pump alternatively may be operated periodically, e.g. in a pulsed manner, such that the controller 50 regulates the amount of water released onto the water evaporation surface 44 during a defined period of time, e.g. a minute, by control of the duty cycle of the water pump. For example, the water pump may be engaged in a range of 2 to 20% of the duration of the defined period of time in order to achieve the desired temperature within the food preparation chamber 20 during the slow cooking mode of the kitchen appliance 10. Of course, other embodiments of the flow control element 43 may be equally feasible. For example, the flow control element 43 may be an adjustable valve under control of the controller 50, wherein the water from the water reservoir 41 is gravity fed onto the water evaporation surface 44 in an amount during a defined period of time controlled by the controller 50 operating the adjustable valve.
As previously explained, the amount of water released onto the water evaporation surface 44 during a defined period of time is typically controlled in order to maintain the temperature within the food preparation chamber 20 within the temperature range of 50 to 90°C. To this end, the controller 50 may implement a transfer function as previously explained that translates the amount of water released onto the water evaporation surface 44 into a projected temperature within the food preparation chamber 20, using pre-set values for the operation of the steam generator 40, e.g., pre-set values for the operation of the flow control element 43 such as pre-set duty cycle values, and/or pre-set values for the operation of the surface heater 45. However, the controller 50 alternatively may be responsive to a temperature sensor 70, in which case the controller 50 controls the steam generator 40, e.g. the flow control element 43 and/or the surface heater 45 dynamically in response to the temperature data provided by the temperature sensor 70 in order to maintain a temperature within a range of 50 to 90°C within the food preparation chamber 20 during the slow cooking mode of the kitchen appliance 10.
The temperature sensor 70 typically is arranged within the food preparation chamber 20 and preferably is arranged in close proximity to the primary heater 32 at or near the top of the food preparation chamber 20 in order to ensure an accurate temperature reading within the food preparation chamber 20. For example, feedback from the temperature sensor 70 may be used by the controller 50 to temporarily enable or disable the flow control element 43 such as to regulate the amount of water released onto the heated water evaporation surface 44 and consequently the amount of steam 46 released into the food preparation chamber 20. Alternatively or additionally, the temperature sensor 70 feedback may be used by the controller 50 to regulate the surface heater 45, e.g. temporarily switch the surface heater 45 on or off, in order to regulate the temperature of the water evaporation surface 44 and consequently the amount of steam produced by the steam generator 40. It is reiterated that although the primary heater 32 may remain switched off for the duration of the slow cooking mode, in some embodiments the controller 50 may control the duty cycles of both the primary heater 32 and the surface heater 45 in order to regulate the temperature within the food preparation chamber 20.
In a further embodiment, the kitchen appliance 10 may be further configured such that a user can specify further settings within the slow cooking mode, such as a low, medium and high cooking setting, which settings in essence regulate the temperature within the food preparation chamber 20 by controlling the duty cycle of the flow control element 43, e.g. a water pump, to control the amount of water that is delivered from the water reservoir 41 onto the water evaporation surface 44 through the outlet 42. For example, in the low operation mode, the duty cycle of the flow control element 43 may be chosen such that 0.2 g of water is delivered each minute onto the water evaporation surface 44. This for example may be achieved a duty cycle of 1/255 of the flow control element 43, i.e. the flow control element 43 has an on-time/off-time ratio of 1/255. In the medium operation mode, the duty cycle of the flow control element 43 may be chosen such that 0.6 g of water is delivered each minute onto the water evaporation surface 44. This for example may be achieved a duty cycle of 1/99 of the flow control element 43, i.e. the flow control element 43 has an on-time/off-time ratio of 1/99, whereas in the high operation mode, the duty cycle of the flow control element 43 may be chosen such that 1.2 g of water is delivered each minute onto the water evaporation surface 44. This for example may be achieved a duty cycle of 1/49 of the flow control element 43, i.e. the flow control element 43 has an on-time/off-time ratio of 1/49. It is noted for the avoidance of doubt that these values are by way of non-limiting example only, e.g. different water pump specifications may cause different duty cycles to be appropriate. Any suitable values for fine tuning the slow cooking mode of the kitchen appliance 10 may be chosen instead. For example, the above values are a function of the air flow speed generated with the fan 30 (here 14 L/sec), and may be adjusted in accordance to different air flow speeds.
FIG. 5 schematically depicts yet another embodiment of the kitchen appliance 10 in which the fan 30, e.g. a centrifugal fan, is fluidly coupled to a conduit arrangement having an air inlet 33 arranged to receive the steam 46 generated by the steam generator 40 such that the steam 46 (and air) is effectively sucked into the fan 30 through the air inlet 33 and mixed with air to generate the circular air flow 35 containing the steam 46. The conduit arrangement further comprises an outlet 34 through which the steam-containing circular air flow 35 is released into the food preparation chamber 20. The outlet 34 preferably is located in a position closer to a ceiling 25 of the food preparation chamber 20 compared to the air inlet 33, such that the steam containing circular air flow 35 is directed along the ceiling 25 of the food preparation chamber 20, e.g. is directed along the transparent lid 21, in order to promote an effective heat transfer into the food product 1. It is noted for the avoidance of doubt that the conduit arrangement may form an integral part of the fan 30, e.g. the fan 30 may comprise the inlet 33 and the outlet 35, and may be located in any suitable location within the kitchen appliance 10, e.g. in a wall of the food preparation chamber 20. The conduit arrangement is typically arranged such that substantially all steam generated by the steam generator 40 is sucked into the fan 30 through the air inlet 33, mixed with air by the fan 30, which air/steam mixture is released into a top part of the food preparation chamber 20 through the air outlet 35, thereby substantially avoiding the direct release of steam from the steam generator 40 into the food preparation chamber 20.
FIG. 6 is a flow chart of a method 100 of slow cooking a food product 1 in the food preparation chamber 20 of the kitchen appliance 10. The method 100 starts in operation 101, e.g. by a user switching on the kitchen appliance 10, placing the food product 1 within the food preparation chamber 20 and selecting the slow cooking operation through the user interface 60. The method 100 may comprise the optional additional operation 103 of pre-heating the food preparation chamber 20, e.g. using the primary heater 32, to a temperature close to 50°C, e.g. 45°C, in the presence or absence of the food product 1 within the food preparation chamber 20. Next, in operation 105, the controller 50 controls the steam generator 40, e.g. the flow control element 43 such as a water pump, to generate steam at a desired rate in order to control the temperature within the food preparation chamber 20 such that the temperature is maintained within a range of 50 to 90°C. In operation 107, the controller 50 may check if the temperature within the food preparation chamber 20 lies within the desired temperature range for the slow cooking operation, e.g. based on temperature data provided by the temperature sensor 70. As will be understood from the foregoing, such checking may not be performed where the controller 50 uses pre-set data to operate the steam generator 40, e.g. to control the flow control element 43 based on the previously described transfer function.
However, where such a checking operation 107 is performed, the method 100 may proceed to operation 109 if the checking operation 107 shows that the temperature within the food preparation chamber 20 does not require adjusting. If on the other hand the checking operation 107 reveals that such a temperature adjustment is required, the method 100 may return to operation 105 in which the controller 50 adjusts the operation of the steam generator 40, e.g. adjusts the operation of the flow control element 43 as previously explained. In operation 109, the controller 50 checks if the slow cooking process has completed, e.g. by monitoring the elapsed amount of time and comparing the elapsed amount of time against a target duration of the slow cooking operation such that upon the elapsed amount of time matching this target duration, the method 100 may proceed to operation 111 in which the kitchen appliance 10 signals completion of the slow cooking operation upon which the method 100 terminates. However, if the controller 50 determines in operation 109 that the slow cooking operation has not yet completed, the method 100 may return to checking operation 107 described above.
It is noted for the avoidance of doubt that the determination of the completion of the slow cooking operation in operation 109 may be achieved in any suitable manner. For instance, instead of determining the duration of the slow cooking operation, the kitchen appliance 10 may be configured to determine a cooking state of the food product 1 such that the controller 50 may terminate the slow cooking operation in response to the determined cooking state of the food product 1. The cooking state of the food product 1 may be determined in any known manner, e.g. by measuring the temperature of the food product 1 using a temperature probe inserted into the food product 1 or a further temperature sensor arranged to measure the temperature of the food product 1 in a contactless manner, using a camera or the like to optically determine the cooking state of the food product 1, and so on. Finally, it is noted that the kitchen appliance 10 may take any suitable shape or form. In example embodiments, the kitchen appliance 10 is one of an air fryer, oven and steamer, although other embodiments of the kitchen appliance 10 will be immediately apparent to the skilled person.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

A kitchen appliance (10) comprising:
a food preparation chamber (20);

a fan (30) for circulating air through the food preparation chamber (20);

a steam generator (40) arranged to introduce steam into the circulating air; and

a controller (50) adapted to control the steam generator, wherein the kitchen appliance comprises a slow cooking mode in which the controller is adapted to control the steam generator such that a temperature in the food preparation chamber is maintained within a range of 50 - 90° C.
The kitchen appliance of claim 1, further comprising a primary heater (32) arranged to heat the circulating air under control of said controller (50), wherein the controller is adapted to disable said primary heater during at least part of said slow cooking mode.
The kitchen appliance (10) of claim 1 or 2, wherein the controller (50) is adapted to control a rate at which steam is introduced into the food preparation chamber (20) by the steam generator (40) based on a transfer function linking said rate to the temperature in the food preparation chamber during said slow cooking mode.
The kitchen appliance (10) of any of claims 1-3, further comprising a temperature sensor (70) within the food preparation chamber (20), said temperature sensor being communicatively coupled to the controller (50), wherein the controller is adapted to control the steam generator (40) in response to temperature data provided by said temperature sensor during said slow cooking mode.
The kitchen appliance (10) of claim 4, wherein the temperature sensor (70) is located proximal to said primary heater (32).
The kitchen appliance (10) of any of claims 1-5, further comprising a pressure releasing element (22) fluidly coupled to the food preparation chamber (20) for releasing pressure from the food preparation chamber.
The kitchen appliance (10) of any of claims 1-6, wherein said fan (30) is a centrifugal fan having an air inlet (33) for receiving the steam (46) from the steam generator (40) and an air outlet (34) for introducing the air carrying the steam into the food preparation chamber (20), wherein the air outlet is located in a position closer to a ceiling (25) of the food preparation chamber compared to the air inlet.
The kitchen appliance (10) of any of claims 1-7, wherein the steam generator (40) comprises a water evaporation surface (44), a surface heater (45) arranged to heat said water evaporation surface and a water reservoir (41) including an outlet (42) arranged to release water onto said water evaporation surface, wherein said surface heater (45) is controlled by the controller (50) during said slow cooking mode such as to control an evaporation rate of water released onto said water evaporation surface (44).
The kitchen appliance (10) of claim 8, wherein said outlet (42) comprises a flow control element (43) controlled by the controller (50) such as to control a water flow rate onto said water evaporation surface (44) during said slow cooking mode.
The kitchen appliance of claim 9, wherein said water flow rate is in a range of 0.2 - 2 g/min.
The kitchen appliance (10) of any of claims 8-10, wherein the steam generator (40) comprises a steam pan including the water evaporation surface (44).
The kitchen appliance (10) of any of claims 2-11, wherein the controller is adapted to control the respective duty cycles of the primary heater (32) and the surface heater (45) such as to maintain the temperature within the food preparation chamber in said range of 50 - 90°C.
The kitchen appliance of any of claims 1-12, wherein a humidity level in said food preparation chamber (20) is in excess of 50g/m3 during said slow cooking mode.
The kitchen appliance (10) of any of claims 1-13, wherein the kitchen appliance is an oven, an air fryer or a steamer.
A method (100) of slow cooking a food product in a food preparation chamber (20) of a kitchen appliance (10) of any of the previous claims, the method comprising introducing (105) steam into the food preparation chamber with the steam generator (40) such that the temperature within the food preparation chamber is maintained within a range of 50 - 90 °C during said slow cooking.