Patent Publication Number: US-2022228739-A1

Title: Apparatus for cooking food

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus for cooking food. 
     PRIOR ART 
     The use of different types of apparatuses for cooking food, which may be classified according to multiple criteria, such as, for example, the type of energy used or based on the type of cooking used, has long been known. 
     A common type of apparatus is the convection oven, which uses hot air which circulates with a forced convection motion inside a cooking chamber, where the food to be heated or cooked is arranged. 
     A disadvantage related to thermal convection cooking concerns the fact that oxygen is present in the cooking chamber and this may cause oxidation of the vitamins contained in food at cooking temperatures, which are generally higher than 35° C. Furthermore, a thermal convection oven requires rather long cooking times and this feature, in combination with the above cooking temperatures, cause the degradation of the nutrients contained in the food. 
     In order to preserve the quality of the food, and, in particular, not to alter the nutritional properties of the food, apparatuses has been designed that enable alternative cooking methods, such as steam ovens, to be implemented. 
     Steam cooking has the advantage of limiting the degradation of the nutritional elements of food and of improving the maintenance of aromas and aesthetic features. 
     A type of steam oven is illustrated in patent application EP 1970634. 
     Apparatuses for cooking food with superheated steam, generally called superheated steam ovens have also been designed. 
     A type of superheated steam oven comprises a casing which forms inside a cooking chamber in which the food is arranged. The casing is associated with a steam generator, which is connected to a steam superheater device. The steam superheater device is connected with the cooking chamber to introduce the heated steam into the chamber at a temperature higher than the boiling temperature, which is generally called superheated steam. 
     The application EP1790909 illustrates an example of a superheated steam oven comprising a casing, internally forming a cooking chamber, and a steam generator arranged outside the cooking chamber. The steam generator comprises a container, suitable for receiving a liquid, comprising a heater consisting of a series of heating elements mounted on an insulating substrate. A superheater device coupled with a recirculation fan is also associated with the outside of the cooking chamber. 
     Despite the advantages offered by ovens that enable steam cooking, the need to preserve the nutritional properties of the food to the greatest extent is felt. 
     DISCLOSURE 
     The present invention aims at solving the aforementioned problems by devising an apparatus for cooking food with superheated steam, which allows the optimal preservation of the nutritional properties of the food and its healthiness. 
     The invention further aims at providing an apparatus for cooking food with superheated steam which is of a simple constructive and functional concept, which is certainly reliable in operation, versatile in use, and relatively inexpensive. 
     The mentioned aims are achieved, according to the present invention, by the apparatus for cooking food with superheated steam according to claim  1 , by the method for generating steam according to claim  13  and by the computer program according to claim  15 . 
     The apparatus for cooking food with superheated steam includes an external casing comprising inside a cooking chamber, suitable for containing one or more foods; a steam generation device associated with said casing, capable of vaporizing a liquid, said steam generation device comprising at least one heating element and at least one thermally conductive element, said at least one heating element being capable of heating said inserted liquid, in use, inside said steam generation device, said heating element also being capable of heating said thermally conductive element so as to store in said thermally conductive element a predetermined quantity of energy to be used to generate steam; a device for superheating said steam, associated with said steam generation device, said superheating device being configured to heat said steam up to an operating temperature higher than the boiling temperature of said liquid and to enable overheated steam to come out towards said cooking chamber. 
     It should be noted that the provision of at least one thermally conductive element which stores a predetermined amount of energy, upon heating by at least one heating element, has the effect of introducing steam into the cooking chamber in an optimized time since the steam is rapidly produced by direct contact of the liquid with at least one thermally conductive element. Consequently, a reduction in the time required for the dislocation of oxygen from the cooking chamber, by replacement with the introduced steam, occurs. An effect of the decrease in the time required to generate steam, and therefore of the decrease in the time required to expel oxygen from the cooking chamber, at least for the most part, is the fact that oxidation of some components of the food is limited or eliminated, such as, for example, vitamins and polyphenols, thus preserving the healthiness of the foods. 
     Said at least one heating element comprises an electrical resistance. 
     Each said electric resistance has a substantially flat spiral shape. 
     The configuration of each substantially flat spiral electric resistance allows an optimal ratio between the generated power and the volume of introduced liquid to be obtained. 
     Preferably the value of the ratio between the generated power and the volume of introduced liquid is at least 8 W/gr of water in the case where the liquid used is water. 
     In practice, each spiral-shaped electric resistance occupies a contained volume and, therefore, reduces the volume of liquid necessary to keep it submerged. Consequently, the volume of liquid that must be introduced into the steam generating device is reduced and the time interval for generating steam is therefore reduced. At the same time, a further advantage offered by the configuration of the spiral resistances is that of exploiting their geometry, and in particular the length, to generate an increased power. 
     Finally, it is also to be considered that each spiral resistance offers a greater surface than that of a linear resistance of the same size and this makes it more resistant to thermal shock, making the steam generation device more rugged and, consequently, more durable. 
     Preferably the steam is heated to an operating temperature between 130° C. and 600° C. 
     Preferably said steam generation device comprises a body comprising a plurality of said electrical resistances, arranged alternated with respective said thermally conductive elements. The alternating arrangement of the electric resistances and of the thermally conductive elements has the advantage of conferring a compact configuration on the steam generation device and allows to reduce its overall dimensions. Another important aspect is that such a compact alternating arrangement has the effect of reducing the internal volume of that casing that may be occupied by the liquid to keep the heating elements submerged. This compact configuration enables the volume of liquid necessary for proper operation to be decreased, therefore, it helps to speed up the generation of steam, mainly at an early stage of the cooking process, in order to quickly replace the oxygen with steam in the cooking chamber. 
     Finally, it is observed, that the provision of a series of substantially flat spiral-shaped resistances and the alternate arrangement of these resistances to the thermally conductive elements so that a compact configuration is obtained, have the synergistic effect of optimizing even more the ratio between the generated power and the volume of the introduced liquid since the volume of liquid to be introduced into the casing is reduced and the increased power that the spiral resistances may generate is exploited. The reduction in the volume of liquid is related both to the compact configuration of each spiral resistance and to the alternate compact arrangement of the resistances with the thermally conductive elements. The reduction in the volume of required liquid involves a reduction in the time required to generate steam, in particular at an early stage of the cooking process, in order to quickly replace the oxygen present in the cooking chamber with steam. 
     Preferably said electrical resistances are alternated with the respective thermally conductive elements along a longitudinal direction. 
     Preferably said electrical resistances are alternated with the respective thermally conductive elements so as to obtain a stacked configuration. 
     Preferably said body is box-shaped. 
     Preferably said body has a prismatic shape. 
     Preferably said electric resistances are aligned along a longitudinal direction. 
     Preferably said electric resistances are equidistant with respect to each other. 
     Preferably each said thermally conductive element is made of a plate, which extends transversely to said body of said steam generating device. It is noted that the plate configuration of each thermally conductive element facilitates the stacking of the resistances and of the thermally conductive elements, contributing to make the configuration of the steam generation device even more compact. 
     Preferably each said thermally conductive element is made of a metallic material. 
     Preferably each said thermally conductive element forms a seat for housing a relative electrical resistance. 
     Preferably each said seat has a shape conjugated to said relative electric resistance. 
     Preferably, each electric resistance is connected to respective terminals to be powered by a source of electric energy. 
     Preferably, said steam generation device comprises a member detecting the level of the introduced liquid, in use, so that the quantity of liquid introduced is monitored in order to not exceed a maximum permitted value. 
     Preferably, said superheating device comprises a containment body, a support member, made of a non-electrically conductive material, which is arranged inside said containment body, said support member having at least one channel, passing through said support member, to enable the passage of said steam. 
     Preferably said support member comprises at least one electrically conductive element, arranged in said at least one channel of said support member, said at least one electrically conductive element being powered, in use, by a source of electric energy to be heated to a temperature such as to emitting electromagnetic radiation, said steam being heated, in use, by said electromagnetic radiation by irradiation. It should be noted that heating the steam by irradiation allows the time for heating the steam up to the operating temperature to be reduced, thus the time necessary to introduce superheated steam into the cooking chamber is decreased. In this way, the time necessary for oxygen to come out from the cooking chamber is reduced, in an initial step, considering that oxygen is replaced more quickly by the introduced steam and, consequently, the oxidation of some components of food is eliminated or limited, such as, for example, vitamins and polyphenols, preserving the healthiness of foods. 
     It should be noted that the combination of the steam generation device and the superheating device enables the time interval necessary for the generation of superheated steam to be optimized, in particular in an initial step of cooking, so as to quickly replace the oxygen present in the chamber with superheated steam. The configuration of the steam generation device comprising at least one thermally conductive element and at least one spiral-shaped electrical resistance makes steam generation faster, and the fact that the superheating device comprises an electrically conductive element arranged in said at least one channel of said support member, which is heated to a temperature such that electromagnetic radiation is emitted, enables the steam provided by the steam generation device to be superheated rapidly by irradiation. 
     Preferably said electrically conductive element comprises an electrically conductive filament. The electrically conductive filament allows it to be heated up to a temperature suitable for heating by irradiation in optimized times. 
     Preferably said electrically conductive element consists of an electrically conductive filament. 
     Preferably said electrically conductive filament is made of a metallic material. 
     Preferably said electrically conductive filament is made of an alloy of metals. 
     Preferably said electrically conductive filament is made of a nickel-chromium alloy. 
     Preferably said nickel-chromium alloy comprises 80% nickel and 20% chromium. 
     Preferably said at least one electrically conductive element emits, in use, electromagnetic radiation having a wavelength in the infrared range. 
     Preferably said at least one electrically conductive element is connected, by means of suitable terminals, to a source of electric energy. 
     Preferably said support member is made of a ceramic material. 
     Preferably said containment body is made of a metallic material. 
     Preferably, said support member has a plurality of said channels passing through said support member, to allow the passage of said steam. 
     Preferably said channels extend along a longitudinal direction of said support member. 
     Preferably, said channels each have a cylindrical shape. 
     Preferably said at least one electrically conductive element comprises a series of longitudinal sections, arranged in the relative channels, and a series of transversal sections which connect the adjacent longitudinal sections. 
     Preferably said channels are regularly distributed in said support member. 
     Preferably said channels are distributed on the periphery of said support member. 
     According to an aspect of the invention, said channels shape respective grooves on an external surface of said support member. 
     Preferably, at least one spacer element is arranged between said external surface of said support member and an internal surface of said containment body, so that the contact cannot be established between said electrically conductive element and said containment body. It should be noted, in fact, that one or more drops from the condensation of said steam may form between said external surface of said support member and said internal surface of said containment body. This may create a contact between the electrically conductive element and the containment body, which, in the event that the containment body is made of metallic material, causes a short circuit. 
     According to a different aspect of the invention, said channels are closed laterally. 
     Advantageously, said containment body has a surface facing towards said support member, which, at least for a portion, is reflective, in order to reflect the radiations emitted by said electrically conductive element, in use, and to limit the dispersions of energy towards the outside of said containment body. 
     Preferably said surface facing towards said support member is subjected to a surface treatment which makes it reflective. 
     Preferably said surface treatment is electrolytic polishing. 
     Preferably, said containing body of said superheating device is inclined with respect to a substantially horizontal plane, in a mounting configuration, to facilitate the flow of the liquid deriving from the condensation of the steam. 
     Preferably said steam generating device is associated with said superheating device through a connection means enabling the passage of said steam from said steam generating device to said superheating device. 
     Preferably said connection means comprise at least one conduit. 
     Preferably, said apparatus comprises a control unit configured to control said steam generating device and said superheating device. 
     Preferably said control unit comprises a computer and a memory readable by said computer, said memory comprising data relating to the steps of at least one method for generating steam. 
     Preferably, said apparatus also comprises recirculation means of the exhausted steam present, in use, in said cooking chamber, said recirculation means being communicating with said cooking chamber and being configured to convey said exhausted steam from said cooking chamber to said superheating device, so as to heat said exhausted steam up to said operating temperature and introduce it into said cooking chamber. 
     It is pointed out that the provision of means of recirculation of the exhausted steam enables the energy consumption to be reduced since the amount of energy necessary to bring the exhausted steam to the operating temperature is lower than the energy necessary to bring the liquid to the state of superheated steam. More specifically, it is observed that to bring the exhausted steam into the superheating device at operating temperature, it is sufficient to supply it with the energy it previously transferred to the food, while, in order to obtain superheated steam starting from the liquid contained in the device for generating the steam, it is necessary to supply the energy to evaporate it and the energy to superheat it. The total energy for evaporation and superheating to be supplied to the liquid is higher than the energy transferred by the exhausted steam to the food. 
     The present invention also relates to a method for the generation of steam, which comprises the step of preparing said apparatus for cooking food with superheated steam and activating said at least one heating element to heat said at least one thermally conductive element until reaching a predetermined temperature, and storing in said at least one thermally conductive element a predetermined amount of energy. 
     Preferably said at least one thermally conductive element is heated to a temperature between 100° C. and 600° C. 
     Preferably said at least one thermally conductive element is heated to a temperature lower than the Leidenfrost temperature. 
     Preferably the activation of said at least one heating element is interrupted when said heating temperature of said at least one thermally conductive element is reached. 
     Preferably the achievement of said heating temperature of said thermally conductive element and the deactivation of said at least one heating element are signaled to a user by a warning signal. 
     The method provides for inserting a liquid inside said steam generation device until a maximum quantity of liquid is reached and, simultaneously, generating steam by direct contact of said liquid with said at least one thermally conductive element, exploiting said predetermined quantity of stored energy. 
     Preferably, before said step of inserting said liquid, said at least one heating element is activated again. 
     The method provides, after a predetermined time interval from the beginning of said step of insertion of said liquid and before the end of said step of insertion of said liquid, for generating steam by direct contact of said liquid with said at least one thermally conductive element and by boiling said liquid. 
     Preferably said predetermined time interval from the beginning of said step of insertion of said liquid is between 30 and 80 seconds. 
     Preferably, in said step of generating steam by direct contact of said liquid with said at least one thermally conductive element and by boiling of said liquid, the boiling of said liquid occurs mainly thanks to the energy transferred by said at least one heating element. 
     Advantageously, at the end of said step of inserting said liquid, the method provides for generating steam by boiling said liquid by means of said at least one heating element and said at least one thermally conductive element. 
     It should be noted that the steam generating method implemented by the apparatus makes it versatile as it is possible to generate steam by direct contact of the liquid with said at least one thermally conductive element, exploiting said predetermined quantity of stored energy and, therefore, rapidly generating steam, but it is also possible to generate steam by direct contact of said liquid with said at least one thermally conductive element and by boiling of said liquid, after a predetermined time interval from the beginning of said step of insertion of said liquid. In this way it is possible to select the most suitable steam generation mode for the type of product to be cooked. 
     Preferably, said step of inserting the liquid inside said steam generation device is carried out discontinuously. 
     Preferably, said step of inserting the liquid inside said steam generating device comprises a series of liquid injections. 
     Preferably between a liquid injection and a subsequent injection elapses a first time interval. 
     Preferably said first time interval is between 1 and 60 seconds. 
     Preferably each injection of the liquid takes place in a second time interval. 
     Preferably said second time interval is between 1 and 60 seconds. 
     Preferably said values of said first time interval and of said second time interval are stored in the memory of said control unit. 
     The present invention also relates to a computer program comprising instructions which, when the program is run by a computer, cause said apparatus to carry out the steps of activating said at least one heating element to heat said at least one thermally conductive element until reaching a predetermined temperature, and storing in said at least one thermally conductive element a predetermined amount of energy; inserting a liquid inside said steam generation device until a maximum quantity of liquid is reached and, simultaneously, generating steam by direct contact of said liquid with said at least one thermally conductive element, using said predetermined quantity of stored energy; after a predetermined time interval from the beginning of said step of insertion of said liquid and before the end of said step of insertion of said liquid, generating steam by direct contact of said liquid with said at least one thermally conductive element and by boiling of said liquid. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The details of the invention will become clearer from the detailed description of a preferred embodiment of the apparatus for cooking food with superheated steam according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: 
         FIG. 1  shows a block diagram of the apparatus object of the present invention; 
         FIG. 2  shows a top view of the apparatus according to the present invention, wherein an outer casing is shown in transparency; 
         FIG. 3  shows a front view of the apparatus wherein the external casing is shown in transparency; 
         FIG. 4  shows a perspective view of a detail of the apparatus; 
         FIG. 5  shows a perspective view of the detail of the apparatus illustrated in  FIG. 4 , wherein further components are visible; 
         FIG. 6  shows a front view of some components of the apparatus in a configuration of assembly; 
         FIG. 7  shows a front view of an enlarged detail shown in  FIG. 6 ; 
         FIG. 8  shows a front view of the detail of  FIG. 7 , wherein an external casing is shown in transparency; 
         FIG. 9  shows a side view of a different enlarged detail shown in  FIG. 6 ; 
         FIG. 10  shows a front view of the detail illustrated in  FIG. 9 . 
     
    
    
     BEST MODE 
     With particular reference to these figures, the reference number  1  indicates the apparatus for cooking food with superheated steam according to the present invention, which is called apparatus, for simplicity. 
     The apparatus  1  comprises an external casing  2  comprising a compartment  3 , suitable for containing one or more foods. 
     More specifically, the compartment  3  internally defines a cooking chamber  4  in which the food to be cooked or heated is arranged. 
     The casing  2  preferably has a prismatic shape but it is possible to provide for any other shape. 
     The compartment  3  preferably has a trapezoidal cross-section. The shape of the compartment  3 , which is basically a trapezoidal-based prism, prevents the formation of areas of stagnation of a fluid contained inside thereof, thus facilitating the circulation of the fluid in the cooking chamber  4 . 
     Advantageously, the compartment  3  has a cross section with a mixtilinear trapezoidal shape, that is, it comprises a series of straight sections and a series of curve arches, in which the straight sections are connected by the curve arches. The trapezoidal configuration of compartment  3  including the curve arches has the effect of minimizing the volume of compartment  3  and, therefore, of allowing oxygen to come out from compartment  3  in the shortest possible time. Furthermore, this configuration has the effect of preventing oxygen stagnation zones from forming in the corners, which may reduce the benefits of cooking with superheated steam. Finally, this configuration enables the exposure of a surface of minor extension to the flow of superheated steam, limiting the formation of condensation and helping the interaction between superheated steam and products. 
     The curved arches create rounded corners of compartment  3  and are present along the entire vertical development of said compartment  3 . 
     The fluid includes steam during the operation step of the apparatus. 
     In an operating step of the apparatus, the fluid mainly comprises steam, or steam mixed with gas, such as mainly oxygen and nitrogen. 
     Preferably the steam used is water vapor. 
     In particular, the compartment  3  is delimited by a first wall  5 , which forms the base, a second top wall  6 , opposed to the first wall  5 , a third wall  7  and a fourth wall  8  mutually facing each other, which define the oblique sides of the trapezoidal based prism. The compartment  3  is also delimited by a further wall  9 , substantially orthogonal to the first wall  5 , which is considered as a rear wall in the following description. 
     The compartment  3 , in use, is closed by a door associated with the casing  2 , as specified below. 
     Preferably the walls  5 ,  6 ,  7 ,  8 ,  9  which delimit the compartment  3  are made as a single body. Alternatively, the walls  5 ,  6 ,  7 ,  8 ,  9  are tightly connected to each other. 
     The cooking chamber  4  may have a prismatic shape, even more preferably a parallelepiped shape. 
     The cooking chamber  4  is delimited by the base  5 , by the top wall  6 , by a protection member  26 , arranged frontally to the rear wall  9  of compartment  3 , and by a pair of conveying members  14 , mounted inside the compartment  3 . The conveyor members  14  and the protection member  26  are described below. 
     Between the compartment  3  and the cooking chamber  4  a region for distributing the fluid  100  is defined, which forms a guide path for the fluid flow towards the cooking chamber  4 , in which the heating or cooking of the food take place in use. 
     A supporting means  10  may be associated with the casing  2 , for example of the type of a series of feet, suitable for supporting the apparatus resting on a work surface. 
     The casing  2  comprises an access opening  11  at the cooking chamber  4 , to enable a user to access the chamber  4 . The access opening  11  is preferably made on a wall of the casing  2  arranged frontally with respect to the rear wall  9  of the compartment  3 . 
     The access opening  11  is closed, during the operation of the apparatus, by a door  12 , to isolate the cooking chamber  4  from the external environment and avoid heat dispersion. 
     The door  12  is hinged to the casing  2  or, alternatively, to the compartment  3 , and is provided with a gripping member  13 , preferably made by a handle, to facilitate the opening of the door  12 . 
     Door  12  is made of a transparent material in order to allow viewing of the interior of the cooking chamber  4 . 
     A control panel, not shown, is preferably associated with the external casing  2  comprising a series of controls, of the type of knobs or buttons, or a touch screen, to allow the switching on and off of the apparatus, as well as the adjustment of certain parameters such as, for example, the temperature or the cooking time. 
     The compartment  3  comprises a pair of conveying members  14 , mounted spaced from relative opposite walls of the compartment  3 , in particular from the third wall  7  and from the fourth wall  8 . 
     A lateral portion of the distribution region  100  is delimited between each conveying member  14  and the relative wall  7 ,  8  of the compartment  3 , which is shaped so as to ensure an optimal distribution of the fluid inside the cooking chamber  4 . 
     Each lateral portion of the distribution region  100  has a cross section which progressively decreases along the depth of the cooking chamber  4 . 
     According to the spatial reference system illustrated in  FIG. 5 , the depth of the cooking chamber  4  is a dimension substantially parallel to the y axis. Preferably each side portion of the distribution region  100  has a substantially trapezoidal plan. 
     The conformation of each lateral portion of the distribution region  100 , in particular the progressive reduction of the cross-sectional area, allows an approximately constant speed of the fluid along the lateral portion to be obtained. In this way, a homogeneous distribution of the fluid in the chamber  4  is guaranteed, which is suitable to compensate for any lack of homogeneity in the distribution of the temperature inside the chamber  4 . 
     It is possible to provide that suitable deflector members, not shown in the figures, are positioned in the areas of curvature of the distribution region  100 . The deflector members facilitate the circulation of the fluid through the distribution region  100 , counteracting the formation of areas of stagnation of the fluid in the path towards the cooking chamber  4 . 
     Preferably each conveying member  14  is made of a plate, which is arranged substantially orthogonal to the rear wall  9  of the compartment  3 . 
     Each conveying member  14  shapes a plurality of openings  15 , configured to enable a uniform distribution of the flow of fluid in the cooking chamber  4 , in particular along the depth of the cooking chamber  4 . 
     The openings  15  are regularly distributed on the surface of each conveying member  14 . 
     Preferably the openings  15  are arranged adjacent along the depth of the cooking chamber  4 , that is along a direction parallel to the y axis. 
     At least one support element  17  is arranged on each plate  14 , and is suitable for supporting a relative food containing member, such as, for example, a pan, which is not shown in the figures. 
     According to an embodiment, each support element  17  comprises a portion protruding from the respective plate  14 , which defines a support surface for the containment member. 
     Preferably the apparatus comprises a plurality of support elements  17 . 
     A set of distribution elements, not shown in the figures, which contribute to improve the distribution of the superheated steam, are mounted on opposite walls of the compartment  3 , which delimit respective side portions of the distribution region, together with respective conveying members  14 . 
     Preferably, each conveying element is made of a fin which protrudes from the compartment wall  3  towards the distribution region  100 . 
     The fins are distributed uniformly on each wall of the compartment  3  and, in particular, are arranged adjacent along a longitudinal direction, forming a series of rows which extend substantially parallel along a transverse direction, which corresponds to the depth of the compartment. 
     The compartment  3  houses inside thereof a ventilation device  18 . 
     The ventilation device  18  is arranged in the distribution region  100 , preferably between the rear wall  9  of the compartment  3  and the cooking chamber  4 . 
     The ventilation device  18  comprises a first impeller member  19 , mounted on a substantially horizontal rotation shaft  20 , which is driven in rotation by an actuator member  21 . 
     The actuator member  21  includes an electric motor associated with the rear wall  9 . 
     The first impeller member  19  comprises a discoidal body  22  from which a series of fins  23  develop, distributed on a peripheral circular rim of the discoidal body  22 . 
     Coaxially to the first impeller member  19  a second impeller member  24  is mounted, which comprises a relative series of fins  25  which develop starting from the discoidal body  22 . The fins  25  of the second rotating member  24  preferably have an extension along the y direction lower than the extension of the fins  23  of the first impeller member  19 . 
     The provision of a pair of impeller members  19 ,  24  allows the fluid to circulate effectively inside the cooking chamber  4 . 
     The ventilation device  18  creates a pressure gradient in the cooking chamber which is used to convey the exhausted steam from the chamber  4  towards the superheating device  31 . 
     Exhausted steam means the steam, which, during the operation of the apparatus, transferred the stored energy to the food or to the cooking chamber  4 . 
     The distribution region  100  may house a series of heating elements, for example of the type of electrical resistances, suitable for heating the fluid flowing in the distribution region  100  towards the cooking chamber  4 . 
     The heating elements may be arranged near the ventilation device  18 . 
     A protection member  26  is arranged in front of the ventilation device  18 , which forms one of the walls of the cooking chamber  4 , as already mentioned. 
     The protection member  26  consists of a plate on which a series of suction openings  27  of the fluid contained in the cooking chamber  4  are obtained. 
     More specifically, the plate  26  forms a preferably disk-shaped suction surface which includes the suction openings  27 . 
     The suction openings  27  are shaped as portions of a circular rim and are arranged contiguous so as to form at least one circular rim. The suction openings  27  may have a different shape, for example may be shaped as slots with straight development. 
     Preferably the suction openings  27  arranged on the periphery of the suction surface have a larger area than the suction openings  27  arranged centrally with respect to the same surface, to facilitate suction at the end regions of the cooking chamber  4 . 
     The suction surface extends at least up to the height of the support element  17 , intended as a position along the z direction. If a plurality of support elements  17  are present, the suction surface extends at least from the height of the support element  17  positioned at one end of the relative conveying member  14 , up to the support element  17  positioned at an opposite end of the conveying member  14 . 
     The feature relating to the extension of the suction surface has the effect of facilitating the suction of the fluid at the pans positioned at the ends of the conveying members  14 . 
     A substantially truncated cone-shaped element is associated at the rear of the plate  26 , and is positioned in front of the ventilation device  18  and contributes to facilitate the aspiration by the ventilation device  18 . 
     The cooking chamber  4  is associated with a cooling conduit  28 , which protrudes, at least in part, outside the casing  2 , to allow the entry of air from the external environment into the cooking chamber  4  and allow the cooling of the chamber  4 . 
     The cooling conduit  28  is connected to an opening  29  made on the rear wall  9  of the cooking chamber  4 , preferably near the ventilation device  18 . 
     The cooling conduit  28  is provided with an adjustment member, not visible in the figures, which is operated by a control unit between an opening configuration, in which it allows the passage of air in the cooling conduit  28  towards the cooking chamber  4 , and a closing configuration, in which the passage of air is blocked. 
     The control unit, also not visible in the figures, is designed for managing the apparatus, and is configured to send command signals to a steam generating device  30  and to a superheating device  31 . 
     The control unit comprises an electronic processor and a memory readable by the electronic processor. 
     According to an embodiment of the invention, the control unit is configured to receive data from sensor means and, on the basis of the data, generate the command signals. The data sent by the sensor means may be stored in the memory. 
     The sensor means, not shown, may be configured to acquire data relating to predetermined fluid dynamic characteristics of the fluid, such as, for example, the temperature, and/or data relating to the composition of the fluid, such as, for example, the percentage of oxygen. 
     The sensor means comprise, for example, at least one temperature sensor and at least one oxygen sensor. 
     The memory is also capable of storing data relating to the phases of at least one cooking method implemented by the apparatus, for example for the duration of the phases of a cooking method. The cooking method includes a series of phases for the generation of steam, as it is better explained below. 
     In this way, the control unit may control the operation of the steam generation device  30  and of the superheating device  31  on the basis of these data relating to the phases of the cooking method. 
     The cooking chamber  4  is provided with a first discharge opening  32 , for the oxygen to come out from the cooking chamber  4  towards the outside, during a cooking start-up phase. 
     The first exhaust opening  32  is preferably positioned on the top wall  6  of the chamber  4 . An exhaust conduit is connected to the first exhaust opening  32 , not illustrated in the figures. 
     A second exhaust opening  33  is made on a wall of the cooking chamber  4 , to release the condensed steam or liquid materials deriving from the food outwards. 
     Preferably the base  5  of the cooking chamber  4  has a portion with a downward inclination and, approximately at the center of the inclined portion, the second exhaust opening  33  is positioned, which collects the liquid material to convey it, by means of a special conduit, towards means collection, not illustrated. 
     The collection means comprise a tank placed below the base  5 . 
     Preferably, the tank is connected to the exhaust conduit, by means of special connection means, so as to direct the oxygen collected in the tank into the exhaust conduit so that it is expelled outwards. 
     In fact, it has been experimentally observed that oxygen has a higher density than that of superheated steam and tends to accumulate in an area arranged below, in use, that is near the base  5  of the cooking chamber  4 . The provision of connection means which connect the tank with the exhaust conduit enables the collection of the oxygen that enters into the tank through the second exhaust opening  33  and expel it. 
     Steam is introduced into compartment  3  through at least one inlet opening  34 , formed on the rear wall  9 . The inlet opening  34  may be made near the ventilation device  18 . 
     The steam is produced by the steam generating device  30 , which is able to vaporize a liquid contained inside it. 
     Preferably the liquid used is water. 
     The steam generating device  30  is associated with the casing  2 . More specifically, the steam generating device  30  is housed in a region between the rear wall  9  of the compartment  3  and the casing  2 . 
     The steam generating device  30  comprises a box-like body  35  which houses, inside thereof, one or more heating elements  36 . 
     The body  35  internally forms a compartment, capable of receiving a predetermined quantity of liquid, in which the heating elements  36  are arranged. 
     Preferably, the heating elements  36  are made of electrical resistances. 
     The electric resistances  36  are connected to respective terminals  37  to allow the supply of electric energy. 
     Each electric resistance  36  has substantially flat spiral shape. The spiral shape of the electric resistances  36  allows an optimal ratio between the generated power and the volume of introduced liquid to be obtained. The value of that ratio, in case the liquid used is water, is at least 8 W/gr of water. The electrical resistances  36  are aligned along a longitudinal direction and are equally spaced apart. More particularly, the electric resistances  36  are arranged alternating with respective thermally conductive elements  38 . 
     Preferably, the electric resistances  36  are alternated with respective thermally conductive elements  38  so that a stacked configuration is obtained. The stacked configuration is compact and particularly advantageous as it allows the volume that may be occupied by the liquid to keep the heating elements submerged, to be to reduced. By decreasing the amount of liquid, the time required to generate steam is reduced and this enables the oxygen to be quickly replaced with steam in the cooking chamber. 
     Each thermally conductive element  38  is made of a plate which extends on a plane transverse to the body  35 . 
     Each thermally conductive element  38  forms a seat for housing the relative electrical resistance  36 . Preferably each seat has a shape conjugated to the electric resistance  36 . 
     Preferably each thermally conductive element  38  is made of metallic material. 
     The conductive elements  38  are heated, in a start-up phase of the apparatus, by the electric resistances  36 , to store a predetermined amount of energy, which is used to generate steam starting from the liquid introduced into the box-shaped body  35  and therefore quickly replace the oxygen initially present in the cooking chamber  4 . It has been observed that the time in which the replacement of oxygen with steam takes place, produced by contact of the liquid with the thermally conductive elements  38 , is less than one minute from the beginning of the cooking phase. 
     The steam generating device  30  comprises a member sensing the liquid level so as to monitor that the quantity of liquid introduced, in use, into the compartment of the body  35 , does not exceed the maximum allowed value. 
     It is possible to provide that the apparatus includes an additional steam generating device, not shown, which is capable of being activated to generate steam, if necessary. 
     The steam generating device  30  is associated with the superheating device  31 , which is configured to heat the steam up to an operating temperature T higher than the boiling temperature of the liquid used. 
     Operating temperature T means the temperature at which the steam is introduced into the cooking chamber  4 , which is approximately between 130° C. and 600° C. 
     The superheating device  31  is placed in communication with the cooking chamber  4  to introduce the superheated steam into the cooking chamber  4 , through the inlet opening  34 . 
     The superheating device  31  comprises a containment body  39  comprising inside at least one channel for the passage of the steam. 
     According to an embodiment, the containment body  39  is preferably substantially cylindrical and is internally hollow. 
     Preferably, the superheating device  31  is inclined with respect to a substantially horizontal plane to facilitate the flow of the liquid coming from the condensation of the steam, in a mounting configuration. 
     Preferably the containment body  39  is made of a metal material. 
     The containment body  39  comprises a support member  40 , which also has preferably substantially cylindrical shape and is made of a non-electrically conductive material. 
     The support member  40  may be made, for example, of a ceramic material. 
     The support member  40  is inserted inside the containment body  39  and is spaced from the internal wall of the containment body  39 , defining a meatus. 
     The support member  40  is connected to a closing element not visible in the figures, for example made of a flange, which is arranged at one end of the containing body  39 . 
     The support member  40  has at least one through channel  41 , through which the passage of steam takes place. The at least one through channel  41  preferably extends from one end of the support member  40  to an opposite end. 
     According to a preferred embodiment, the support member  40  has a series of channels  41 , which extend along a longitudinal direction of the support  40 . These channels  41  are regularly placed in the support member  40 , for example they may be arranged on the periphery of the support  40 . 
     The channels  41  are open at the side of the external surface of the support member  40  and are communicating with the meatus. The channels  41  therefore form a series of grooves on the external surface of the support  40 . 
     According to a different embodiment, each channel  41  is closed laterally, that is surrounded laterally by the non-conductive material of the support  40 . 
     The channels  41  preferably have a cylindrical shape. 
     The superheating device  31  comprises at least one electrically conductive element, not visible in the figures. 
     The at least one electrically conductive element is arranged in the channels  41  of the support member  40 . 
     The electrically conductive element includes an electrically conductive filament. More specifically, the electrically conductive element consists of an electrically conductive filament. 
     Preferably the electrically conductive filament is made of a metallic material or an alloy of metals. 
     Preferably the metal alloy used is the Nickel-Chrome alloy. Even more preferably, the filament is made of 80% Nickel and 20% Chrome alloy. 
     The filament is inserted in the channels  41 , in particular the filament comprises a series of longitudinal sections that run along relative channels  41  for the entire length, and a series of transversal sections which connect the adjacent longitudinal sections. 
     The filament is connected, by means of special terminals  42 , to a source of electrical energy to be heated to a temperature such as to emit electromagnetic radiation which allow the steam to be heated up to the operating temperature T by irradiation. It must be noted that the filament in use quickly reaches a temperature suitable for the emission of electromagnetic radiation, reducing the time required to heat the steam. 
     The filament emits radiation with a wavelength within the infrared wavelength range. 
     It is noted that the filament reaches temperatures of about 1100° C. in an optimized time interval of about 7 seconds. 
     In the case of the embodiment which provides the channels  41  forming respective grooves, it is possible that a series of spacer elements  43  are arranged between the external surface of the support  40  and the internal surface of the containing body  39 . The spacer elements  43  prevent contact from being established between the electrically conductive filament and the containing body  39 , in the presence of any condensation drops of the steam. 
     The internal surface of the containment body  39  is subjected to a surface treatment which makes it reflective. The surface treatment is, for example, electrolytic polishing. The reflective surface increases the efficiency of the heat exchange as it limits the dispersion of energy towards the outside of the superheating device  31 . 
     In addition to the steam generated by the steam generating device  30 , the superheating device  31  also receives the exhausted steam produced in the cooking chamber  4  during operation. 
     More specifically, the apparatus comprises recirculation means  44 , communicating with the cooking chamber  4 , which are configured to convey the exhausted steam from the cooking chamber  4  to the superheating device  31 , so that the exhausted steam is heated up to the operating temperature T and then inserted again into the cooking chamber  4 . 
     The recirculation means  44  are arranged in the casing  2  and include a recirculation conduit  45 , which allows the exhausted steam to flow from the cooking chamber  4  towards the superheating device  31 . 
     The recirculation conduit  45  is connected, at one end, with a recovery opening  46 , made on a wall of the cooking chamber  4 . 
     At the opposite end, the recirculation conduit  45  is connected to a connection conduit  47 , which conducts the steam entering the superheating device  31 . 
     A further conduit is connected to the connection conduit  47 , which transports the steam from the steam generating device  30  to the superheating device  31 . 
     It is possible to provide that the recirculation conduit  45  is connected directly to the superheating device  31 . 
     The recovery opening  46  is obtained on a wall of the cooking chamber  4 , in a region of the chamber in which the fluid has worse predetermined thermo-fluid dynamic characteristics than the fluid dynamic characteristics of the fluid in the remaining regions of the chamber, during an operating step of the apparatus. 
     Preferably said thermo-fluid dynamic characteristics include the temperature of the fluid and/or the average speed of the fluid and/or the percentage of oxygen. 
     From the results of fluid dynamic studies conducted on the fluid circulating in the cooking chamber, in a steady-state operating step, it has been observed that the exhausted steam is concentrated in the region or regions where the thermo-fluid dynamic characteristics of the fluid are worse than the corresponding characteristics of the fluid in the remaining regions of the chamber. 
     It is possible to divide the chamber  4  into a series of regions, characterized by different average values of the thermo-fluid dynamic characteristics of the fluid. 
     The recovery opening  46  is made, for example, in the region or in one of the regions having the lowest average speed value with respect to the average speed values in the remaining regions of the chamber. 
     According to an embodiment of the invention, the recovery opening  46  is obtained on the top wall  6  of the cooking chamber  4 . In particular, the recovery opening  46  is made close to one side of the top wall  6  opposite to the connection side with the rear wall  9 . 
     It has been observed in the aforementioned fluid dynamic studies that the positioning of the first exhaust opening  32  and the recovery opening  46  in the regions of the cooking chamber  4  in which the average speed of the fluid is lower, prevents the formation of areas of stagnation in chamber  4  and promotes the circulation of the fluid. 
     The recirculation conduit  45  comprises a first portion, which develops starting from the recovery opening  46  above the cooking chamber  4 , and a second portion, which extends in the region of the casing  2  comprised between the rear wall  9  of the compartment  3  and the casing  2 . 
     A valve means, not shown, suitable for adjusting, on command of the control unit, the quantity of exhausted steam which is conducted to the inlet to the superheating device  31  may be associated with the recirculation conduit  45 . 
     The valve means are movable, on command of the control unit, between an opening configuration, in which they allow the passage of the exhausted steam from the cooking chamber  4  to the superheating device  31 , and a closing configuration, in which they block the passage of the exhausted steam to the superheating device  31 . 
     Preferably, the valve means comprise a valve provided with a shutter which may be actuated by the control unit to set the quantity of exhausted steam which passes through the recirculation conduit  45 . 
     The operation of the apparatus for cooking food with superheated steam is easily understood from the foregoing description. 
     At an early stage, a user proceeds to switch on the apparatus through the control panel, and, if the steam cooking mode is selected, the control unit activates the steam generating device  30  to store a predetermined quantity of energy to be used, in a subsequent step, for generating the steam to be introduced into the cooking chamber  4 . 
     The step of activating the steam generating device  30  provides for supplying the heating elements  36  to heat the thermally conductive elements  38  and storing the energy that will be used, subsequently, to generate steam in the thermally conductive elements  38 . 
     The heating of the thermally conductive elements  38  is carried out for an interval of time sufficient to allow the achievement of a suitable temperature T 1 . 
     Preferably the temperature T 1  is between 100° C. and 600° C. Even more preferably, the temperature T 1  is lower than the Leidenfrost temperature. 
     The supply of the heating elements  36  is interrupted when the aforementioned temperature T 1  of the thermally conductive elements  38  is reached, and this is signaled by a warning signal. 
     The warning signal may be visible, for example, in the control panel, to promptly inform the user that the apparatus is ready for use. 
     The user then inserts one or more food to be cooked or heated inside the cooking chamber  4 , through the access opening  11 , placing them resting on at least one pan. 
     The user then closes the door  12 , in order to isolate the cooking chamber  4  from the external environment, and the control unit activates again the steam generating device  30  to generate the steam. The steam generating step involves feeding the heating elements  36  and inserting a liquid inside the device until a maximum quantity of liquid is reached. 
     The step of inserting the liquid is carried out discontinuously and between one liquid injection and the next injection a first time interval Δt 1  lapses. 
     Preferably the first time interval Δt 1  is between 1 and 60 seconds. 
     Each step of injection of liquid takes place in a second time interval Δt 2 . 
     Preferably the second time interval Δt 2  is between 1 and 60 seconds. 
     The values of the above time intervals are stored in the memory of the control unit. 
     Steam is generated initially by direct contact of the liquid with the previously heated thermally conductive elements  38 . 
     After a predetermined time interval Δt 3  from the beginning of the step of injection of liquid and before the end of the step of injection of liquid, the steam is generated by direct contact of the liquid with the thermally conductive elements  38  and by boiling the liquid. 
     The boiling of the liquid takes place mainly thanks to the energy transferred by the heating elements  36  to the liquid. 
     In this steam generating step, the synergistic action of the heating elements  36  and of the thermally conductive elements  38  is exploited. 
     Preferably said predetermined time interval Δt 3  from the beginning of the step of injection of liquid is between 30 and 80 seconds. 
     At the end of the step of injection of liquid, the steam is generated by boiling the liquid by the heating elements  36 . The thermally conductive elements  38  contribute to the boiling by transferring the remaining energy to the liquid. 
     The produced steam flows into the superheating device  31  and, when passing through the device  31 , is heated by irradiation by the electrically conductive filament up to an operating temperature T. 
     Preferably the steam is heated to an operating temperature T between 130° C. and 600° C. 
     The superheated steam passes through the inlet opening  34  in the cooking chamber  4  and is distributed in the chamber  4  independently or by the action of the ventilation device  18 . 
     The superheated steam introduced into the cooking chamber  4  replaces, completely or for the most part, initially present oxygen, which is expelled out of the cooking chamber  4  through the first discharge opening  32 . 
     In an operating step of the apparatus, essentially steam or steam mixed with further gases, such as nitrogen and oxygen, may be present inside the chamber  4 . 
     Reference is made below only to the exhausted superheated steam as the fluid recovered from the recirculation means, considering however that the recovered fluid may comprise steam together with further gases, as specified above. 
     According to an aspect of the invention, the exhausted superheated steam is conducted, thanks to the pressure gradient generated by the action of the ventilation device  18 , inside the recirculation conduit  45  to be conveyed to the inlet of the superheating device  31 . The exhausted steam passes through the superheating device  31  to be heated again up to the operating temperature T. 
     The quantity of exhausted steam entering the superheating device may be controlled by the control unit through the valve means. 
     The control unit constantly monitors the quantity of steam necessary to cook the food on the basis of the data it receives from the sensor means and/or according to the data relating to the duration of the cooking process steps stored in the memory, and controls the supplying of the steam generating device  30 , as well as the superheating device  31 , so as to have an adequate supply of superheated steam in the cooking chamber  4 . 
     Before the end of the cooking step, the chamber  4  is dried in order to allow easy extraction of the food. 
     The drying step provides for operating the adjusting member of the cooling conduit  28 , to allow the entry of air from the outside towards the inside of the chamber  4 , through the cooling conduit  28 . 
     The apparatus object of the present invention achieves the aim of optimally preserving the nutritional properties of foods and their healthiness thanks to the provision of a steam generating device comprising one or more heating elements and one or more thermally conductive elements, which are heated by the heating elements to store a predetermined amount of energy to be used for the generation of steam at an early stage, in which each heating element comprises an electrical resistance having a substantially flat spiral shape. 
     More specifically, it should be emphasized that the thermally conductive elements, heated by the heating elements, allow the steam to be produced by direct contact with the liquid, decreasing the time necessary for generating of steam, at an early stage of operation of the apparatus. Therefore, an injection of steam into the cooking chamber is obtained in an optimized time, as well as a consequent reduction in the time required for the dislocation of oxygen from the cooking chamber, by replacement with the introduced steam. An important aspect is that the configuration of each substantially flat spiral electric resistance allows an optimal ratio between the generated power and the volume of introduced liquid to be obtained, since each spiral-shaped electric resistance occupies a limited volume and, therefore, allows the reduction of the volume of liquid necessary to keep it submerged. Consequently, the volume of liquid that must be introduced into the steam generating device is reduced and the time interval for generating steam is therefore reduced. At the same time, a further advantage offered by the configuration of the spiral resistances is that of exploiting their geometry, and in particular the length, to generate an increased power. 
     An effect of the decrease in the time required to generate steam, and therefore of the decrease in the time to expel oxygen from the cooking chamber, at least for the most part, is the fact that oxidation of some components of the food is limited or eliminated, such as, for example, vitamins and polyphenols, thus preserving the healthiness of the foods. 
     The apparatus also optimally preserves the nutritional properties of foods and their healthiness thanks to the fact that cooking with superheated steam is implemented. 
     A further aspect to be highlighted is that the method for generating steam object of the present invention guarantees a continuous flow of steam, since it provides for initially exploiting the energy stored in the conductive elements to generate steam and to exploit, until the insertion of the liquid, the synergistic action of the heating elements and the thermally conductive elements, generating steam in two ways, that is by direct contact of the liquid with the conductive elements and by boiling. 
     The steam generating method implemented by the apparatus makes it versatile, as it is possible to generate steam by direct contact of the liquid with said at least one thermally conductive element, exploiting the predetermined quantity of stored energy and, therefore, rapidly generating steam, but it is also possible to generate steam by direct contact of said liquid with said at least one thermally conductive element and by boiling of said liquid, after a predetermined time interval from the beginning of said step of insertion of said liquid. In this way it is possible to select the most suitable steam generation mode for the type of product to be cooked. 
     A further aspect to underline is that the superheating device contributes, in turn, to decreasing time required to generate superheated steam, considering that the electrically conductive filament heats the steam by irradiation and that this method of heat transfer is rather rapid. The decrease in the time required to superheat the steam leads to greater efficiency of the apparatus and helps to reduce the time of expulsion of oxygen from the chamber. 
     Finally, it is to be considered that the provision of the recirculation means, which recover the exhausted steam to re-energize it, reduces the time necessary to be able to have the superheated steam and therefore to obtain a more efficient apparatus. 
     The apparatus described by way of example is subject to changes according to different needs. 
     In the practical embodiment of the invention, the materials used, as well as the shape and the dimensions, may be modified depending on requirements. 
     Should the technical features mentioned in any claim be followed by reference signs, such reference signs were included strictly with the aim of enhancing the understanding of the claims and hence they shall not be deemed restrictive in any manner whatsoever on the scope of each element identified for exemplifying purposes by such reference signs.