EP0286505A1 - Microwave heating method and microwave oven - Google Patents

Abstract

Microwave method of heating a food product (1) of the type comprising a base (3) of dough or equivalent, and a more or less water-rich topping (4) characterised in that the food product (1) is firstly placed with its base (3) on a support (5) comprising a microwave absorbing material (6); then the food product (1) and the microwave absorbing material (6) are subjected to microwave radiation, and finally the topping (4) is subjected to infrared radiation. <IMAGE>

Description

The invention relates to a microwave heating method, more particularly to a food product in particular comprising a slice of bread or equivalent and a filling, and a microwave oven for carrying out the method.

Microwave ovens for heating food are well known (see for example Larousse Gastronomique - 1984 edition, page 449). It is therefore not necessary to recall in detail the principle and the methods of heating food by microwaves, these being, in general, within the reach of the skilled person.

Many alternative embodiments of oven have been proposed, which comprise, in the type of application considered here, an external enclosure; a heating cavity limited by metal walls, one of which incorporates a door; a microwave generating magnetron (frequency 2450 Mhz and wavelength 12.2 cm usually) housed in the enclosure; waveguides from the magnetron to the cavity; an electric power supply unit associated with the magnetron; a support for food products to be heated in the cavity; conventional security means such as microwave sealing means, cutting microwaves with the opening of the door etc ...; and control means generally placed on the enclosure, outside, in particular near the door.

According to documents FR 2 220 959 and FR 2 489 646, the microwaves are introduced into the cavity through its upper part and there is provided, also in the upper part, a dynamic wave diffuser for an adequate distribution of the waves by reflection on the walls of the heating cavity. According to documents FR 2 524 616 and US 4 427 867, the oven comprises means of dynamic or static microwave radiation respectively, at the top, and means of static microwave radiation at the bottom. The magnetron is placed laterally and waveguides connect it to these upper and lower microwave radiation means respectively. According to documents FR 2 441 802, FR 2 442 405 and US 4 409 453, the oven is also convection, hot air being introduced into the cavity. According to documents FR 2 410 414 and US 4 327 266, the oven comprises dynamic microwave radiation means placed in the lower part associated with additional heating means placed in the upper part. Another embodiment in which the introduction of microwaves is made in the vertical middle part of the bottom of the oven, statically, is also known (document FR 2 341 101). According to documents FR 2 427 554, FR 2 532 510), the oven comprises a rotating antenna radiating hyper frequency energy, placed in the upper part and, associated, heating elements in particular placed in the upper part and in the lower part. The support dish of the food product to be heated is fixed and placed in the lower part. The magnetron is placed laterally in the upper part and associated with the rotating antenna by a waveguide. According to document US Pat. No. 3,536,878, the antenna is fixed, at the top, heating elements are placed at the top and bottom, the food product is supported by a movable dish at the bottom. According to document US Pat. No. 4,357,513, a generally similar structure is proposed with a fixed and non-movable food product support plate. According to documents GB 2 152 790, FR 2 428 954, FR 2 428 955 and FR 2 428 956, the oven comprises microwave radiation means and additional radiation heating means. According to document GB 978 197, the waveguide arrives at the bottom of the oven, under a support plate for the product to be heated.

These variants and many others are currently known or offered for sale by the main household appliance companies, for multipurpose household uses. These companies offer ovens with microwave heating exclusively or associated with a natural convection operation and / or with air circulation and / or with an infrared grill. These ovens include a rotating plate or a fixed plate supporting the food product to be heated, most often at the lower end of the heating cavity against its lower part; a mode mixer, most often at the top, to improve the distribution of microwaves in the heating cavity; one, two or even three magnetrons releasing microwaves by the upper part, most often, but also, sometimes by the lower part or both. The power restored in such ovens by microwaves varies generally from 70 W to 1600 W and, most often is between 200 W and 1000 W approximately. The volume of the heating cavity is generally between 18 l and 36 l, and most often between 201 and 30 l approximately. The internal dimensions of the heating cavity generally vary, for the length, between 175 mm and 650 mm, for the depth between 240 mm and 570 mm, and for the height between 180 mm and 530 mm; typical dimensions of the cavity being, for example, of the order of approximately 340 mm, 400 mm and approximately 315 mm, respectively. Such ovens are supplied with 220 V, 50 Hz electric current, the microwave frequency being 2450 Mhz.

There are also known, from the prior art, improvements made to the components of such ovens, in particular the turntable (document FR 2 587 423), waveguides, wave brewers, micro seals -waves, the support of the product to be heated (document EP 0 007 522).

The state of the art also reveals (documents FR 2 479 423, FR 2 210 072) the discontinuous operation of microwaves, the emission of microwaves being followed by an interruption, in order to avoid the phenomenon known as the name "thermal runaway".

There are also known devices for browning the food product to be heated intended for microwave ovens. According to documents FR 2 243 575, FR 2 586 921 and US 4 398 077 these browning devices consist of a coating absorbing microwave energy, such as metal oxides or ferrites, on a bottom or a plate made of a material transparent to microwaves such as glass or ceramic glass, receiving the food product to be heated. According to document US 3 878 350, this device comprises heating elements and an associated reflection plate.

Another form of microwave oven is known from document FR 2 412 221. This oven comprises a cylinder-shaped enclosure supplied in microwave by coaxial cables having radiating slots curved in the form of loops located in perpendicular planes to the axis of the cylinder. The cables are connected to a microwave power source. However, such an oven is not suitable, due to its design, for restoration or domestic use individual.

There are also known ovens more specifically intended for baking (documents FR 2 356 373, FR 2 443 205, FR 2 494 562 and FR 2 531 828). However, these ovens are also not suitable for catering or individual domestic use. Bakery product support plates for microwave ovens are also known (document US 4,369,346) in order to ensure regular baking of the dough.

Finally, it has already been demonstrated that microwave ovens are unsuitable for heating a food product of the pizza type, in particular frozen prepackaged, which comprises a base of bread dough covered with cheese, tomato coulis, garnish meat, fish, vegetable. Indeed, the dough is not sufficiently dry, after heating, to be crisp. It has been proposed to remedy this problem by means of an additional device (patent FR 2 504 378) placed in a microwave oven comprising a base provided with feet and an annular support part; a dish intended to rest on the annular part of the base, reflecting the microwaves and provided on its underside with a material which heats up in the presence of microwave energy such as ferrite particles; and, finally, a removable cover intended to rest on the base, enclosing the dish, in a material reflecting microwaves. The method of using this device consists in carrying out a first initial cycle of microwave radiation of two minutes without cover and then a second terminal cycle of microwave radiation of ten minutes with cover, the dish being garnished with the pizza to be heated . Besides that this device is complex, bulky, expensive, unsuitable for variable forms of food, its implementation is long (at least twelve minutes) and tedious (since it supposes heating in two distinct phases, therefore discontinuous, with intermediate handling of the cover, thus opening the oven). In document FR 2 367 003, the pizza is heated, by microwave in a special packaging, lost, which is inconvenient. In document US 4,369,346, the composition of the support plate is special.

The invention therefore essentially aims to solve the problem of microwave heating of a food product of the same type general than that mentioned above, that is to say comprising a base in bread dough or equivalent and a filling more or less rich in water or capable of giving off water or steam when heated, so that this heating is carried out by a single continuous operation (and not several successive operations as mentioned above), for a limited total time not exceeding about seven minutes for the food products more specifically targeted here and with a quality of the remarkable heated food product, namely hot as a whole with an interior temperature which is sufficiently well distributed and homogeneous, a "toasted" base sufficiently dry to present a mechanical resistance for the filling and to be pleasant to the taste and finally a "gratinage" of the filling , Above.

More specifically, the invention is intended for food products of the type generally described in document EP 85904833.2, consisting of a lower slice of bread and an upper culinary preparation forming a garnish.

Indeed, both the knowledge of a person skilled in the art and the experiments carried out demonstrate that household microwave ovens or the like currently known are unsuitable for this type of food product, as mentioned in document FR 2 504. 378.

To this end, the invention provides a microwave heating method of a food product more especially of the type comprising a base of bread dough or equivalent and a filling more or less rich in water in which:
. the food product is first placed by its base on a support comprising an absorbent material for microwaves;
. then the food product and the microwave absorbent material are subjected to microwave radiation;
. and, finally, the lining is subjected to infrared radiation.

The invention also provides a microwave oven of the type comprising an external enclosure; a generally shaped heating cavity parallelepipedic bounded by metal walls, one of which incorporates a door; a microwave generating magnetron; means for circulating the magnetron waves to the heating cavity; an electric power supply unit associated with the magnetron; a support for the body to be heated in the cavity; security means; control means; this oven being more especially intended for heating a body constituted in particular by a food product more especially of the type comprising a base of bread dough or equivalent and a filling more or less rich in water, characterized in that on the one hand, the magnetron is dissociated from, placed outside and separated from the enclosure and, on the other hand, the means of circulation of the waves comprise a coaxial cable.

According to other characteristics, the oven is such that the wave circulation means comprise a waveguide in the form of a tube with an axis perpendicular to the upper horizontal wall of the cavity, located with respect to this wall. , on the side opposite this cavity, to the right, at its lower end, of a window closed by a cover made of a material transparent to microwaves; the support of the body to be heated is fixed during the operation of the oven, constituted by a material transparent to microwaves, comprising an absorbent material for microwaves and provided with integrated means able to allow the release of water vapor; it includes heating means by infrared radiation located in the middle part of the height of the heating cavity, more particularly spaced from the cover of the upper horizontal wall; microwave radiation is static and direct on the body to be heated; the heating cavity has equal internal dimensions or of the order of 26 cm for the length, 16 cm for the width, 26 cm for the height.

• . La figure 1 est une vue en coupe, partielle (magnétron exclu), d'une forme de réalisation possible d'un four selon l'invention.
• . La figure 2 est une vue en coupe selon la ligne II-II de la figure 1.

The other characteristics and advantages of the invention will emerge from the description which follows with reference to the appended drawings in which:

• . Figure 1 is a partial sectional view (excluding magnetron) of a possible embodiment of an oven according to the invention.
• . Figure 2 is a sectional view along line II-II of Figure 1.

The invention provides a microwave heating method for a food product 1, shown diagrammatically, by means of a microwave oven 2. The food product 1 is more especially of the type comprising a bread dough base 3 or equivalent and a filling 4 more or less rich in water.

In the process according to the invention, the food product 1 is first placed by its base 3 on a support 5 of the oven 2 comprising an absorbent material 6 for microwaves; then the food product 1 and the absorbent material 6 for the microwaves are subjected to microwave radiation; and, finally, the lining 4 is subjected to infrared radiation.

The invention also provides a microwave oven of the type comprising an external enclosure 7; a heating cavity 8 of generally parallelepipedal shape limited by metal walls, in particular upper horizontal 9, lower horizontal 10, vertical bottom 11, left and right sides 12 and front 13, one of which - in particular the front wall 13 - incorporates a door 14 ; a microwave generating magnetron (not shown); means 15 for circulating the waves of the magnetron to the heating cavity 8; an electric power supply unit associated with the magnetron (not shown); a support 5 of the body to be heated placed in the cavity 8; security means (not shown); control means 16. This oven is more especially intended for heating a body constituted in particular by a food product 1 more especially of the type comprising a lower base 3 of bread dough or equivalent and an upper filling 4 more or less rich in water.

The food product 1 considered is not, in itself, the subject of the present invention. It is for example of the general type described in document EP 85904833.2.

However, the oven 2 may possibly be intended for other types of body to be heated or for other types of food products.

According to the invention, the heating method and the oven 2 are more specifically intended for the food product 1 originally frozen. and having to be, after heating by microwave, hot as a whole with a temperature sufficiently well distributed and homogeneous, a base 3 "toasted" sufficiently dry to have a mechanical resistance and be pleasant to the taste and finally a "gratinage" of the trim 4, from above. In addition, heating from the frozen state has a limited total duration, in particular less than about seven minutes for the kind of food products considered here and is carried out automatically by a single continuous operation, that is to say without need for manual intervention on the food product, without the need to open the oven.

More specifically, the food product 1 considered here has a base 3 having a thickness of the order of 1 cm to 1.5 cm and a filling 4 having a thickness of the order of 4.5 cm maximum. the base 3 can have an overall dimension of between 4 cm x 5 cm and 10 cm x 17 cm approximately. Such a food product 1 has a unit weight of between 10 grams and 350 grams approximately and, more specifically, of the order of 150 grams. It is understood that the method applies, as well, to a single food product of 150 grams, as to several similar food products, simultaneously, together representing a similar mass, for example two food products of approximately 75 grams each. It is clear that the values given for the heating time may vary within a certain limit depending on the mass of food product 1, these values therefore being only indicative.

The method and the oven 2 according to the invention are more especially intended for food products 1 divided into several distinct groups corresponding to several particular types of food products 1 each characterized by specific heating methods. These groups are determined in particular by the dimensions and the mass of the food product 1 and the nature as well as the thicknesses of the base 3 and of the filling 4.

According to another characteristic of the invention, the food product 1 is subjected essentially to direct and static radiation from the microwaves, this direct radiation being thus made possible due to the structure of the oven itself, as described below, and the specific application of oven 2 to the product food 1 considered here. More particularly, the microwave radiation is such that once introduced into the heating cavity 8, it reaches the food product 1 directly, at least to a large extent, without any particular reflection of the microwaves being sought on the walls 9 to 13 - as in the known state of the art - for a homogeneous distribution of the microwaves throughout the heating cavity 8, and without mixing modes.

The food product 1 having been placed on the support 5 comprising the absorbent material 6 for the microwaves, the support 5 and the material 6 are also, at least in part, bombarded directly by the microwaves. The support 5 is generally made of a material transparent to microwaves while the material 6 absorbs microwaves and, for this reason heats up, the heat being communicated to base 3 by conduction.

In the method according to the invention, the food product 1 is subjected to intermittent or chopped microwave radiation comprising alternating successions of emission periods and periods of interruption of microwave radiation. Such operation by cycle is known per se and the invention relates on the one hand, to the application of this operation to the specific method described here as well as to the specific methods of this operation per cycle.

According to another characteristic, the periods of emission of the microwave radiation are of the same duration and / or the periods of interruption of the microwave radiation are of the same duration and / or the periods of emission and the periods of interruption of radiation are of the same duration. The periods of emission of the microwave radiation or the periods of interruption of the microwave radiation have a unit duration of, for example, between approximately 10 seconds and approximately 60 seconds and, in particular, between approximately 20 seconds and approximately 30 seconds. In addition, provision is made for example between 3 and 12 cycles each comprising a succession of an emission period and an interruption period of the microwave radiation and in particular between 4 and 10 cycles. Naturally these values can be adapted, as necessary, according to each food product 1.

Possible purely illustrative examples of implementation comprise 4, 6, 8, 10 cycles with periods of microwave radiation and periods of interruption, the durations of which are for example both equal to approximately 20 seconds, or to approximately 30 seconds or alternatively 25 seconds and 50 respectively about seconds.

Other examples of implementation are possible depending on the food products 1.

According to another characteristic of the method according to the invention, the lining 4 is subjected to infrared radiation in the immediate vicinity in particular of the lining 4, more especially at a distance from the lining 4 of the order or less than a few centimeters, in particular less than 7 cm approximately and preferably less than 5 cm approximately. More specifically, the distance between the top of the lining 4 and the source of the infrared radiation is of the order of a centimeter or less than 3 cm.

The lining 4 is subjected to infrared radiation during and at the end of the submission of the food product 1 to the microwaves. More specifically, the duration of infrared radiation is short compared to that of microwave radiation. For example, the lining 4 is subjected to infrared radiation for a period of the order of 1 minute to 1 minute 30 seconds, for a total duration of the infrared radiation (duration of the periods of interruption included) of the order of 7 minutes. or less. To this end, infrared radiation with low thermal inertia is preferably used. In the same way as mentioned previously for microwaves, the duration indicated here for infrared radiation is only indicative and can be adapted as required.

According to another characteristic of the process according to the invention, the food product 1 is preferably subjected to microwave radiation with a power of the order of 1000W to 1200W, this with a view to satisfactory economic exploitation of the process.

Finally, according to another characteristic of the method according to the invention, the support 5 for the food products 1 is kept fixed during operation (microwave and infrared) and spaced from the wall in look of the oven 2, namely the lower horizontal wall 10 of the cavity 8. More particularly, as mentioned below, this spacing is equal to or of the order of magnitude of a quarter or a multiple of a quarter of the wavelength of the microwave radiation, in particular of the order of 40 mm (this for the low position of the support 5).

The invention also relates to a food product 1 of the general type described above, characterized in that it is heated by the process which has just been described. This food product 1 is originally, normally, in frozen form, at the usual freezing temperatures, that is to say below -18 ° C. The implementation of the process which has just been described allows on the one hand , to defrost this food product 1 and, on the other hand, to bring it to the temperature desired for its consumption, that is to say a temperature of the order of 40 ° to 60 ° C. In addition, the filling is at a sufficiently homogeneous temperature to avoid that the consumer does not experience the sensation of very hot zones and very cold zones, even though the lining 4 may possibly be highly heterogeneous as to its nature and possibly of very variable thickness, more important in the center of base 3 than on its edges. Finally, in combination, not only the food product 1 is heated as a whole but in addition the base 3 undergoes a "toasting" effect which has the result of stiffening it and giving it a mechanical strength enabling the lining 4 to be supported, while the lining 4 undergoes, for its part, a "gratinating" effect on the top which results in a satisfactory visual appearance, an improvement in the taste and a reinforced cohesion.

The general structure and the methods of producing details of certain components of the microwave oven 2 according to the invention are known per se to those skilled in the art and, for this reason, are not described in detail here. This is in particular the case of the microwave generating magnetron, as well as its power supply unit.

In a possible but non-limiting embodiment of the invention, the external enclosure 7 has a generally parallelepiped shape and is made of metal or plastic or equivalent with walls respectively upper horizontal 18, lower horizontal 19, bottom vertical 20, left and right sides 21 and front 22. For example, the enclosure 7 has equal external dimensions or of the order of 86 cm for the length (between the left and right side walls 21), 25 cm for the width (between the bottom 20 and front 22 walls), and 52 cm for the height (between the walls 18, 19). These dimensions are relatively modest and make it easy to incorporate the microwave oven 2 according to the invention among other devices for preparing food products in a kitchen or to increase the number of ovens in the case of use in restoration. The oven 2 can be placed on a work surface thanks to feet or even suspended, even built-in.

The heating cavity 8 is housed in the enclosure 7 and, more specifically, the front wall 13 of the cavity 8 constitutes a part of the front wall 22 of the enclosure 7. The upper horizontal walls 9, lower horizontal 10, vertical bottom 11 and left and right side 12 of the cavity 8 are spaced from the corresponding walls 18, 19, 20 and 21 of the enclosure 7 so as to provide an upper space 23 (essentially between the upper horizontal walls 9 and 18), a bottom space 24 (essentially between the vertical bottom walls 11, 20) and a bottom space 25 (between the bottom horizontal walls 10 and 19) and side spaces (not shown) between the side walls 12, 22 facing each other. The height of the upper space 23 is for example of the order of 20 cm, the depth of the bottom space 24 for example of the order of 7 cm and the height of the lower space 25 for example of l 'around 6 cm. These spaces 23, 24, 25 serve as a "technical gallery" for housing certain components of the oven 2 and also for maintaining thermal insulation (not shown).

The door 14 is not in itself the subject of the invention. Preferably, it is a pivoting door 14, for example by means of a vertical lateral or horizontal bottom hinge. The door 14 is preferably full and devoid of porthole, contrary to the usual practice, taking into account the control means 16 used.

The oven 2 includes means for evacuating the vapors, for example associated with the door 14 or arranged in any other way.

The control means 16 comprise keys, buttons, indicators, etc., described below, more especially located on the front wall 22 above or next to the door 14.

According to a first characteristic of the oven according to the invention, the magnetron is dissociated from, placed outside and separated from the enclosure 7. In addition, the means 15 for circulation of the waves comprise a coaxial cable 17, connecting the magnetron to enclosure 7.

The power supply unit is also dissociated from, separated from and outside of the enclosure 7, in order to be associated with the magnetron.

In general, although this is not in itself decisive, the magnetron and the power supply unit form a unitary block.

This constructive characteristic makes it possible to use a high power power supply, in particular of the order of 2 KW, therefore bulky, for example of a total size (power supply unit and magnetron) of the order 38 cm x 38 cm x 21.5 cm, without increasing the size of the enclosure 7 or affecting the dimensions of the heating cavity 8. In addition, this constructive arrangement is such that the magnetron and the supply unit are separated infrared radiation existing in the oven 2, which prevents their deterioration by heat. This constructive arrangement and the use of a separate antenna from that of the magnetron as described below, favor the direct microwave radiation mentioned above, which contributes to the heating efficiency of the food product 1.

The coaxial cable 17 for transmitting microwaves is known per se from the state of the art and is not in itself the subject of the invention.

This cable 17 includes the necessary connectors also known per se.

Preferably, the coaxial cable 17 passes through the upper space 23 and the bottom space 24 and emerges from the enclosure 7 through a passage provided for this purpose, in particular in the lower horizontal wall 19. The coaxial cable 17 comprises, side of the heating cavity 8, an elbow connector 26, rigidly fixed to a waveguide tube 27.

According to another characteristic of the oven 2 according to the invention, the means 15 for circulation of the waves also comprise a waveguide in the form of the tube 27 mentioned above, of axis 28 perpendicular or substantially perpendicular to the upper horizontal wall 9 of the heating cavity 8, in particular in the center or in the central zone of this wall. The waveguide tube 27 is located, with respect to the wall 9, on the side opposite to the cavity 8, that is to say in the upper space 23, at right, at its lower end 29, of a window 30 of the wall 9, closed by a cover 31 made of a material transparent to microwaves.

At its lower end 29, the waveguide tube 27 has returns 32 directed towards the outside forming a flange for fixing to the upper horizontal wall 9.

The waveguide tube 27 is terminated, at its upper end 33, opposite the window 30, by an adjustment piston 34. This piston 34 is of adjustable axial position by means of manual control means such as a knob 35 situated above the upper horizontal wall 18 of the enclosure 7.

The waveguide tube 27 has, for example, an equal axial length or of the order of 160 mm and a transverse cross section, for example rectangular, of equal dimensions or of the order of 43mm x 86mm. As can be seen in the figure to which reference is expressly made, the waveguide tube 27 vertically occupies most of the space existing between the upper horizontal walls 9 and 18, the spacing between these walls being determined by the axial length of the tube 27.

A microwave antenna 36, static, opens into the waveguide tube 27, in particular radially or substantially radially, that is to say perpendicularly or substantially perpendicular to the axis 28 while being spaced from the cover 31. The antenna 36 is spaced from the cover 31 by a distance equal to or of the order of magnitude of a quarter of the wavelength of the microwave radiation, in particular equal to or about 43 mm. The antenna 36 preferably has a generally cylindrical shape of approximately 15 mm in length and 8.7 mm in diameter.

Preferably and in the case where the oven 2 uses coaxial cable 17 as circulation means 15, the antenna 36 is associated with the central extension of the coaxial cable 17.

The cover 31 is made of any suitable material transparent to microwaves, such as, for example, silicone. This cover is rigidly and tightly fixed to the upper horizontal wall 9. It makes it possible in particular to prevent the vapors produced in the heating cavity 8 from being able to be introduced into the waveguide tube 27.

According to another characteristic of the invention, the support 5 is fixed, when the oven 2 is in operation, consisting of a material transparent to microwaves, but comprising or incorporating an absorbent material 6 for microwaves, this support 5 further comprising means 37 capable of allowing the release of vapors produced during "toasting".

The support 5 is, for example, constituted by a ceramic glass plate. The absorbent material 6 is constituted, for example, by particles of ferrite or metal oxide covering one or / and the other of the faces of this plate or incorporated in its thickness. Preferably, the absorbent material 6 is located in the central part of the surface of the support 5, that is to say in the zone where the food product 1 to be heated rests.

The means 37 capable of allowing the release of water vapor consist of upper grooves of the support 5 located on the side to be heated, that is to say that on which the food product 1 rests, in this case the upper force of the support 5 and, preferably opening at the periphery of the support 5 or in an equivalent manner outside the zone where the food product 1 rests. Failing to provide such means 37, it has been found that the "toasting" of the base 3 of the food product 1 caused water retention in this base 3 against the desired goal. Thanks to the grooves 37 thus provided, the water vapor emerging at the interface between the support 5 and the base 3 can be evacuated and does not soak the base 3. Then, the water vapor is evacuated from the cavity heating 8 by the evacuation means already mentioned previously integrated, for example, in door 14.

Preferably, the support 5 is devoid of absorbent material 6 at the bottom of the grooves 37, this constructive arrangement being optional.

According to another characteristic of the oven according to the invention, the support 5 is spaced from the lower horizontal wall 10 of the heating cavity 8. For example, this spacing is equal to or of the order of magnitude of a quarter of the length of microwave radiation wave, in particular of the order of 40 mm and this for the support 5 in the low position.

To this end, there are provided on the side walls 12 and optionally on the vertical bottom wall 11 of the cavity 8 means for holding the support 5. For example, these holding means can be constituted by grooves 38. Preferably, several grooves 38 - for example three - are provided, corresponding to three levels of spacing of the support 5 relative to the lower horizontal wall 10.

The grooves 38 make the support 5 removable.

In a possible embodiment (illustrated by the figure), there is provided in addition to a groove 38 spaced from the lower horizontal wall 10 by a distance of the order of 40 mm, two other grooves placed above at a distance respectively approximately 20 mm and 40 mm from the first groove 38. The different grooves are used depending on the food products 1 to be heated.

According to another characteristic of the oven according to the invention, the oven 2 also comprises means of heating by infrared radiation 39 situated in the middle part of the height of the heating cavity 8, more particularly spaced from the cover 31 provided in the upper horizontal wall 9.

The infrared radiation heating means 39 are placed in the immediate vicinity of the food product 1 in particular above the lining 4 and away from the cover 31. For example, the infrared radiation heating means 39 are placed at a distance of the order of a centimeter or a few centimeters from the top of the lining 4 and at a distance equal to or on the order of more than 140 mm from the cover 31.

The infrared radiation heating means 39 are preferably with low thermal inertia and are constituted, for example by quartz tubes. They are carried by the left and right side walls 12 and by means of appropriate insulation parts and are associated with an electrical connector. The maintenance of the heating means by infrared radiation 39 and the passage of the corresponding electrical supply, as well as the housing of the connector, are made possible by the lateral and bottom spaces 24.

Preferably, there are provided two infrared radiation tubes spaced horizontally from one another, parallel to each other, spaced from each other by a distance of the order of 3.5 cm.

The infrared radiation heating means 39 are protected and masked frontally by a cover 41 capable of absorbing the high temperature produced by the infrared heating. This cover 41 is also carried by the side walls 12. It prevents the user inadvertently from affecting the radiation tubes 39.

The spacing between the infrared radiation heating means 39 and the support 5 of the body to be heated is of the order of a few centimeters, as has been said above, in particular between approximately 3 and 8 cm depending, in particular on the support position 5.

The presence of the infrared heating means 39 makes it possible not only to ensure the "gratinating" of the lining 4, but also to a favorable effect on microwave radiation, in any event does not adversely affect this radiation. In addition, the infrared heating means 39 being placed in the middle part of the heating cavity 8, it follows that they cannot damage the cover 31, neither the magnetron nor the power supply unit placed outside enclosure 7.

According to another characteristic of the oven according to the invention, the microwave radiation is static and direct on the food product 1 to be heated. This means that the oven does not have a mode mixer or a rotating antenna or equivalent, and that the waveguide tube 27 is placed in such a way that the waves produced are directed directly to the support 5 and, more precisely, to the area of the support 5 receiving the food product 1.

According to another characteristic of the invention, the heating cavity 8 has equal internal dimensions or of the order of 26cm for the length, 16cm for the width, and 26cm for the height.

It should be understood here that the dimensions indicated which correspond to a possible form of implementation may however vary according to the food products 1 considered. In any event, the present invention also relates to all dimensions included in a range of plus or minus 10% relative to the given values.

The control means 16 comprise, for example, an on-off button accompanied by a visual signal, as well as several selection keys - for example, four keys - corresponding to several - for example four - types of given products. Each of these keys corresponds to a given oven 2 operating cycle (total duration of microwave infrared radiation, sequence of cycles of microwave radiation). The oven being more specifically intended, because of its structure, for specific food products 1, it is possible to program, according to the types of food products to be heated, the operating cycles of the oven. In addition, the control means may include a visual and / or audible signal indicating the end of an operating cycle. In this way, it is not necessary to provide in the door 14 a window for checking the heating state of the food product 1.

It is emphasized here that the oven 2 according to the invention is characterized both by the above-mentioned constructive arrangements taken individually but also by these various constructive arrangements combined with each other, this combination allowing the optimal operation of the oven.

Claims (24)

1) Method for heating by microwave a food product (1) of the type comprising a base (3) of bread dough or equivalent and a filling (4) more or less rich in water, characterized in that:
. the food product (1) is first placed by its base (3) on a support (5) comprising an absorbent material (6) for microwaves;
. then the food product (1) and the absorbent material (6) for the microwaves are subjected to microwave radiation, essentially direct;
. and, finally, the lining (4) is subjected to infrared radiation. 2) Method according to claim 1, characterized in that the food product (1) is subjected to intermittent microwave radiation comprising alternating successions of emission periods and periods of interruption of microwave radiation. 3) Method according to claim 2, characterized in that the periods of emission of the microwave radiation are of the same duration and / or the periods of interruption of the microwave radiation are of the same duration and / or the periods of emission and the periods of interruption of microwave radiation are of the same duration; and the periods of emission of the microwave radiation or the periods of interruption of the microwave radiation each have a duration of between 10 seconds and 60 seconds, more especially between approximately 20 seconds and approximately 30 seconds. 4) Method according to any one of claims 2 and 3, characterized in that it comprises between 3 and 12 cycles of succession of a period of emission and a period of interruption of microwave radiation, more especially between 4 and 10 cycles. 5) Method according to any one of claims 1 to 4, characterized in that the lining (4) is subjected to infrared radiation, in the immediate vicinity, more particularly from a distance of the order of or less than a few centimeters, in particular less than about 5 cm, during and at the end of submission to the food product (1) to microwave radiation. 6) Method according to any one of claims 1 to 5, characterized in that a food product (1) is heated whose base (3) has a thickness of the order of 1 cm to 1.5 cm, and the lining (4) of which has a thickness of the order of 4.5 cm maximum, the base (3) possibly having a dimension of between 4 cm x 5 cm and 10 cm x 17 cm approximately, the mass of the food product being between 10g and 350g in particular of the order of 150g. 7) Method according to any one of claims 1 to 6, characterized in that the lining (4) is subjected to infrared radiation for a period of the order of 1 minute to 1 minute and 30 seconds. 8) Method according to any one of claims 1 to 7, characterized in that the food product (1) is subjected to microwave radiation with a power of the order of 1000W to 1200W. 9) Method according to any one of claims 1 to 8, characterized in that the support (5) of the food products (1) is kept away from the wall (10) opposite the microwave oven (2) . 10) Microwave oven of the type comprising an external enclosure (7); a heating cavity (8) of generally parallelepipedal shape limited by metal walls (9, 10, 11, 12, 13) one of which (13) incorporates a door (14); a microwave generating magnetron; means for circulating (15) waves of the magnetron to the heating cavity (8); an electric power supply unit associated with the magnetron; a support (5) of the body to be heated in the cavity (8); security means; control means (16); this oven being intended to heat a body constituted in particular by a food product (1) more especially of the type comprising a base (3) of bread dough or the equivalent and a filling (4) more or less rich in water, characterized in that on the one hand, the magnetron is dissociated from, placed outside and separated from the enclosure (7) and, on the other hand, the means (15) of circulation of the waves comprise a coaxial cable (17). 11) Microwave oven according to claim 10, characterized in that the wave circulation means (15) comprise a waveguide in the form of a tube (27) with an axis (28) perpendicular to the upper horizontal wall (9) of the cavity (8), located, with respect to this wall (9) on the side opposite this cavity (8), at right, at its lower end (29) of a window (30) of the wall (9) closed by a cover (31) made of a material transparent to microwaves. 12) Microwave oven according to claim 11, characterized in that the waveguide tube (27) is terminated, at its upper end (33) opposite the window (30) by an adjustment piston (34) of the waveguide. 13) Microwave oven according to any one of claims 11 and 12, characterized in that a radiation antenna (36) of the microwaves (27) opens into the waveguide tube, in particular radially or substantially radially and away from the cover (31). 14) Microwave oven according to claim 13, characterized in that the antenna (36) is associated with the central extension of a coaxial cable (17). 15) Microwave oven according to any one of claims 10 to 14, characterized in that the antenna (36) is spaced from the cover (31) by an equal distance or of the order of magnitude of a quarter of the wavelength of the microwave radiation, in particular equal to or of the order of 43 mm; the waveguide tube (27) has an equal axial length or of the order of 160 mm, or has a rectangular cross section of equal size or of the order of 43cm x 86 cm. 16) Microwave oven according to any one of claims 10 to 15, characterized in that the support (5) of the body to be heated is fixed when the oven is in operation, constituted by a material transparent to microwaves, comprising an absorbent material (6) for microwaves and, comprises means (37) capable of allowing the release of water vapor. 17) Microwave oven according to claim 16, characterized in that the means (37) able to allow the release of water vapor are constituted by upper grooves of the support (5) located on the side to be heated, leading to the periphery of the support (5). 18) Microwave oven according to any one of claims 16 and 17, characterized in that the support (5) is devoid of absorbent material (6) at the bottom of the grooves (37). 19) Microwave oven according to any one of claims 16 to 18, characterized in that the support (5) is spaced from the lower horizontal wall (10) of the heating cavity (8), with an equal spacing or of the order of magnitude of a quarter of the wavelength of the microwave radiation, in particular of the order of 40 mm. 20) Microwave oven according to any one of claims 10 to 19, characterized in that it comprises heating means by infrared radiation (39) located in the middle part of the height of the heating cavity (8) , more particularly spaced from the cover (31) of the upper horizontal wall (9), the spacing between the heating means by infrared radiation (39) and the cover (31) is in particular equal to or of the order of 140 mm. 21) Microwave oven according to claim 20, characterized in that the heating means by infrared radiation (39) are protected and masked frontally by a cover (41). 22) Microwave oven according to any one of claims 20 and 21, characterized in that the spacing between the heating means by infrared radiation (39) and the support (5) of the body to be heated is order of a few centimeters, in particular between 3 cm and 8 cm. 23) Microwave oven according to any one of claims 10 to 22, characterized in that the microwave radiation is static and direct on the body to be heated. 24) Microwave oven according to any one of claims 10 to 23, characterized in that the heating cavity (8) has equal internal dimensions or of the order of 26 cm for the length, 16 cm for the width, 26 cm for height.

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