EP1074171A1

EP1074171A1 - Device and method for preparing food portions

Info

Publication number: EP1074171A1
Application number: EP99913202A
Authority: EP
Inventors: Gunnar Paul; Oskar Wipf; Harald Lang; Albert Enzl
Original assignee: GVL Gesellschaft zum Vertrieb von Lebensmittelautomaten und -produkten mbH
Current assignee: GVL Gesellschaft zum Vertrieb von Lebensmittelautomaten und -produkten mbH
Priority date: 1998-02-27
Filing date: 1999-03-01
Publication date: 2001-02-07
Also published as: AU3142499A; WO1999044394A1

Abstract

The invention relates to a device for preparing food portions (4) comprising a microwave compartment (1) in which a portion (4) can be heated. At least one part of a boundary (2) of the microwave compartment (1) is configured as a cooking surface (2'). An extremely quick preparation can be carried out by means of heating and cooking when the portion is placed on the cooking surface (2') in the microwave oven. The dimensions of the device can be adjusted to extremely small sizes such that it adapts to the size of possible portions. The method for preparing food portions (4) provides that during heating by means of microwaves, two opposite outer surfaces of the portion (4) are in contact with cooking surfaces (2').

Description

- 1 -

Device and method for preparing food portions

The invention relates to a device according to the preamble of claim 1 and to a method according to the preamble of claim 9.

In restaurants and especially in fast food establishments, ready-to-eat portions of food must be delivered shortly after ordering. The preparation must not be labor intensive. For this purpose, entire menus or parts of them are prepared beforehand and stored until the order, or until shortly before delivery. Immediately before delivery, these menus are heated to the desired delivery temperature in a microwave oven or, if appropriate, in a steam heater. With fried or roasted food, it is not advisable to store them in the roasted state. Therefore, roasted side dishes, such as grated potato masses, corn slices, dough products, patties or even pieces of meat, are roasted directly before delivery. Because the food is stored frozen or chilled, the portion to be roasted is heated in a microwave oven, for example, and then roasted or seared on a roasting surface. The manipulations required are complex and include inserting and removing the microwave oven and setting the desired roasting temperature in the roasting device, inserting the roasted product, monitoring the roasting process, in particular also turning over on both sides, and finally removing.

In order to shorten the preparation time, a frying pan was developed in accordance with US Pat. No. 5,166,485, which can be used in a microwave oven. When preparing a hamburger, it is first fried on one side in the heated frying pan, then it is turned over and placed in the microwave oven together with the pan. There the interior of the hamburger is heated by microwaves. At the same time carried out on the still hot skillet a further ^¬ the second page of the hamburger fry. The disadvantage of this solution is that one person goes through the process during the entire preparation process. - 2 -

or monitor the times of the two main steps. In addition, a frying pan and the microwave oven are occupied during the preparation time. The best possible preparation time is still 6 minutes and is therefore not significantly less than the time of 9 minutes which is required for conventional preparation in the frying pan.

From US 5 1 07 087 a container is known which convey approximately in the microwave oven allows the browning of near ^¬. For this purpose, the container comprises a heat absorption layer which, due to a high dielectric constant, converts energy from the microwave field into heat. This warmth is as

Contact heat can be transferred to the food so that it is browned in the contact area with the container. Due to the high dielectric constant of the container, the microwave field is changed significantly. This affects the heating of the food through the direct absorption of energy from the microwave field. This in turn affects one

Slowing down of the preparation process, because the heat transfer from the container to the good takes place through contact heat and is therefore slow.

A microwave oven with a device for providing a high-frequency magnetic field is known from US Pat. No. 5,698,125. This magnetic

Alternating field is used for inductive heating - ie for heating by means of induction currents - of a receptacle, in particular a frying pan, on the support surface in the microwave oven. The bottom of the oven is designed so that the alternating magnetic field can penetrate into the interior of the oven, but the microwaves cannot escape from the oven. For this purpose, two layers with a large number of straight conductor tracks are arranged in the bottom of the furnace interior. The conductor tracks of the two layers run transversely to one another. If, for example, a hamburger is to be fried on both sides and heated sufficiently in the center, the frying pan must be removed from the oven to turn the hamburger. This involves a control effort because the turning must take place at the right time. Also, taking it out of the oven - 3 -

turning and reinserting in the oven involves work and a loss of time.

From US 5 61 6 266 a microwave oven is known, on the rear wall of which an electrical resistance heating element is arranged. The flat heating element enables the interior of the furnace to be heated. As a result, a preparation process which can be carried out in conventional ovens can also be carried out in a microwave oven. The overall process can be accelerated somewhat due to the microwave contribution. Nevertheless, quick searing or browning cannot be achieved.

EP 247 574 A1 discloses a microwave oven with a radiant heat element arranged on its ceiling. As a radiation source, the radiant heat element comprises electrical resistance wires, a halogen lamp or a quartz lamp. To protect the radiation source, an infrared-permeable glass ceramic plate is arranged below it. The additional radiant heat source in a standard microwave oven cannot ensure that the preparation is quick enough. In addition, the underside of the product cannot be browned.

The known microwave ovens are very large in relation to the portion portions to be heated.

The invention is based on the object of finding a small-sized device and / or a method which, with little effort, makes it possible to roast or roast portions of food in an extremely short time on at least one side and on the inside bring a desired temperature.

This object is solved by the features of claim 1 or 9. The dependent claims describe advantageous variants. As a rule, this also avoids major weight losses in the food portion when heated. When the task was solved, it was recognized that the microwave ovens used for preparing food are standard ovens. Their inner dimensions are much larger than the outer dimensions of side dishes or product portions. The dimensions are so large that different plates, plates or bowls with food, as well as cups with drinks can be used. In addition, the interior should have as many resonances as possible for the microwaves used. In order to ensure that the foodstuffs introduced are heated essentially independently of their position in the oven, an attempt is made to build up a multimod microwave field by superimposing frequently reflected partial waves, the energy density of which is distributed as evenly as possible. To enable the partial waves to be reflected undisturbed and the partial waves to act on the product from all directions, an edge area is kept clear along the inside of the furnace. The support surface is arranged at a distance from the peripheral surface in the interior of the furnace. Because a comparative energy density cannot be achieved easily enough with simple means and the field also depends on the introduced material, a turntable is arranged in many microwave ovens for receiving the material to be heated. On the rotating plate, the goods pass through various field areas, which leads to a more even heating effect.

In a first step towards solving the task, it was recognized that the approaches of the standard microwave ovens should not be used. Rather, a solution had to be found that initially assumes that the differences in dimensions of the different portions of the side dish are not great and that the portions can always be positioned essentially the same in the microwave oven. Instead of a spatially constant distribution of the energy density of the microwave field, the microwave field should be designed in the presence of the product portion so that it is heated as quickly and as completely as possible. - 5 -

The common product portions are essentially layered and have longitudinal and transverse dimensions in the range from 5 to 20 cm. The layer thickness is in the range of 0.5 to 6 cm. A recording area of approx. 20x20x6 cm is sufficient to accommodate such portions. Because the microwave field is built up from a source or a magnetron, a spreading area for the microwaves must be provided between the magnetron and the portion to be heated. The common products have large dielectric constants in the thawed state and accordingly lead to a strong microwave absorption. If, for example, penetration depths in the range of approx. 3 cm are assumed, it is clear that the

Microwave propagation in the layer direction through the product is not sufficient to apply a sufficiently high energy density to the area of the product facing away from the magnetron. The product would be very strong in the area against the magnetron, but only very slightly warmed in the area facing away from it. If only a partial area facing the magnetron was heated, it would be possible to even out the temperature distribution by rotating the product portion. Instead of the predominant heating of the partial area facing the magnetron, the spreading and the receiving area should preferably be dimensioned such that the microwave field can also spread around the product portion.

As a result, sufficiently high energy densities are also available in the remote area.

When dimensioning the microwave space, the frequency or the wavelength of the magnetron must be taken into account. When choosing the frequency, you are bound to the permitted frequencies of 2.45, 5.8 or 24 GHz. Although there are lower diffusion paths at 5.8 GHz and may therefore be advantageous under certain conditions, the magnetons commonly used for heating purposes, in particular due to the low cost, generally have a frequency of 2.45 GHz and correspondingly a wavelength in a vacuum of approx. 1 2.5 cm. If a layered recording area with a length and a width in the range of approx. 20 cm and a thickness of 6 cm was assumed above, it can be seen that the - 6 -

Extension in the layer direction, or the longitudinal dimension is between one and two wavelengths of the microwaves to be used with preference.

In a second step to the solution of the problem, it was recognized that when using a magnetron with a frequency of 2.45 GHz, the longitudinal extent of the layered recording area should preferably be essentially in the range of 25 cm, that is to say of two wavelengths. The feed or feed area with the magnetron should preferably be in the longitudinal direction in the range of a wavelength, that is in the range of 1 2.5 cm.

By dimensioning the longitudinal extent of the receiving area and the feed area of a layered overall area in the range of a few multiples of the wavelength and by providing essentially planar reflection surfaces for delimiting the longitudinal extent, a quasi standing wave structure with few knot lines or a monomod structure can be achieved . Such a monomodal structure is also conceivable to achieve at least part of the effect according to the invention regardless of the formation of at least one boundary surface of the microwave space as a roasting surface. The microwave room has only a few for the wavelength used

Resonances. The wave structure is not characterized by an overlay of multiple reflected partial waves. This also applies if the effective wavelength deviates somewhat from this wavelength due to the dielectric constant of the product. Multiple reflections are not possible because the area is layered and because a large proportion of waves would have to run through the product portion several times, which fills a large part of the recording area. However, the absorption in the product portion is so high with a common product that a partial wave cannot pass through the product portion several times. Therefore, the process may require minor adjustments to the products. Only a quasi standing wave structure can build up as a forced vibration excited by the magnetron. A standing wave has the advantage that it extends over the entire recording area and thus over the entire portion of the product. The node areas, - 7 -

in which little heat is generated are so narrow that heat from neighboring areas with large amplitudes reaches these node areas sufficiently quickly.

Impedance measurements and subsequent heating tests in the layered recording or microwave room with a disk-shaped product portion arranged at different distances from the magnetron have shown that the position with the maximum impedance does not match the position of the most uniform heating. If the product is arranged in such a way that the impedance is at a maximum, then it is overheated or burned in the form of a sector of a circle on the side facing the magnetron, while it otherwise remains cold. It seems that in the situation with the maximum impedance, no standing wave structure can be built up, but a predominant part of the energy emanating from the magnetron is directly absorbed as radiation. By increasing the distance between the product portion and the magnetron, a position could be found in which the impedance is lower, but the heating takes place extremely quickly and essentially over the entire portion. It was found that the temperature distribution has a radial gradient immediately after heating. The inside was the lowest and the outside the highest. In a test, a temperature of 95 ° C was measured immediately after heating and a temperature of 70 ° C in the center. Approximately 30 seconds after the removal, the temperatures had essentially equalized and a temperature above 85 ° C. was measured everywhere.

The layered microwave space can have a thickness that is directly adapted to the thickness of the product portion. This means that the microwave amplitude required for heating can also be achieved in the vicinity of the large boundary surfaces. The microwave space closed off on both sides by these large boundary surfaces, in particular above and below, can thus have a layer thickness which is less than 12 cm, or less than one wavelength, and in particular also less than 6 cm, or less than half a wavelength is. Because placing the product in contact with - 8th -

the large boundary surfaces do not lead to undesirable disturbances in the monomodal microwave field, there is no need for a contact surface in the interior of the microwave space. Accordingly, at least a large boundary surface will be formed as a receiving or contact surface for the product. However, the two large boundary surfaces are preferably designed as contact surfaces. Because the boundary surface is now designed directly as a contact surface for the product, it can be designed both as a reflection surface for the microwaves and as a heating or roasting surface for giving off heat to the adjacent product.

In order to ensure the microwave reflection, the border must include an electrically conductive layer, for example a wire mesh or a metallic coating. In order to be able to emit heat supplied from the outside, the edges must be heat-conducting or let heat radiation pass through. At the heat-emitting contact surface, what is to be heated can be

Sear the product or roast it. In order to prevent the product from sticking to the contact surface, it is preferably designed with a low-adhesion coating.

If the product is only in direct contact with the lower frying surface designed as a frying surface, then radiant heat can be supplied to the upper product boundary from the upper boundary surface without a contact surface being on top of the product. Radiant heat sources for this purpose are known, for example, from EP 247 574 A1, which was recognized at the front. However, any other known radiant heat sources can also be used, in particular if these are arranged in a microwave-free area, such as, for example, over a metallized glass ceramic plate. If there is no contact surface on the product at the top, the product cannot stick to the top and products with an uneven surface, such as pizza, can also be browned from above. In addition, the

Free space above the product - as already described - a better spread of the microwave field. - 9 -

The combination of searing on at least one roasting surface and heating in a microwave field enables frozen products, in particular e.g. Roasti portions can be prepared within 1 00, if necessary also only 90 seconds. When a frozen product is prepared, the combination of the microwaves with one or two roasting plates attached to the product has an effect that goes beyond the sum of the individual effects. This further effect is due to the fact that the dielectric constant of ice is significantly lower than that of water. In the frozen state, the product can absorb significantly less energy from the microwave field than in the molten state. A hot roasting pan quickly thaws the edge of the product. There the microwave heating becomes more effective due to the greater dielectric constant of the water, which leads to a rapid melting process from the edge towards the center of the product. The initially rapid melting on the at least one frying plate enables a different melting process than when melting only with microwaves. Experiments with a test product have shown that for defrosting from - 1 8 ° C to 0 ° C approx. 40 see and for the subsequent heating from 0 ° C to 70 ° C approx. 50 see are required.

In order to obtain a versatile device, the electrical components are preferably designed and operated in such a way that the maximum electrical power required does not exceed 10 A. For example, two roasting surfaces or roasting plates are each heated with a 900 W heating device. The microwave cooking power, or the electrical power of the magnetron, is set at 1 260 W (with a power consumption of 1 800 W). It goes without saying that an upper radiant heat source can be provided instead of the heating device for an upper frying plate, or that an upper radiant heat source can always be meant by the heating device. In order not to need more than 10 A, the magnetron or the heating devices or the radiant heat source are operated alternately. - 1 0 -

The roasting plates preferably have a heat storage capacity and can therefore also give off heat that was provided before the product was inserted, even when the plates were not heated. In the ready-to-roast state, the roasting plates are kept at a roasting temperature of preferably substantially 275 ° C., or particularly rapid heating is provided. The frozen product is conveyed to a desired position between the roasting plates, or between the lower roasting plate and a radiant heat source arranged at the top. The roasting plates are pressed against the introduced product with slight pressure, whereby approximately one of the two roasting plates is elastically supported and thereby achieves the pressing effect. The heating devices for the frying plates are switched off, the microwave field is built up and maintained for about 90 seconds. The roasting pan temperature drops continuously due to the heat given off. The drop and the minimum temperature reached depends on the heat capacity of the frying plates and the heat absorption of the product. In a final phase it will be

Magnetron switched off and the heating devices are switched on again. The roasting pan temperature rises again towards the roasting temperature. The product is now browned on the surface for a period of approx. 20 seconds. Then the product is dispensed into a receptacle or on a plate. The core temperature should be at least 65 ° C at or shortly after the dispensing. Different products and portion sizes can be prepared with the device according to the invention in less than 3 minutes.

It goes without saying that in the case of a solution with a lower frying plate and a radiant heat source arranged at the top, the pressing of the two heat sources on the product is dispensed with. The product then lies only on the lower roasting pan due to its weight. The radiant heat source can be operated in parallel to the heating device of the lower frying plate. If necessary, however, it is more expedient to provide the supply of radiant heat during the entire preparation time or during other periods than the heating of the lower frying plate. - 1 1 -

The advantageous frying temperatures and the time intervals during which the frying plates are kept above a predetermined minimum temperature and in particular heated, or the radiant heat is supplied, depend on the product to be heated. If the electrical supply at 220 V is not limited to 10 A, or the power is not limited to 2200 W, then it may be appropriate to supply the heating devices or the radiant heat source and the microwave field at the same time. With a power limitation, the alternation between microwave and griddle or Radiant heat sources are also supplied at shorter intervals or more frequently. For a fish product, the effective heat output of the microwave field must be reduced. This could be achieved by reducing the power of the magnetron or by switching the microwave field on and off. If necessary, a turntable known per se can also be inserted into the device according to the invention.

The advantages of the small microwave space can also be gained in large industrial plants by multiplying the device according to the invention for the mass or series preparation of food portions.

A control, the control functions of which depend in particular on a measured value, preferably on a temperature measurement, makes it possible to carry out the heating process in accordance with the respective product. In addition to the temperature of the frying plates, other sizes can also be determined, in particular, for example, a radiation value of the product that is recorded laterally, or a temperature recorded in the product. If necessary, the crust formation is also recorded using a measuring method. The controller can preferably switch two roasting plates, or a lower roasting plate and an upper radiant heat source, on and off independently of one another and, in particular, also heat them to different temperatures. With an extremely versatile

Embodiment, the magnetron and the frying plate (s) or the radiant heat source can be switched on and off by the control at any time. For devices that automatically insert the product into the micro - 1 2 -

Promote wave space and also automatically remove after preparation, the control must also control the closing device of at least one opening to the microwave space, as well as the feed and removal elements. With an infeed device, the control system ensures that the roasting surfaces are pressed against the product at the beginning of the roasting process and that the roasting surfaces move apart at the end of the preparation. In order to avoid dangers, the control is also connected to control sensors which, for example, check whether a product has been introduced and whether the microwave compartment is properly closed.

In addition to the variations in the control of the roasting and heating process, the device and the preparation process can also be adapted to a specific product. In order to provide products with only one roasted outer surface, only one roasting plate may be provided, or only one of the two roasting plates may be heated. For special products, especially fried eggs, no plate may be pressed onto the product from above. The device according to the invention can also be designed for the preparation of products which are fried on the underside and grilled from above. For this purpose, an upper grill device is provided in addition to a lower roasting plate. The radiation energy of the grill device is optionally radiated into the microwave space through an electrically conductive layer, for example a wire mesh or a metal-coated glass plate. This prevents the microwave field from interacting with the grill device.

The drawings explain the invention using an exemplary embodiment. Show

1 shows a vertical section through a device with a microwave space and two frying surfaces;

2 shows a plan view of a roasting surface with a disk-shaped portion of potato rasps; - 1 3 -

Fig. 3 is a schematic representation of a vertical section through two

Roasting surfaces and the microwave space in between; 4 shows a plan view of the roasting surface with the product, with the magnetron and its cooling fan; 5 shows a side view of the magnetron with fan, the feed waveguide and the microwave space; Fig. 6 is a vertical section through a skewed device according to Fig.1, in which on a top or bottom narrow borders a Einzw. Outlet opening is formed; 7 shows a vertical section through a device with a drawer-like lower frying surface, the extended state being shown at the top and the inserted state at the bottom; 8 shows a vertical section through a box-like device, in which the base part can be moved upwards into or downwards from the cover part;

9 shows a vertical section through a device with a belt conveyor system; Fig. 10 shows a vertical section through a device with a drawer-like lower frying surface and an upper radiant heat source.

1 shows a device for preparing food portions with a layered microwave space 1, which has two large, flat borders 2 and narrow borders 3 connecting them. The edges are electrically conductive or they are provided with a conductive coating so that they reflect microwaves. At least partial areas of the large borders 2 are designed as frying areas 2 '. The roasting surfaces 2 'have a low-adhesion surface, so that a product 4 lying on them can be removed essentially without residue even after roasting.

The frying surfaces 2 'are optionally formed from material which is permeable to heat radiation, optionally from glass, so that the heat radiation directly makes the contact surface or outer surface of the product 4 heatable. A glass plate, in particular a ceramic plate, would have to be electrically - 1 4 -

tending layer and optionally with a low-adhesion layer, in particular Teflon which is essentially transparent for heat radiation, but preferably transparent PFA. The electrically conductive layer could also be arranged on the outside of the glass plate facing away from the product. Instead of a vapor-deposited metal layer, a wire mesh could also be arranged on the outside as an electrically conductive layer that is permeable to heat radiation. The combination of a heat radiation source with a frying plate, to which the product does not adhere and which allows the heat rays to pass through but reflects microwaves, is very advantageous. If the food to be roasted is in contact with such a roasting plate, in particular a glass plate, and the radiation source is switched on, heat immediately enters the food to be roasted. The glass plate is also heated and after a short time also allows the already heated product to be seared. Such searing is advantageous for frozen products.

However, a frying plate is preferably used which absorbs heat from a heating device and emits it as contact heat to the product. In the embodiment shown, an exchangeable aluminum plate, or preferably an anti-adhesive, rustproof and acid-resistant stainless steel plate, is provided as the roasting plate 2 '. The frying plate 2 'is connected to a basic structure 5. A heating coil 6 is arranged on the basic structure, which makes radiant heat transferable over a distance region 7 to the rear of the roasting plate 2 '. The basic structure 5 is preferably formed from ceramic material. It goes without saying that any other known heating arrangements can be used to heat the roasting plates 2 '. In order to be able to bring the temperature of each roasting plate 2 'to a desired value, a temperature sensor 13 is assigned to each roasting plate 2'. The temperature sensors 1 3 are connected via cables 14 to a control (not shown).

In order to be able to adapt the spacing of the frying plates 2 ′ to the product 4 used, at least one guide device and preferably also a pressing device is arranged between the two basic structures 5. The connection between - 1 5 -

see the large and narrow borders 2 and 3 is designed so that the escape of microwaves is prevented in all positions. In the example shown, electrical contact strips 1 6 are used, as are known, for example, from switch boxes. If necessary, the seal with the contact strips 16 is designed such that the two roasting surfaces 2 'can be pivoted somewhat from their parallel position. This is advantageous for products whose large outer surfaces are not aligned in parallel. During pressing, the pressed frying surface 2 'can adapt to the surface facing it by means of a small tilting movement.

The preferred dimensioning of the microwave space 1 and a feed area 8 can be seen schematically in FIGS. 2 and 3. The microwave space 1 has a longitudinal dimension in the range of 20 to 30 cm, preferably of substantially 25 cm, a transverse dimension in the range of 15 to 30 cm, preferably of essentially 20 cm and a thickness in the range of 1 to 7 cm lies, but is preferably adjustable in this range. To feed the microwaves, a feed area 8 or a waveguide with a transmitter 9 is provided, which connects centrally to this in the longitudinal direction of the microwave space 1 and extends over a length in the range from 10 to 20 cm, preferably essentially 15 cm extends. The width of the feed area 8 is slightly less than a third of the transverse extent of the microwave space 1 and widens somewhat against it.

According to FIGS. 4 and 5, the transmitter 9 belongs to a magnetron 10 which generates microwaves with a frequency of 2.45 GHz. To cool the magnetron, a fan 11 is attached to it. The position of the transmitter 9, the feed area 8 and the microwave space 1 must be matched to one another and to the product in such a way that the product is optimally or quickly and essentially homogeneously prepared at the selected position. In order to enable simple fine tuning, an adjustable tuning element is preferably arranged between transmitter 9 and product 4. In addition to the tuning element, guiding or polarizing elements can also be used. - 1 6 -

Fig. 6 shows an embodiment in which a device according to Fig.1 is tilted. An inlet opening 3a is formed in the narrow border 3 above, and an outlet opening 3b is formed in the narrow border 3 below. The inlet opening 3a can be closed by an upper closure surface 15. In the closed state, a contact strip 16 leading around the entry opening is pressed between the upper closure surface 15 and the border area around the entry opening 3a, so that an electrically conductive connection between the border area and the top closure surface 15 along the entire contact strip 16 is guaranteed. This ring-shaped, closed, electrically conductive connection is necessary to prevent microwaves and arc-like discharges from escaping. Leaking microwaves and discharges are intolerable for safety reasons and would also lead to energy losses. The opening 3a is opened and closed via an upper guide and actuation device 1 7. With the opening 3a open, this can be done

Due to the force of gravity, product 4 slide into the microwave space 1 via a feed surface 1 8.

In order to hold the product 4 in the microwave space 1 at the desired position, a stop element 19 made of non-dielectric material is provided.

As soon as the product 4 lies against the stop element 19, the upper frying surface 2 'can be pressed against the product 4 from above. The stop element 19 is fastened, for example, to a lower closure surface 20, which makes the outlet opening 3b closable, and can be used to pull it out of the microwave space 1. In the closed state one is around

The outlet opening of the leading contact strip 16 is pressed tightly between the lower closure surface 20 and the edge area around the outlet opening 3b, so that an electrically conductive connection between the edge region and the lower closure surface 20 along the entire contact strip 16 is ensured. The outlet opening 3b is opened and closed via a lower guide and actuation device 21. With the outlet opening 3a open and the stop element 19 lifted off the product 4, the product 4 can leave the microwave chamber 1 due to the force of gravity - 1 7 -

slip on a continuation surface 22. With this solution, gravity can be used to load and empty the microwave space. In addition, any liquid that may be released runs out of the microwave room.

FIG. 7 shows a device in which the lower frying surface 2 'with its basic structure 5 can be moved like a drawer under the upper frying surface 2'. A straight guide 23 is designed to guide this movement. In the extended state, a product 4 is placed at the desired position on the lower frying surface 2 'by a laying device (not shown). Then the lower roasting surface 2 'is pushed under the upper roasting surface 2' and then the upper roasting surface 2 'with the narrow edges 3 is moved downwards. A λ / 4 seal 24 runs around the narrow borders 3. This λ / 4 seal 24 comprises at a distance λ / 4 or a quarter of the microwave wavelength from the narrow borders 3 Central region of a groove 25 running in a ring around the microwave space 1, formed upwards and in a contact region 26 parallel to the frying surface 2 '. The groove depth is λ / 4 and the groove width λ / 8. The distance from the utility center to the outer edge of the contact area 26 is again λ / 4. If the contact area 26 now rests on a support surface 27 for the contact area 26, or the λ / 4 seal, which is tightly connected to the lower frying surface 2 ', the microwave space 1 is sealed radially outward in a microwave-tight manner. The λ / 4 seals have the advantage over the contact strips 1 6 that a micro-wave-tight seal is possible even with slightly spaced surfaces. After preparation, the bottom one

Roasting surface 2 'pulled out with the product 4 after the upper roasting surface 2' has been lifted off. In the extended state, the product 4 is carried on by a removal device, not shown.

In the exemplary embodiment shown, the seal between the narrow edges 3 and the upper frying surface 2 'which can be pressed against the lower frying surface 2' is also designed as a λ / 4 seal 24 '. The upper frying surface 2 'is pressed on via a pressing surface 28 of a (not shown) - 1 8 -

Actuating device which is connected to the base structure 5 of the upper frying surface 2 'via spring elements 29.

It goes without saying that the λ / 4 seals can also be designed in different designs and with different dimensions.

In particular, dielectric material can be arranged in the groove, which shortens the required mass by a factor of 1 / Vε. In order to create completely tight connections, additional electrical contacts are recommended, through which a small current flows and which are preferably self-cleaning.

8 shows a box-like device in which a base part 30 with a lower frying surface 2 ′ can be moved upwards into or downwards out of a cover part 31. In order to close the microwave space 1 between these two parts in a microwave-tight manner, a λ / 4 seal 24 'is formed. When the base part 30 is completely pulled out of the cover part 31, a manipulation device, not shown, can place or remove the product. The lower frying surface 2 'with the product is pressed against the upper frying surface 2' via a pressing surface 28 of an actuating device (not shown) which is connected to the basic structure 5 of the lower frying surface 2 'via spring elements 29.

The device according to FIG. 8 is preferably designed such that the lower frying plate 2 'can be moved like a drawer under the upper frying plate 2'. A horizontal straight guide according to FIG. 7 can be used for this. In the extended state, a product 4 is placed on the lower frying plate 2 'at the desired position. The lower roasting plate is then pushed under the upper roasting plate. The lower frying plate 2 'is then moved upwards by a lifting device into a hood-like cover part with the feed unit for the microwave field. Instead of the λ / 4- shown in Fig. 8

However, a seal can also be used in a design with an annular groove on the cover part that is outwardly open towards the inside and vertical edge surfaces of the lower frying plate. - 1 9 -

The lifting device comprises a positioning device which, preferably via an adjustable upper stop or off switch, makes it possible to adjust the frying plate distances adapted to the respective product thickness. In order to ensure that the frying plate spacing can be adapted to changes in thickness that occur during the melting of deep-frozen products, a pressing device, in particular with spring elements 29, is provided. It is expedient if the contact pressure of this press unit can also be adjusted according to the respective product.

In a preferred embodiment, the lower frying plate 2 'is placed only on first supports of the horizontal straight guide and can be lifted from the first supports in the retracted state by upwardly moving second supports of the lifting device. A spring unit is inserted between the lifting drive and the second supports to achieve the desired pressing effect. If the lower frying plate and its heating device are not connected to one another but are only moved together by the carriers, the lower frying plate can be lifted off without a heating device in the extended state. This simple removal of the frying plate makes it possible to replace and / or clean it with little effort.

In order to make the upper frying plate easily accessible for cleaning purposes, the cover part is pivoted upwards with the upper frying plate. It goes without saying that, in a further embodiment, the upper frying plate can also be designed analogously to the lower one, so that it can also be easily removed. For this purpose, the boundary of the microwave room is divided into three parts. A jacket area with vertical borders and an upper and a lower λ / 4 sealing groove is connected to the microwave feed. From below and above, the roasting plates are together with the

Heating devices can be used in the jacket area and ensure the necessary microwave tightness with vertical surfaces lying against the respective λ / 4 sealing groove. Both frying plates are then independent of the heating device - 20 -

detachable. In order to avoid the spread of taste, it would be possible to use different heating plates for products with different spices, in particular with or without onions or garlic, or salty or sweet.

It has also been shown that, depending on the product, steam and / or oil escapes during preparation. The vapor condenses on cooler surfaces and forms condensed liquid. It would be possible to remove the steam, but this is also associated with heat loss and requires complex exhaust air purification. To prevent this, one is preferred

Embodiment designed a drainage and in particular collecting arrangement for condensed liquid and oil. A simple solution provides for small passage openings in a drip area of the lower frying plate, preferably in the form of a segment of a circle. These are arranged radially outside the heating device, so that the dripping liquid can be collected in a collecting container under the heating device. In order to ensure a good flow to the dripping area, the lower frying plate is treated in such a way that it slightly bulges upwards within the dripping area due to the central heating during roasting.

It has now been shown that in the case of preparation devices with a sufficiently high thermal output, the removal and cleaning of exhaust air can also be used advantageously. For this purpose, a circulation device is provided which guides air from the area around the microwave space or air from the microwave space through a cleaning device in suction or blowing operation.

If air circulation through the microwave space is provided, the inlet and outlet openings must be air-permeable and microwave-tight, which can be achieved, for example, with a wire mesh at the mouth openings of the air duct system or at the boundary areas of the microwave space. If the air only circulates outside the microwave space, the odor-laden exhaust air should be fed as completely as possible to a cleaning device when the microwave space is opened and the portion is removed. - 21 -

The cleaning device preferably comprises an exchangeable filter or a filter mat. The filter retains larger particles and / or well adhering parts of the exhaust air. If necessary, the exhaust air is passed through a condensation device in order to collect and dispose of the condensable portion of the exhaust air in the form of condensate. It would also be conceivable to pass the exhaust air through a washing device, but this is usually associated with great effort. It has now been shown that good cleaning effects can be achieved with an absorber substance which is brought into contact with the exhaust air, in particular the odor emission can be significantly reduced. The absorber active ingredient is preferably fat-dissolving and in particular temperature-resistant up to temperatures of 280 ° C. The absorber active ingredient optionally comprises catalytic and / or germ-inhibiting constituents. If the absorber active substance is in liquid form, it is introduced into the exhaust air stream by a spraying or atomizing device.

The control mentioned above should also make it possible to set the distance between the frying plates and, if necessary, the contact pressure when roasting. In order to be able to optimally carry out the roasting process for different products with little effort, the control preferably comprises a storage unit for storing target parameter sets. After determining the optimal parameters for a very specific, predetermined product, for example for the roasting times, roasting temperatures, the plate spacing and the microwave times, these are stored in the storage unit and can be called up for preparation for this particular product with a single keystroke.

FIG. 9 shows an embodiment in which the product can be conveyed from a feed and forwarding device 32, possibly with pivotable conveyor belts, to the microwave space 1 and away from it. When products with different seasonings are prepared in succession, in particular with or without onions or garlic, or salty or sweet, carryover of flavor carriers must be prevented. Since the roasting surfaces 2 'are not easy to clean in the microwave room, a solution was found. - 22 -

winds, in which tapes 33 are guided over the roasting surfaces. The tapes 33 are coated with or formed from non-stick material such as Teflon and are each held by a tape guide device 34. It is possible to continue these belts 33 with each product preparation by a product length and to carry out cleaning in the area outside the microwave room. Another possibility is to assign a band area to each seasoning, which is then positioned on the roasting surfaces 2 ′ in accordance with the desired product in the microwave space 1 before the product 4 is fed. For feeding or removing a product 4, the narrow border 3 facing the forwarding device 32 becomes

Approval of the microwave room access moved away. The narrow borders 3 are connected to the upper and lower roasting surfaces in a microwave-tight manner by means of λ / 4 seals 24 ', 33 gap areas remaining free for the strips to be passed through.

Fig. 1 0 shows an embodiment in which a pizza, or a product 4 'with an uneven top, rests on a lower roasting plate 2' and is browned from above by radiant heat without contact. The radiant heat comes from a radiant heat element, such as a heating coil 6. In order to protect the heating coil 6 from contamination by substances emerging from the product 4 ', a cover plate 1 02 is arranged under the heating coil 6. The cover plate 102 consists of a material which is permeable to heat radiation, optionally made of glass or glass ceramic, so that the heat radiation directly makes the uneven top of the product 4 'heatable. In order to limit the microwave space at the cover plate 102, the glass or. Ceramic plate can be coated with an electrically conductive layer. The electrically conductive layer could also be arranged on the outside of the glass plate facing away from the product. Instead of a vapor-deposited metal layer, a wire mesh could also be arranged on the outside as an electrically conductive layer that is permeable to heat radiation. Because the

Radiant heat source or its cover plate 1 02 is not pressed onto the product 4 ', a λ / 4 seal between the narrow borders 3 and the radiant heat source can be dispensed with. About the schma- - 23 -

len borders 3, a support bracket 103 is arranged with a lower support edge 1 03a for the cover plate 102 and an upper support edge 103b for a support plate 1 28. The radiant heat source or the heating coil 6 are attached to the support plate 1 28. The support plate 1 28 with the heating coil 6 and the cover plate can be used for cleaning and maintenance purposes

1 02 can be easily removed.

As in the embodiment according to FIG. 7, the lower frying plate 2 'can be moved in a drawer-like manner and, in the inserted state, is connected to the vertically movable narrow border 3 in a microwave-tight manner via a λ / 4 seal 24.

It goes without saying that the features described using various examples can also be combined in any other way.

Claims

- 24 patent claims

1 . Device for preparing food portions (4), with a microwave space (1) in which a portion (4) can be heated, characterized in that at least a part of at least one - preferably the lower - edge (2) of the microwave space (1) is designed as a frying surface (2 ').

2. Device according to claim 1, characterized in that the microwave space (1) is layer-shaped and in this case has two large borders (2) and narrow borders (3) connecting them, wherein a radiation heat source is optionally arranged in the area of the top border. but preferably facing partial areas of the two large borders (2) - but possibly also the narrow borders (3) - are designed as frying surfaces (2 ').

3. Apparatus according to claim 1 or 2, characterized in that the distance between the two roasting surfaces (2 ') is adjustable and / or the temperature of the two roasting surfaces (2') can be regulated independently of one another.

4. Device according to one of claims 1 to 3, characterized in that the microwave space (1) and a feed device (8,9) with a magnetron (10) are designed so that a monomodal microwave structure can be achieved, or that Microwave room (1) with the portion (4) for the wavelength used has only a few resonances.

5. Device according to one of claims 1 to 4, characterized in that the microwave space (1) has a longitudinal extent in the range of 20 to 30 cm, preferably of substantially 25 cm, a transverse extent in

Range of 15 to 30 cm, preferably of essentially 20 cm and has a thickness which is in the range of 1 to 7 cm, but is preferably adjustable in this range. - 25 -

6. The device according to claim 5, characterized in that a feed area (8) or a waveguide with a magnetron (1 0), preferably with a frequency of 2.45 GHz, is provided for feeding the microwaves, which is central in the Connects to the longitudinal direction of the microwave space (1) and extends over a length in the range from 1 0 to 20 cm, preferably from essentially 1 5 cm, the effective heat output being variable.

7. Device according to one of claims 1 to 6, characterized in that each frying surface (2 '), preferably replaceable, is attached to a base structure (5) which also carries a heating device (6), in particular a radiant heat source, wherein the heat from the heating device (6) passes through the roasting surface (2 ') to the food portion (4) which is in contact with it during preparation.

8. The device according to claim 7, characterized in that the frying surface (2) is permeable to heat radiation, has a low-adhesion surface and reflects microwaves, wherein it is preferably formed from glass which is essentially against the microwave chamber (1) for heat radiation transparent non-stick coating and optionally on the side facing away from it is provided with an essentially transparent layer for heat radiation, an electrically conductive layer or a wire mesh.

9. Apparatus according to claim 7 or 8, characterized in that it comprises a control which makes the microwaves or the magnetron (10) and the heating device (6) of each roasting surface (2 ') switchable on and off.

1 0. Device according to one of the preceding claims, characterized in that a circulation device is provided for removing and cleaning exhaust air, the air around in the suction or blowing operation - 26 -

makes the microwave space or air out of the microwave space feasible through a cleaning device, the cleaning device having an exchangeable filter or a filter mat and / or a spraying or nebulizing device which makes it possible to supply the exhaust air with an absorber or odor-neutralizing liquid, includes.

1 . Method for preparing food portions (4), in which heating takes place by means of microwaves, characterized in that an edge surface of the portion (4) is in contact with a roasting surface (2 ') during the microwave action, while an opposite edge surface of the portion is in contact with another roasting surface (2 ') or is heated by a radiant heat source.

2. The method according to claim 1 1, characterized in that the supply of the magnetron (10) for generating the microwaves and the supply of the

Heating devices (6) for introducing heat to at least one roasting surface (2 ') or from the radiant heat source are switched on alternately, the heating devices (6) preferably during an initial phase and in particular during a final phase, but the magnetron after the initial phase (1 0) can be fed.