Patent Application
20050196491
The present invention relates to a heating attachment for improving the uniformity of microwave heating. More particularly, the invention relates to heating attachments that can trap a food container with food to be heated and for which reuse can be controlled.
Microwave reheating of frozen meals provides convenience for people seeking quick meal solutions because of the rapid thermal energy transfer into the food materials by the microwaves. However, microwave heating of frozen food is, in general, perceived as difficult and has many problems associated with it, such as overcooking of some portions of meals, cold spots, burnt edges and sauce splatter. In many instances, the meal experiences serious burnt spots yet some places are still very cold, even often below 0° C. Furthermore, the concentration of the microwave energy on spots tends to create local boiling of the water contained in the food and/or sauce and therefore splattering off the dish. Many attempts have been made in the past to solve this issue of re-heating frozen food in a more effective way.
It has been proposed in U.S. Pat. No. 4,351,997 to provide a modified form of tray structure to attempt to provide a more even heating of foodstuff in the tray when exposed to microwave radiation. This prior art has a bottom wall of microwave-transparent material and an upwardly-extending peripheral wall that is outwardly curved at its upper end to define a horizontal peripheral rim. The rim is partly or completely coated with a material that is reflective and opaque to microwave radiation, such as aluminum foil. The peripheral wall also is partly or completely coated with the foil material. The effect of this aluminum foil coating on the wall is to provide reflection of microwave energy toward the center of the tray.
U.S. Pat. No. 4,626,641 describes an embodiment in which a similar structure is provided. In addition to the provision of aluminum foil in the side wall of a tray, the foil also extends into the base of the container but leaves a rectangular open area in the bottom wall.
U.S. Pat. No. 5,310,980 relates to a tray useful for the microwave cooking of prepared foodstuff that comprises an outer layer formed of paperboard or molded plastic to which is laminated an inner polymeric film layer. A layer of microwave-reflective material, usually aluminum foil, is positioned between the outer and inner layers in the location of the peripheral wall of the tray and in a pattern in a portion of the bottom wall.
JP 09-369450 relates to a container for a microwave oven that comprises a first microwave reflecting plate placed along a circumferential lateral parts and a second microwave reflecting plates in the base section of the container.
It is apparent from the prior art that attempts have essentially been made to provide energy transmission structures with reflective material placed in locations that enable energy transfer from the edges and corners of the plate to a more central area of the plate. However, experimental trials have shown that these structures are, by themselves, insufficient to overcome the problems of uneven heating. In particular, cold areas are still present in the food despite the presence of these structures. Thus, improvements in these devices are needed and are provided by the present invention.
The invention is directed to a heating attachment for improving uniformity of microwave heating of a food product in a food container. In the preferred embodiment, a microwave shield of microwave-reflective material is provided. Also, an attachment member is configured for attaching the shield to a food container in an operative association, in which the container is disposed in a heating space within the shield. In this association, the shield improves the uniformity of microwave heating of a food product within the container. Additionally, the heating attachment is configured and sufficiently surrounds the container in the operative association to capture the container for promoting breakage of the heating attachment when the container is removed therefrom to inhibit or prevent reuse of the heating attachment.
Preferably, the shield in the operative association promotes propagation of resonant modes microwaves during the microwave heating in the food product in the container to improve the uniformity of the heating throughout the food product. The shield also preferably extends about a horizontal periphery of the container in the operative association.
A support member of a preferred embodiment, such as a cradle member, captures the container in the operative association to promote breakage of at least a portion of the cradle when the container is removed therefrom. The support member extends beneath the container in the operative association to hold the container elevated above a microwave over floor during the microwave heating. The support member or the microwave shield, or both, can be configured for tearing to remove the container from the heating attachment. Also, the support member and shield can have a low volume, packaging configuration for shipping, and a larger expanded-volume configuration to capture the container in the operative association. The support member and/or shield can be folded to change between with the low-volume and expanded configurations.
Preferably, the heating attachment includes first and second portions that are attached to each other around the container in the operative association to trap and hold the container in the heating space. The attachment member may have a ledge, hook, rim, or other protrusion for positively trapping the container in the heating space in the operative association.
In the operative configuration, preferred shield is configured to generate a microwave resonating layer having a generally horizontal length of up to about 15 cm, an generally horizontal width of up to about 20 cm, and a generally vertical height of between about 1 and 6 cm. Preferably, the resonating layer is arranged so that TE (transverse electric) modes predominantly supported within the food product are TEn,m,l modes, where n, m, l are such that 0≦n≦2, 0≦m≦1, and 0≦l≦1.
Also, in the preferred operative association, a bottom side of the container and heating space is substantially free of the microwave reflective material. The container can include a dish, bowl, or other type of plate or tray, which is preferably used for serving a portion of food while dining. In addition, the shield is preferably disposed substantially adjacent a sidewall of the container in the operative association, and the container can be made of suitable materials, including ceramic or plastic.
A preferred embodiment of a packaged unit includes a heating attachment and a frozen food product configured and dimensioned for reception in the container for microwave heating. A package contains the heating assembly and frozen food product. Where more than one unit of the frozen food product is packaged, preferably at least that number of heating attachments are also packaged therewith.
The present invention allows reuse of a plate or other container for serving eaters at a table, with a low cost and preferably single-use and disposable heating attachment that provides better and more uniform microwave heating.
The present invention relates to a device and method for improving heating of food in a microwave oven. The invention addresses the problems of cold spots, uneven heating and splattering that traditionally occur when foods are heated in a microwave oven. In particular, the present invention proposes a method for handling and evenly heating frozen food that can be economically, conveniently and rapidly served in a foodservice location to the consumer. The invention also relates to a stand-like device adapted to receive a food container for improving the reheating of the food in a microwave oven.
The present invention aims at providing a satisfactory solution for evenly heating a frozen food in a plate by adopting a different approach where not only energy transfer is carried out but more importantly a modification of the overall heating pattern inside the food block is achieved by changing the wavelength inside the food. Thus, the present invention aims at providing a convenient and easy way for improving microwave reheating of food while enabling the use of standard dishes such as ceramic and ceramic-like plates that are commonly be found in restaurants, cafeterias, hotels, or other foodservice locations.
The present invention relates to a method for ensuring a more uniform heating of frozen food by microwaves. This method is conducted by providing food in a portion having a predetermined size and shape and providing a container adapted for receiving and reheating with microwaves the food portion. The container is associated with a cradle so that the peripheral sides of a supporting cavity of the container, which has peripheral sides and a bottom side, are circumferentially shielded by a microwave reflective material with axial and transverse distances that are determined so as to change the wavelength of resonant modes in the supporting cavity. The method includes placing the portion of food in the supporting cavity and heating the food and container with microwaves so as to expose the food to the changed wavelengths of resonant modes in the cavity thereby resulting in a more uniform heating food pattern and a more uniform heating of the food.
It has been surprisingly found that it is possible to render the heating of the food in the container relatively even by shortening the wavelength of the resonant modes inside the cavity of the food, especially for the transverse electric (TE) modes. Shortening of the wavelength and supporting of specific resonant modes can be obtained more specifically by determining the distances that separate the microwave reflective material when placed circumferentially along the side of the container in a manner to promote modes that show a more even electric field distribution.
In a preferred embodiment, the microwave reflective material forms a resonating layer having a transverse dimension of 15 cm or less. Preferably, the transverse dimension of the resonating layer is less than 13 cm, and more preferably from about 10 to 12 cm. Preferably, the axial dimension of the resonating layer is of 20 cm or less, and more preferably of less than 18 cm.
Therefore, the resonating layer can be regarded as a resonator or wave guide where shortened standing waves occur inside the food. As the transverse dimension of the resonating layer is shortened, transverse electric (“TE”) modes which carry more power than transverse magnetic (“TM”) modes are propagated in the cavity of the food. In particular, the TE modes that are permitted for the selected geometry are those with a more concentrated heating in the center area of the cavity. More preferably, TE modes that are predominantly supported in the food cavity are TEn,m,l modes wherein n may be 0, 1, or 2, m may be 0 or 1, and l may be 0 or 1.
Preferably, the microwave reflective material forms a resonating layer having a closed rounded contour. Even more preferably, the resonating layer has an oval contour with an axial dimension of less than 20 mm, preferably less than 18 mm. In an alternative embodiment, the resonating layer has a circular contour. In a preferred embodiment, the bottom side is completely or substantially free of shielding material. In one embodiment, microwave material can have a small amount of microwave material, preferably at the longitudinal tips of the bottom side, such as where there is a gap adjacent the shielded tip of the bottom side.
Remarkable results have been obtained by using such shapes and dimensions of a resonating layer. Comparative trials have shown that these are the preferred configurations for evenly heating food in the container.
The invention also relates to a method of using a container having the resonating layer as previously defined wherein, prior to placing the food portion in the container, the food portion is removed frozen from a package of defined shape and size which are predetermined to substantially match the shape and size of the cavity of the container. The frozen food can be produced and packaged in the manufacturing facility according to specific standards of size and shape that are predetermined to provide optimal re-heating properties afterwards. The food product may be packaged in a package that is not the final heating tray with its resonating layer so as to reduce the packaging costs. Contrary to the package, which may usually be disposable, the final heating tray may be a dish made of a non-disposable material for repeated uses in a foodservice location such as a restaurant, a fast-food or a cafeteria, with a disposable cradle to improve the microwave heating.
U.S. Patent Application Publication U.S. 2003/0189042 A1 (“the '042 publication”), the entire content of which is hereby incorporated herein by reference thereto, teaches a method and devices for uniform microwave heating of food in a container. The present invention provides a removable attachment for a food container that employs a microwave shield as disclosed in the '042 publication.
The method of the invention aims at providing a solution for re-heating a frozen food product of predetermined size and shape in a plate, which is placed within the inventive heating attachment that is adapted for modifying the wave pattern during a microwave heating process in a manner that enables the transverse electric (TE) modes of higher power and more evenly distributed pattern to propagate inside the food product. The present invention aims at providing a method for quickly and evenly reheating food, preferably frozen food, with microwaves, preferably those provided by a conventional microwave oven that is 2450 MHz.
Referring to
Referring to
The cradle 42 defines an interior recess 58 configured and dimensioned to receive and clasp the plate 2. Preferably, the interior recess 58 is defined by similar interior recesses in each of the cradle portions 44 and has a shape corresponding substantially closely with the exterior shape of the plate 2 to be clasped when the cradle portions 44 are spread to an open cradle position, as shown in
The cradle 42 includes several portions for preventing extraction of the plate 2 from the interior recess 58 in various directions. Hooks 56 prevent upward extraction, the base portions 50 prevent downward extraction, and side members 54 prevent horizontal extraction. With the cradle portions 44 spread in an X-shape in the open cradle position, the cradle portions 44 prevent extraction of the plate in substantially any horizontal direction, and also provide a stable base formed by the two spread base portions 50. The interior recess 58 preferably closely corresponds to the external shape of the plate 2. For instance, in the embodiment shown, the side members 54 are angled similarly to the outer wall of the plate 2, and include rim receiving portions 60 that cooperatively receive an upper rim 62 around the top opening of the plate 2.
The microwave shield 45 of this embodiment includes two shield portions 64, as shown in
Adhesive is provided on one or both of the cradle 42 and shield 45 for adhering the shield 45 to the cradle 42, preferably at locations 66,68. One location 66 is preferably at a longitudinal end of the band, and the other is in an intermediate portion. Location 68 is preferably at an end of the band, and preferably includes a reinforcing member 70 that protrudes above the band for ease of manipulation.
The plate is loaded into the heating attachment 40 with end flap portions 72 of the shield 45 still awaiting needing final attachment, preferably at one end. As shown in
When the heating attachment 40 is operatively attached to the plate 2, the plate 2 and the food 1 are positioned in a heating space 74. In this position, the shield 45 is associated with and positioned with respect to the food 1 in the plate 2 disposed in the heating space 74 such that the shield 45 improves the uniformity of microwave heating of a food product within the container.
The cradle 42 is preferably made of semirigid paperboard or of a plastic that can be bent by hand to spread the cradle portions 44. Other materials, such as plastics and other preferably microwave-transparent materials can alternatively be used. The preferred material for the microwave shield 45 is aluminum foil, although other materials can be used. The preferred material is flexible and capable of readily being torn by hand.
Another embodiment is shown in
The halves 78 preferably have upper and lower ledges 88,90 or other surfaces to capture and hold the plate 2 in the heating space 74 when the halves 78 are adhered together. To facilitate insertion of the plate 2, the halves are split at the longitudinal ends of the heating space 74. The microwave shield 80 is provided along the inside of the interior recess 92 of the halves 78 and preferably extends horizontally around the heating space 74, leaving the bottom and top sides substantially open or substantially free of microwave-reflective material.
Once the halves 78 are attached to each other, the attachment captures the plate 2, and the attachment preferably has to be broken to release the plate 2, preferably rendering the attachment non-reusable. In this embodiment, the cradle portions are preferably made of a frangible foam material that is significantly weaker than the adhesive so that the foam and shield 80 brake when the plate 2 is removed, although other suitable materials can be used.
Referring to the embodiment of
Bottom portions 102 of the cradle are configured to prevent downward extraction of the plate 2 from the heating attachment 94 when associated with the plate 2. An attachment extension 104, preferably having adhesive, is provided to connect to the tab 106 of its opposite bottom portion 102, as shown in
The microwave shield can extend along bottom portions 102 as well, to provide a more continuous microwave shield around the food product to improve the uniformity of the microwave heating. Even if the shield does extend along bottom portions 102, the coverage on the bottom side of the plate 2, if any, is minor compared to the total area of the bottom side, and the substantial majority of the bottom side preferably remains free of microwave reflective material. Preferably less than about 80%, more preferably less than about 90%, and most preferably less than about 95% of the total bottom side area is shielded with microwave reflective material. In one embodiment, the microwave shield has a small lip that extends over a small distance on the bottom side along most of the periphery thereof.
In the preferred embodiments, in the operative position, the shield promotes propagation of resonant modes of the microwaves in the food product that is in the container in the heating space to improve the uniformity of the microwave heating throughout the food product. Also, the preferred attachment members can be packaged in a low-volume configuration to facilitate shipping. In the embodiments of
Referring again to
In the diagrammatic embodiment of
The distances A and T are preferably measured at the circumference of the band 3 at a level of the upper surface 5 of the food when the food is properly placed in the cavity for re-heating. However, in certain circumstances where the container is shallow and/or has sidewalls that form a low inclination relative to the bottom surface; e.g., the edges of a dinner plate, the food may usually project upwardly beyond the height of the sidewalls. In that event, the circumference for considering distances A and T will be regarded at the upper edge of the resonating layer.
According to one essential aspect of the invention, the distances A and T of the band are determined to provide a shortening of the wavelength when the food plate, as surrounded by the band 3, is heated in the microwave oven. Therefore, reflection or transfer of the microwave beam is not the primary effect that is sought. The primary effect that is sought is related to the modification of the propagation of the waves in the dielectric food material between two or more conductors that support a certain number of electromagnetic waves. These waves have a uniquely defined voltage, current and impedance. Wave guides, often consisting of a single conductor, support transverse electric (TE) and/or transverse magnetic (TM) waves, characterized by the presence of longitudinal magnetic or electric, respectively, field components. Therefore, the principle of the invention is to look at determining the boundaries of the band that acts as a wave guide so that high power TE modes of even density are primarily induced. More particularly, TEnm modes of evenly distributed density such as TE01, TE11, TE21 are primarily supported while TEnm or TMnm modes of less evenly distributed density such as TE31, TE41, TE51 or TM31 are preferably discarded.
In order to promote domination of the desired TE modes, it has been found that the transverse distance T of the resonating band should be of about 15 cm or less, preferably lower than about 13 cm, even preferably ranging of about from 6 to 12 cm. Similarly, the axial distance A of the band should be of 20 cm or less, preferably lower than about 18 cm, even preferably ranging of about from 6 to 15 cm. Remarkable and surprising results on the final temperature distribution have been obtained if those distance are properly respected. This effectively changes the wavelength of the resonant modes inside the dielectric cavity of the plate (inside the food), especially for those TE modes. This shortening of the wavelength intensifies the heating in the center of the food, therefore promoting a more uniform heating pattern.
The band may comprise tapered surfaces as shown in
It has also been found that the microwave reflective material band should preferably be a continuous or substantially continuous peripheral band of a height of at least about 10 mm, preferably of from about 10 to 60 mm, even preferably of from about 25 to 45 mm. In embodiments in which the band is discontinuous, gaps in the band can be provided between sections of the band. The gaps are preferably about between 3 mm and 7 mm. Gaps that are too small can cause arcing, while gaps that are too large can reduce the effectiveness of the microwave shield. Any gaps or discontinuities selected preferably are sufficiently large to avoid arcing, while being sufficiently small to preserve the shield's effectiveness. The food should preferably be placed so that its upper surface 10 is placed below the upper line 30 of the band 3, preferably at 0 to 15 mm below, even preferably at 2 to 10 mm below. Similarly, the food lower surface 11 contacting the bottom of the plate should be at a level above the lower line 31 of the band of from about 0 to 10 mm, preferably about 0.5 to 5 mm, and more preferably about 2 to 3 mm.
Although an oval contour is preferred for the band, since the best results have been found with such a configuration, it remains possible to have a band of uneven contour and other shapes such as a circular contour. Where there is a substantially circular contour, the transverse distance T and the axial distance A form a diameter that should be preferentially determined, as for the previous example, to be a distance equal to or less than about 15 cm, preferably less than about 13 cm, even preferably of about from 6 to 12 cm.
The band or layer 3 may preferably comprise a metallic material that is placed adjacent the sidewall 22 of the plate. The band may be either attached or simply positioned in close contact with the outer surface of the sidewall 22. In another embodiment, the band may be positioned adjacent to the inner surface of the sidewall 22 of the plate.
In one embodiment, the band may be a coating material, such as a metal coating, for a cradle or other structural member of the attachment. In order to provide a sufficient microwave resonating effect, the coating has a thickness that preferably is at least about 3.2 microns, and even more preferably of at least about 10 microns. The coating may be applied out by any suitable means such as by vacuum metalizing or chemical etching. Those coating techniques are well known by the man skilled in the art of surface treatment and, therefore, do not need to be described further herein.
The inside volume and shape demarcated by the circumferential band may be determined to match the external volume and shape of the plate and, therefore, can take a variety of possible cross-sectional configurations, such as parallel, frustoconical or a stepped configuration.
The portioning and packaging are preferably carried out in a food manufacturing facility utilizing all hygienic and quality standards required in the food manufacturing art. The food portions are preferably packaged in a pre-formed package that predetermines the final shape and size of each individual food portion that are subsequently re-heated, and for fitting within the plate 2 of predetermined dimensions. Preferably, the pre-formed package comprises at least one and preferably a plurality of packaging cells. The cells forms a plurality of individual cavities wherein each of them have a shape and a size adapted to precisely fit in the cavity of the plate 2 for the microwave re-heating while considering the positioning constraints that have been determined earlier in the present description for obtaining the intended result on uniformity of heating. If the plate and the band has an oval contour, the cavity of the cell should also preferably have an oval contour of predetermined length X and width Y. The dimensions X and Y are measured at the outer surface of the food. The dimensions X and Y are determined to substantially correspond to the internal dimensions of the heating plate 2 it fits in so that no large gaps are left in the cavity between the product and the plate. It has been noticed that large gaps provide the edge of the food a higher than desired heating. Therefore, gaps, if any, between the product and the inner surface of the plate 2 should be of less than about 8 mm, preferably of less than about 5 mm. Even more preferably, there should be no gap at all between the side surface of the dish and the side surface of the food. For example, the contour of the food may have dimensions of X of between about 15 to 19 cm and for Y between about 8 to 15 cm.
The pre-formed package may be made of a thermoformed plastic foil or any equivalent formable material that can retain a given shape after forming. The foil is thermoformed to form the cavities and edges that surround the cavity. The material should advantageously be sufficiently deformable to allow easy removal of the food block from the cell. The preformed package can be a foodgrade polypropylene or any other suitable plastic of from about 0.1 to 1 mm in thickness. A plurality of cell can be formed in a single sheet of plastic as illustrated for cost manufacturing reasons and can be separated along cutting lines, if necessary, or be kept grouped as a collective package, if there is a need for distributing or selling more than one food package at a time.
The cells can be filled in by food to form the food portions. Depending on the food recipes, freezing may be required before filling in the cells. Freezing may be carried out on discrete food components, for instance, pasta layers, vegetable pieces, meat balls, etc., or on the food block itself whereas other components such as sauce, cheese and the like, may be placed, poured or deposited in the cells at ambient or just at chilled temperature.
As a matter of safety, freezing of the filled cells should always be subsequently completed until the whole food portion has reached the frozen temperature range required. The food containing cells are usually rapidly cooled to the required freezing temperatures, i.e., minus 18 to 40° C. Freezing may usually be carried out in a spiral freezer or in a freezing tunnel under liquid nitrogen jets or any other suitable freezing technology. Then, the cells may be closed by thin plastic wrap that is sealed onto the edges of the cells or, alternatively, the preformed package 4 may be simply stacked and packed in a cardboard box with a partition film to separate them in the box.
In another embodiment, the cells may also be made of a flexible non-preformed material such as in thin plastic wrap with the shape and size of the cell's cavity to shape the food portion being defined by an external mould. In that event, the plastic wrap is covered onto the mould surface, the food components are deposited into the plastic wrap and the final block is frozen and removed from the mold.
The advantage of the packaging cells resides in that packaged food blocks can be mass produced in an inexpensive manner that are properly sized to fit the plate 2. The plate 2, which term is used generically to include any suitable container, preferably with side walls to contain the food, and preferably with an open top so that the heated food can be served directly in the plate 2, may be such as a reusable ceramic dish used in restaurant or other foodservice catering areas. The food can, therefore, be transferred from the cell to the ceramic dish to be reheated in a microwave oven and served directly to the consumer in its dish. Thus, the food portion and plate are preferably sized for a single typical serving that a would be consumed in a desired meal. After food consumption, the plate 2 can thus be washed and re-used as a normal dish.
While illustrative embodiments of the invention are disclosed herein, it will be appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. For example, other materials that can be used for microwave-transparent portions include ceramics. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments that come within the spirit and scope of the present invention.
