Reusable microwaveable vessel

Abstract

The present invention relates to a vessel having an area for holding at least one food item for being heated in a solid state microwave oven. Additionally, disclosed is a method for heating a food item in a solid state microwave oven. Particularly, the vessel comprises a tray having an area for holding at least one food item and a susceptor wherein there is a thermal insulation between the susceptor and the food item. The tray may include two- or multi-compartment configurations wherein the susceptor only spans at least along a portion of one compartment to heat various food item simultaneously within a solid state microwave oven.

Claims

1. A method for heating food items in a solid state microwave oven, the method comprising: i) placing a first food item onto a first area of a vessel, the first area being configured for holding the first food item, the vessel comprising a susceptor integrated in or attached to a bottom surface of the vessel, the susceptor spans at least a portion of the first area, the vessel comprises a thermal insulation between the susceptor and the first area for holding the first food item, and the first food item is selected from the group consisting of a vegetable product, a pasta, a noodle, a rice product, a potato product, and combinations thereof; ii) placing a second food item onto a second area of the vessel, the second area being configured for holding the second food item and is not spanned by any susceptor, and the second food item is a meat product; and iii) heating the food items simultaneously in the vessel in the solid state microwave oven, the heating of the food items simultaneously in the vessel providing a lower final temperature for the first food item than the second food item, wherein the thermal insulation is provided by a layer of material selected from the group consisting of plastic material, glass material, ceramic material, porcelain, silicon, Teflon, and combinations thereof, and wherein the layer of material is at least 0.3 mm thick, and the vessel is washable and re-usable.

2. The method according to claim 1, wherein heating in the solid state microwave oven is at a selected frequency between 2400 and 2500 MHz.

3. The method according to claim 2, wherein the selected frequency corresponds to the frequency which results in the highest energy absorption of the susceptor.

4. The method according to claim 1, wherein the solid state microwave oven is operated at a power from 100 to 1600 Watts and the food item is heated for 1 to 30 minutes.

5. The method according to claim 1, wherein the layer of material is at least 0.5 mm thick.

6. The method according to claim 1, wherein the thermal insulation has a thermal resistance value R of at least 0.0004 m.sup.2K/W.

7. The method according to claim 1, wherein the thermal insulation has a thermal resistance value R of at least 0.001 m.sup.2K/W.

8. The method according to claim 1, wherein the susceptor spans up to 50% of the first area.

9. The method according to claim 1, wherein the susceptor spans at least 20% of the first area.

10. The method according to claim 1, wherein the susceptor is in the form of a horseshoe.

11. The method according to claim 1, wherein the first and second areas are compartments.

12. A method for heating food items in a solid state microwave oven, the method comprising: i) placing a first food item onto a first area of a vessel, the first area being configured for holding the first food item, the vessel comprising a susceptor integrated in or attached to a bottom surface of the vessel, the susceptor spans at least a portion of the first area, the vessel comprises a thermal insulation between the susceptor and the first area for holding the first food item, and the first food item is selected from the group consisting of a vegetable product, a pasta, a noodle, a rice product, a potato product, and combinations thereof; ii) placing a second food item onto a second area of the vessel, the second area being configured for holding the second food item and is not spanned by any susceptor, and the second food item is a meat product; and iii) heating the food items simultaneously in the vessel in the solid state microwave oven, the heating of the food items simultaneously in the vessel providing a lower final temperature for the first food item than the second food item, wherein the thermal insulation has a thermal resistance value R of at least 0.005 m.sup.2K/W, and the vessel is washable and re-usable.

13. The method according to claim 12, wherein the vessel is made of a material selected from the group consisting of plastic material, glass material, fiberglass material, ceramic, porcelain, silicon, and combinations thereof.

14. The method according to claim 13, wherein the susceptor is entirely enclosed in the material.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an top schematic view of a package having a two compartment tray with defined zones without susceptors containing frozen mashed potatoes (left) and an infrared image corresponding to the tray indicating temperature from ‘Low’ to ‘High’;

(2) FIG. 2 is a perspective view of an embodiment of a susceptor (left) and its placement on a bottom outer surface of the tray (right);

(3) FIG. 3 illustrates bottom views of various designs of the susceptors attached to the two compartment trays;

(4) FIG. 4 is a graph of a frequency scan measuring energy absorption of the two compartment trays of FIG. 3 in a solid state microwave oven;

(5) FIG. 5 is a bottom schematic view of vessel according to sample #4 of FIG. 3 with defined zones containing frozen mashed potatoes (left) and an infrared image corresponding to the tray indicating temperature from ‘Low’ to ‘High’;

(6) FIG. 6 is a cross sectional perspective view of an embodiment of the vessel with a susceptor on a bottom outer surface of the tray;

(7) FIG. 7 is a cross sectional perspective view an another embodiment of the vessel with a susceptor placed on a bottom outer surface of a sub-tray and a bottom inner surface of a base tray;

(8) FIGS. 8A-8H illustrate cross sectional views of eight (8) additional embodiments of the vessel with susceptor(s) along various portions of the tray;

(9) FIGS. 9A-9C illustrate a various views of other embodiments of the vessel with a general triangle shape having at least one susceptor placed on the tray;

(10) FIG. 10 is a bottom plan view of another embodiment of the vessel having a polygon configuration with a pair of different shaped susceptors along the tray;

(11) FIG. 11 is a bottom plan view of another embodiment of the vessel having a rounded configuration with a pair of different shaped susceptors along the tray;

(12) FIG. 12 is a bottom plan view of another embodiment of the vessel having a generally asymmetric configuration with a pair of different shaped susceptors along the tray; and

(13) FIG. 13 is a bottom plan view of another embodiment of the vessel having a hexagonal configuration with a pair of different shaped susceptors along the tray.

DETAILED DESCRIPTION

(14) Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. It is to be understood that other embodiments may be utilized and structural and functional changes may be made. Moreover, features of the various embodiments may be combined or altered. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments.

(15) The present invention pertains to vessel having an area for holding a food item to be heated in a solid state microwave oven. As illustrated by FIG. 2, the vessel 10 comprises a tray 20 and a susceptor 30, wherein the susceptor is integrated or attached to a bottom 22 of the tray and covers a part of the surface of the bottom of said tray 20. The vessel 10 may be made from a material selected from the group including plastic material, glass material, fiberglass material, ceramic, silicon, cellulose material, or a combination thereof. A thermal insulation is provided between the susceptor and the food to be placed in the tray. In the embodiment illustrated by FIG. 2, the susceptor 30 is in the form of a horseshoe. However, various shapes and sizes of the susceptor 30 are contemplated by this disclosure and this feature is not limited.

(16) A “solid state microwave oven” is a microwave oven delivering solid state electromagnetic energy. Typically, production of such solid state energy is transistor-based and not magnetron produced.

(17) A “susceptor” is a material used for its ability to absorb electromagnetic energy and to convert it to heat. Susceptors are usually made of metallized film or paper.

(18) A “tray” is a shallow platform for carrying or holding things such as food items. For example trays are typically used for holding food items in the area of prepared dishes and frozen meals. Trays usually have a more or less flat bottom part which allows to stably placing the tray onto a surface e.g. for heating it in an oven or for putting it onto a table for ease of consumption.

(19) “Thermal insulation” is the reduction of heat transfer between two objects of different temperatures which are in thermal contact or in range of thermal radiative influence.

(20) In the vessel 10 of the present invention, the thermal insulation can for example be provided by a layer of plastic material, glass material, ceramic material, porcelain, cellulose based material, paper material, paperboard, silicon, Teflon or a combination thereof. Thereby the plastic material can be selected for example from PP (polypropylene) or Polyethylene terephthalate (PET), or particularly from crystallized Polyethylene terephthalate (CPET), and combinations therefrom with paper material such as for example PET laminated paperboard.

(21) Preferably, the layer of plastic material, glass material, ceramic material, porcelain, cellulose based material, paper material, paperboard, silicon, Teflon or a combination thereof, is at least 0.20 mm thick, preferably at least 0.25 mm or 0.30 mm thick, more preferably at least 0.50 mm thick. These are preferred minimal thicknesses to assure an adequate thermal insulation between the susceptor and the closest food item in contact or which can be placed into the vessel.

(22) In an embodiment, the tray 20 of the present invention is not thicker than 20 mm, preferably not thicker than 15 mm, more preferably not thicker than 12 mm. The tray is preferably designed to be washable and re-useable. Therefore, the tray should be thick enough to support the amount and weight of the food items to be placed therein, and to support a certain handling of the tray by the consumer such as placing it into a microwave oven, carrying it around and using it as a tray for directly eating from the package. Furthermore, the tray should be thick enough that it can be washed, for example in a dish-washer, and be re-used multiple times. However, the tray should not be too thick as to be not too heavy by itself, and not to require more production material as absolutely necessary in order to reduce production costs and environmental impact, particularly when the tray may be used multiple times by the user and stored for later use.

(23) In a preferred embodiment, the thermal insulation of the vessel 10 has a thermal resistance value R of at least 0.0004 m.sup.2K/W, preferably of at least 0.001 m.sup.2K/W, more preferably of at least 0.005 m.sup.2K/W, even more preferably of at least 0.01 m.sup.2K/W. R stands for thermal resistance value R. R is measured in m.sup.2K/W, wherein K stands for Kelvin and W for Watt. Thermal conductivity (k-value) is the ability of a material to conduct heat and it is measured in W/mK. Consequently, the value R is determined by assessing the k-value of an insulating material and measuring its thickness L as follows: R=L/k. Table I provides some k-values for materials typically used for making packaging trays.

(24) TABLE-US-00001 TABLE I Material k = W/mK at ca. 25° C. Aluminum 205 Cellulose 0.23 Celluloid 0.12-0.21 Ceramic 0.10-1.80 Cork board 0.043 Crystallized PET (CPET) 0.15-0.4  Fiberglass 0.04 Glass 1.05 Nylon 0.25 Paper 0.05 Polycarbonate 0.19 Polyester 0.05 Polyethylene 0.33-0.51 Polypropylene (PP)  0.1-0.22 Polytetrafluorethylene (PTFE) 0.25 Polyvinylchloride (PVC) 0.19 Porcelain 1.50 Pyrex glass 1.005 Silicon 0.15-0.32 Teflon 0.25 Vinyl ester 0.25

(25) As illustrated by the embodiments of FIG. 3, the portion of the tray 20 covered by the susceptor 30 of the vessel 10 may be up to 50% of the surface of the bottom of the tray 20. Preferably, the portion of the tray 20 covered by the susceptor 30 may be up to 40% of the surface of the bottom 22 of the tray 20. Typically however, the portion of the tray 20 covered by the susceptor 30 may be at least 20% of the surface of the bottom 22 of the tray 20.

(26) In one embodiment of the present invention, the tray 20 of the vessel 10 may include an area for holding the food items wherein the vessel comprises at least two compartments. The area for holding the food items may be a two-compartment tray or a multi-compartment tray. A multi-compartment tray may have three, four, five or even more compartments in one tray. One of the advantages to using a two- or multi-compartment tray is that it allows to easily separate individual different food items from each other. In this way and in combination with a use and design of one or more specific susceptor(s), the bundled energy of a solid state microwave application can be very clearly local and specifically be directed and targeted to the appropriate food item(s) to be heated.

(27) In one embodiment, only one of the compartments of the tray of the vessel is provided with a susceptor 30. However, preferably, the susceptor only spans one compartment or a part of one compartment of the vessel 10. As such, at least one of the compartments of the tray may not be provided with a susceptor 30. A further possibility may be that at least one of the compartments of the tray is shielded from microwaves in the solid state microwave oven. This would allow to include a food item into a multi-food item dish which will not be heated in the solid state microwave application. This food item may be for example a salad, a pastry, a dessert, or an ice cream.

(28) Preferably, the vessel according to the present invention may receive at least one food item, which may comprise one, two, three or even more food items. Thereby, for example, one food item may be a meat product, preferably selected from beef, pork, chicken, lamb or fish, or a meat analogue product. A second food item may be a carbohydrate based food product, preferably selected from potato, pasta, noodle or a cereal product, including rice. A third food item may be a vegetable product, a salad, a dessert or a bakery product. In one embodiment of the present invention, the packaged food product is frozen or chilled.

(29) The vessel of the present invention may be suitable for being used for heating a food item. In one embodiment of the present invention, the vessel is suitable for being used where the food item is frozen or chilled. For example, the vessel of the present invention can be frozen and kept frozen for a long time, e.g. several months, without cracking or deteriorating. On the other hand, this same vessel can also be used to be heated in a solid state microwave oven without cracking or deteriorating, and withstanding the general heat.

(30) A second aspect of the present invention relates to a method for heating a food in a solid state microwave oven comprising the steps of i) placing the food item onto an area for holding the food item of the vessel according to the present invention, and ii) heating the food items or parts thereof in the vessel in a solid state microwave oven at a selected frequency of between 900 and 5800 MHz. Preferably, the selected frequency may be between 900 and 930 MHz or between 2400 and 2500 MHz.

(31) Solid state microwave ovens have a degree of heating process control unavailable with classical magnetron driven microwave ovens. With this additional control and feed-back from the heating cavity of the oven, these solid state microwave ovens can determine how much power is reflected back and adapt the heating process accordingly. In some cases, solid state microwave ovens can sweep phase and frequency of the applied microwave wavelengths methodically over a wide range and determine the highest return loss modes. This allows these ovens to set frequency and phase in such a way to ensure that the maximum microwave energy is retained within the cavity of the oven, where it is available for an optimal preparation of the food item. Therefore a preferred embodiment of the present invention pertains to a method, wherein the selected frequency corresponds to the frequency which results in the highest energy absorption of the susceptor. Thereby, the solid state microwave oven is then preferably operated at a power from 100 to 1600 Watts and for 1 to 30 minutes or more particularly, for 1 to 30 minutes.

(32) Those skilled in the art will understand that they can freely combine all features of the present invention disclosed herein. In particular, features described for the product of the present invention may be combined with the method of the present invention and vice versa. Further, features described for different embodiments of the present invention may be combined.

(33) Further advantages and features of the present invention are apparent from the figures and examples.

Example 1

(34) Reference sample before microwave heating.

(35) As illustrated by FIG. 1, equal quantities of mashed potato (132 g±2 g) were placed in a two compartment tray and frozen to −18° C. The two compartment tray was a common tray as used commercially for frozen meals and did not comprise a susceptor. It had a dimension of ca. 18.4 cm to 14.6 cm and a height of ca. 3 cm. It was made of Crystallized Polyethylene terephthalate (CPET) and had a material thickness of 0.5 mm. FIG. 1 shows the nomenclature used for the two zones/compartments of mashed potato and their corresponding infrared images taken using a FLIR Infrared Camera. It can be seen that the mashed potatoes are about equally well frozen in both compartments.

Example 2

(36) Test samples with a susceptor fixed at the bottom of the tray in zone 2.

(37) Susceptors used in this study were of a very thin metal layer applied to the non-food contact side of the film and laminated to a paper based substrate (from Lorence & Pesheck, 2009). Susceptors in certain selected designs were then fixed to the outer bottom at zone 2 of the same CPET trays as described in Example 1 (FIG. 2). The susceptors were fixed to the trays in such a way that the metal part of the susceptor faced the surface of the tray.

(38) Different designs and forms of the susceptor as shown in FIG. 3 were used and tested in a solid state microwave oven. For this, each sample tray was filled with mashed potatoes as described in Example 1 and thereafter frozen at −18° C. Thereafter, the samples were put into a solid state microwave oven, where the oven system identified first the frequency with the highest energy absorption, i.e. the highest return loss. One example is shown in FIG. 4 where a highest absorption peak was observed at 2483 MHz. The highest absorption peak is related basically only to the energy absorption by the susceptor as frozen food does not absorb microwave energy well because of its low dielectric loss. The obtained frequency of the absorption peak depends on the susceptor, its form and design, and its ultimate location within the cavity of the microwave oven.

(39) The trays were then heated in a solid state microwave oven operating at the determined frequency with the maximum energy absorption at 500 Watts for 5 minutes. Infrared images were then captured at the end of the heating and the temperatures along the edges and centre of the mashed potatoes placed in the two zones were recorded. The results are shown in the Table II here below.

(40) TABLE-US-00002 TABLE II Peak Susceptor Temp. Zone 1 Temp. Zone 2 Sample Freq. area *.sup.) Edge Center Edge Center Nr. [MHz] [%] [° C.] [° C.] [° C.] [° C.] #1 2450  0% 38 0 53 0 #2 2423 50% 40 10 16 −1 #3 2451 20% 61 4 27 −1 #4 2409 30% 49 28 20 0 #5 2417 25% 58 9 10 2 #6 2451 20% 60 3 27 −1 #7 2408 30% 62 11 33 1 #8 2471 80% 31 2 36 0 #9 2457 50% 62 7 50 1 #10 2452 100%  51 0 62 1 *.sup.) Total bottom area of the tray covered by the susceptor in percent of total bottom surface of the tray. Sample #1 is a control sample having no susceptor. As can be seen from the results, heating of the food is about identical in both zones (see temperature in centre). Heating at the edges is pretty inconsistent and variable. Samples #2-#7 are working examples of the present invention. Particularly when looking at the temperatures in the centre of the food there is clear evidence that heating in Zone 1, not having the susceptor, is superior to heating in Zone 2, having the susceptor. Temperatures measured at the edges of the food confirm this as well. Samples #8-#10 are again control examples. Those samples have susceptors in both zones and cover 50% or more of the bottom surface of the tray with susceptor. As can be seen from the results, there is no or much less targeted heating of only one zone. Particularly, the result of #10 (with 100% coverage of susceptor) is very similar to the result of #1, which has no susceptor at all.

CONCLUSION

(41) As shown in the examples presented, the invention allows to specifically target heating to e.g. only one specific compartment of a multi-compartment tray. Particularly sample #4 gave a very good result as also shown in FIG. 5. Hence, it will now be possible with the teaching of the present invention to design new vessels 10 which have for example in one compartment a meat item which needs to be cooked very well, and in another compartment a vegetable or salad item which does not need to be heated as much.

Example 3

(42) Further vessels of the present invention can be produced with using trays having for example the following thermal resistance value R of the tray between the susceptor and the food items as specified in Table III.

(43) TABLE-US-00003 TABLE III Type of tray: R value of tray CPET Tray + PET film of Susceptor 0.001232 − 0.000462 PP Tray + PET film of Susceptor 0.001316667 − 0.000594773 Pressed Paper tray + PET film of 0.002697102 − 0.002667935 susceptor CPET Tray + Paperboard of Susceptor  0.00273142 − 0.001990587 PP Tray + Paperboard of Susceptor 0.002816087 − 0.00212336  Pressed Paper Tray + Paperboard of 0.004196522 Susceptor

(44) PET films typically used in the prior art on the surface of susceptors to protect for example the food item and/or the susceptor have an R value ranging from 1.75 E-05 to 4.7E-05. This R value is not sufficient to provide thermal insulation as claimed in the present invention.

(45) Alternatively, further vessels of the same type can be produced for example with materials selected from glass, ceramics, porcelain, silicon, Teflon, or a combination therefrom.

(46) FIGS. 6 through 13 illustrate various embodiments of the vessel 10 in accordance with the present disclosure. FIG. 6 is a cross sectional perspective view of an embodiment of the vessel 10 with a susceptor 30 on a bottom outer surface 22 of the tray 20. This vessel 10 includes a single compartment for receiving at least one food item therein.

(47) FIG. 7 is a cross sectional perspective view of another embodiment of the vessel 10. Here the vessel includes the susceptor 30 placed between a bottom outer surface 42 of a sub-tray 40 and a bottom inner surface 24 of the tray 20. Preferably, the susceptor 30 is attached to the bottom outer surface 42 of the sub-tray 40. This embodiment of the vessel 10 includes two compartments wherein the sub-tray 40 is the first compartment that may expose the food item to influence from the susceptor 30 and the remaining portion of the tray 20 is the second compartment that may contain a separate food item from the first compartment that is not exposed to the influence from the susceptor 30. Notably, the sub-tray may be movably positioned within the tray 20 in various arrangements such that the tray 20 may be adapted to include an additional compartment adjacent the sub-tray 40 within the tray 20. This additional compartment may contain a separate food item that is not exposed to influence from the susceptor 30.

(48) FIGS. 8A-8H illustrate cross sectional views of eight (8) additional embodiments of the vessel 10 with the susceptor(s) 30 that spans a section of the area for holding the food item and along other portions of the tray 20. In FIG. 8A the susceptor 30 is attached to the bottom of the tray 20 and spans up to about half of the bottom surface of the tray. In FIG. 8B, the tray includes two compartments wherein a first susceptor 30 is attached to the bottom of the first compartment and a second susceptor 30 is attached to the bottom of the second compartment. A wall 50 separates the first and second compartments and extends upwardly from the bottom of the tray 20 partially separating the first and second compartments. In FIG. 8C, the tray includes two compartments wherein a first susceptor 30 is attached to the bottom of the first compartment and a second susceptor 30 is attached to the bottom of the second compartment. The wall 50 separating the first and second compartment extends from the bottom of the tray 10 to a rim 60 of the tray 20.

(49) FIG. 8D illustrates the susceptor 30 attached to the bottom of the tray 20 and spans up to about the entire bottom surface of the tray 20. FIG. 8E illustrates the tray 20 having a perimeter ridge 70 that extends along the bottom of the tray 20 and defines the bottom surface 22. The susceptor 30 may be attached to the bottom surface 22 of the tray 20 defined by the perimeter ridge 70 and spans up to about the entire bottom surface 22 of the tray 20. FIG. 8F illustrates the tray 20 having a single compartment with a plurality of susceptors 30 each aligned along the bottom surface of the tray 20. Three susceptors 30 may be attached to the bottom surface wherein each susceptor 30 may span various sized portions of the bottom surface.

(50) FIG. 8G illustrates the vessel 10 including the tray 20 having susceptor 30 attached to the sides 80 of the tray 20. The sides 80 may define the compartment and the susceptor 30 may extend along the entire perimeter of the tray 20. Optionally, there may be a plurality of susceptors 30 positioned along the various sides 80 of the tray 20. FIG. 811 illustrates the vessel 10 including the susceptor 30 is entirely enclosed in the material of the vessel 10. Here, the susceptor 30 is positioned within the bottom portion of the tray 20.

(51) FIG. 9A illustrates the vessel 10 with a general triangle shaped tray 20 having the susceptor 30 having a general triangle shape that spans about the entire bottom of the tray 20. FIG. 9B includes the vessel 10 with a general triangle shaped tray 20 having the susceptor 30 with a general triangle shape that spans only a portion of the bottom of the tray 20. FIG. 9C illustrates the vessel 10 with a general triangle shaped tray 20 having a plurality of triangle shaped susceptors 30 that span a portion of the bottom of the tray.

(52) FIG. 10 illustrates another embodiment of the vessel 10 having a polygon shaped tray 20 with a pair of different shaped susceptors 30 positioned along a portion of the bottom of the tray 20. FIG. 11 illustrates an embodiment of the vessel 10 having a rounded tray 20 with a pair of different shaped susceptors 30 positioned along a portion of the bottom of the tray 20. FIG. 12 illustrates another embodiment of the vessel 10 having a generally asymmetric tray 20 with a pair of different shaped susceptors 30 positioned along a portion of the bottom of the tray 20. FIG. 13 is an embodiment of the vessel 10 having a hexagonal shaped tray 20 with a pair of different shaped susceptors 30 positioned along a portion of the bottom of the tray 20. Notably, the various features described for the different embodiments of the present invention illustrated by FIGS. 8A-8G, 9A-9C, and 10-13 may be combined in various arrangements as desired for optimal heating of food items within a solid state microwave oven.

(53) Although the present embodiments have been illustrated in the accompanying drawings and described in the foregoing detailed description, it is to be understood that the vessel is not to be limited to just the embodiments disclosed, but that the vessel described herein is capable of numerous rearrangements, modifications and substitutions. The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.