IES20110370A2 - Microwave crisping dish - Google Patents

Abstract

This invention describes a utensil for browning/crisping in a microwave oven. A metal dish is provided with a ferrite silicone matrix moulded to the underside and forms a number of moulded feet to elevate and support the tray. The advantage of the invention is that it will substantially improve the efficacy of the crisping process and allow for much reduced preheating times.

Description

Field of the invention This invention relates to the browning or crisping of food in a microwave oven. In particular the invention relates to a new design of Crisping Dish which will reduce the required preheat and improve the efficacy of the crisping process.

Background of the Invention io Microwave energy is a very fast and efficient way to heat/cook food. It has long been a problem, when cooking foods like pizza or burgers in the microwave oven, that the outside surface of the food is not browned/crisped as is normal in conventional ovens. is Producing a crispy surface on foods (such as pizza) in the microwave oven using existing knowledge involves applying a lossy material to the underside of an Aluminium dish, preheating this dish to temperatures in excess of 2OO°C and then adding the food and cooking for the required time. The results can be described as mediocre at best. A very important aspect of the current browning process is the differential temperature (ΔΤ) between the crisper and the food at the end of the cooking cycle. This is IE 1 1 Ο 3 7 0 when all the browning/crisping takes place. The final temperature of the dish (T2) is controlled by the preheat temperature, the thermal conductivity of the material used in the dish and the projected area of the food.

The Preheat temperature (TI) The maximum preheat is controlled by the binding material used to bond the lossy material to the crisper. This is normally silicone as it is a relatively low cost material with a very high use io temperature. In practice the preheat temperature is >2OOoC.

TI > 200oC The Projected Area of the Food The projected area of the food is also important to the crisping is process. Foods with a large surface area will capture a high proportion of the available microwave energy. The remaining energy is absorbed by the crisping dish and is used to support the final dish temperature(T2). Foods with a large surface contact area will also absorb a lot of the Preheat Temperature (TI).

It is important that the final temperature of the dish is a minimum of 25°C higher than the food temperature (T3) for IE 1 1 0 37 0 adequate crisping to take place T2-T3 > 25oC.

US Patent 4266108, Anderson discloses a device for browning food which uses the curie temperature of the ferrite to control and limit the maximum temperature that the dish can attain. It does not address the importance of the design of the dish to control the Crisping process. io US Patent 4398077, Freedman discloses a dish where substantially all of the microwave energy is directed to the lossy material so that searing temperatures are maintained. It suggests the use of a conductive lid to shield the food which will have a steamed effect rather that a crisping texture. It does is not address the thermal conductivity of the cooking surface to better enhance the crisping process. Nor does it maximise the fast efficient cooking afforded by microwave energy whilst producing an appetising crispy crust. 2o 4542271 Tanonis and 4496815 Jorgensen recommend that a good conductor of heat, such as Aluminium, Steel or copper should be used for the metal pan and gives no direction regarding the IE 1 1 0 3 7 0 thermal conductivity of this aspect of the dish. It is a claim of this invention that good heat conductors are detrimental to the crisping process.

US Patent 4883936, Maynard teaches the development of differential temperature zones by the differential application of a lossy material. Again he directs no attention to the thermal conductivity of the cooking surface or the need to vent the steam/moisture to better enhance the crisping process. Nor does io he address means to reduce the required preheat.

It is an object of the present invention to reduce the necessary preheat by 50% and to improve the efficacy of the crisping process.

IE 1 1 0 3 7 0 Statement of Invention Accordingly there is provided a dish dimensioned to allow it to fit a domestic microwave oven. The dish should be made from a material with a thermal conductivity between 10 W/(M.oC) and 70 W/(M.°C). The dish should have a side wall height of at least 15% of the diameter. The sides of the dish can be detached. Alternatively, the sides of the dish are formed as a separate attachment. The dish should have a lossy material applied to the underside to allow it to heat in a microwave environment. The io dish should be supported and balanced on a number of feet. The feet can be made from a thermally insulating material.

The advantage of this invention is that by increasing the height of the side walls of the dish (>15% of the diameter), the food is signature is reduced whilst the steam is vented and the crisping surface can capture significantly more of the available energy (Q3).

The materials used in the crisping dish aiso have a signif icant effect. Having designed the dish to capture more of the available microwave energy, it is very important that this energy is used to enhance the crisping process.

IE 110 37 0 Aluminium is the current material of choice for frying pans because it will transmit the heat energy of the tray to the food very quickly and efficiently. This feature of Aluminium makes it a poor choice for the crisping process. In fact, it is better to inhibit the heat dissipation so that more energy is stored in the dish until the end of the cooking process when all of the crisping takes place. If Q1 is a measure of the energy dissipated to the air in the oven through the exposed surface area of the dish and io Q2 is a measure of the energy conducted to the food through surface contact, it is desirable for an optimised crisping process that Q3 (captured energy) > (Q1+Q2) is Aluminium has a very high Thermal conductivity (250 W/M.°C) compared to mild steel (36 W/M.°C). The use of a material with a low thermal conductivity (<75 W/M-C) used in conjunction with a dish with raised side walls (>15% of the diameter), will allow the use of much lower preheat times as the extra microwave energy captured by the crisper is greater than the preheat energy loss to the food and the air. This means that the difference between the crisper temperature and the food temperature throughout Ί IE 1 10 3 7 0 the cooking process is maintained or even increased.

This is extremely beneficial for the following reasons • Much lower preheat temperatures are necessary which means the consumer is less likely to be burned when they touch the sides of the crisper.

• The crisper has a longer life and less damage due to accidental overheat • Second and subsequent batches do not require additional preheat.

· Additional preheat time gives a much higher ΔΤ at the end of the cooking cycle. This means that the user can control the level of crispiness to taste.

IE 1 1 0 370 Brief Description of Drawings The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a front view in section Figure 2 shows a plan view of the base of the dish Detailed Description Referring now to the drawings and initially to figure 1 wherein io similar letters are used to denote similar materials, there is shown a dish of diameter B and height A. The Microwave Crisping Dish (fig 1) comprises a metal pan consisting of a circular steel base with an annular side wall. The height of the side wall (A) is greater than 15% of the diameter (B). The pan is fabricated from is a metal with a thermal conductivity less than 70 W/(M.oC).

A microwave lossy material such as a ferrite is mixed with a high temperature binder such as silicone rubber and moulded to the underside of the pan (C). A plurality of feet (D) may be moulded as part of the lossy coating. The purpose of these feet is to raise the Crisper from the floor or turntable of the oven to allow microwave energy access to the base of the dish and to insulate the heat energy of the dish from the microwave oven.

Claims (5)

1. A microwave dish comprising a metal dish having a layer incorporating a microwave lossy material applied to the base of the dish, said dish having a number of feet attached to raise and 5 insulate the dish from the base or turntable of the microwave oven, said dish having a side wall dimension which is greater that 15% of the base dimension and having a thermal conductivity less than 70 W/(M.oC). io

2. A microwave dish according to claim 1 where the feet can be formed as part of the microwave lossy material.

3. A microwave dish according to claim 1 where the feet can be made from a thermally insulating material.

4. A microwave dish according to claim 1 where the sides of the dish can be detached.

5. A microwave dish according to claim 1 where the sides of 20 the dish are formed as a separate attachment