CA1309751C - Microwave cooking - Google Patents

Abstract

MICROWAVE COOKING
ABSTRACT
The invention relates to a method of cooking or reheatinq a comestible with microwave energy by utilizing a double-boiler cooking utensil. The double-boiler utensil contains a microwave susceptible liquid within an outer vessel and a cooking oil or fat within an inner vessel with the inner vessel providing conductive heat transfer between the microwave susceptible liquid and the cooking oil or fat. The process involves placing a comestible in the cooking oil or fat within the inner vessel and irradiating the cooking utensil containing the comestible for a period of time effective to cook the comestible. The microwave susceptible liquid when subjected to microwave energy functions to transfer sufficient heat to the cooking oil or fat to maintain a temperature on the surface of the comestible within the range of from 125°C to 225°C.

Description

~ 3~7~ case 3630 MICROWAVE COO~ING

3 BACKGROUND OF TH~INVENTION

5 FIELl?_OF THE INVE;NTIO~3:
This invention relates to the microwave cooking of 7 food. More particularly, it relates to microwav~ cooking at higher temperatures than those conventionally 9 obtained. This invention especially relates to the use of liquids whose dielectric properties permit the 11 microwave cooking of foods at temperatures higher than those conventionally obtained.

DESC~IP~ION OF ~ pRIOR ~
Microwave ovens for home use have found widespread acceptance. The fact that the cooking and/or reheating 17 of food in the domestic microwave oven is achieved in such relatively short periods of time is probably the 19 principal reason for the high sales of these units in recent years.
21 Essentially all domestic microwave ovens operate at 2450 MHz. The dielectric properties of food at this 23 frequency parallels those of water which is the principal lossy constituent of food. The absorption of microwave 25 energy by food by the interaction of the dipole water molecule in the microwave energy field results in a - -27 loc~lized heating-not greatly exceeding 100C producing ~3~7~ 1 1 the desired cooking or reheating. Despite the widespread use of microwave ovens, there are several shortcomings to 3 which attention has been directed to increase the utilization of these devices. The uneven absorption of 5 microwave energy by different parts of the same meal placed in th0 microwave oven results in not all of the 7 separate food components reaching the same temperature.
Further, the edges of a particular comestible may be hot g while the center may be cold. In addition, the distribution of microwave energy is usually not uniformly 11 distributed throughout the cross section of the oven.
Some of these difficulties have been alleviated 13 heretofore by the use of turntables which rotate slowly while the food is subjected to the microwave energy.
15 Since microwave cooking is dependent upon the absorption of the microwaves which in the case of food 17 means the absorption by water molecules, typical temperatures achieveable in conventional microwave 19 cooking for foods possessing a significant moisture content is approximately 100C due to the evaporation of 21 water. Since microwave ovens operate with cold walls, the surface of an article in the oven loses heat to the 23 cool oven walls thereby reducinq the surface temperature significantly below that of the temperature obtainable 25 deep within the foodstuff.
Cooking in a microwave is faster than in a 27 conventional thermal oven since the microwave energy has the ability to penetrate deeply into foods and produce 29 heat instantaneously as it penetrates. The conventional thermal oven depends upon the conduction of heat from the r31 surface of the comestible to the interior portions thereof. In microwave cooking the surface temperatures 33 of most moisture-containing foods rarely e~ceed 100C
before the inside portion if the food is overcooked, 35 therefore, most foods cooked in a-microwave oven lack the ~ 3 ~

1 brown surface colo~ achieved when using conventional thermal techniques. Thus, breads and pies cooked in a 3 microwave oven have a pale app~a~ance while meats usually have a gray surface appearance when prepared in a 5 microwave oven. The golden brown, crispy te~ture of roast turkey or chicken, the dark brown appearance of 7 meat roasts and the golden brown crust of pies and cakes are the result of a nonenzymatic browning reactions 9 and/or caramelization. These reactions require temperatures in excess of 125C which are not typically 11 obtainable in the microwave oven.
A number of techniques have been utilized heretofore 13 to impart a brown color to comestibles prepared in a microwave oven. In some, browning sauces are utilized to 15 impart the desirable brown color to meats while in others materials are added to cooking utensils which cause an 17 increase in the surface tPmperature of the comestible being prepared in the microwave oven. U.S. 4,252,832 19 discloses an aqueous syrup of a melted, carmelized and foamed disaccharide for basting or recipe-inclusion to 21 effect browning of foods cooked in a microwave oven.
By far the more common approach to the problem has 23 been to utilize cooking utensils of various designs whose surfaces include materials designed to be susceptible to 25 heating by microwave radiation thereby causing the surface of the comestible in contact therewith to reach a 27 temperature at which the browninq reaction will take place. Among the problems in designing browning utensils 29 are the fact that with some materials susceptible to heating by microwave radiation and under some geometric 31 configurations there is no practical upper limit to the temperature to which they will heat so that with 33 prolonged exposure to microwave energy these materials are subject to thermal runaway due to their non-linear 35 dielectric loss cha.acteristics. However~ those microwave absorbing ma~erials which exhibit a Curie 7 5 ~

1 temperature theoretically have an upper temperature, of about the Curie temperature, which can be attained when 3 subjected to even prolonged microwave radiation. Thus, a number of browning dishes have incorporated one of these 5 desirable class of materials, ferrites, which absorb energy to their Curie temperature, beyond which power 7 absorption decreases and heating does not continue. (See for example, U.S. 2,830,162, 4,266,108 and 4,663,506, g which disclose ferrite-containing browning utensils.) Thus, foods in heat exchange contact with surfaces 11 containing ferrites will be, when placed in a microwave oven, subject to temperatures sufficiently a~ove 100C to 13 cause a browning and/or a crisping of the surface of the comestible.
Other cooking utensils are designed to provide a variety of surface temperatures so that different 17 portions of a comestible receive different rates of heating. Some surfaces may be transparent to microwave 19 energy thereby remaining cool but permitting the portion of the comestible adjacent thereto to become heated by 21 the microwaves passing therethrough. Other surfaces of a utensil may contain microwave lossy materials which can 23 cause these surfaces to become sufficiently hot to promote the browning reaction of the portion of the 25 comestible in heat transfer relationship with that hot surface. U.S. 4,542,271 incorporates into a microwave 27 cooking utensil a heating matris absorbent to microwave energy composed of a blend of three plastics having 29 magnetite dispersed therein which is said to provide a fast heating time. Other cooking utensils utilize 31 liquids to achieve desirable results. In U.S. 4,439,656, food is packaged in a metal container which in turn is 33 placed in a non-metallic holder slightly larger than the container. The space between the containel and holder is 35 filled with a liquid, such as water, which absorbs ~ 3 ~

1 microwavP energy, thereby uniformly generating heat which is transferred to the surfaces of the sides and bottom o~
3 the metal container. The use of water, however, does not generate a suf ficiently high temperature to promote the 5 brow~ing reaction. U.S. 4,316,070 discloses a moderator for cooking foods evenly in a microwa~e oven. ~he 7 moderator is in the form o~ a plastic bag having a fluid impervious outer layer. The inner surface of the plastic 9 bag has attached thereto a liquid forming layer which may be a layer of a water-soluble surfactant or an absorbent 11 substrate of paper, tissue, cellulosic film or fabric.
The liquid used in conjunction with the film forming 13 layer has dielectric properties which influence the bag's ability to moderate or even out the microwave fields.
15 Preferably, the liquid has a dielectric constant above two and a loss tangent below one. Water is the only 17 liquid material esemplified in the patent although suitable dielectics disclosed are water, vegetable oil, 19 ethanol and polyols. The purpose of the surfactant is said to modify the dielectric properties of the liquid by 21 decreasing the dielectric constant and increasing the loss tangent. The film forming layer converts the 23 dielectric fluid placed in contact with the layer into a thin liquid film which surrounds the cooking comestible.
25 By cooking the comestible within the disclosed plastic bag, the microwave energy is moderated prior to its 27 interaction with the comestible so as to cause more even cooking of the comestible.
29 Much of the prior art has been concerned with providing packages for such food products as pizza, r31 popcorn and fruit and meat pies. These packages are designed to be inespensive so as to permit their one-time 33 use not only for packaging and consumer-purchase of the comestible, but also to serve as the utensil for 35 microwave cookinq of the comestible. Browning of pastry ~3a~

1 dough while providing even heati~g of the remaining portion of the comestible is achieved in a vari~ty of 3 techniques involving the use of microwave transparent paper and cardboard together with microwave reflective or 5 microwave shielding materials and microwave lossy materials. These latter mat~rials heat up and radiate or 7 conduct heat to adjacent areas. A variety of the microwave materials, also known as microwave interactive 9 materials, may be used. Because of their dielectric properties, these materials absorb a portion of the 11 microwave energy impinging thereon so that the surface of th~ material heats up. E~amples of suitable microwave 13 interactive materials include metalized layers of polyethylene terephthalate or polyester as disclosed in 15 U.S. Patents 4,553,010, 4,590,349 and 4,594,492. Typical e~amples of commercial packaqing utilized for microwave 17 use include the container disclosed in U.S. 4,553,010 for preparing popcorn wherein the container is formed of a 19 bottom panel o~ paperboard coated with a microwave interactive material of metalized polyethylene 21 terephthalate and the remaining parts of the container are constructed of paperboard which i8 transparent to the 23 microwave energy. The bottom panel has the microwave reactive material formed on the inner surface thereof in 25 heat transfer relationship with the kernels of popcorn.
A number of prior art patents are devoted to 27 providing a pasteboard or paper container which may be effectively utilized in cooking the pizza contained 29 therein. In U.S. 4,555,605, the package contains a tray, the walls of which ara of microwave transparent 31 paperboard and the top of which, also of paperboard, is provided with a microwave interactive layer which 33 converts microwave energy into heat. The pizza is placed on top of the microwave interactive layer and the 35 combination placed in the microwave oven. The pizza ~L 3 ~ ~ ~ c~ ~

1 filling will be heated directly by the action of the microwave energy while the dough portion of the pizza 3 will be cooked by the heat transferred to it from the microwave reactive film. U.S. 4,59~,91~ discloses 5 another type of cook-in container for pizza. The container is made from two separate paperboard blanks, 7 one of which forms an outer package while the other forms an inner food supporting tray. The outer package 9 contains a microwave shielding layer of thin aluminum foil to prevent overcooking of the top portion of the 11 pizza. The outer package also contains a section which is removed prior to insertion of the package into the 13 microwave oven to e~pose several ventilation holes. The inner food supporting tray serves to support the pizza in 15 an elevated position above the bottom wall of the package and at the same time contains a microwave interactive 17 material formed from a metalized layer of polyester which in the presence of microwaves heats up to brown and crisp 19 the crl~st of the pizza. With a package designed in this fashion, the pizza filling is cooked to a proper 21 temperature while the pizza crust is cooked and browned without becoming soggy.
23 U.S. 4,626,641 discloses a microwavable container for fruit or meat pies having crusts. The container includes 25 an outer carton formed from a paperboard blank, and an insert formed from a separate paperboard blank containing 27 a microwave transparent area. The outer carton has its entire inner surface laminated with a crisping means 29 constructed from a metalized polyester for converting microwave energy into heat capable of hrowning and 31 crisping the surface crust of the pie contained within the container. The second paperboard blank i formed 33 into a container to hold the pie which is formed with an upper crust. The insert includes a microwave transparent 35 area in its bottom panel to admit microwave energy into 1 the bottom of th~ insert and consequently the bottom of the food product held therein. The insert is otherwise 3 shielded on its side and bottom with a microwave reflective material such as aluminum foil to prevent 5 excessive exposure of the food product to direct microwave energy. In this fashion the upper crust of the 7 pie will be brown and crisp while the contents of the pie will be cooked by receiving a controlled amaunt of 9 microwave energy. Where the pie is made with crust on the bottoms and the sides, the insert design is modified 11 by lining the insert with the same microwave interactive material as was used in the crisping means. In this 13 fashion the insert will provide a crisping and browning effect to the bottom and side crust of the pie while the 15 upper crisping means browns and crisps the upper crust and the pie contents receives appropriate microwave heat 17 for cooking the contents.
U.S. 3,256,101 is directed to materially reducing the 19 time required to heat food in a microwave oYen by e~tracting part of the water from the ood and 21 substituting in its place organic liquids having a significantly lower specific heat capacity and latent 23 heat of fusion than water. Typical liquids for this purpose are said to include fatty oils, such as corn oil, 25 cottonseed oil, peanut oil, safflower oil and glycerol.
Substitution of an organic liquid for the water 27 significantly reduced the heating time required for heating the food in a microwave oven and also resulted in 29 a more uniform distribution of microwaYe heating energy in the food. The benefits achieved by the substitution 31 of organic liquids for water are said to occur because these organic oils have a lower dielectric constant than 33 water and, therefore, absorb microwave energy less readily than water.
It is a feature of one embodiment of this invention to provide a means ~3a~7~

1 for cooking in a microwave oven at temperatures significantly higher than achieved conventionally. It is 3 another object of this invention to provide liquids for use in preparing comestibles in microwa~e ovens at 5 temperatures significantly above 100C.
A further feature of an embodiment of this invention 7 provides a process for conducting cooking or reheating in a microwave oven so as to achieve browning and crisping of 9 foods as is conventionally obtained in a thermal oven.

These and other features are achieved by means of a 13 microwave susceptible or interactive liquid. In particular, by maintaining particular microwave 15 susceptible liquids in contact with a comestible while the comestible is subject to microwave energy, a 17 sufficiently high temperature can be achieved to effect browning, crisping and aroma development,.
19 Mbre paxticularly, in accordanc~ wlth an ~xx~m~-t of the p~esent invention there is provided a method of cooklng or 21 reheating a ccmestible with microwave ene ~ which ~rises:
(a) placing a double-boiler type cooking utensil in 23 a microwave oven, said utensil containing a microwave susceptible liquid in an outer vessel and a cooking oil 25 or fat within an inner vessel wherein the walls of the inner vessel provide conductive heat transfer between the 27 liquid and cooking oil or fat;
~b) inserting a comestible which is to be cooked or 29 reheated into the cooking oil or fat within the inner vessel;
31 (c) irradiating the comestible with microwave energy for a period of time which is effective to cook or reheat 33 the comestible, said microwave susceptible li~uid being effective to transfer sufficient heat to said cooking oil or fat to maintain a temperature on the surface of the comestible in the range of from 125C to 225C during irradiation with microwave energy.
In accordance with another embodiment of the present invention there is provided ~ cooking utensil for cooking or reheating comestibles with microwave energy comprising: an inner vessel; an outer vessel; means for maintaining a space between the outer surface of the bottom of the inner vessel and the inner surface of the outer vessel; and a quantity of a microwave susceptible liquid placed in the outer vessel wherein the inner vessel is in conductive heat transfer contact with the microwave susceptible liquid contained within the outer vessel, the microwave susceptible liquid is an organic liquid which possesses a high dielectric loss !15 factor as well as a boiling point greater than 150C.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an isometric view of a cooking utensil in which the process of the subject invention may be practised;
Figure 2 is an elevation view of the utensil of Figure l along the lines "2-2";
Figure 3 is an isometric view of a cooking utensil which may be utilized to practice the present invention; and Figure 4 is an elevational view of the utensil of Figure 3 along the lines "4-4".
DESCRIPTION OF THE PREFERRED EMBODIMENT~
The present invention relates to a method of conducting microwave cooking or reheating of the comestible surface at temperatures which will typically result in the browning or crisping of the surface of comestibles and the development of food or cooking aromas which conventionally occur when cooking, baking, roasting or reheating in a thermal oven.
In accordance with the present invention, the elevated tem-perature necessary to initiate the non-enzymatic browning reactions for producing the surface browning of comestibles is obtained in a microwave oven by the use of a microwave ~097~1 - lOa -susceptible liquid. By a microwave interactive liquid (also known as a microwave susceptible liquid) is meant a liquid that absorbs a portion of the microwave energy impinging on it so that its temperature rises. By maintaining the comes-tible within the cooking oil or fat contained in the inner vessel of the double boiler in conductive heat transfer contact with the outer vessel containing a 7 ~ ~

1 microwave susceptible liquid of this invention, a temperature in the range of about 125 to about 225C, preferably 150 to 200C, may be obtained on the surface of the comestible when it is radiated with microwave 5 energy in a microwave oven.
In order to be useful ~s a microwave interactive 7 liquid, the liquid must be susceptible to microwave radiation to the e~tent that it will heat up sufficiently 9 and conduct heat to the coo~ing oil or fat which will in turn maintain the surface of a comestible at a 11 temperature sufficient to a~hieve surface browning and ideally, aroma development and release. Organic liquids 13 which possess a high dielectric loss factor as well as a high boiling point i.e. greater than 150C may be 15 employed. The microwave reactive liquids are preferably selected from the following groups; polyols between 17 C2-C6; polyoxyethylene sorbitan esters i.e. Tweens;
sorbitan esters i.e. Spans; acetates of glycerol, 19 i.e., monoace~in, diacetin and triacetin and combinations of liquids representative of two or more of the groups.
21 Most preferred liquids are glycerol and propylene glycol.
It is possible to select one of these liquids or 23 mistures thereof in order to achieve a particular desirable temperature at the surface of the comestible 25 being cooked.
This invention incorporates the concept of frying 27 along with microwave cooking by employing a ~double-boiler~ type of cooking utensil. The microwave 29 susceptible liquid is placed in the outer vessel of the double-boiler and a triglyceride-containing cooking oil 31 or fat, which does not heat up rapidly when e~posed to microwave energy, is placed in the inner vessel of the 33 double-boiler. Foods merely placed in a cooking oil or rat, and then subjected to microwave energy will not be 13~7t~1 1 fried since the vegetable cooking oil is not very susceptible to microwave energy and the oil will not 3 reach frying temperatures when e~posed to microwave energy for a reasonable period of time, i.e. 5 to 7 5 minutes. Furthermore, if the oil is able to reach frying temperatures by longer e~posure to microwaves, it will 7 cool down when a comestible is added (in an attempt to fry the comestible) and the oil will again take 9 considerable time to reach frying temperatures. During the time the oil is being heated to reach fryins 11 temperatures, the comestible is being cooked internally by the microwaves. Thus the comestible will be 13 overcooked internally before the cooking oil reaches frying temperatures or before frying is completed.
Reference should now be made to Figures 1 and 2 which illustrate a version of the ~double-boiler~ type of 17 utensil 2 which may usefully be employed in the practice of this invention. The same numerals in each of these 19 two drawings are utilized to depict the same elements of the cooking utensil. The utensil consists of an outer 21 rounded vessel 4 having a flat bottom and straight side walls. Vessel 6 having a similar shape but of smaller 23 diameter and taller side wall height than vessel 4 is placed within outer vessel 4 on spacers 8 which maintain 25 a space between the outer surface of the bottom of vessel 6 and the inner surface of outer vessel 4. Both 27 vessels may be composed of materials which are essentially transparent to microwave energy, and inner 29 vessel 6 should be composed of material which permits the rapid transmission of heat. In one embodiment both 31 vessels were composed of heat resistant glass such as *Pyrex glass. Spacer 8 may also be composed of the same 33 material as the vessels and may have a circular configuration or comprise short rectangular cylinders of 35 this material. Alternately a one-piece double-boiler .

*Trade mark ~ 3 ~

1 apparatus may be constructed wherein the microwave susceptible liquid is permanently sealed between the 3 upper and lower walls of a coo~ing apparatus. A quantity of triglyceride-containing ~egetable cooking oil 10 is 5 placed inside vessel 6. This oil is the type conventionally used for frying comestibles which does not 7 heat up quickly when radiated by microwave energy. The space between outer vessel 4 and inner vessel 6 is filled g with a microwave susceptible liquid 12 of the subject invention for esample, glycerol.
11 To utilize cooking utensil 2, it is placed in the microwave oven and subjected to microwave energy 13 typically at a frequency of about 2450 MHz and a power level in the range of about 300 to about 1,000 watts for lS a period of time to cause the microwave susceptible liquid 12 to heat up sufficient to transmit adequate heat 17 through the walls of vessel 6 to heat the vegetable cooking oil 10 to a temperature sufficient to conduct 19 frying. At this point the door to the microwave oven is opened, a comestible 14, such as breaded chicken filets, 21 is placed in the cooking oil, the oven door is closed and the entire assembly is subjected to microwave energy for 23 a sufficient period of time to cook the comestible.
Usually a period of less than one minute is sufficient to 25 adequately cook a small, breaded chicken filets. Since the cooking action is a combination of microwave cooking 27 and deep frying, the outside of the breaded chicken piece is deep fried to a golden brown while the interior of the 29 chicken filet is still moist and soft and thoroughly cooked by the action of the microwave energy. By 31 utilizing a device of this type, the desired degree of browning is obtained at the temperatures necessary to 33 effect that appearance; an effect which is not otherwise obtainable in conventional microwave cooking.

~ ~ ~ ^ 7 ~ ~

1 Reference should now be made to figures 3 and 4 which illustrate another version of the ~double boiler~ type of 3 cooking utensil 20 similar in operation and design to Figures 1 and 2 which may usefully be employed to 5 practice the present invention. This version differs from that set forth in Figures 1 and 2 in that this 7 version illustrates a one piece cooking utensil where the microwave susceptible liquid 26 is permanently placed in 9 a one piece utensil between a top portion 22 of the utensil and ~ottom portion 24 of the utensil. The top 11 and bottom portion are joined at a lip 28 of the utensil. Optionally a vent space, not shown, may be 13 incorporated into the utensil design. The numerals utilized in Figures 3 and 4 are utilized to depict the 15 same elements of the cooking vessel (however the numerals differ from those set forth in Figures 1 and 2). In 17 order to utilize this utensil, a quantity of cooking oil not shown is placed within the open U-shaped to~
19 portion of the utensil and the utensil is then utilized in a similar manner as described above. Therefore in its 21 operation, the utensil incorporates an inner vessel represented by the top, open U-shaped component of the 23 utensil which will contain the cooking oil or fat and an outer vessel represented by bottom component of the 25 utensil which contains the microwave susceptible liquid.
Useful cooking oils or fats which are employed in the 27 present invention include such animal and vegetable fats as lard, tallow, butter and mono, di and triglycerides.
29 The cooking oil or fat is of the type used in the art to deep fat fry comestibles. Also in lieu of utilizing a 31 fat or oil per se, a comestible which will esude a fat or oil upon heating such as bacon, salt pork, sausaqe and 33 oil-coated comestible may be incorporated as a source of cooking oil or fat.

1 The process employed in the present invention may simply comprise the addition of a comestible to the oil 3 or fat containing inner vessel of the utensil and placing the utensil in a microwave oven and subjecting the 5 combination to microwave energy for a period of time to cook or reheat the comestible. Alternately the 7 double-boiler cooking utensil containinq the microwave susceptible liguid within the outer vessel and the 9 cooking oil or fat within the inner vessel may be subjected to microwave radiation without addin~ the 11 comestible for a period of time effective to preheat the oil or fat to a temperature within the range of from 150 13 to 180C. Thereafter, the comestible is added to the hot oil and the combination is placed in a microwave oven.
Although it may be possible to cook comestibles by merely placing them in the microwave susceptible liquid 17 utilized in the practice of this invention, most of the useful liquids impart an undesirable flavor to the 19 comestible. Where this is undesirable, the double-boiler type utensil described above provides an appropriate 21 means to effect deep frying in a microwave oven combined with conventional microwave cooking of the comestible.
23 The taste effect achieved is not obtained by either deep frying or microwave cooking. The ~micro-fried~
25 comestible provides a new and most pleasing organoleptic esperience.
27 The present process may be employed to cook the following comestibles: meats, i.e., chicken and veal 29 cutlets; potatoes, i.e., french fried potatoes and potato chips; dough based products, i.e., biscuits, donuts, eggs 31 and combinations of these comestibles.
The present process may be utlized to reheat 33 commestibles which have been totally or partially precooked and then refrigerated or frozen. The main 35 diffsrence in the process compared to cooking is that the ~ 3 ~

1 comestible is subjected to microwave radiation for a shorter period of ti~e sufficient to he~t and/or finish 3 cook the comestible.
The following e~amples illustrate tbe practice of 5 this invention.

A series of comestibles were prepared in a microwave g oven utilizing the "double-boiler~ vessel depicted in Figures 1 and 2 and described hereinabove. A *Pyrex Petri 11 Dish was utilized as the outer vessel and a 12.5 cm crystallizing dish was utilized as the inner vessel, the 13 two dishes were separated from each other by a lmm thick capillary cylinder. Approsimately 50g. of triglyceride 15 vegetable cooking oil was placed in the inner vessel of the utensil and appro~imately 20g. of glycerol was placed 17 in the annular space surrounding the inner vessel (space between the inner and outer vessels). The assembled 19 utensil was placed in a microwave oven and the oven was energized for appromimately 3 minutes which was 21 sufficient to heat the glycerol and the cooking oil to a temperature of approsimately 180C. In a series of three 23 cooking runs, the following materials were cooked for the indicated periods of time:
1. An uncooked *Pillsbury bran~ buttermilk biscuit was placed in the hot vegetable cooking oil, the 27 microwave oven door was closed and the switch energized to subject the oven contents to microwave energy ~at the 29 high power setting). After a time period of 30 seconds, the biscuit was turned over and cooked for an additional 3~ 30 seconds after which it was removed from the cooking oil. The e~terior surface was light brown in color and 33 upon breaking the biscuit, the interior of the biscuit appeared to be cooked. ~hen eaten, the biscuit had the *Trade mark - 17 - ~3~3~

1 flavor and all the or~anoleptic qualities of a baked butter~ilk biscuit~
3 2. Several pieces of chicken cutlets were breaded and placed in the hot cooking oil of the double-boiler 5 utensil. The utensil was placed in a microwave oven which was energized (at the high power setting) for 7 appro~imately 45 seconds (30 seconds on one side and 15 seconds on the other, after the piece was turned 9 over). Upon removal from the oven, the exterior of the chicken filet had a crispy, golden brown appearance, 11 while the interior of the filet was thoroughly cooked and moist. The eating qualities of the cooked filet gave a 13 flavor of cooked chicken which was a pleasant combination of roasted and deep-fried chicken.
3. Several raw potatoes were sliced into pieces suitable for the preparation of french steak fries. The 17 potato slices were placed in the hot cooking oil of the "double-boiler~ utensil and the inner vessel containing 19 the fries was covered with a microwave reflective material such as aluminum foil which functioned to reduce 21 the microwave energy available to cook the potatoes.
Therafter the ~double boiler~ utensil was placed in the 23 microwave oven which was energized for appro~imately 3 to 4 minutes on the high power setting. The shielding by 25 aluminum foil allowed the potatoes to remain in the hot oil for a sufficiently long period of time to cause 27 browing on the surface while maintaining a soft interior. The exterior of the cooked potatoes had a 29 light brown crispy appearance and their interior appeared fully cooked. When eaten, the cooked potatoes had the 31 flavor and organoleptic properties of french fried potatoes prepared in a deep vegetable oil frier.

~ 3 ~

1 EX~PLE 2 Potato crisps similar to comercially produced potato 3 chips were produced utilizing a disposible double-boiler apparatus which consisted of an outer vessel made out of 5 filled polyester and an inner vessel which is identical in its size and composition to the outer vessel. The 7 inner vessel is tightly fit within the outer vessel. The bottom of the inner vessel had 8 small protruding ridge 9 which functioned as a spacer between the inner and outer vessels. The space between the two snugly fit vessels 11 was filled with 15g. of slycerol. Inside the inner vessel 50g. of Wesson brand vegetable oil was placed.
13 The utensil containing the glycerol and oil was placed in a microwave oven on the high power setting for 2 to 15 3 minutes. Russet potatoes were cut producing round slices approsimately 1 to Zmm. thick. The potato slices 17 were added to the hot oil and the apparatus was again subject to microwave radiation at the high power setting 19 for 3~ to 4 minutes. The potato crisps were then removed from the oil and were placed on paper towels for 21 drainage. The potato pieces were an attractive light brown color and were crisp possessing a pleasant deep 23 fried taste.
Alternatively, the potato slices can be browned and 25 crisped without preheating the oil (by placing the utensil without potato slices containing therein in the 27 microwave). In this instance the potato slices can be produced by placing them in the room temperature oil 29 within the utensil and placing the utensil in the microwave at the high power setting for 4~ to S minutes.

EXAMPL~ 3 33 The disposable double-boiler apparatus described in Example 2 was utilized to prepare a fried egg. In this 35 instance 15g. of glycerol and 40g.-of oil were utilized ~3~J~ ~

1 to produce the double-boiler apparatus. The apparatus was placed in the microwave oven at the high power 3 setting for 2 to 3 minutes to preheat the oil. An egg was cracked, placed into a saucer and the yolk was 5 pierced with a needle 3 or 4 times. Thereafter the egg was placed into the preheated apparatus and the apparatus 7 was subject~d to microwave radiation at the high power setting for approximately 45 seconds. The fried egg 9 produced was similar in organoleptic character and appearance to a fried egg prepared in a frying pan.

13 Bacon and eggs were cooked in the disposable double-boiler cooking utensil previously described in 15 Example 2. The following modifications were made: 15g.
of glycerol was placed in the space between the outer and 17 inner vessels but no liquid was poured in the inner vessel. Instead bacon was used as a source of hard fat.
19 Two strips of regular cut bacon was placed in the inner vessel of the utensil and the utensil was placed into the 21 microwave oven and cooked on the high power setting for 1 to 1~ minutes. During cooking, the bacon exuded 23 sufficient fat to serve as a vehicle to cook the egg.
Thereafter an egg was cracked, the yolk pierced and the 25 pierced egg was placed into the bacon fat in the inner vessel of the utensil. The utensil was then placed in a 27 microwave oven and was subjected to microwave radiation at the high power setting for 4S to 60 seconds to produce 29 a bacon and egg breakfast.

This example demonstrates the use of the present 33 process to reheat comestibles which have been precooked and frozen. The disposable double boiler cooking utensil 35 previously described in Example 2 was utilized. Fifteen ~ 3 ~

1 gramS of glycerol was placed between the two vessels and a thin layer of oil (measuring approximately 15 to 3 20 grams) was placed into the inner vessel. The utensil containing the glycerol and oil was preheated by placing 5 it in a microwave oven on the high power setting for two minutes. Two pieces of prefried and frozen chicken 7 cutlets were placed in the hot oil and the combination was subjected to microwave radiation (at the high 9 setting) for 30 to 45 seconds (depending on the sizes of the cutlets). Thereafter the cutlets were turned and the 11 combination subjected to microwave radiation for an additional 30 to 45 seconds. The results were pieces of 13 chicken that had the organoleptic qualities of freshly prepared and fried chicken cutlets. The chicken cutlets 15 possessed a hot, moist interior and a crispy, brown exterior.

Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of cooking or reheating a comestible with microwave energy which comprises:
(a) placing a double-boiler cooking utensil in a microwave oven, said utensil containing a microwave susceptible liquid in an outer vessel and a cooking oil or fat within an inner vessel wherein the walls of the inner vessel provide conductive heat transfer between the liquid and cooking oil or fat;
(b) inserting a comestible which is to be cooked or reheated into the cooking oil or fat within the inner vessel; and (c) irradiating the comestible with microwave energy for a period of time which is effective to cook or reheat the comestible, said microwave susceptible liquid being effective to transfer sufficient heat to said cooking oil or fat to maintain a temperature on the surface of the comestible in the range of from 125°C to 225°C during irradiation with microwave energy.

2. The method of Claim 1 wherein said microwave susceptible liquid is an organic liquid which possesses a high dielectric loss factor as well as a boiling point greater than 150°C.

3. The method of Claim 2 wherein the microwave susceptible liquid is selected from the group consisting of polyols between C2-C6, polyoxyethylene sorbitan esters, sorbitan esters, acetates or glycerol and combinations thereof.

4. A method of Claim 3 wherein the microwave susceptible liquid is glycerol.

5. The method of Claim 3 wherein the microwave susceptible liquid is propylene glycol.

6. The method of Claim 1 wherein the temperature ranges from 150°C to 200°C.

7. The method of Claim 1 wherein the microwave energy is at a frequency of abut 2450 MHZ and a power level in the range of about 300 to about 1,000 watts.

8. The method of Claim 1 wherein the comestible is meat.

9. The method of Claim 1 wherein the comestible is french fried potatoes.

lo. The method of Claim 1 wherein the comestible is a dough-based product.

11. The method of Claim 1 wherein a comestible which will exude a fat or oil upon heating is utilized as the source for the cooking fat.

12. The method of Claim 11 wherein the fat or oil exuding comestible is selected from the group consisting of bacon, salt pork, sausage and oil-coated comestible.

13. The method of Claim 1 wherein prior to the inser-tion of the comestible, the cooking utensil is irradiated with microwave energy for a period of time effective to preheat the oil or fat to a temperature within the range of from 150 to 180°C.

14. A cooking utensil for cooking or reheating comes-tibles with microwave energy comprising:
an inner vessel;
an outer vessel;
means for maintaining a space between the outer surface of the bottom of the inner vessel and the inner surface of the outer vessel; and a quantity of a microwave susceptible liquid placed in said outer vessel wherein said inner vessel is in conductive heat transfer contact with the microwave susceptible liquid contained within the outer vessel, said microwave suscep-tible liquid is an organic liquid which possesses a high dielectric loss factor as well as a boiling point greater than 150°C.

15. The cooking utensil of Claim 14 wherein the microwave susceptible liquid is selected from the group consisting of polyols between C2-C6, polyoxyethylene sorbitan esters, sorbitan esters, acetates of glycerol and combinations thereof.

16. The cooking utensil of Claim 15 wherein the microwave susceptible liquid is glycerol.

17. The cooking utensil of Claim 15 wherein the microwave susceptible liquid is propylene glycol.

18. The cooking utensil of Claim 14 wherein the microwave susceptible liquid is permanently sealed between the inner and outer vessels.