CA1144811A - Simulation of deep fat fried foods - Google Patents

Abstract

ABSTRACT
A process for simulating the taste and texture of freshly deep fat fried comestibles by heating frozen food products on a heat transferring apparatus.
The heat transferring device has a plurality of open spaces and a minimum amount of contact with the frozen food products. When the frozen comestibles are heated in an oven on such a device, desired moisture content is obtained. The cooked comestibles are uniform in color and crust thickness similar to freshly deep fat fried food products.

Description

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SIMULATION OF DEEP F~T FRIED FOOD_ BACKGROUND OF TH:~: INVENTION
In the field of frozen foods, it has been the general prac-tice to employ formed or sheet aluminum, plastic, wood and/or paper pulp food packages to merchandise the product. Such products have been unsatisfactory in that they function solely as a marketing package, have little utility outside the scope of a packaging container, generally use com-paratively large quantities of materials andnecessitate preparation of the food before it can be cooked.
Those concerned with the development of foods that have the distinctive taste of freshly fried foods have long recognized the need for a comestible which, after oven preparation, yields a product with a desired moisture content which contributes to a freshly fried texture and taste. Results have indicated that such high-quality, oven-reheated products cannot be made by simply manipulating par-fry ~partially fry) cooking and reheating temperature and times.
One of the most critical problems confronting developers of frozen food comestibles has been to develop a uniform color and crust thickness in the comestible. ~rozen foods cooked in typical baking pans are heated mainly by conduction, which results in localized burned areas.

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' Conventionally prepared foods, whether ~heated and/or cooked, often have overcooked exterior and/or undercooked in-terior portions. This problem has received the attention of appliance developers through the utilization of microwave ovens. However, the use of these ovens often produces products with an undesirable coLor, texture or taste to the consumer.
The color and appearance of food plays a vital role in consumer appeal. If it does not look right, consumers are less likely to consume it.
Another problem resulting from cooking frozen foods is the resulting soggy product or technically a food product whose mois-ture content is quite high.
~hen the final cooked product has an uneven moisture distribution, the additional problem of uneven texture is presented.
Another area of concern has been the time it takes to prepare and produce the Eood. Mos-t con-sumers wish to process the comestibles as quickly as possible without burning them.
S~ ARY
The general purpose o:E this invention is to pro-vide a novel technique for cooking frozen comestibles.
One embodiment of -the invention further provides a container for packaging frozen foods, particularly frozen french fried potatoes, chicken and fish. Such container may be used for cooking the food without removal therefrom, in a minimum of time and with a minimum of preparation beforehand.
It is an additional objec-t of this invention to provide an article of packaged food comprising a frozen food and a novel container for the frozen food which is made from suitable ovenable material, and which is capable of serving as a cooking utensil for the -food. It is a further object of this invention to provide a container for frozen foods which is simple and rugged in construc-tion, commercially practical, economical to manufacture, and easily adapted to func-tion as a cooking u-tensil for the frozen food.
Essentially, the new technique comprises packag-ing frozen food products in combination with a screenor other such uniform heat transferring device. Dur-ing cooking, warm air convects around the food product from below as well as from above. The reswlting primary mechanism of heating is natural convection and radiation. Because of the improved preparation technique, a more appetizing product results in both taste and appearance. The technique permits prepara-tion of frozen foods in such manner so as -to give a deep fat fried appearance when heated in an oven.
It is preferable that the frozen foods be precooked, such as par-frying, also known as flash frying.
Other objects, features and advantages of this invention will be apparent from the Eollowing detail-ed description and appended claims, reference being made to the accompanying drawings forming a part of the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph of the internal temperature of a par-fried potato product measured in degrees fahrenheit versus the heating time measured in minutes. The oven temperature averaged ~50F, and a heat transferring apparatus (HTA) was employed. The apparatus consisted of Number 8 mesh stainless steel wire of 0.028 inch diameter.
Figure 2 is a graph of the theoretical model) calculated by computer analysis, of internal product temperature measured in degrees fahrenheit versus the heating time measured in minutes when an oven maintains an average ~50F -temperature and the par-fried potato product was heated on a heat transferring .
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device (HTA). The apparatus consisted of Number 8 mesh stainless steel wire of 0.028 inch diameter.
Figure 3 is a graph of the heating time measured in minutes versus the moisture con-tent of the par-fried potato product measured on a wet basis for anoven maintained at an average temperature of 450F, and employing a hea-t transferring device (HTA). The apparatus consisted of Number 8 mesh stainless steel wire of 0.028 inch diameter.
Figure 4 is a graph of the theoretical model, calculated by computer analysis, of the heating time measured in minutes versus -the par-fried potato prod-uct moisture content measured on a wet basis for an oven maintained at an average temperature of 450F, and the comestible was heated on a heat transferring apparatus (HTA). The apparatus consisted of Number 8 mesh stainless steel wi.re of 0.028 inch diameter.
~ igure 5 is a graph of the heating time measured in minutes versus the i.n-ternal temperature of a par-fried potato product measured in degrees fahrenheit.
The oven temperature was maintained at an average of 450F, and a heat trans-ferring apparatus (HTA) was utilized. The apparatus consisted of Number 8 mesh stainless steel wire of 0.028 inch diameter.
Figure 6 is a graph of the theoretical model, calculated by computer simula-tion, of heating time measured in minutes versus the internal par-fried potato produc-t temperature measured in degrees fahrenheit when an oven maintains an average 450F
-temperature. A heat transferring apparatus (HTA) was utilized. The apparatus consisted of Number 8 mesh stainless steel wire of 0.028 inch diameter.
Figure 7 is a graph of the heating time measured in minu-tes versus the moisture content of the par-fried potato product measured on a wet basis for an , ~4~

oven maintained at an average temperature of ~50F.
A heat transferring apparatus (HTA) was used. ~he apparatus consisted of Number 8 mesh sta:inless steel wire of 0.028 inch diame-ter.
Figure 8 is a graph of the theoretical model~
calculated by computer simulation, of the heating time measured in minutes versus the moisture conten-t oE the par-fried potato product measured on a wet basis when an oven maintains an average 450F -tempera-ture. A heat transferring device (HTA) was employed.
The apparatus consisted of Number 8 mesh stainless steel wire of 0.028 inch diameter.
DETAILED DESCRIPTION OF THE IN~ENTION
This invention consists of a novel device and a unique technique for cooking frozen comestibles to reproduce color, taste, moisture and texture profiles of freshly deep fat fried comestibles. The Erozen foods are packaged in combination with a heat trans-ferring apparatus. A heat transferring apparatus or device is defined as a means of supporting discrete pieces of food in an oven, whereby the effect of con-duction heating is minimized and the effect of con-vection heating is maximized. In order -to maximize such type of heating, a minimum amount of structure should support the comestibles in the oven. A pre-ferred embodiment of this invention would position the food products in a monolayer. This special arrangement would decrease piece-to-piece food con-tact and provide greater convection heating since there would be no obstacles to such heating principles.
One embodiment of this invention represents a screen or grid having a maximum amount of "free" or open space. As such, only a minimum amount of con-tact occurs between the screen or grid and the frozen food product. While the -type and diameter of 4~

wire utilized to -fabrica-te -the grid-like members of the present inven-tion is not critical, it has been found that the open area should be maximized, yet still be able to suspend the food product in the oven. Since the grid-like wire members are to be used in connection with food products, the wire members should also preferably be rust resistant and capable of being sanitized. Exemplary of such wire members are those which have been tin coated or which are fabricated from stainless stee~L and the like. When carbon steel or a material having a high coefficient of heat transfer is selected for use as -the wire members, it is preferred that -these types of wire members be coated with a material having a low coefficient of friction such as polytetrafluoroethylene, available under the trade name Teflon~, and the like.
When -thusly coated, a smooth, durable, sanitary sur-face is provided which is easy to maintain and keep clean. Further, such a coating also acts as a heat insulating medi-um covering the highly conductive metal of the grid-like member and thereby eliminates or sub-stan-tially reduces any "hot spots" in the assembled grid-like members.
Other embodiments can be made from various materials including thermoplastics, natural fibers, aluminum, wood and/or paper pulp. The heat trans-ferring apparatus could also be a container, pouch, or package having a plurality of open spaces.
As stated above, uniformity of color and crust thickness is essential in producing an appetizing food product. Table I below gives comparison data -for crust thickness obtained by cooking a par-fried french fry with 62% po-tato solids by variows methods.
As demonstrated, both suspension in air and the maximum heat transferring apparatus are superior in *Trademark ,~ .

approximating the crust thickness of the deep fat fried control. ~lowever, with present technology suspension i-n air is dif:Eic-ult to perform. The heat transferring apparatus is the most feasible solution S to the approximation of the cooking principles in deep fa-t frying. In the previously mentioned methods of food preparation, the warm air is allowed to cir-cula-te around -the food product much like the oi.ls circulate around the food produc-t in deep fa-t fry:ing.
The heat transferring apparatus used in Table I con-sisted of Number 8 mesh stainless steel wire o:E 0.028 inch diameter having an open area of 60%. The ridged bottom tray used consisted o-f a molded aluminum tray having a plurality of peaks and valleys.

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Table II demonstrates the principle that the greater the amount of open area available, the more -the crust -thickness, cooking time, and organoleptic properties resemble the freshly deep fat fried french fries. Heat transferring apparatuses in the form of stainless steel screens were used in combination with a par-fried french fry potato product. Cooking times were varied to produce the best quality produc-t based on appearance, color, texture and organoleptic prop-er-ties.
As can be seen from the table, when using a rela-tively planar apparatus, highly desirable product is obtained using a heat transfer apparatus with free area greater than 35% and even more preferable, greater than 50%.

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To ~eter~ine the commercial success for comes-tibles prepared utilizing a heat transfer apparatus, consumer preference was polled. In tables III, IV
and V, the apparatus consisted of Number 8 mesh stain-less steel wire of 0.028 inch diameter.
Table III presents consumer preference data forfrozen foods prepared by two different methods. The first method utilizes a heat transferring apparatus while the second method employs an ordinary baking pan. Thirty people judged three different types of foods. The results received show that on an average, people preferred the food cooked on a heat trans-ferring apparatus as compared to a baking pan by a ratio of 2:1.
The same panelists then analyzed the food prod-ucts with respect to the problems of texture, appear-ance and mois-ture. In Table IV, thirty people evalu-ated commercially available batter-dipped frozen fish sticks. Both fish products were preparecl at ~25F
for twenty-five minu-tes, as the package instructions recommended. The resultant product prepared on the heat transferring appara-tus had a ~miform crust thick-ness of 0.045 inches as compared to an average 0.075 inches normally obtained when using a baking pan.
In Table V, thirty people evaluated commercially available pre-fried frozen chicken breast. One por-tion of chicken was cooked on the baking sheet at 400F for 15 minutes, then turned over on their other side for an additional 15 minutes as ~he package instructions directed. The other sample of chicken was cooked on the heat transferring apparatus at 400F for 30 minutes without any turning.

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TABLE III
AVERAGE CONSUMER PREFERENCE
FOR PREPARED FROZEN FOOD

Fish Chicken Pota-toes Heat Transferring Apparatus 78% 64% 60%
Baking Pan 22% 36% 40%

TABLE IV
CONSUMER PREFERENCE FOR
-ATTRIBUTES OF PREPARED FROZEN FISH STICKS

Texture Appearance Moistness Heat Transferring Apparatus 77% 80% 79%
Baking Pan 23% 20% 21%

TABLE V
CONSUMER PREFERENCE FOR
ATTRIBUTES OF PREPARED FROZEN CHICKEN
-Texture Appearance Moistness Heat Transferring Apparatus 57% 58% S2%
Baking Pan 43/O 42% 48%

Another aspect of this invention is the packaging of frozen comestibles on or in a heat transferring apparatus, such as a screen, net or lace-like element which may either be preformed or expandable and in the form of a single layer or pouch. The package composition may comprise a regular spaced embossed pattern on at least one surface of each single layer sheet heat transferring apparatus. The combination ..
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of two single layer sheets would form a pouch in which the comestibles would 'be heated. The sheet wou:Ld be drawn sufficiently to develop a preferential weakness in one direction. When stretched in the direction traverse to the first drawing, a multiplicity of short splits appear and develop into a net-like struct-ure.
Packages of various shapes and sizes can be pro-duced according to procedures known in the art. ~fter the desired contents have been placed in the package, it can be readily sealed or overwrapped. Packages can be prepared with 'both sides of the packaging material embossed or only one side as long as open areas may be created to allow a minimum amount of lS contact between the apparatus and comestible and per-mit convective and radiant heating. For example, food packages can be prepared by fusing -the edges of two embossed drawn shee-ts of packaging ma-terial of -this invention. If desired, tabs or loops can 'be provided by which the package can be grasped when stretching. The provision of tabs or loops is beneficial in that they indicate the direction in which the package is to be stretched. It may also be desirable to seal a ribbon or string inside the package to prevent its being stretched so far that it tears.
While the present invention has been described in conjunction with french fries, chicken, and fish, it is to be clearly understood that it is not to be limited in this respect. The heat transferring ap-paratus can also be used with any food which requires the collection and absorp-tion of cooking juices. In this special embodiment of this invention, an absorbent medium is incorporated with the heat transferring de- ' vice which is particularly effective as a means for ~ . . , .
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preventing dripp:Lngs cluring cooking, from creating a dirty oven, or building up around the food product.
With this arrangement, any danger of drippings pass-ing out of the device as a result of the maximum open area is eliminated. The incorporation of the absorbent medium may be accomplished by coating it onto the screen or layering the apparatus with a perforated sheet such that an amount of free area remains so as not to impede the free flow of air. The la-tter embodi-ment may consist of three layered materials ~per-forated aluminum, oven-resistant absorbent material, perforated aluminum) which has been indented to pro-vide minimum contact points and then hole punched -to provide the free flow of natural convection heating.
By way of explanation and not limi-tation, the absorp-tion of the juices is best characterized as a wick-type phenomena.
Another aspect of this special embodiment is a single layer indented and perforated heat transferring apparatus. The indentations create a waffling effect and are in the form of troughs and crests. The per-forations are of two types. The first kind of per-foration creates the majority of open area so as to optimize heat transference by convection and radia-tion, while simultaneously providing minimum contactbetween the food and apparatus. The indentations also contribute to providing minimum contact between the food and apparatus. When using this embodiment, open areas as small as 20% will yield good quality product. The second type of perforations is nearly pinlike. These create a surface tension on the heat transferring apparatus which collects and holds the oils that are released during cooking.
Still yet another embodiment of this invention relates to an improved cooking utensil for supporting ' I. ,r ~

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and cooking foods within an oven. In this embodiment of the invention, rather than the heat transferring apparatus being designed having a narrow thickness, the apparatus would have a broad thickness with long tapered holes. These tapered holes would create a higher veloci-ty of warm air than would ordinarily occur with holes in a thin body such as sheet me-tal.
The beneficial effect of the higher velocity warm air jets lies in their increased ability to do work, to cook food in this instance.
As shown above, it is essential that the heat transferring device have as little contact with the food product as possible. The ideal system approaches suspension of a food product in the cooking apparatus without contacting it with any device.
Referring now to Figure 1, one may graphically note the higher internal product tempera-ture which resul-ts when using the heat transferring device rather than the conventional cookie sheet or baking pan. Thermodynamically, this translates into a mechanism of heat transfer differing from the conven-tional cooking utensil. Figure 2 confirms the ex-perimental internal product temperature data in accordance with a computer simulated model.
The overall heat transfer is more uniform in products prepared on the heat transferring apparatus than on the baking pan. As has been shown, this corresponds to product quality which is improved at higher percentages of free area.
Heat transfer uniformity is determined by com-paring the total heat transfer coefficients for each side of a food produc-t. In Table ~I, surface co-effi.cien-ts of heat transfer into a 0.25 inch shoe-string potato were calculated. I'he heat transferring apparatus employed was a Number 3 mesh stainless .. .~

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s-teel wire of 0.028 inch diameter.
In the baking sheet, the ratio of total heat transfer between the bottom surface and the side sur-face of a comestible is 11:1, whereas in the hea-t transferring apparatus, the ratio of total heat transfer between the bottom surface and the slde sur-face of a comestible is 1.8:1. In deep fat frying, this same ratio would be 1:1 since the o:ils circu-la-te around the comestible. Therefore, in simulating deep fat frying, t is preferred that -the conductive heat be minimized and the convective heat be maximized.
Additionally, it is preferred to make -the ratio of the total heat transfer between every two surfaces of the comestible less than 5:1. At ratios of 2:1 and below, more preferred comestibles are obtained.

TABLE VI
HEAT T~ANSFER COEFFICIRNTS

Surface MechanismCoefficient (BTU/ft2-F-hr) 20 Baking Bottom Conduct:ion 10.0 Sheet Each Side Convection 0.9 Top Convection 0.9 Heat Bottom Convection 1.32 Trans- Radiation2.64 25 ferring Each Side Convection 2.2 Apparatus Top Convection 2.2 To compute convective heat transfer coe-fficients, air velocity over cooking appliances in an oven at an average temperature of 450F had to be determined.
This was measured by a single channel laser anemo-meter system (15 milliwatt, Helium-Neon laser, wa~e -': ~ - . ' , - ~

length ~ 632.8 nanometers). Elec-tric oven air velo-city over a heat transferring appara-tus increased with increased percent free area of the apparatus.
According to standard heat -transfer principles~ the higher air velocity reduces the thermal boundary layer s-urrounding the cooking product, resulting in an increased convective heat transfer.
From the values in Table VII, the percentclge of conductive, convective and radiant heating was deter-mined. These percentages distinc-tly sho~ tha~ differ-ent heat transfer mechanisms are involved in cooking foods on a baking shee-t and a heat transferring ap-paratus.

TABLE YII
HEAT TRANSFER MECHANISMS

Conduction Convection Radiation __ Heat Trans-ferring Ap-paratusNegl-igible 75% 25%

20 Baking Sheet79% 21% Negli-gible Figure 3 graphically shows that the moisture content of the final cooked product is higher when using the heat transferring appartus than a conven-tional baking sheet. However, quite suprisingly,the utilization of the apparatus creates a lower mass transfer rate as opposed to the baking sheet.
One would normally predict that a higher mass trans-fer rate as predicated by a function of the higher internal product temperature as shown in Figures I

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The following hypothesis is used to explain this phenomena of the invention. However, this hypothesis of the existence and mechanism by which the inven-tion may operate, is not clesigned to limit the scope of the present invention, but is advanced only as a means of explaining the effects produced.
A metal sheet has a high energy flux which con-ducts energy quite rapidly. The primary method of energy transference is conduction. This causes mois-ture excitation which in turn drives the moisture from the product in the form of vapor. The moisture is driven from the bottom to the top of the food product. The bottom layer, depleted of moisture case hardens and acts as an irlsulator. This results in a product which is characterized as having a bo-t-tom that is crisp and a top that is soggy. As would be expected, the smaller -the food product, the less this differential may be observed.
On -the other hand, the heat transferring appara-tus has a more uniform energy flux which radiates and convects energy rapidly and uniformly. Because of the open areas in the apparatus, the primary energy transferences are convection and radiation.
The moisture diffuses out from the food product on all sides. A uniform crust is formed on the envelope of the comestible. As the warm air con-tinually circulates around the food product, theporosity of the envelope is reduced trapping mois-ture uniformly within the interior of -the product.
Relative to the interior of the product, the crust would contain most of the oil which is an attribute of deep fat fried foods.

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Temperature measurements above the heat -trans-ferring apparatus are greater than above a baking sheet. This finding confirms the unique heat transfer phenomena.
As stated previously, the food prod-uct cooked on the apparatus has an unexpected higher final moisture content. Thls results in minimizing food shrinkage.
Figure 4 relates to the -theoretical model, developed by computer analysis, which provides pro-duct moisture conten-t predictions in close agreement with experimental data.
As stated previously, it is desired to maximize the amount of open area of the heat transferring ap-paratus. At a minimum, this requires an opening onthe bottom of the apparatus to allow heated alr to flow past the food product. The apparatus is separate and distinc-t from a ridged solid bo-ttom tray. Al-though the ridged bottom tray encompasses the concept of having a minimum contact with the food product, it does not produce synergis-~ic results of crust thickness, moisture content, deep fat fried appear-ance or texture profiles of freshly deep fat fried comestibles like the heat transferring apparatus.
Referring now to Figures 5 and 6, one may graph-ically note the higher internal product temperature produced by the heat -transferring apparatus before the inflex point. Again, this result corresponds to an unexpected lower rate of moisture loss for the apparatus. After the inflex point, the ridged bottom container demonstrates a higher produc-t temperature.
This is generally caused by the large extended metal surface area of the ridges which conducts the heat.
However, the temperature distribution is not uniform.
'rhe concentrated temperature distribution point at the ridges results in slight browning or localized crust formation at the ridge site and an uneven moisture distribution throughout the comestible. This is objectionable when attempting -to produce a uniform crust.
Referring now to Figure 7, one notes that generally, a higher in-ternal product temperature will cause a lower rate of moisture loss. However, the higher the temperature, -the more moisture excitation one would expect. When a crust -is formed on the envelope of the food product, the porosity of this envelope is reduced. This results in lower moisture loss and a rise in internal temperature. The heat-ing principles for the -three cooking utensils are as follows. The ridged bottom conkainer heats primarily by conduction and convection. The hea~ transferring apparatus heats primari]y by convection and radiation.
The baking sheet heats primarily by conduction.
The method of heating is directly correlated to the internal product temperature which is related to the product mois-ture. Through the utilization of the heat transferring apparatus, the resultant food product can be characterized as not being too soggy as produced by the ridged bottom container nor too dry or brittle as produced by the baking pan.
Figure 8 provides product moisture content pre-dic-tions based on a computer simula-ted model in close agreement with the experimental data.
It is to be understood, that the present inven-tion also includes -unique techniques disclosed herein for cooking frozen foods. The food package as finally rendered may be made suitable for cooking in a broiler arrangement, an oven, a toaster, a toaster-oven, or by other suitable means as may be selected.
Once the food has been packaged, it may be chilled so that the food product is ~rozen. Likewise, .
~ , the food product may not only be fro~en prior to be ing packaged, but also at anytime during the packag-ing process. It is also within the purview of the invention that the ultimate user wrap, enclose, or station the food product on the heat transferring apparatus for its ultima-te intended purpose. The ultimate intended purpose is to provide a technique for cooking the food product as has been stated. ~on-sequently, the ingenui-ty of the present invention is such that a package is provided which may protect the food product while it is being refrigerated and maintained in the store and then may be utilized as a disposable cooking utensil.
From the above detailed descrip-tion of the in-vention, it will be obvious that the heat -transferring apparatus can be applied in the preparation of various selected types of fresh and frozen solid materials that either contain oil or have oil applied in order to render the prepared produc-t having those char-acteristics of deep fat fr:ied foods.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of heating discrete pieces of frozen par-fried foods in an oven to obtain heated food pieces having the appearance, texture, moisture content and uniformity of color and crust thickness approximating that of deep fat fried foods, comprising supporting discrete pieces of the frozen foods in a monolayer with minimum piece to piece contact on an open mesh ovenable support member having openings constituting at least 50%
of the area of the support member to provide free flow of air therethrough and to minimize contact between the support member and supported pieces, and heating the supported pieces in an oven while mini-mizing the effect of conduction heating and maximizing the effect of natural convection heating whereby the ratio of total heat transfer between two surfaces of a piece is less than 5:1.

2. Method according to claim 1, wherein the food pieces are selected from the group consisting of chicken, fish and potatoes.

3. A frozen food package comprising an open mesh oven-able support member and discrete pieces of frozen par-fried foods supported thereon which upon oven heating provides heated food pieces having the appearance, texture, moisture content, and uni-formity of color and crust thickness approximating that of deep fat fried foods, the ovenable support member having openings constituting at least 50% of the area of the support member enabling free flow of air therethrough and minimizing contact between the support member and food pieces, the frozen food pieces being supported in a monolayer with minimum piece to piece contact on the support member whereby upon heating in an oven conduction heating is minimized and con-vection heating is maximized and wherein the ratio of total heat transfer between two surfaces of a piece is less than 5:1.

4. A package according to claim 3 wherein the open mesh ovenable support member is a stainless steel mesh formed of 0.028 inch diameter wires.

5. A package according to claim 3 or 4, wherein the food pieces are selected from chicken, fish and potatoes.