Abstract:
A cooked food staging device and method is provided. The cooked food staging device allows previously cooked food items, particularly sandwich fillings such as hamburger patties, fish fillets, biscuits, Canadian bacon, pork sausage, eggs, chicken patties, chicken fillets and nuggets, to be stored over extended periods of time at an elevated temperature without significant deleterious effects to the appearance, taste and texture of the food while avoiding risk of bacterial contamination. The food staging device is composed of a plurality of discrete compartments bounded by upper and lower heated compartment surfaces. Food can be stored within the compartments in trays having side walls of a height such that a gap is achieved between the top of the tray and the upper compartment heated surface to limit and control the evaporation of liquid from the food stored therein.

Description:
This is a continuation of U.S. patent application Ser. No. 08/439,160 filed May 11, 1995, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a device and method for storing cooked food portions at elevated temperatures and more particularly to a staging device for holding previously cooked food portions at elevated temperatures. 
     BACKGROUND OF THE INVENTION 
     Quick service restaurants face a number of conflicting factors when striving to provide fast, palatable and safe food. First, the customers expect to receive their food quickly, with a minimum of delay and with predictable and constant high quality. Moreover, the rate of customer demand varies over time, with some periods, such as lunch and dinner times, having extremely high rates of customer demand. However, the kitchens of many quick service restaurants are of limited size and/or production capacity and thus necessarily have a limited number of food cooking devices. 
     Typical food products that are of most interest include sandwiches that are composed of a bun or other bakery cooked bread product and a sandwich filling that is cooked at the quick service restaurant. Typical sandwich fillings include hamburger patties, breaded fish fillets, Canadian bacon, pork sausage, eggs and breaded chicken patties, for example, as well as other products, such as chicken nuggets, biscuits, muffins and hotcakes. Consequently, the cooked food supply capacity of the restaurant is limited by the size and number of food cooking devices located at the restaurant. 
     To meet the competing factors of quick service and consistent high quality, it is advantageous for quick service restaurants to frequently cook a number of individual food sandwich filling portions which are then almost immediately incorporated into individual sandwiches and then wrapped and held ready in advance of actual customer orders in an open storage bin for a relatively short predetermined period of time. To insure constant high quality, if the items are not sold prior to the expiration of that time, the sandwiches are destroyed. Holding the previously cooked, prepared and wrapped sandwiches incorporating the previously cooked sandwich fillings is thus of limited utility. 
     Since some quick service restaurants sell very large quantities of food, even a small increase in the efficiency of handling cooked sandwich fillings and other food would be desirable. 
     A need exists for a device and method that acts as a buffer between the relatively fixed and limited capacity of the sandwich filling cooking step and the highly variable completed sandwich demand without any significant adverse impact on sandwich quality or food safety. In addition, a need also exists for a food staging device which promotes efficient food handling and use of space within the kitchen of the quick service restaurant. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved food staging device and method for holding previously cooked food items at elevated temperatures is provided. 
     The device is particularly adapted for storing over extended periods of time cooked sandwich fillings such as hamburger patties, fish fillets, Canadian bacon, pork sausage, eggs, chicken patties, chicken fillets, as well as other types of food, including biscuits, muffins and hotcakes. When used in combination with trays specifically configured for use in the staging device, the appearance, taste, and texture of the previously cooked food items is maintained over extended storage periods (such as about up to two hours or more depending on the type of food) without risk of bacterial contamination. 
     In accordance with another aspect of the invention, a method is provided for storing previously cooked food, that is especially suited for a plurality of individual portion sandwich fillings, over extended periods of time without any significant detrimental effect on the quality of the food, including the appearance, taste and texture and without risk of bacterial contamination. 
     The food staging device in accordance with the invention includes a cabinet containing a plurality of discrete compartments, each bounded by an upper heated compartment surface and a lower heated compartment surface. The upper and lower compartment surfaces are constructed from a material having a high thermal conductivity, preferably from anodized aluminum. The previously cooked food portions are held within the compartments until the food portions are sold or otherwise disposed of. The air currents throughout the cabinet, if any, are limited because each of the compartments is segregated from other compartments and has solid upper and lower surfaces as well as closed sidewalls and limited access doors, the combination of which limits air flow in the compartments. In addition, air currents within the compartments are limited because both the lower and upper surfaces of the compartments are heated, thereby minimizing regions of thermal gradients within the compartments. 
     The device also includes at least one inlet door on one side of the device for inserting the food portions into the compartments and one complementary outlet door on the opposite side of the device for removing therethrough food portions contained in the compartments. This pass-through configuration of the doors promotes an efficient use of space in the kitchen containing the device because, for example, the device can be positioned intermediate the food cooking area and the cooked food assembly area, thereby providing cooking and assembly restaurant personnel separate access to the device. One inlet and corresponding outlet door may be provided to service one, two or more compartments. 
     In accordance with another aspect of the invention, the device may include a plurality of opposed corresponding inlet and outlet doors such that each of the compartments has its own inlet and outlet door. In addition, the inlet and outlet doors preferably are vertically spaced apart from each other by a distance approximately equal to the thickness of the doors to enable the doors to open by swinging in a generally upward direction, without any further structure enclosing the cabinet interior in the area between adjacent doors from the exterior. Thus, there is provided a relatively narrow, elongated slot opening permitting limited air flow between the compartment of the device and the atmosphere. Typically, the slot height should be no more than about 0.25 inches. Using a separate inlet and outlet door for each compartment further limits air transfer between the interior of the device and the atmosphere, thereby Limiting vapor transfer from the cooked food articles contained therein and further protecting the appearance, taste, and texture of the food portions. The inlet and outlet doors preferably are attached to the cabinet by pins located at the upper opposed edges of the doors, enabling the doors to open by swinging in a generally upward direction. If desired, no stops are provided for holding the doors open. Consequently, the doors automatically close by their own weight, thereby further minimizing air transfer and promoting a relatively constant temperature within the compartments. Alternatively, a stop may be provided for each door as desired to hold it in an open position. 
     In accordance with still another aspect of the invention, the device includes a plurality of trays for containing the food portions. One type of tray includes a sidewall having an upper edge and a lower edge, a closed bottom attached to the lower edge, and an open top defined by the upper edge. The trays have a height such that the top edges of the trays are a predetermined vertical distance, generally in the range of from 0 to 0.25 inches and most preferably about 0.16 inches, from the upper heated compartment surface when the trays are inserted into the compartments. The preferred gap for biscuits and hotcakes is about 0.125 inches. A typical tray height is in the range of from about one inch to about 2.5 inches. By limiting the space between the top edges of the trays and the upper compartment surface, evaporation of liquid from the cooked food portions is minimized, thereby maintaining the appearance, taste, and texture of the cooked food held in the device over extended storage periods such as up to about two hours. In addition, the trays can be configured such that the length of the trays is less than but approximately equal to the depth of the compartments thereby enabling easy removal of the trays through the outlet doors of the compartment. 
     Typical storage temperatures are in the range of from about 145°-200° F. and preferably about 160° F. for biscuits, about 170° F. for hamburger patties, grilled chicken, eggs, Canadian bacon, pork sausage, and muffins, about 200° F. for breaded chicken nuggets, breaded chicken fillets, breaded fish fillets and hotcakes. Trays with solid bottoms and raised sides are preferred for unbreaded meat and other food products such as hamburger patties, grilled chicken, eggs, Canadian bacon, pork sausage, biscuits and hotcakes. Flat trays with a mesh or wire grid with no sides are preferred for breaded products including breaded chicken nuggets, breaded chicken and fish fillets and also for muffins (preferably longitudinally cut in half and stored with the cut side up for both halves). 
     In accordance with yet another aspect of the invention, each of the compartments includes an upper electric resistance heating element for heating the upper compartment surface and a lower electric resistance heating element for heating the lower compartment surface. The temperatures generated by the heating elements therefore can be individually controlled by appropriate control circuitry. Consequently, the temperatures of the compartments can be separately controlled thus providing different holding temperatures in different compartments. As a result, the device can be used to simultaneously hold previously cooked food items at two or more temperatures, therefore eliminating the need for separate staging devices and further promoting an efficient use of space within the kitchen containing the staging device. 
     In accordance with another aspect of the invention, a method of storing previously cooked food products is provided. In accordance with this method, the previously cooked food products (such as individual portion sandwich fillings) are stored in a device that is composed of at least one compartment for holding the food portions, with the compartment bounded by upper and lower heated compartment surfaces. A cabinet defines an enclosed volume for housing the compartment therein, the cabinet including at least one door for inserting and removing the food portions from the compartment, where the compartment has a predetermined compartment height and width. The method includes placing the previously cooked sandwich fillings and at least one tray having a solid bottom and upwardly extending tray walls resulting in a tray height that is about 0 to 0.25 inches less than the compartment height. Thereafter, the tray containing the cooked sandwich fillings is placed in the heated compartment with the heated compartment surfaces having a temperature in the range of from about 145° F. to less than the boiling point of water. A gap is achieved between the top of the tray and the upper heated compartment surface between about 0 and 0.25 inches for restricting water vapor evaporating from the sandwich fillings contained in the tray. Thereafter, the inlet door is closed and the sandwich fillings in the tray are stored for a desired period of time. 
     Preferably, in accordance with the foregoing method, the cooked sandwich fillings stored in the tray fill at least about 5% and most preferably at least 17% of the tray volume. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a cooked food staging device according to the invention; 
     FIG. 2 is a front elevational view of the device in FIG. 1; 
     FIG. 3 is a partially cut-away side elevational view of the device in FIG. 1 showing the placement of food-containing trays within the device; 
     FIG. 4 is a partially cut-away front elevational view of a second cooked-food staging device according to the invention; 
     FIG. 5 is a partially cut-away side elevational view of the device in FIG. 4; 
     FIG. 6 is an exploded view of two of the heated shelves within the device in FIG. 4; 
     FIG. 7 is a sectional view taken along line 7--7 in FIG. 5 showing the attachment of the shelves to the cabinet of the device in FIG. 4; 
     FIG. 8 is a partial perspective view of a portion of the food staging device of FIG. 1; 
     FIG. 9 is a perspective view of a tray for use in the device of FIG. 1; 
     FIG. 10 is a perspective view of an alternative tray used in the device; 
     FIG. 11 is a perspective view of a wire grid support used in the device; 
     FIG. 12 is a sectional view of the wire grid support of FIG. 11 taken along line 12--12 of FIG. 11 and having schematic food portions depicted thereon; 
     FIG. 13 is a partial elevational view of the interior of a cooked food staging device according to the invention and showing an alternative means for securing shelves within the device; 
     FIG. 14 is a perspective view of the interior of the device in FIG. 13; and 
     FIG. 15 is a sectional view of a portion of the interior of the device in FIG. 13 taken along line 15--15 of FIG. 14 and showing a shelf therein. 
    
    
     DETAILED DESCRIPTION 
     Referring to the Figures generally, where like reference numerals refer to like structure, and in particular to FIGS. 1-3, there is illustrated a cooked food staging device 20 according to the invention. Device 20 includes a cabinet 22 having two sidewalls 24 and 26, a closed top 28, and a closed bottom 30. As shown in FIG. 1, device 20 may be supported by a separate support structure 31. Alternatively, device 20 may rest directly on the floor (not shown) or on a table (not shown) via bottom 30. Front 27 of device 20 also includes vertically spaced apart inlet doors 32A-E and 34A-B, located on inlet side 1 of device 20, as illustrated in FIG. 3. Inlet doors 32A-E swing open upwardly and generally are all the same width and height. Inlet doors 34A-B, however, are larger than inlet doors 32A-E to provide access to larger holding compartments for larger cooked food items, such as biscuits 36, as shown in FIG. 3. Alternatively, all inlet doors can have the same dimensions. As shown in FIG. 3, device 20 also includes outlet doors 33A-E, located opposite inlet doors 32A-E, and outlet doors 35A--B, located opposite inlet doors 34A-B. For each inlet door 32A-E or 34A-B there is a corresponding outlet door 33A-E or 35A-B located on outlet side O of device 20 as illustrated in FIG. 3. Each of inlet doors 32A-E and 34A-B, as well as outlet doors 33A-E and 35A-B, are hinged to cabinet 22 along their upper edges and can include a reinforcing member 38 (shown in FIGS. 1-3 and 8) attached to their upper edges. Reinforcing members 38 generally are U-shaped channels extending along the length of each door 32-35, with the top portion of each door 32-35 being disposed in a force-fit relationship in the channel portion of its respective reinforcing member 38. Each of reinforcing members 38 has ends 39 that are closed as illustrated in FIGS. 2 and 8 and each has a pin 39&#39; mounted thereto and extending parallel to the length of member 38. Each pin 39&#39; is disposed in a corresponding aperture (not shown) in cabinet 22, to provide the hinging mechanism for doors 32-35. 
     Raising doors 32A-E, 33A-E, 34A-B and 35A-B provides access into the discrete, heated compartments 40A-E and 42A-B, respectively, contained within cabinet 22, as best seen in FIG. 3. 
     Doors 32A-E, 33A-E, 34A-B and 35A-B include handles 44 to facilitate opening doors 32A-E, 33A-E, 34A-B and 35A-B to gain access to compartments 40A-E and 42A-B. Doors 32A-E, 33A-E, 34A-B and 35A-B do not include any stop members which would retain them in an open position. Each of doors 32A-E, 33A-E, 34A-B and 35A-B thus moves to a closed position under its own weight when its respective handles 44 are released, thereby preventing sustained heat losses from compartments 40A-E and 42A-B. Each door is spaced apart from its adjacent door(s) by a predetermined distance approximately equal to and slightly greater than the thickness of the lower of the two doors. For example, as seen in FIG. 2, door 34B is spaced apart from adjacent door 34A by a distance 37 which is approximately equal to the thickness of door 34B. In a preferred embodiment, the door thickness is about 0.25 inches and distance 37 is slightly greater than about 0.25 inches. Cabinet 22 can also include a fixed upper front panel 46 located above top inlet door 32A and a fixed lower front panel 48 located below bottom inlet door 34B, as seen in FIGS. 1 and 2. Similar panels 46&#39; and 48&#39; are provided for the outlet side O of device 20. A control keyboard 50 and a display 52 located along panel 46 are operatively connected to the control circuitry of device 20 and enable programming and monitoring of the temperatures and times within each of the heated compartments 40A-E and 42A-B. 
     Preferably, control keyboard 50 controls a microprocessor controller (not shown) that is programmed in a known manner to provide the desired temperature control, time control and display information. Preferably, each of compartments 40A-E and 42A-B is programmable to a desired set point temperature within the specified temperature range for upper and lower heated surfaces 64 and 66, depending on product type. 
     If desired, a separate display can be provided for breakfast, lunch and dinner types of food. The display can be divided into a series of rows and columns, each row corresponding to one of compartments 40A-E and 42A-B. Each column corresponds to a horizontal tray position. For example, as shown in FIG. 2, there are five horizontal tray positions (trays 54A-E) and seven compartments resulting in a display having seven rows and five columns. Each column and row can be set to display the row and column number, the name of product stored in that position in device 20 and the countdown hold time remaining for that particular product. Preferably, the row and column display with the lowest time remaining for that product will be highlighted on the display so that the operator can select that tray first. 
     When a product type is selected for a particular row and column, the desired temperature set points are implemented for the corresponding upper and lower heated surfaces 64 and 66. The microprocessor controller checks the other columns (positions) in that row (shelf) for compatible temperatures considering food products already in storage on that shelf, and if not compatible, an audible beep can be generated, the input not accepted and &#34;incompatible product selection&#34; or other warning as desired displayed on display 52. For example, chicken nuggets (200° F. storage temperature) should not be stored on the same shelf with hamburger patties (170° F. storage temperature.) 
     FIG. 2 shows device 20 with inlet door 32B raised to provide access to trays 54A-E within compartment 40B. For ease of handling by a person, trays 54A-G preferably are constructed from a material having a low heat capacity, such as polycarbonate. Preferably, each of trays 54A-E, as well as trays 54F-G shown in FIG. 3, has a width 56 smaller than the width 58 of compartments 40A-E and 42A-B to permit placing more than one tray within a compartment. FIGS. 9 and 10 depict trays 54G and 54A, respectively. In the preferred embodiment shown in FIG. 2, width 56 is chosen relative to width 58 such that five trays 54A-E will fit within any of compartments 40A-E and 42A-B. In addition, each of the trays has a length almost equal to the depth 62 of compartments 40A-E and 42A-B, as seen in FIG. 3. For example, tray 54F is of length 60. 
     Each of compartments 40A-E and 42A-B is bounded by an upper heated compartment surface 64A-G and a lower heated compartment surface 66A-G, as shown in FIG. 3. Each of lower heated compartment surfaces 66A-G is flat and substantially horizontal to provide uniform heat transfer to trays 54A-G and permit easy sliding of those trays along the surface of lower heated compartment surfaces 66A-G. Each of trays 54A-F has a height 68 defined by the distance between the upper edge 70 of the sidewall 72 and the lower edge 74 of sidewall 72 of trays 54A-F. Height 68 is chosen so that upper edge 70 of any of trays 54A-F is at a predetermined distance 76 from upper compartment surfaces 64A-F when trays 54A-F are placed within compartments 40A-E so that vapor transfer out of the interior of the trays is minimized, thereby also minimizing the fluid loss of the cooked food portions stored therein which is important for cooked food stored in trays 54 such as egg products, hamburger patties, grilled chicken, pork sausage and Canadian bacon. Preferably for such food, the cooked food portions fill more than about 5% and more preferably about 17-30% or more of the volume of trays 54 when stored in device 20. Generally, minimal vapor transfer is achieved out of the interior of the trays when distance 76 is in the range of 0-0.25 inches. Most preferably, height 68 is chosen so that the distance 76 is approximately 0.16 inches (0.125 inches for biscuits). In the embodiment shown in FIGS. 1-3, compartments 42A-B are of greater height than compartments 40A-E to accommodate larger food portions such as biscuits 36. Consequently, when trays 54A-F are placed within compartments 42A-B, upper edges 70 are at a substantial distance greater than distance 76 from upper heated compartment surfaces 64F-G. Sidewall 73 of tray 54G has an increased height 69 so that a gap 77 is provided between the upper edge 70&#39; of tray 54G and upper heated compartment surface 64G. Gap 77 is about 0.16 inches (0.125 inches for biscuits). 
     For cooked, breaded food such as breaded chicken nuggets, breaded fish and chicken fillets, achieving minimal vapor transfer is usually not desirable because such food may have a tendency to become soggy. Sogginess is usually objectionable for cooked, breaded food products. Consequently, a larger gap than distance 76 should be employed such as at least 1.0 inch, for example. Alternatively, cooked, breaded food products may be stored within one or more of compartments 40A-E or 42A-B on a wire grid support or on a tray having a wire grid support therein. FIGS. 11-12 illustrate a wire grid support 79 that is suitable for supporting cooked, breaded food products within compartments 40A-E and 42A-B. 
     Wire grid support 79 comprises a polycarbonate tray 81 that houses a removable frame 87. Frame 87 is connected to a grid having wires 83 and perpendicular wires 85 as shown in FIGS. 11 and 12. Cooked, breaded food products P are placed on wire grid support 79 in order to provide air circulation beneath breaded food products P so that they do not become soggy. Wires 83 and 85 have a diameter of about 0.06 inches, thereby providing a spacing from the surface of tray 81 of about 0.12 inches. It is advantageous to minimize the distance from the heated surface yet still provide an airspace from the heated lower compartment surfaces 66A-G. 
     Returning now to FIG. 3, upper heated compartment surfaces 64A-G and lower heated compartment surfaces 66A-G are constructed from a material having a high thermal conductivity and preferably are constructed from anodized aluminum. 
     The previously cooked food portions are held within compartments 40A-E and 42A-B, preferably within trays 54A-G, until sold or otherwise disposed of. Because compartments 40A-E and 42A-B are discrete, with well-defined upper heated compartment surfaces 64A-G and well-defined lower heated compartment surfaces 66A-G, air currents throughout cabinet 22, if any, are limited because surfaces 64A-G and 66A-G obstruct air flow within cabinet 22. In addition, air currents within compartments 40A-E and 42A-B, if any, are limited because both upper heated compartment surfaces 64A-G and lower heated compartment surfaces 66A-G are heated thereby reducing or eliminating thermal incongruities within compartments 40A-E and 42A-B. By restricting the air currents throughout cabinet 22 and within compartments 40A-E and 42A-B, device 20 reduces the amount of moisture lost from the food portions held therein and thus protects the appearance, taste, and texture of the food portions. Evaporation of liquid from the food portions is further minimized by choosing height 68 of trays 54A-F such that upper edges 70 of trays 54A-F are at a small, predetermined distance 76, generally preferably greater than 0 and less than about 0.25 inches and most preferably 0.16 inches, from upper compartment surfaces 64A-E when trays 54A-F are placed within compartments 40A-E for minimizing vapor loss from the food contained therein. For increasing the amount of vapor loss, gap 76 can be increased. 
     Device 20 also promotes an efficient use of space within a kitchen containing device 20. A kitchen in a quick service restaurant is frequently divided into two or more work areas. For example, the food cooking area can include food cooking devices such as grills, deep fat fryers, and other cooking devices, for example, for cooking sandwich fillings such as hamburger patties, fish fillets, chicken fillets, eggs and chicken nuggets. After being cooked, the food portions are transported to the sandwich assembly area for sandwich assembly which can include applying condiments to the cooked food portions, placing the cooked food portion in a roll or bun, and/or wrapping the cooked food portions. Consequently, restaurant personnel in the food cooking area and in the sandwich assembly area handle the cooked food portions. Device 20 promotes an efficient use of space when device 20 is located within the kitchen intermediate the food cooking area and the sandwich assembly area. When so positioned, the restaurant personnel responsible for cooking can place a tray 54E containing the cooked food portions within compartment 40A through inlet door 32A of device 20 inlet side I, as shown in FIG. 3. Then, when the cooked food portions are needed for assembly into a sandwich, restaurant personnel remove tray 54E from compartment 40A through outlet door 33A of outlet side O of device 20, as shown in FIG. 3. The flow-through configuration of inlet doors 32A-E and outlet doors 33A-E thus enables the cooking and assembly personnel to have completely separate access to cooked food portions held within device 20. 
     FIGS. 4 and 5 illustrate a second embodiment of a cooked-food staging device 80 according to the invention. Device 80 includes a cabinet 82 having two sidewalls 84, 86, a closed top 88, a closed bottom 90, an upper front panel 92, a lower front panel 94, and a right front panel 96. Keyboards 114 and displays 116 are provided in right front panel 96 to program and monitor the temperatures within the holding chambers 100A-F contained within cabinet 82. Holding chambers 100A-F are bounded by upper heated chamber surfaces 102 and lower heated chamber surfaces 104. Chambers 100A-F are also bounded by inlet doors 108A-F and outlet doors 112A-F hingedly attached along their upper surfaces to cabinet 82 in a manner as described previously with respect to device 20. Doors 108A-F and 112A-F are lifted by grasping handles 118 to thereby gain access to chambers 100A-F. In FIG. 4, inlet doors 108A and 108B are raised to reveal trays 120 contained within chambers 100A and 100B. The width 122 of trays 120 is such that three trays 120 will fit within any of chambers 100A-F. The length of trays 120 is almost equal to the depth of chambers 100A-F so that trays 120 may be readily handled through inlet doors 108A-F and through outlet doors 112A-F, as best seen in FIG. 5. Cabinet 82 can also include a compartment 98 for holding non-heated food portions. Compartment 98 is bounded by an inlet door 106 and an outlet door 110, both of which provide access to compartment 98. Doors 106 and 110 include handles 118 for rotating doors 106 and 110 along their upper hinged edges. 
     FIGS. 6 and 7 illustrate one system for attaching upper heated chamber surfaces 102 and lower heated chamber surfaces 104 to cabinet 82. Surfaces 102 and 104 are parts of shelves 126 and 128 which contain heating components for heating surfaces 102 and 104. Preferably, the source of heat is an electric resistance heating element, the construction of which is well known in the art. In addition to surface 102, shelf 126 includes a hollow housing 130 overlying surface 102. The heating component is positioned within the space between housing 130 and surface 102. Similarly, shelf 128 includes surface 104, an underlying housing 132, and a heating component positioned inside housing 132. Surfaces 102 and 104 are attached to housings 130 and 132 by conventional methods, such as rivets 134. Surfaces 102 and 104 extend beyond housings 130 and 132 to form flanges 136 and 138 which contain holes 140 and 142 for attaching shelves 126 and 128 to cabinet 82. Surfaces 102 and 104 are separated by two spacers 144, each of which includes posts 148 for engaging the holes of the overlying flange, for example, holes 140 of flange 136. Clips 150 underlying shelf 128 include posts 152 for engaging holes 142 of flange 138. Clips 150 also include prongs 154 for engaging shelf brackets 156 attached to sidewalls 84 and 86. 
     As best seen in FIG. 7, shelf 128, including lower heated chamber surface 104, is attached to clip 150 by inserting post 152 through hole 142 of flange 138. Clip 150 in turn is attached to bracket 156 via prongs 154. Spacer 144 is then positioned over shelf 128 and clip 150 so that post 152 is inserted into an opening in the bottom of spacer 144. Finally, shelf 126 is aligned with and mounted on spacer 144 so that post 148 extends through hole 140 in flange 136. The height 158 of trays 120 is chosen so that the top edges 160 of trays 120 are at a predetermined distance from upper heated chamber surfaces 102, as previously described with respect to device 20, when trays 120 are placed within chambers 100A-F. However, since the height of chambers 100A-F is determined by the height of spacers 144, different chamber dimensions can be achieved by using differently sized spacers. Consequently, device 80 can be readily configured to provide holding chambers which can accommodate trays having various heights. 
     An alternative embodiment device is depicted in FIGS. 13-15 as staging device 180. Staging device 180 has an exterior sidewall 182 and an interior sidewall 183 attached thereto, as most clearly seen in FIG. 14 by any suitable structure, such as by a weld or fastener, for example. Angle irons 184A-G are mounted to interior side wall 183 to support shelves 186A-G. Each end of angle irons 184A-G uses an upturned tab 184&#39; for preventing lateral movement of shelves 186A-G when mounted thereon. Shelves 186A-G define heated compartments 188A-H. 
     FIG. 15 is an enlarged view of shelf 186C, which is representative of the other shelves. Shelf 186C includes an upper heated surface 190, a lower heated surface 192 and a housing 194 for storing the heating components (not shown). 
     In use, device 80 can be positioned within the kitchen of a quick service restaurant in an area intermediate the food cooking area and the food finishing area. The flow-through design of inlet doors 106 and 108A-F and outlet doors 110 and 112A-F thus promotes an efficient use of space within the kitchen. Device 80 also protects the appearance, taste, and texture of cooked food potions held therein because the discrete upper and lower heated chamber surfaces 102 and 104 limit air currents within device 80, thereby reducing or eliminating moisture losses from the food portions. In addition, electrical resistive heating elements can be used as the heating components for heating surfaces 102 and 104. Such heating elements can be individually controlled by the control circuitry of device 80. As a result, device 80 can be used to simultaneously hold previously cooked food portions at two or more temperatures, therefore eliminating the need for separate staging devices and further promoting an efficient use of space within the kitchen containing device 80. Generally, the heated chamber surfaces will be maintained in the temperature range from about 145° F. to less than the boiling point of water during the period of time that the sandwich fillings are stored in the chambers. 
     Whereas the present invention has been described with respect to specific embodiments thereof, it will be understood that various changes and modifications will be suggested to one skilled in the art and it is intended that the invention encompass such changes and modifications as fall within the scope of the appended claims.