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 sidewalls 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:
RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 09/037,291, filed Mar. 9, 1998, now U.S. Pat. No. 5,947,012, which is a continuation of U.S. patent application Ser. No. 08/665,781, filed Jun. 18, 1996, now U.S. Pat. No. 5,724,886, which 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  32 A-E and  34 A-B, located on inlet side I of device  20 , as illustrated in FIG.  3 . Inlet doors  32 A-E swing open upwardly and generally are all the same width and height. Inlet doors  34 A-B, however, are larger than inlet doors  32 A-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  33 A-E, located opposite inlet doors  32 A-E, and outlet doors  35 A-B, located opposite inlet doors  34 A-B. For each inlet door  32 A-E or  34 A-B there is a corresponding outlet door  33 A-E or  35 A-B located on outlet side O of device  20  as illustrated in FIG.  3 . Each of inlet doors  32 A-E and  34 A-B, as well as outlet doors  33 A-E and  35 A-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 FIG.  8  and each has a pin  39 ′ mounted thereto and extending parallel to the length of member  38 . Each pin  39 ′ is disposed in a corresponding aperture (not shown) in cabinet  22 , to provide the hinging mechanism for doors  32 - 35 . 
     Raising doors  32 A-E,  33 A-E,  34 A-B and  35 A-B provides access into the discrete, heated compartments  40 A-E and  42 A-B, respectively, contained within cabinet  22 , as best seen in FIG.  3 . 
     Doors  32 A-E,  33 A-E,  34 A-B and  35 A-B include handles  44  to facilitate opening doors  32 A-E,  33 A-E,  34 A-B and  35 A-B to gain access to compartments  40 A-E and  42 A-B. Doors  32 A-E,  33 A-E,  34 A-B and  35 A-B do not include any stop members which would retain them in an open position. Each of doors  32 A-E,  33 A-E,  34 A-B and  35 A-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  40 A-E and  42 A-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  34 B is spaced apart from adjacent door  34 A by a distance  37  which is approximately equal to the thickness of door  34 B. 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  32 A and a fixed lower front panel  48  located below bottom inlet door  34 B, as seen in FIGS. 1 and 2. Similar panels  46 ′ and  48 ′ 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  40 A-E and  42 A-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  40 A-E and  42 A-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  40 A-E and  42 A-B. Each column corresponds to a horizontal tray position. For example, as shown in FIG. 2, there are five horizontal tray positions (trays  54 A-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 “incompatible product selection” 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 temperature). 
     FIG. 2 shows device  20  with inlet door  32 B raised to provide access to trays  54 A-E within compartment  40 B. For ease of handling by a person, trays  54 A-G preferably are constructed from a material having a low heat capacity, such as polycarbonate. Preferably, each of trays  54 A-E, as well as trays  54 F-G shown in FIG. 3, has a width  56  smaller than the width  58  of compartments  40 A-E and  42 A-B to permit placing more than one tray within a compartment. FIGS. 9 and 10 depict trays  54 G and  54 A, respectively. In the preferred embodiment shown in FIG. 2, width  56  is chosen relative to width  58  such that five trays  54 A-E will fit within any of compartments  40 A-E and  42 A-B. In addition, each of the trays has a length almost equal to the depth  62  of compartments  40 A-E and  42 A-B, as seen in FIG.  3 . For example, tray  54 F is of length  60 . 
     Each of compartments  40 A-E and  42 A-B is bounded by an upper heated compartment surface  64 A-G and a lower heated compartment surface  66 A-G, as shown in FIG.  3 . Each of lower heated compartment surfaces  66 A-G is flat and substantially horizontal to provide uniform heat transfer to trays  54 A-G and permit easy sliding of those trays along the surface of lower heated compartment surfaces  66 A-G. Each of trays  54 A-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  54 A-F. Height  68  is chosen so that upper edge  70  of any of trays  54 A-F is at a predetermined distance  76  from upper compartment surfaces  64 A-F when trays  54 A-F are placed within compartments  40 A-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  42 A-B are of greater height than compartments  40 A-E to accommodate larger food portions such as biscuits  36 . Consequently, when trays  54 A-F are placed within compartments  42 A-B, upper edges  70  are at a substantial distance greater than distance  76  from upper heated compartment surfaces  64 F-G. Sidewall  73  of tray  54 G has an increased height  69  so that a gap  77  is provided between the upper edge  70 ′ of tray  54 G and upper heated compartment surface  64 G. 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  40 A-E or  42 A-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  40 A-E and  42 A-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  66 A-G. 
     Returning now to FIG. 3, upper heated compartment surfaces  64 A-G and lower heated compartment surfaces  66 A-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  40 A-E and  42 A-B, preferably within trays  54 A-G, until sold or otherwise disposed of. Because compartments  40 A-E and  42 A-B are discrete, with well-defined upper heated compartment surfaces  64 A-G and well-defined lower heated compartment surfaces  66 A-G, air currents throughout cabinet  22 , if any, are limited because surfaces  64 A-G and  66 A-G obstruct air flow within cabinet  22 . In addition, air currents within compartments  40 A-E and  42 A-B, if any, are limited because both upper heated compartment surfaces  64 A-G and lower heated compartment surfaces  66 A-G are heated thereby reducing or eliminating thermal incongruities within compartments  40 A-E and  42 A-B. By restricting the air currents throughout cabinet  22  and within compartments  40 A-E and  42 A-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  54 A-F such that upper edges  70  of trays  54 A-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  64 A-E when trays  54 A-F are placed within compartments  40 A-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  54 E containing the cooked food portions within compartment  40 A through inlet door  32 A of device  20  inlet side  1 , as shown in FIG.  3 . Then, when the cooked food portions are needed for assembly into a sandwich, restaurant personnel remove tray  54 E from compartment  40 A through outlet door  33 A of outlet side O of device  20 , as shown in FIG.  3 . The flow-through configuration of inlet doors  32 A-E and outlet doors  33 A-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  100 A-F contained within cabinet  82 . Holding chambers  100 A-F are bounded by upper heated chamber surfaces  102  and lower heated chamber surfaces  104 . Chambers  100 A-F are also bounded by inlet doors  108 A-F and outlet doors  112 A-F hingedly attached along their upper surfaces to cabinet  82  in a manner as described previously with respect to device  20 . Doors  108 A-F and  112 A-F are lifted by grasping handles  118  to thereby gain access to chambers  100 A-F. In FIG. 4, inlet doors  108 A and  108 B are raised to reveal trays  120  contained within chambers  100 A and  100 B. The width  122  of trays  120  is such that three trays  120  will fit within any of chambers  100 A-F. The length of trays  120  is almost equal to the depth of chambers  100 A-F so that trays  120  may be readily handled through inlet doors  108 A-F and through outlet doors  112 A-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  100 A-F. However, since the height of chambers  100 A-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  184 A-G are mounted to interior side wall  183  to support shelves  186 A-G. Each end of angle irons  184 A-G uses an upturned tab  184 ′ for preventing lateral movement of shelves  186 A-G when mounted thereon. Shelves  186 A-G define heated compartments  188 A-H. 
     FIG. 15 is an enlarged view of shelf  186 C, which is representative of the other shelves. Shelf  186 C 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  108 A-F and outlet doors  110  and  112 A-F thus promotes an efficient use of space within the kitchen. Device  80  also protects the appearance, taste, and texture of cooked food portions 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.