Unitemp food bar

Abstract

A food bar for controlling the temperature of a food in a food pan inserted into the food bar is described. The food bar comprises an energy source that circulates a fluid at a desired temperature through ducts and then into the interior of the bar.

Description

FIELD OF THE INVENTION

The present invention relates to open-top food displays that refrigerate or, alternatively, heat foods in pans.

BACKGROUND OF THE INVENTION

Food bars are used in food service facilities such as restaurants, hotels, institutions, and the like to prepare and serve food. The food bar typically consists of a self-contained free standing unit with a counter top on a base. The counter top is constructed with openings to support removable pans containing food. A lip or flange at the top of each pan typically rests on support cross-pieces of the counter top. Support cross-pieces are positioned so that when a pan is placed in the food bar with the lip resting on the cross-pieces, the remainder of the pan is housed within the base of the bar. Pans and the openings formed by the cross-pieces may be rectangular or circular.

Food bars may be heated or refrigerated. Typical heated food bars may have wet or dry wells designed to accept a pan containing food. The heat source may be temperature controlled and may serve the entire bar, or may be arranged to heat one pan or a specific area of pans. Refrigerated food bars may use cooling coils located within the walls of the base. A fan may be employed to circulate the air beneath and around the pans. The compressor is generally located in a side or bottom of the cabinet with an exterior panel to facilitate easy access for maintenance.

NSF International (founded as the National Sanitation Foundation) specifies criteria for food refrigeration performance. NSF Standard 7 requires easily cleanable materials used to construct food bars to deter areas that could promote bacterial growth within the food area of the units. Food bars are generally constructed of heavy gauge stainless steel in order to conform to Standard 7. NSF Standard 7 also mandates that refrigerated buffet units and refrigerated food preparation units maintain product in the open display area at temperatures not greater than 5° C. (41° F.) and not less than 1° C. (33° F.). The air temperatures within the enclosed refrigeration compartments must remain between 1° C. (33° F.) and 4° C. (40° F.).

A problem exists with existing bars in conforming to the NSF standard of maintaining the required temperature of food contained within the pans. The heating/cooling source is typically located in the bottom of the food bar base, which transfers more heat/cooling to the food in the bottom of the pan than is transferred to food located at the top and central portions of the pans. Existing refrigeration systems typically allow ice to form on the exterior of the pans; existing heating systems may cause the food to burn on the bottom of pans. An air circulation device is sometimes added to better circulate the cooled/warmed air, but no existing food bar currently solves these problems. Existing methods typically circulate air over the food, reducing the moisture content and drying out the food. A need exists for a food bar that transfers more energy to the food located in the top portion of the food pan placed in a food bar.

SUMMARY OF THE INVENTION

The present invention comprises a device to uniformly heat and or cool foods in an open serving environment. The present invention comprises a generally open compartment capable of accepting a food pan. The compartment comprises a floor and generally parallel walls connected to the floor and extending upward from the floor. The walls are connected to each other to form the compartment. The ends of the walls opposite the floor comprise one or more duct.

In an embodiment, the compartment comprises at least one duct extending from one wall to a wall opposite the first wall. The ducts are located near the upper surface of the compartment. The ducts comprise an opening. The opening may be located near an energy source or may be a connection from another duct. The duct comprises at least one vent. The vent is located distal to the energy source and placed on a portion of the duct facing the interior of the compartment.

The present invention further comprises an energy source. The energy source circulates a fluid at a desired temperature, which can be cooler or warmer that room temperature. Fluids are defined herein to include liquids, gases, and plasmas. The energy source is located on a wall of the compartment to provide ease of cleaning. In an embodiment, the energy source is located on a wall of the compartment and forces the fluid into the opening of the duct. The force is sufficient to drive the fluid though the duct and out the vent.

A food pan typically has a flange or a lip at the opening. When a-food pan is placed in the present invention, at least a portion of the lip of the food pan is supported by the duct. The present invention provides a sufficient number of ducts to support the desired number of food pans in a food bar. When a food pan is placed in the compartment of the present invention, the lip of the food pan forms a generally closed top across the open end of the compartment.

The duct is formed such that it corresponds to portion of the pan near the lip. As the fluid flows through the duct, a food placed in the food pan conducts the energy from the flow in the duct through the side of the pan. The fluid exits the vent and flows between and under the pans and is generally prevented from escaping the compartment by the floor, the walls, the exterior of the duct facing the interior of the compartment, and the surface formed by the food pan(s) placed in the compartment. The fluid circulates through the compartment back to an inlet in the energy source to be re-cooled or reheated and reintroduced to the duct(s).

The fluid exiting the energy source and entering the duct contains more energy than the fluid as it reaches the interior of the compartment so that the fluid in the duct transfers more energy to that portion of the food in the food pan than the fluid that is in contact with the other portions of the food pan.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is prospective view of an embodiment of the present invention with arrows showing the paths of the fluid flow.

FIG. 2 is a detail of an embodiment of a duct vent.

FIG. 3 is a sectional view depicting the interior of the compartment and the arrangement of the ducts.

FIG. 4 is a sectional side view depicting the fluid flow through the ducts to the interior of the compartment and returning to the energy source.

FIG. 5 is a sectional side view showing the fluid circulation in a reverse flow.

FIG. 6 is a top view of an embodiment having three compartments with separate energy sources within each compartment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is similar to conventional food serving bars that presents food in pans on a surface. As shown in FIG. 1, the present invention comprises a compartment 100, at least one support duct 102, and an energy source 103.

The compartment 100 is of sufficient size to contain at least one food pan (shown in dotted line in FIG. 4) and may contain numerous pans. The compartment 100 may be used alone, or may be housed in a larger unit, such as a cabinet. The compartment 100 may be combined with other compartments and or other devices, such as ice bins, storage units, electrical components, sinks, freezers, refrigerators, ovens, sneeze shields, railings, lighting, and the like.

In an embodiment depicted in FIG. 6, the present invention comprises a top surface 601 with at least one compartment 100, 100n. The top surface may be a counter top. The top surface 601 may be integral with the compartment, or may be a separate component. The top surface may be made of any durable, cleanable material. The compartment 100 of the present invention may be formed of any durable, easily cleanable material, such as ceramics, plastics, woods, metals and the like and may be a mixture of different materials.

In an embodiment, the compartment 100 is formed from stainless steel. In an embodiment, the compartment 100 is generally a rectangular cube, but any shape including circular, oval, triangular, free-form and the like, may be employed.

In an embodiment depicted in FIG. 3, the compartment 100 comprises a floor 301 and at least one wall 302a-302d. The floor 301 may comprise other objects, such as but not limited to a drain 303. The floor 301 may be planar or comprise different elevations including but not limited to a slope that falls to the drain 303. The walls 302a-302d are connected to the floor 301 at an outer edge of the floor 301 to form the outer perimeter of the compartment 100. In an alternate embodiment, a wall 302a-302d may be located anywhere on the surface of the floor 301. In an embodiment, the walls 302a-302d are generally vertical. In an embodiment, the compartment 100 comprises two sets 302a/302c, 302b/302d of generally opposite parallel walls. The walls 302a-302d may be one structure, or may include an inner and outer wall. Cooling/heating mechanisms may be located within the inner and outer surface of a wall or may alternatively be attached to a surface of the wall 302a-302d. The walls 302a-302d may comprise additional objects, such as, but not limited to, access porticos, storage units, and the like.

A duct 102 is attached to an end of each wall 302a-302d at a position opposite the floor 301. The duct 102 is a generally hollow tube and may be formed of any material that conducts energy. In an embodiment, the duct 102 is formed of similar materials as the material used to form the compartment 100. In an embodiment, the duct 102 is formed of stainless steel. The duct may be integral or separately attached to the wall. In an embodiment, the duct 102 is connected to the compartment 100 by metal welding. The duct 102 provides an upper exterior surface 105a that engages a lip of a food pan such that the food pan lip rests on the upper exterior surface 105a of the duct 102 and the remainder of the food pan extends into the interior of the compartment 100. The size of the compartment 100 and the placement of the duct 102 are such that the inserted food pan does not touch the floor 301 or any wall 302a-302d of the compartment 100. When more than one food pan is placed in a compartment 100 of a food bar, the pans do not touch each other but are spaced by the width of the duct 102 and any lip width of the pan. In an embodiment, more than one duct 102 support a pan. In an embodiment, two ducts 102 support a pan. In an alternate embodiment, three ducts 102 support a pan. In an additional embodiment, multiple ducts support a pan. The duct 102 may support more than one pan. In an embodiment, support bars may for use in conjunction with the ducts 102 and or walls 302a-302d to accommodate different sizes and shapes of pans.

The duct 102 comprises an opening 400 (best seen in FIG. 4) and at least one vent 200 (best seen in FIG. 2). The cross sectional shape of the duct 102 may be any shape that allows unobstructed fluid flow and supports the lip of the food pan. In an embodiment, the perimeter of the duct 102 is generally rectangular. In an embodiment, the duct 102 is a generally rectangular hollow tube having a height and width of about 1″ by about 1″.

In an embodiment, the compartment 100 comprises at least one inner duct 102a extending from a first wall 302b to a second wall 302d opposite the first wall. The inner duct(s) 102a have an upper exterior surface 105n. As shown in FIG. 3, the ducts 102, 102a are located near the upper surface of the interior of the compartment 100. In an embodiment, the compartment 100 comprises more than one inner duct 102a. In an embodiment, the interior of the compartment is generally rectangular with a duct 102 at the upper surface of each wall 302 and at least one inner duct 102a.

In an embodiment, the upper exterior surface 105a engages at least one lip of a food pan and the upper exterior surface 105n engages at least one other lip of the same food pan when the pan is placed in the compartment 100. In an embodiment, the upper exterior surface 105n engages each lip of the same food pan when the pan is placed in the compartment 100.

The present invention further comprises an energy source 103. The energy source 103 circulates a fluid (depicted by arrows in FIGS. 1, 4 and 5). The energy source 103 comprises means to cool and or heat the fluid to a desired temperature. In an embodiment, the temperature is controlled by a thermostat. In an embodiment, the thermostat is located within the energy source 103. In an alternate embodiment, the thermostat is located within the interior of the compartment 100. In an embodiment, the energy source 103 cools the fluid. In an embodiment, the energy source 103 cools the fluid to a temperature from about 18° F. to about 40° F. In an embodiment, the energy source 103 cools the fluid to a temperature from about 20° F. to about 27° F. at the energy source 103. In an embodiment, the energy source 103 cools and circulates the fluid at a temperature that creates a temperature of about 33° F. to 41° F. in a food in a pan placed in the compartment 100. In an embodiment, a food in a pan placed in the compartment 100 is maintained at a temperature that meets the standards of NSF Standard 7.

In an alternate embodiment, the energy source 103 heats and circulates the fluid. In an embodiment, the energy source 103 heats the fluid to a temperature from about 145° F. to about 165° F. in the energy source and a temperature of about 145° F. in a food in a pan placed in the compartment 100. One skilled in the art would understand that the temperature of the circulated fluid will vary based on such factors as ambient room temperature, the type of food in the pan, the moisture content of the food in the pan, the size of the compartment, and the like.

In an embodiment, the energy source 103 is located on or within a wall 302 of the compartment 100. In an embodiment, the energy source 103 is located on a wall 302 vertical surface to provide ease of cleaning. In an embodiment, the energy source 103 is located lower than a top surface 601 of the compartment 100. The energy source 103 is any device that changes the temperature of the fluid, such as but not limited to a compressor, a pump, a cooling element, a heating element, and the like. The energy source's power is derived from any appropriate supply, such as but not limited to electrical, solar, or battery powered. The energy source 103 comprises means to circulate the fluid. The fluid is circulated by any circulation device including but not limited to a fan, moving diaphragms, bellows, blowers, and the like. In an embodiment, the energy source 103 is heating/cooling coil and a fan. In an embodiment depicted in FIG. 5, the circulation device is capable of reversing the fluid flow.

The fluid may be a liquid, a gas, a plasma and the like. In an embodiment, the fluid is a gas. In a preferred embodiment, the fluid is air. In an embodiment, the fluid is a liquid. In an embodiment using a liquid, the liquid may be further enclosed to prevent contact with food.

As best seen in FIG. 4, the energy source 103 forces the fluid (shown by arrows in the figure) into the opening 400 of the duct 102, 102a. In an embodiment, the invention comprises more than one duct 102, 102a wherein the ducts are connected at an opposite end 107 of the duct having the opening 400 in communication with the energy source 103. In an embodiment, the ducts are interconnected.

Returning to FIG. 1, the force of the energy source 103 is sufficient to drive the fluid though the duct 102, 102a and to any connecting ducts and through the vent 200. The energy source 103 forces the fluid out of the duct 102, 102a through the vent 200 into the compartment 100. In an embodiment, the vent 200 is located at on any surface of the duct 102 facing the interior of the compartment 100. In an embodiment, the vent 200 is located at a junction of an inner duct 102a and the duct 102 located on the wall 302 opposite the energy source 103. In an embodiment, the vent 200 is located on a duct placed on a side of the compartment 100 generally opposite the side of the compartment where the energy source 103 is located. In an embodiment, the duct 102 located at the top surface 601 of the compartment wall 302d opposite the compartment wall 302b housing the energy source 103 comprises a multitude of vents 200-200n spaced along the duct such that the vents allow the fluid to circulate from the duct 102 into the compartment 100.

As shown in FIG. 4, the duct opening 400 is in communication with an outlet 401 of the energy source 103. In an embodiment, more than one duct 102, 102a opening 400 is in communication with the outlet 401.

The energy source 103 comprises means to circulate a fluid heated or cooled at a desired temperature at a desired point in any given duct. The present invention comprises a temperature controlled food bar with means to move a fluid through the duct 102, 102a to the interior of the compartment 100 where it circulates under and between food pans placed in the compartment. As shown in FIG. 1, the fluid is forced from the energy source 103 by the energy source to the opening 400 and through the hollow chamber of the duct 102, 102a to the vent 200, 200n. The energy source 103 comprises sufficient force to move the fluid through the duct(s) and into the compartment 100 though one or more vent 200, 200n. The energy transferred to the fluid by the energy source 103 is conducted though an exterior of the duct 102, 102a. When a food pan is placed in the present invention, food in the food pan located adjacent to the duct 102, 102a receives the energy via conduction through the side of the food pan adjacent to the duct 102, 102a. The conduction reduces the energy in the fluid as it is transferred to the food. The fluid contains less energy as it is forced through the vent 200, 200n into the interior of the compartment 100. The fluid circulates between and under the pan(s) as it returns to the energy source 103 through an intake 402 located within the interior of the compartment 100. The intake 402 is connected to the energy source 103 and directs the fluid through the energy source 103 where it is re-cooled/reheated and re-circulated to the duct(s) 102, 102a. When the food pan(s) are in place in the present invention, the fluid is contained in a generally closed system comprising the energy source 103, the duct(s) 102, 102a and the interior of the compartment 100.

In an embodiment, the present invention comprises a compartment 100 having refrigeration/heating coils 403 in the walls 302 and the floor 301, one or more duct 102 located adjacent to an upper surface of the interior of the compartment 100, and an energy source 103 comprising a refrigeration/heating coil and a fan housed within an interior and exterior wall of the compartment 100. The compartment and ducts are shaped and configured to support at least one food pan so that the food pan bottom does not touch the floor of the compartment and the lip of the food pan and the upper exterior surface 105a-n of the duct 102, 102a form a relatively closed surface of the compartment 100. The duct 102 is a hollow tube approximately 1″×1″ and about 20″ to about 60″ long, preferably, about 50-51″ long, located along a top perimeter of the walls 302 of the compartment 100 with two (2) interior ducts 102a that extend between two parallel walls 302b, 302d. The ducts are interconnected.

In an embodiment, the desired temperature is selected via the thermostat and the energy source 103 provides cooled air to an opening 400 of a duct 102. The cooled air is circulated through an interconnection of ducts, transferring cooling to the exterior surfaces of the ducts. The cooled duct exterior cools the portion of the pan adjacent to the exterior surface of the duct. The pan transfers the cooling to food in the pan located near the cooled portion of the pan. In an embodiment, this portion of the food is approximately the top 1″ of the food. The air circulated from the energy source 103 to the duct 102 increases in temperature as it travels through the interconnected ducts. When the air reaches the wall of the compartment opposite the wall housing the energy source 103, the warmer (but still cooled) air travels though at least one vent 200, 200n in the duct. The vent 200 is placed on an exterior surface of the duct so that the air exits the duct and enters the compartment interior. The air circulates under and between the pans where it transfers more cooling to the lower portion of the pan and the food adjacent to the lower portion of the pan. The air warms as it transfers the cooling to the lower portion of the pans. The wall of the compartment housing the energy source 103 comprises an intake 402 that pulls the warmer yet (but still cooled) air into the energy source 103 where it is re-cooled to the desired temperature and reintroduced to the duct(s).

The system cools or in an alternate embodiment, heats, about 1″ of food at the surface of the pan located in the compartment at a different rate than the remainder of the food in the pan. The present invention minimizes frost (or excess heat) on the exterior lower portion of the pans. The device complies with the National Sanitation Foundation (NSF) Standard Number 7, which requires open top food tables to maintain product temperatures between 33° and 41° F. under ambient (operational) conditions of 86° F. for a time period of four (4) hours.

In an embodiment depicted in FIG. 6, three compartments 100, each having an energy source 103, are combined in a unit having additional features. As shown in FIG. 6, different sized food pans (depicted as the interior rectangles) may be used with the present invention. In combination, the compartments may all be heated, cooled, or some heated and some cooled. The circulation of the air may be through the ducts first or reversed in direction to flow first through the interior of the compartment.

The foregoing descriptions of specific embodiments and examples of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. It will be understood that the invention is intended to cover alternatives, modifications and equivalents. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A food bar for controlling the temperature of a food in a food pan inserted into the food bar comprising:

a compartment having an interior formed by a floor and at least one wall attached to the floor, said interior shaped to contain at least one food pan; said wall comprising an intake;

an energy source, said energy source located adjacent to and in communication with the intake and comprising means to circulate a fluid; and

at least one duct having an inner surface forming a hollow chamber, said duct 1) located on a portion of the wall opposite the portion attached to the floor; 2) having an upper exterior surface shaped to support at least one food pan; and in communication with the interior of the compartment and the energy source such that the fluid is circulated one of a) from the energy source through the hollow chamber to the interior of the compartment and back to the energy source through the intake and b) from the energy source through the intake to the interior of the compartment through the hollow chamber and back to the energy source.

2. The food bar of claim 1 wherein at least one duct is connected to at least one other duct.

3. The food bar of claim 1 comprising at least one of a cooling device and a heating device located in at least one wall.

4. The food bar of claim 1 wherein the energy source is in communication with a temperature control device that maintains the fluid at a desired temperature.

5. The food bar of claim 1 wherein the duct comprises an opening and at least one vent.

6. The food bar of claim 1 wherein the fluid is air.

7. The food bar of claim 1 wherein the desired temperature is selected via a thermostat.

8. The food bar of claim 1 wherein a sensor for selecting the desired temperature is located within one of the energy source and the interior of the compartment.

9. The food bar of claim 1 wherein the duct is interconnected to at least one second duct.

10. The food bar of claim 1 wherein the energy source circulates the fluid though the duct to one or more vent located on an opposite wall of the wall containing the energy source.

11. The food bar of claim 1 wherein a food in a food pan placed in the food bar is cooled to a temperature from about 33° F. to about 41° F.

12. The food bar of claim 1 wherein the food pan and the upper exterior surface form a generally closed top surface of the compartment when at least one food pan is placed in the compartment.

13. The food bar of claim 1 comprising at least one of an ice bin, a countertop, a storage unit, an electrical component, a sink, a freezer, a refrigerator, an oven, a sneeze shield, a railing, an access portico, and a lighting fixture.

14. A food bar for controlling the temperature of a food in a food pan inserted into the food bar comprising:

a compartment having an interior formed by a floor and at least one wall attached to the floor, said interior shaped to contain at least one food pan; said wall comprising an intake;

an energy source comprising a temperature control device and a fluid circulation device, said energy source located adjacent to and in communication with the intake and comprising means to circulate a fluid at a desired temperature;

at least one of a cooling device and a heating device located in at least one wall;

at least one duct; and

a thermostat and a sensor for selecting a desired temperature, the sensor located at one of the energy source, the duct and the interior of the compartment, said duct comprising an opening and at least one vent and having an inner surface forming a hollow chamber, said duct 1) located on a portion of the wall opposite the portion attached to the floor; and 2) having an upper exterior surface shaped to support at least one food pan; said duct in communication with the interior of the compartment and the energy source such that the fluid is circulated one of a) from the energy source to the opening through the hollow chamber through the vent to the interior of the compartment and back to the energy source through the intake, and b) from the energy source through the intake to the interior of the compartment through the vent through the hollow chamber and back to the energy source though the opening.

15. A food bar for maintaining a food in a food pan inserted into the food bar at a temperature from about 33° F. to about 41° F. comprising:

a compartment having an interior formed by a floor and at least one wall attached to the floor, said interior shaped to contain at least one food pan; said wall comprising an intake;

an energy source comprising a temperature control device and a fluid circulation device, said energy source located adjacent to and in communication with the intake and comprising means to circulate a fluid at a desired temperature;

a cooling device located in at least one wall;

at least one duct comprising an opening and at least one vent and having an inner surface forming a hollow chamber; and

a thermostat and a sensor for selecting a desired temperature located within one of the energy source, the duct and the interior of the compartment, said duct 1) located on a portion of the wall opposite the portion attached to the floor; and 2) having an upper exterior surface shaped to support at least one food pan; said duct in communication with the interior of the compartment and the energy source such that the fluid is circulated from the energy source to the opening through the hollow chamber through the vent to the interior of the compartment and back to the energy source through the intake.

16. The food bar of claim 15 wherein at least one duct is connected to at least one other duct such that the fluid is circulated from the energy source to the opening through one or more hollow chambers through the vent to the interior of the compartment and back to the energy source through the intake.

17. A food bar for maintaining an upper portion of a food in a food pan inserted into the food bar at a temperature of about 145° F. comprising:

a compartment having an interior formed by a floor and at least one wall attached to the floor, said interior shaped to contain at least one food pan; said wall comprising an intake;

an energy source comprising a temperature control device and a fluid circulation device, said energy source located adjacent to and in communication with the intake and comprising means to circulate a fluid at a desired temperature;

a heating device located in at least one wall;

at least one duct comprising an opening and at least one vent and having an inner surface forming a hollow chamber; and

a thermostat and a sensor for selecting a desired temperature located within one of the energy source and the interior of the compartment, said duct 1) located on a portion of the wall opposite the portion attached to the floor; and 2) having an upper exterior surface shaped to support at least one food pan, said duct in communication with the interior of the compartment and the energy source such that the fluid is circulated from the energy source through the intake to the interior of the compartment through the vent through the hollow chamber and back to the energy source though the opening.

18. A method of maintaining a temperature of a food in a pan placed in a food bar from comprising:

placing a food in a food pan located in a compartment having an interior formed by a floor and at least one wall attached to the floor, said interior shaped to contain at least one food pan; said wall comprising an intake;

circulating a fluid through an energy source comprising a temperature control device and a fluid circulation device, said energy source located adjacent to and in communication with the intake and comprising means to circulate the fluid at a desired temperature;

circulating the fluid though at least one duct comprising an opening and at least one vent and having an inner surface forming a hollow chamber, said support duct 1) located on a portion of the wall opposite the portion attached to the floor; and 2) having an upper exterior surface shaped to support at least one food pan, said duct in communication with the interior of the compartment and the energy source such that the fluid is circulated one of a) from the energy source to the opening through at least one hollow chamber through the vent to the interior of the compartment and back to the energy source through the intake, and b) from the energy source through the intake to the interior of the compartment through the vent through at least one hollow chamber and back to the energy source though the opening; and

providing a thermostat and a sensor for selecting a desired temperature located within one of the energy source, the duct and the interior of the compartment.

19. The method of claim 18 wherein the fluid is circulated from the energy source to the opening through the at least one hollow chamber through the vent to the interior of the compartment and back to the energy source through the intake to maintain the food at a temperature from about 33° F. to about 41° F.

20. The method of claim 18 wherein the fluid is circulated from the energy source through the intake to the interior of the compartment through the vent through the at least one hollow chamber and back to the energy source though the opening to maintain an upper portion of the food at a temperature of about 145° F.