Abstract:
An apparatus is disclosed in the form of a cabinet having doors and interior side walls with supports for receiving trays of food products to be rapidly rethermalized and held. The apparatus can also condition the rethermalized food product, as well as act as a cooking oven. A steam generator is provided for supplying steam to the cabinet interior where it is continuously mixed with air. Thermocouples control both the steam and air mixture temperature for rethermalizing cooking and holding the food products and an air heater for conditioning the food products prior to use.

Description:
The field of the present invention relates to steam devices and method for rethermalizing food products and holding the rethermalized food products at desired temperatures, including cooking and then conditioning the food products prior to use. More particularly, the invention relates to an oven-type device, which utilizes a steam and air mixture to rethermalize the food products. 
     BACKGROUND OF THE INVENTION 
     The rethermalization of foods and the ability to hold the rethermalized foods for periods of time and at temperatures where the foods are ready for consumption is old in the art. For example, if the foods are prepared in final consumption form prior to freezing or where the foods are ready for further processing, e.g. cooking, in a thawed state, larger institutions, such as schools, hospitals and restaurants, use such rethermalization. Time and labor can be saved if the frozen foods can be taken from a freezer and immediately rethermalized without the necessity of subjecting the foods to a slow defrosting step, which could result in bacterial growth. 
     The low rate of heat transfer in conventional rethermalizers, e.g. hot air ovens, and the limited capacity of microwave ovens make them undesirable for rethermalization of frozen foods. However, as is known, the latent heat of vaporization makes steam a very effective heat transfer medium because of the large amount of thermal energy contained in the steam. As steam condenses on a food product, this thermal energy will be transferred directly to the food product. Steam is, thus, a much more effective heat transfer medium than hot air. However, because low-pressure steam is generated at a temperature of approximately 212° F., steam is generally too hot for direct contact with food products and, thus, can cause damage to some food products. Accordingly, rethermalizing with steam has not been satisfactory for most rethermalizing uses. 
     SUMMARY OF THE INVENTION 
     Applicants have discovered that by continuously mixing air with low pressure steam and circulating the mixture around the food products, with controlled temperatures of the mixture below 212° F., fast, but safe rethermalization of food products can result. This steam-air mixture of the present invention can be established to provide any desired condensing temperature or dewpoint and therefore rethermalize the food products with a high heat transfer rate but at a safe temperature below 212° F. Preferably, the steam and air are continuously mixed together. 
     Further, according to the invention, when the rethermalized food products are left in the present rethermalizer, dry, hot air (without steam) is circulated around the rethermalized food products, and the condition and appearance of the food products can be improved by the evaporation of condensed steam remaining on the products, while at the same time the temperature of the food products is maintained, thus making the food products ready for consumption or further processing as the case may be. 
     As noted above, the thawing and cooking of food products by circulating steam thereover is not now. Examples of devices for thawing, cooking or otherwise treating food products with steam are disclosed in U.S. Pat. Nos. 3,744,474, 4,426,923, 4,700,685 and 5,613,423. However, none of these patents disclose a device for rapidly rethermalizing food products at temperatures below 212° F. without the use of some additional device, such as a vacuum pump, to lower the pressure in a cabinet. Also, as noted above, rethermalizing at or above 212° F. can damage some food products. In contrast, the present invention has the advantage to condition the food products utilizing dry, hot air, and thus also avoids the necessity of having to physically move the food products from the thermalizing device. 
     Thus, briefly stated, the present invention provides a device for rethermalizing food products. An oven chamber has side, top and bottom walls in which at least one is provided with a door to provide access into the chamber. Spaced-apart supports on the side walls support trays in the chamber for containing the food products. A steam generator is provided for generating steam. A plenum adjacent one of the walls has inlets and outlets between the plenum and the chamber. A fan in the plenum mixes air with the steam and moves the mixture from the inlets, through the plenum, to the outlets, preferably horizontally, across a top of each tray, and back to the inlets. A controller controls temperatures of the air and steam mixture to temperatures below 212° F. to rethermalize the food products, in part, by the steam in the mixture condensing thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the present rethermalizer; 
     FIG. 2 is a sectional top view along lines  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional side view along lines  3 — 3  of FIG. 2; 
     FIG. 4 is a sectional side view along lines  4 — 4  of FIG. 2; and 
     FIG. 5 is an illustration of a typical wiring diagram for control and operation of the device. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1-4, wherein the same reference numerals indicate the same parts throughout the several views, rethermalizing, cooking, holding and conditioning device  10  is shown including cabinet  12  having doors  14 ,  16  (see FIGS.  1  and  2 ), which are secured by means of a latch  18 . The doors  14 ,  16  are supported by hinges  20 . A control panel  22  is provided, as well as a switch  24  and a temperature controller  26  (see FIG.  5 ), the function of which will be more fully described below. As shown in FIG. 1, cabinet  12  further has side walls  28  and  30 , a top wall  32  and a bottom wall  34 . The walls of the cabinet  12  have insulating material between wall panels of the walls as in conventional ovens and the doors  14 ,  16  have insulation around the glazing  36  on each. 
     The walls of cabinet  12 , in part, form an oven chamber  38  (see FIG.  2 ), which chamber is defined by top wall  32 , side wall  28 , partition  40  and removable cover  42  (also see FIG. 3) for a pan  43 . A plurality of horizontally, spaced-apart supports, e.g. rails,  41  are secured to, or integrally formed with, partition  40  and side wall  28  to support a plurality of trays  45  (in phantom lines in FIG. 3) on which food products can be supported during rethermalizing, cooking, conditioning and holding. Partition  40  has vertically extending openings forming inlets  44  (see FIGS. 2 and 4) to plenum  46  from chamber  38  and openings forming outlets  48  from the plenum  46  back to chamber  38 . The plenum  46  is further defined by an interior wall  50  (see FIGS. 2 and 3) to which are mounted a plurality of fans  52  adjacent outlets  48 . The term “fans” is intended herein to include any desired gas mover, e.g. blowers, jets, etc. The fans  52  circulate a steam-air mixture, in one mode of operation, or warmed air, in another mode of operation, as will be more fully described below, from the inlets  44 , through the plenum  46 , through outlets  48 , through the chamber  38  and back to inlets  44 . The inlets  44  are preferably spaced apart and perpendicular to the horizontally extending trays  45  (see FIGS. 3 and 4) so that the circulated steam-air or warmed air can pass over the top and parallel to each tray  45  and around food products placed thereon. 
     A preferred low pressure steam generator has a pan  43  which is further defined by an upwardly projecting ridge  56  (see FIG. 3) extending around an upper edge of the pan  43 . The ridge  56  has a horizontally extending surface  58  in the form of a flange which extends from the ridge  56  to the side wall  28  and partition  40  and to a location adjacent doors  14 ,  16 . A pan cover  42  has a downwardly depending peripheral flange  60  around a top surface  62  (see FIG. 2) which rests on surface  58  and completely covers the opened top of pan  43 . The pan cover  42  further is provided with a layer of insulation  64 , preferably beneath the surface  62  (see FIG. 2) and the flange  60  has openings  66  formed on opposite sides thereof to permit steam generated in pan  43  to flow into chamber  38 . The pan cover  42  also serves to prevent circulating air from contacting the surface of the water in the pan and evaporating the water or heating the air above a desired setpoint. 
     While the above-described pan-form steam generator is preferred, quite obviously, any other conventional steam generator in or outside cabinet  12  could be used. 
     The doors  14 ,  16  are provided on their interior lower edge portion with a condensation deflection shield  68  (see FIG. 4) which extends over the horizontally extending surface  58  to permit any condensation from the inside surface of doors  14 ,  16  and associated glazing to run down and be deflected onto surface  58 . In addition, any condensation forming on the interior surfaces of chamber  38  is permitted to run down or be collected on surface  58 . A drain  70  (see FIG. 3) is provided having an opening  72  (see FIG. 2) in surface  58  and is connected by piping  74  (see FIG. 3) to a drain outlet  76  beneath the cabinet  12 . The opening  72  is threaded to receive a plug (not shown) which when threaded into opening  72  causes any condensate collected on surface  58  to build up and eventually run back into pan  43  rather than to outlet  76 . An outside lower edge portion of cabinet  12  beneath the doors  14 ,  16  has a trough  80  (see FIG. 4) mounted thereon for collecting any condensate running down the outside surface of the doors. A drain pipe  82  connects the inside of the trough  88  to a drain outlet  76 . 
     A heating element(s)  84 , which may be of any desired type, but preferably an electric heating element (see FIG.  2 ), is located in plenum  46  (see FIG. 2) in the path of air flowing therethrough so as to heat the air prior to its discharge through outlets  48 . A thermocouple  86  is also located in the chamber  38 , the operation of which will be more fully described below. 
     The level of water in pan  43  is controlled by float switch  88  (see FIGS. 4 and 5) which, in turn, controls a solenoid valve  90  (see FIG. 5) in water feed line  92 . A plurality of heating elements  94 , especially electrical heating elements, are associated with or mounted on a wall of the pan  43  and such electric heating elements extend a distance into the water to heat the water and turn it into low pressure steam, e.g. atmospheric steam. Typically, three electrical heating elements  94  would be used, each of which can advantageously be connected to a separate phase line of a three-phase electric power service input or connected in parallel to a single-phase input. The heating elements  94  are surrounded on three sides by a U-shaped trough  96  (see FIG. 2) resting on the bottom of pan  43 . The trough  96  is opened at one end to permit water from the pan to slowly enter as it is being boiled away into steam. By thus keeping the quantity of water adjacent the length of the heating elements  94  small, steam can be immediately and rapidly generated as the heating elements are energized, thus eliminating the necessity of heating the entire quantity of water in the pan  43  to form the steam. 
     The present invention also contemplates the use of the identical devices  10  ideally placed in side-by-side relationship. Rethermalized food products being held in one unit would be ready of immediate use, while food products could be simultaneously loaded and rethermalized in the adjacent unit. The only operational connection between the two units may be a device to ensure that the water heating elements of both units would not be simultaneously energized due to the excessive electric power consumption caused by such an occurrence. 
     As an alternative, the device  10  could be constructed without the heating element  84  (see FIG. 2) so that it only operates for rethermalizing of food products without the “conditioning” features, as described above. 
     In addition, the controller  26  (see FIG. 5) could be the type that has a timing feature such that after food has been rethermalized for a first period of time at, for example, 200° F., the controller  26  would switch to a holding temperature of, for example 170° F., for a second period of time. 
     In order to prevent damage to the heating element  94  or a possible fire hazard in the event the water level in the pan  43  falls below elements  94 , a thermocouple may be mounted on the upper surface of the element  94  and connected to high temperature cutout  95  (see FIG. 5) in the line feeding power to element  94 . 
     OPERATION 
     Referring now to the Figures, and in particular to FIG. 5 thereof, the operation of the device  10  will now be described. After the food products have been loaded onto trays  45  in chamber  38 , the temperature controller  26  is first set to the desired temperature to be maintained in chamber  38  to rethermalize or cook the food products, e.g. 160° F. to 210° F. Switch  24  is then moved to the “steam” position. Thermocouple  86  senses that the temperature in plenum  46  is below the set temperature of approximately, for example, 170° F. and causes temperature controller  26  to energize solid state relay  102 , which in turn energizes water heating elements  94 . The fans  52  are, preferably, connected to always be in operation as long as the main power to the device  10  is on. 
     As generated steam rises and enters chamber  38  from beneath pan cover  42 , it mixes with air in the chamber  38  and the mixture is drawn into inlets  44 , through plenum  46 , one outlets  48  and, preferably, over the top of the trays  45 . The steam generated mixes with the air in the chamber  38  and settles on the food products positioned on the trays where it condenses and gives up its thermal energy directly to the food products, thus, rethermalizing or cooking the food products. 
     Once the food products have been rethermalized (this process can be controlled by a timer—not shown), the switch  26  is moved to the “hold” position, thus ending steam generation. The temperature controller  26 , still operating in response to signals from thermocouple  86  in plenum  46 , causes solid state relay  98  to energize heating element  84 . The circulated hot air now causes evaporation of any remaining condensed steam in the chamber  38  as well as that on the food products, thus, in effect, “conditioning” the food products both as to appearance and feel. After the condensed steam has been evaporated, the rethermalized and conditioned food products are held at the temperature set on the controller  26  and are ready for serving or further processing. A transformer  100  may be used to provide a control voltage for the energization of solenoid valve  90 . 
     If dual units are employed in side-by-side relationship, it may be desirable, but not necessary, to provide a means to ensure that the water heater elements of both units are not on at the same time due to the great amount of electrical current that their combined usage could draw which may overload the electric supply circuit. This could, for example, consist of a normally closed relay that could be connected in the control circuit to ensure that both water heat elements could not be energized at the same time. The operation of the single or dual units could also be handled by a programmable device, rather than manually as shown. In addition, the door(s)  14 ,  16  could have a switch actuated by the door to shut off the fan when the door is opened.