Abstract:
A cooking device that is capable of rapidly cooking food products such as in toasting bread products or cooking pizza. The cooking device uses air impingement from above and/or below the food product. In some cases an infrared heater is additionally used to impart a desired color and crunchiness about a surface of the food product. In some cases, a boost in thermal energy is applied to the bottom of the food product vis-à-vis the top thereof. In some cases, the boost is due to an extra heater, which may be gas or electric. The device is particularly adapted for toasting bread products, cooking sandwich products (toasting the bread and heating the sandwich filler) and/or cooking pizza. Rapid cooking times are achieved by delivering more thermal energy to the top or bottom of the food product, depending on the type thereof, to give quality and speed. For example, a pizza can be cooked to have a crisp bottom without burning a cheese topping.

Description:
[0001]     This Application is a continuation-in-part of U.S. application, Ser. No. 09/632,417, filed on Aug. 4, 2000, which claims the benefit of U.S. Provisional Application No. 60/147,119, filed Aug. 4, 1999. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a cooking device and method, and, in particular, to a cooking device and method that is capable of rapidly cooking bread products, such as pizza, muffins, bagels and the like, such that the cooked bread products exhibit a crunchiness. The cooking device is also capable of heating other food products, such as, meats, vegetables and/or garnishes.  
         [0004]     2. Description of the Prior Art  
         [0005]     In the fast food industry, there is an on going need for faster cooking times for high quality cooking of bread products, such as pizza, muffins, bagels and the like. One type of prior art toaster used in the fast food industry is a contact toaster. An example of a contact toaster is shown in U.S. patent application Ser. No. 09/257,149, filed on Feb. 24, 1999, assigned to the same assignee as this application, now U.S. Pat. No. 5,983,785, granted Nov. 16, 1999. This patent discloses a contact toaster in which a bread product is conveyed by a conveyor belt in pressure contact with a surface of a heated stationary platen. Contact toasters generally toast only one surface of a bread product, such as the surface that is pressured against the heated platen. Such contact toasters require a relatively long time to achieve high quality toasting of a bread product, such as a bagel or muffin. Increasing the speed of the conveyor belt and increasing temperature of the platen may decrease toasting time, but could burn the food product or produce product low in temperature.  
         [0006]     An example of a non-contact toaster is the common household toaster that uses two electrical heater elements on either side of a slot that holds the bread product. Non-contact toasters of this type toast the opposed generally flat surfaces of a bread product. Such toasters generally include a rheostat control that allows regulation of the heater element temperature so that the temperature can be increased or decreased depending on the product being toasted. For example, the temperature may be increased to obtain better and faster toasting for a thick bread product, such as a muffin or a bagel. Frequently, the temperature for a desired toasting time is so hot that the bread product burns.  
         [0007]     Tunnel ovens that use air impingement heating are known for cooking a broad range of food products, including pizza. An example of a tunnel oven is shown in U.S. Pat. No. 4,873,107. This patent discloses a pair of oppositely rotating conveyor belts arranged to form a gap along a cooking path. Separate heated air manifolds are positioned with each conveyor belt for directed pressurized hot air on the upper and lower surfaces of a pizza item conveyed along the cooking path in the gap. A tunnel oven of this type is capable of cooking a food product at high temperature in a short time without burning. However, there is still a need for tunnel ovens with even faster cooking times. Conventional tunnel ovens do not have any capability to impart crunchiness to the cooked food product.  
         [0008]     The tunnel oven of U.S. Pat. No. 4,873,107 uses rectangularly cross-sectioned air jet apertures spaced from one another and from the food items so as to diffuse or plume prior to impingement on the food items. This provides a very even cooking pattern on the food items, thereby tending to prevent streaking on the surfaces thereof. The air jet arrangement allows air flow tuning without disturbing lateral imbalance across the air jet finger by adjustment of fan speed. This tuning, when used with vertical height adjustment of the upper plenum or air jet finger, accommodates food items of varying heights. That is, a manual vertical height adjustment is needed to accommodate food items of different heights.  
         [0009]     Thus, there is a need for a tunnel cooking device with even faster cooking times.  
         [0010]     There is also a need for a cooking device that can achieve high quality and fast toasting without burning and still provide the crunchiness of a toasted bread product.  
         [0011]     There is also a need for a tunnel cooking device with tuning capability to accommodate food items of varying heights without adjustment of the vertical height of the air jet fingers.  
         [0012]     The present invention provides a cooking device that meets the aforementioned need for faster toasting/cooking without burning and still providing crunchiness.  
         [0013]     The present invention provides a cooking device that heats food products and garnishes.  
       SUMMARY OF THE INVENTION  
       [0014]     A cooking device according to one embodiment of the present invention includes a housing having an inlet and an outlet. A toasting/cooking passageway is defined within the housing. A conveyor assembly moves food products inserted at the inlet along the toasting/cooking passageway. A heated air impingement assembly is arranged to deliver to a top surface of the food product hot air for heating the food product as well as for browning the top surface. An electrical heater is located below the passageway for delivering heat and infrared energy to a bottom surface of the food product. After toasting/cooking, the food products are delivered to the outlet.  
         [0015]     The hot air has a temperature that rapidly heats the food product to a toasting temperature in less than  60  seconds. The hot air provides a temperature environment that facilitates the infrared heat to produce a crunchiness effect of the bottom and side surfaces of the food product by the end of the rapid toasting time.  
         [0016]     The conveyor assembly has a conveyor belt loop that is spaced from the heated air impingement assembly by a gap. The passageway is located in the gap. Preferably, the air impingement assembly is adjustable by raising and lowering to vary its distance above the food product and thus vary the hot air velocity at the point of impingement.  
         [0017]     Preferably, the heated air impingement assembly and the electrical heater assembly can be structured to provide two or more toasting/cooking areas along the passageway so that different toasting/cooking temperatures and air velocities can be employed.  
         [0018]     In an alternate embodiment, the conveyor belt assembly has a pair of side by side lower belt loops that form side by side passageways with the air impingement assembly. This allows each passageway to be set for concurrent toasting/cooking of food products of different thickness or height. Alternatively, the passageway gaps can be the same so as to double the toasting/cooking capability of same thickness food products.  
         [0019]     In another alternate embodiment heated impingement air is also delivered from below the food product. The electrical heating assembly is disposed relative to columns of the heated impingement air so that there is no substantial interference between the infrared energy and the impingement air.  
         [0020]     In still another embodiment of the cooking device of the present invention, thermal energy is delivered to a top and a bottom of a food product such that the thermal energy delivered to one of the top and bottom is greater than that delivered to the other. The thermal energy is delivered at least in part by an air impingement assembly that provides upper columns of air to the top and lower columns of air to the bottom.  
         [0021]     The delivery mechanism comprises a means for heating the air that forms the upper and lower columns of air and a first heater disposed between the means for heating and the bottom of the food product. Preferably, the first heater is disposed between the air impingement assembly and the bottom. The first heater preferably includes a heater element that is disposed to weave about the lower columns of heated air without being directly within the first columns of air. The air impingement assembly preferably includes a surface with a plurality of apertures through which the lower columns of heated air are delivered, and the heater element does not overlie any of the apertures.  
         [0022]     In alternate embodiments, the first heater is disposed inside the air impingement assembly. The first heater element may be disposed to weave about jet apertures that form the lower columns of heated air so as to provide minimal interference therewith. Alternatively, the heater element may be disposed in the lower plenum nearer to a fan assembly.  
         [0023]     According to another embodiment of the present invention, the cooking device also comprises an oven cavity and a heating chamber. The air impingement assembly is at least partly disposed in the oven cavity, and the first heater is disposed in the heating chamber. The means for delivering preferably provides a circulating air stream that is heated by the heating means. The circulating air stream is divided into a first path that includes the lower columns of air and into a second path that includes the upper columns of air. The first heater boosts the temperature of the circulating air stream in the first path above the temperature of the circulating air stream in the second path.  
         [0024]     Preferably, the first heater is located either between the air impingement assembly and the bottom of the food product, inside the air impingement assembly or between the air impingement assembly and the heating means.  
         [0025]     The means for delivering also comprises a fan assembly disposed in the circulating air stream and the first heater is disposed in the fan assembly. The means for delivering also preferably comprises a divider that divides the circulating air stream into the first and second paths. The first heater is disposed relative to the divider to boost the temperature of the circulating air stream in the first path. The first heater is disposed either in the first path or in the divider, in which case the divider includes a heat transfer communication, such as one or more louvers, with the first path. The first heater may be either a gas heater or an electrical heater.  
         [0026]     In the various embodiments, the cooking device may alternatively or additionally comprise means for cooling the air that forms the upper columns of air. Thus, delivery means comprises means for altering the temperature of the lower or upper columns of air. According to one aspect of this embodiment, the means for altering either boosts the temperature of the lower columns of air, cools the temperature of the upper columns of air or both.  
         [0027]     The method of the present invention cooks a food product by providing a stream of heated air that is applied as columns of heated air to the top of the food product. Also, heat is provided to the bottom of the food product. The thermal energy applied to the top and bottom of the food product is controlled so that the thermal energy applied to the bottom is greater than that applied to the top.  
         [0028]     Preferably, infrared energy is also applied to the bottom of the food product. Alternatively, or additionally, a portion of the stream of heated air is cooled for use in forming the upper columns of air. Preferably, the heated air stream is controlled so that the lower columns of air are warmer than the upper columns of air.  
         [0029]     A further embodiment of the cooking device of the present invention comprises a means that includes a plurality of jet apertures for providing columns of impingement air. The columns of impingement air form a blanket of impingement air for cooking food products of different heights without adjustment of the distance between the jet apertures and the food products. The cooking device is capable of cooking the food products of different heights in substantially identical cooking times.  
         [0030]     Preferably, the jet apertures have a cross-section that is shaped to provide different BTU delivery rates for cooking the food products of different heights. The cross-section preferably has at least one elongated member with one or more enlarged portions located at an end, a center or a combination thereof. The cross section is preferably selected from the group consisting of: dog bone, jack and starburst.  
         [0031]     In an alternate embodiment, the columns of impingement air are directed toward the food products from a direction above, below or above and below the food products. The impingement columns preferably include upper columns and lower columns of impingement air that are directed toward the food products from above and below. A conveyor is preferably provided to move the food products through the blanket of impingement air.  
         [0032]     In an alternate embodiment, a control means is provided to control the thermal energy applied to a top and a bottom of the food products with a capability of applying a balanced or unbalanced thermal energy thereto. Preferably, a greater thermal energy is applied to either the top or bottom of the food products than to the other.  
         [0033]     In another alternate embodiment, one or more radiant heaters are disposed to provide heat to the food products. One of the radiant heaters is disposed above or below a top or a bottom of the food products and the columns of impingement air are directed to the other thereof. Alternatively, first and second ones of the radiant heaters are disposed above or below the top and bottom sides of the food products. Preferably, a control means is provided to selectively control the on/off states thereof by selecting a state from the group consisting of: both on, both off and one on and the other off.  
         [0034]     In a further embodiment of the method of the present invention, food products of different heights are cooked by providing columns of impingement air via jet apertures that form a blanket of impingement air. The blanket of impingement air cooks the food products of different heights without adjustment of the distance between the jet apertures and the food products. The method is capable of cooking the food products of different heights in substantially identical cooking times.  
         [0035]     Preferably, the jet apertures have a cross-section that is shaped to provide different BTU delivery rates for cooking the food products of different heights. The cross-section preferably has at least one elongated member with one or more enlarged portions located at an end, a center or a combination thereof. The cross section is preferably selected from the group consisting of: dog bone, jack and starburst.  
         [0036]     The columns of impingement air are directed toward the food products from a direction above, below or above and below the food products.  
         [0037]     In another embodiment of the method, the thermal energy is controllably applied to a top and a bottom of the food products with a capability of applying a balanced or unbalanced thermal energy thereto. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]     Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and:  
         [0039]      FIG. 1  is a perspective view from the food inlet side of a high speed cooking device according to the present invention;  
         [0040]      FIG. 2  is a perspective view from the food outlet side of the  FIG. 1  cooking device;  
         [0041]      FIG. 3  is a skeletal view in elevation of the conveyor belt assembly and heating elements of the  FIG. 1  cooking device;  
         [0042]      FIG. 4  is a partial view of the conveyor assembly and heating elements for the  FIG. 1  cooking device;  
         [0043]      FIG. 5  is an enlarged fragmentary perspective view of one of the jet curtain plates through which heated impingement air flows against food items traversing the interior of the  FIG. 1  cooking device;  
         [0044]      FIG. 6  is a perspective view of an alternate embodiment of the jet curtain plate;  
         [0045]      FIG. 7  is a plan view of the jet curtain plate of  FIG. 6 ;  
         [0046]      FIG. 8  is a plan view of another alternate embodiment of the jet curtain plate;  
         [0047]      FIG. 9  is a fragmentary cross-sectional view of the fan of  FIG. 4 ;  
         [0048]      FIG. 10  is a perspective view of an alternate embodiment that has twin conveyor belts;  
         [0049]      FIG. 11  is a front view with front cover removed of an alternate embodiment of the high speed cooking device of the present invention;  
         [0050]      FIG. 12  is a view taken along line  12 - 12  of  FIG. 11 ;  
         [0051]      FIG. 13  is a front view with front cover removed of another alternate embodiment of the high speed cooking device of the present invention;  
         [0052]      FIG. 14  is a top view of another alternate embodiment of the high speed cooking device with top cover removed of the present invention;  
         [0053]      FIG. 15  is a view taken along line  15  of  FIG. 14 ;  
         [0054]      FIG. 16  is a view taken along line  16  of  FIG. 14 ;  
         [0055]      FIG. 17  is a view with side wall removed of another alternate embodiment of the high speed cooking device of the present invention;  
         [0056]      FIG. 18  is a diagram depicting BTU tuning range for some of the embodiments of the cooking device of the present invention;  
         [0057]      FIG. 19  is a cross-section view of a circular air jet aperture;  
         [0058]      FIG. 20  is a heat trace depicting contours of enthalpy of the circular air jet aperture of  FIG. 19 ;  
         [0059]      FIG. 21  is a cross-section view of a rectangular air jet aperture;  
         [0060]      FIG. 22  is a heat trace depicting contours of enthalpy of the rectangular air jet aperture of  FIG. 21 ;  
         [0061]      FIG. 23  is a cross-section view of a cross air jet aperture;  
         [0062]      FIG. 24  is a heat trace depicting contours of enthalpy of the cross air jet aperture of  FIG. 23 ;  
         [0063]      FIG. 25  is a cross-section view of a dog bone air jet aperture;  
         [0064]      FIG. 26  is a heat trace depicting contours of enthalpy of the dog bone air jet aperture of  FIG. 25 ;  
         [0065]      FIG. 27  is a cross-section view of a jack air jet aperture;  
         [0066]      FIG. 28  is a heat trace depicting contours of enthalpy of the jack air jet aperture of  FIG. 27 ;  
         [0067]      FIG. 29  is a cross-section view of a starburst air jet aperture;  
         [0068]      FIG. 30  is a heat trace depicting contours of enthalpy of the starburst air jet aperture of  FIG. 29 ; and  
         [0069]      FIG. 31  is a diagram of alternate embodiment of the cooking device of the present invention. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0070]     With reference to  FIGS. 1 through 3 , there is provided a high speed cooking device  11  according to a preferred embodiment of the present invention. High speed cooking device  11  includes a housing  14 , a conveyor assembly  13 , an air impingement assembly  17  and a heater assembly  19 , such as an electrical heater assembly or an air impingement assembly. By way of example, heater assembly  19  is shown as an electrical heater assembly.  
         [0071]     Housing  14  includes an inlet  26 , an outlet  28  and an outlet  29 . A food product  12  enters cooking device  11  via inlet  26  and is conveyed by conveyor assembly  13  to either outlet  28  or outlet  29  along a toasting/cooking passageway  30 . Conveyor assembly  13  includes a conveyor belt loop  136  that rotates in the direction illustrated by the arrow in  FIG. 3  to convey food products  12  along toasting/cooking passageway  30  from right to left. Food products  12  are deposited by gravity at the left end of conveyor belt loop  136  onto either a pass through chute  40  that leads to outlet  28  or onto a return chute  42  that leads to outlet  29 . Pass through chute  40  is used when it is desired to have food products  12  exit via outlet  28 . When it is desired to exit food products via outlet  29 , pass through chute  40  is either removed or moved to a position that allows food products  12  to enter return chute  41 .  
         [0072]     Toasting/cooking passageway  30  is divided into a first toasting/cooking area  31 A and a second toasting/cooking area  31 B. Air impingement assembly  17  is located above conveyor belt loop  136  and has a first air impingement heater  17 A and a second air impingement heater  17 B. Conveyor belt loop  136  and air impingement assembly  17  are separated by a gap ‘g’. Toasting/cooking passageway  30  is located in gap ‘g’. Electrical heater assembly  19  has a first electrical heater element  19 A and a second electrical heater element  19 B located below belt loop  136  in toasting/cooking areas  31 A and  31 B.  
         [0073]     An important feature of the present invention is the use of air impingement heating to rapidly heat food products  12 , such as bread, to a toasted temperature that corresponds to a desired temperature specified by the user of the cooking device  11 , while browning an upper surface of food products  12 . For toasting bread products, the temperature of the impingement air is in the range of about 500° F. to 700° F. Most preferably, the temperature of the impingement air is about 600° F. to achieve a toasting time of less than 60 seconds.  
         [0074]     To give a crunchiness to food product  12 , electrical heaters  19 A and  19 B are operated at a temperature that produces infrared radiation to be incident on the lower surface and side surface of food product  12 . It has been observed that for the environment created by the above noted air impingement temperatures, crunchiness is achieved by the end of the toasting time with infrared heating temperatures in the range of about 1,000° F. to 1,800° F.  
         [0075]     The division of toasting/cooking passageway  30  into separate toasting/cooking areas allows the flexibility of using the same or different toasting/cooking temperatures in toasting/cooking areas  31 A and  31 B. For example, if food product  12  is frozen or cooled, the temperature of toasting/cooking area  31 A can be set high to rapidly thaw and bring food product  12  to a warm but not toasted temperature during its traverse of zone  31 A. The temperature of zone  31 B can be set somewhat lower to finish heating food product  12 . On the other hand, some applications may use substantially equal temperatures in zones  31 A and  31 B.  
         [0076]     Referring to  FIG. 4 , housing  14  also includes an internal framing structure  16  of which only a portion is shown that corresponds to toasting/cooking area  31 B. Internal framing structure  16  includes upper and lower horizontally extending rectangular frame portions  18  and  20  that are vertically spaced apart by vertically extending frame elements  22 ,  24 ,  30  and  32 . A vertically disposed rectangular frame portion  36  is located within and secured at its corners to upper and lower rectangular frame portions  18  and  20 . An intermediate vertically extending frame element  38  is also secured to rectangular frame portion  36 . Internal framing structure is secured to the exterior walls of housing  14  in any suitable manner.  
         [0077]     Air impingement heater  17 B includes a supply duct assembly or plenum  70  that is positioned slightly above outlet  28 . Supply duct assembly  70  includes an inlet or base portion  78  that is positioned generally between the housing vertical frame portion  36  and a vertical frame portion  35  of the rectangular frame formed by frame portions  18  and  20 . Base portion  78  extends parallel to the toasting/cooking passageway. Supply duct assembly  70  also includes three supply ducts or jet fingers  80  joined to base portion  78  for ducting air supplied via base portion  78 . Base portion  78  and jet fingers  80  have generally rectangular cross-sections.  
         [0078]     Referring to  FIG. 5 , each of the jet fingers  80  has a bottom surface  82  that faces passageway  28 . Each of the bottom surfaces  82  has, along its length, a corrugated cross-section defined by alternating series of generally V-shaped ridges  84  and  86  that extend parallel to the lengths of jet fingers  80 . Ridges  84  project downwardly toward passageway  28 . A plurality of generally rectangular shaped air slot openings  88  are formed in the apex of each ridge  84 .  
         [0079]     Referring to  FIGS. 6 and 7 , each of the jet fingers  80  in an alternate embodiment has a generally flat bottom surface  182  with a plurality of side wall tabs  183  for attachment to a jet finger  80 . A plurality of generally circular apertures  188  is formed in bottom surface  182  to direct air  156  as impingement air toward food products  12  (not shown in  FIGS. 6 and 7 ). Apertures  188  are arranged in an array that includes diagonal rows of apertures  188 .  
         [0080]     Referring to  FIG. 8 , bottom surface  182  has formed therein a plurality of multiple point shaped apertures  198  that have three or more points according to another alternate embodiment of the invention. Preferably, apertures  198  have four points or a cruciform shape as shown in  FIG. 8 . Preferably, apertures  198  are formed, as by a punch operation, such that the cruciform points extend generally downward from bottom surface  182  toward food products  12 . This configuration has been found to give improved air impingement flow.  
         [0081]     Duct assembly  70  is supported within housing  14  for selective vertical movement relative thereto by a pair of rack members  92 . Rack members  92  are secured to the outer jet finger  80   a  and a pair of cooperating pinion gears  94  that are operatively mounted on vertical frame elements  22 ,  30 ,  36  and  38  by suitable support brackets  96 . Pinion gears  94  for each jet finger  80   a  are operatively connected by elongated drive shafts  98  that extend parallel to jet fingers  80   a . Drive shafts  98  are rotated to selectively raise or lower duct assembly  70  to thereby selectively change the gap ‘g’. Alternatively, conveyor belt assembly  13  can be raised or lowered to change the gap ‘g’.  
         [0082]     Referring to  FIGS. 4 and 9 , heated cooking air from within housing  14  is supplied to plenum duct assembly  70  by a fan  106  mounted within housing  14 . Fan  106  has an opening  114  that faces the interior of housing  14 , an electrical heating coil  116 , a drive shaft  118  extending outwardly through an adjacent wall  119  of housing  14  and a motor  120 , suitably secured to wall  119 . An outlet duct  126  extends vertically from fan  106  and is slidably and telescopically received in a supply duct section  130  that in turn is secured to base portion duct  78  by mounting bracket  132 . This construction allows duct assembly  70  to freely move vertically when drive shafts  98  are rotated. Electrical heating coil  116  serves to heat air  156 . Heating coil  116  may be located downstream of fan opening  114  as shown in  FIG. 9  or in any other position that heats air  156 .  
         [0083]     Conveyor belt loop  136  includes a pair of looped roller chains  138  and  140  that extend transversely to jet fingers  80  and  80   a.  Outer end portions of conveyor belt loop  136  are rotatably supported at corner portions thereof by suitable sprockets  142  that operatively engage roller chains  138  and  140 . Sprockets  142  are secured to housing  14  by mounting brackets  144 .  
         [0084]     Laterally opposed sprockets  142  are interconnected by suitable connecting rods  146 . At least one connecting rod  146  is rearwardly extended to define a drive shaft  146   a.  Drive shaft  146   a  may suitably be driven (by a conventional drive, not shown) to rotate belt loop  136  in the direction indicated by the arrow to horizontally convey food product  12  along passageway  30  ( FIG. 3 ).  
         [0085]     Conveyor belt loop  136  includes a series of individual transverse sections  150  that are operatively secured between roller chains  138  and  140  for movement therewith.  
         [0086]     Referring to  FIGS. 3 through 9 , supply fan  106  draws air  156  ( FIG. 9 ) from within housing  14  into opening  114  across heating element  116 . Heated air entering fan  106  is forced upwardly into base duct portion  78  and through jet fingers  80  and  80   a  and then exits via air slots  88  downwardly toward passageway  30 . The rectangularly cross-sectioned jets of hot air impinge upon conveyor belt loop  136  and upon food products  12  in passageway  30  to thereby heat food product  12  and brown its upper surface. After impinging on food product  12 , the air continues in a recirculating path to fan opening  114  via heating element  116 .  
         [0087]     Electrical heater  19 B is shown in  FIG. 4  as an electrical heating coil that has a serpentine coil pattern, although any shape or type of infrared heating element capable of imparting the desired crunchiness to the food product is also contemplated by the present invention. Electrical heaters  19 A and  19 B may be separate coils with separate temperature regulators or may be a combined coil that extends across both toasting/cooking areas  31 A and  31 B with one temperature regulator. As previously mentioned, electrical heaters  19 A and  19 B are heated to a temperature that produces infrared radiation. The infrared radiation acts in the heated environment produced by hot air impingement assembly  17  to toast the bottom and side surfaces of food product  12  to the desired crunchiness.  
         [0088]     Referring to  FIG. 10 , an alternate embodiment of the present invention has a pair of conveyor belt loops  134 A and  134 B. Each lower belt loop  134 A and  134 B is situated beneath upper belt loop  136  to form separate toasting/cooking passageways for the conveyance of food products  12 . A single heater coil  199  is used for both lower belt loops  134 A and  134 B. The gap ‘g’ of each passageway may be separately adjusted so that food products of the same or different thickness can be concurrently cooked or toasted. For example, both passageways can be set to the same gap so as to double the number of food items of the same thickness that can be cooked or toasted. Alternatively, one passageway can be set to a gap ‘g’ that accommodates the heel of a muffin and the other to a gap ‘g’ that accommodates the crown of a muffin. Additionally, air impingement assembly  17  can be extended to cover both passageways in each toasting/cooking area. Alternatively, separate air impingement assemblies can be used for each passageway and toasting/cooking area.  
         [0089]     The distance between electrical heating assembly  19  and conveyor belt loop  136  may be adjustable to vary the intensity of the heat and infrared energy incident on the food products  12 . In some embodiments, heating assembly  19  may be located within conveyor belt loop  136 .  
         [0090]     In still other embodiments of the present invention, air impingement assembly  17  can be located in other positions that can deliver impingement air to food products  12 . For example, air impingement assembly  17  can be located anywhere in housing  14  with an impingement air delivery ductwork that provides impingement air to food products  12 .  
         [0091]     In some embodiments, conveyor belt assembly  13  may be vertically adjustable to vary the gap ‘g’.  
         [0092]     Referring to  FIGS. 11 and 12 , an alternate embodiment of the present invention is shown as a high speed cooking device  200 . High speed cooking device  200  includes a housing  202 , a conveyor assembly  204 , an air impingement assembly  206  and an electrical heater assembly  208 . Housing  202  defines a toasting/cooking passageway  203  located above conveyor assembly  204 . Conveyor assembly  204  rotates to convey food products (not shown) on one or more conveyor belts (not shown) along toasting/cooking path  203 . Air impingement assembly  206  includes an upper air plenum  220 , a lower air plenum  226 , a fan  214 , air heaters  216  and an air plenum  218 . Upper air plenum  220  has a distribution ramp  222 , a bottom surface  223  and a plurality of apertures  224  formed in bottom surface  223 . Lower air plenum  226  that has a distribution ramp  228 , a top surface  229  and a plurality of apertures  230  formed in top surface  229 .  
         [0093]     When fan  214  rotates, an airflow is generated in air plenum  218  that is heated by air heaters  216 . The heated air flows from air plenum  218  via a slot  232  into upper air plenum  220  and a slot  234  into lower air plenum  226  as indicated by arrows  236  and  238 , respectively. The heated airflow in upper air plenum  218  is deflected by ramp  222  to flow downwardly through apertures  224  as indicated by arrows  240  toward the top of conveyor assembly  204  and into toasting/cooking passageway  203 . The heated airflow in lower air plenum  226  is deflected upwardly by ramp  228  through apertures  230  as indicated by arrows  242  toward the bottom of and through conveyor assembly  204  into toasting/cooking passageway  203 .  
         [0094]     Upper air plenum  218  may suitably be a single jet finger that has a length substantially along toasting/cooking passageway  203 . Alternatively, upper air plenum  218  may be a plurality of jet fingers. Preferably, apertures  224  have a cruciform shape.  
         [0095]     Referring to  FIG. 12 , lower air plenum  226  has a jet finger  244  located at one end of toasting/cooking passageway  203  and another jet finger  246  located at the other end of toasting/cooking passageway  203 . Apertures  230  are disposed in the tops of jet fingers  244  and  246  and preferably have a cruciform shape.  
         [0096]     Electrical heater  208  includes a heater element  248  disposed above jet finger  244 , a heater element  250  disposed above jet finger  246  and a heater element  252  disposed above a space  254  located between jet fingers  244  and  246 . Heater elements  248 ,  250  and  252  are infrared heaters that are each formed in a serpentine pattern. The serpentine patterns of heater elements  248  and  250  are arranged to wind about apertures  230 , but to avoid overlying apertures  230 . This arrangement permits infrared energy emitted by heater elements  248  and  250  and convection energy of air impingement columns flowing upwardly from apertures  230  to have minimal interference with one another. That is, the heater elements do not impede the air flow and the air flow does not reduce the infrared emissions by cooling the heating elements.  
         [0097]     Cooking device  200  provides a cooking environment that is extremely hot from above and below toasting/cooking passageway  203 , while gaining the benefit of added crunchiness afforded by infrared heating assembly  208 . By using three different heater elements  248 ,  250  and  252  and spaced lower jet fingers  244  and  246 , three distinct cooking zones are defined that can be controlled for heating temperatures and food product resident times within each zone. This affords great flexibility in the toasting/cooking process.  
         [0098]     Referring to  FIG. 13 , an alternate embodiment of the invention is shown as a cooking device  260 . Cooking device  260  is similar to cooking device  200  of  FIGS. 11 and 12  and like components thereof bear like reference characters. Cooking device  260  differs from cooking device  200  in that electrical heater  208  is disposed within lower air plenum  226 . Thus, heater element  250  is disposed in jet finger  246  as shown in  FIG. 13 . Though not shown in  FIG. 13 , heater element  248  is disposed in jet finger  244  (see  FIG. 12 ). It will be appreciated by those of ordinary skill in the art that cooking device  200  and cooking device  260  may or may not need to use heater element  252  (see  FIG. 12 ) based on the spacing between jet fingers  244  and  246 . Like cooking devices  11  and  200 , cooking device  260  provides heat to the top and the bottom of a food product such that the heat applied to the bottom is greater in thermal energy (hotter) so as to cook the food products more rapidly. Heater elements  208 ,  248  (not shown in  FIG. 13 ) and  250  may be any suitable heating element that boosts the temperature of the lower impingement air relative to the upper impingement air. By way of example, heater elements  248  and  250  may be infrared heater elements.  
         [0099]     Referring to  FIGS. 14-16 , an alternate embodiment of the present invention is shown as a cooking device  300 . Cooking device  300  includes an oven cavity  302  and a heating chamber  304  disposed in a housing  306 . A conveyor assembly  308  is disposed in oven cavity  302 . An air impingement assembly  312  is disposed partly in oven cavity  302  and partly in heating chamber  304 . A cooking passageway  314  is located above conveyor assembly  308 . Conveyor assembly  308  rotates to convey food products (not shown) on one or more conveyor belts (not shown) along cooking passageway  314 .  
         [0100]     Air impingement assembly  310  includes a pair of upper air plenums  316  and  318 , a pair of lower air plenums  320  and  322 , a fan assembly  324 , an air heater assembly  326  and an air plenum  318 . Upper air plenums  316  and  318  are substantially identical. For example, upper air plenum  316  has a distribution ramp  322 , a bottom surface  323  and a plurality of apertures  324  formed in bottom surface  323 . Although only three apertures  332  are shown in  FIG. 16 , it will be appreciated that there are many more apertures  332  distributed across most of bottom surface  330 .  
         [0101]     Lower air plenums  320  and  322  are substantially identical. For example, lower air plenum  320  has a distribution ramp  334 , a top surface  336  and a plurality of apertures  338  formed in top surface  336 . Although only three apertures  338  are shown in  FIG. 16 , it will be appreciated that there are many more apertures  338  distributed across most of top surface  336 . Alternatively, a single upper air plenum extending along the length of passageway  314  could be used in place of upper air plenums  316  and  318  and/or a single a single lower air plenum could be used in place of lower air plenums  320  and  322 .  
         [0102]     Fan assembly  324  and air heater assembly  326  are disposed within heating chamber  304 . Fan assembly  324  includes a pair of centrifugal fans  340  and  342  mounted on an axis  344  and disposed in separate fan housings  346  and  348 . Axis  344  is parallel to the direction of travel of the food product along conveyor assembly  308 . Fan housing  346  is in fluid communication with upper plenum  316  and lower plenum  320 . Fan housing  348  is in fluid communication with upper plenum  318  and lower plenum  322 . An air stream divider  345  penetrates into fan housing  346  to divide a circulating air stream developed by fans  340  and  342 .  
         [0103]     Air heater assembly  326  may include any suitable heating element or elements, such as gas or electric elements, and is positioned at a suitable location in heating chamber  304  to heat the circulating air stream.  
         [0104]     When fans  340  and  342  rotate, a heated air stream is developed in fan housings  346  and  348 . The heated air stream is divided by divider  345  into upper air plenums  316  and  318  and into lower air plenums  320  and  322 . In  FIG. 16 , this air stream is indicated by arrows  350  and  352  for upper plenum  316  and lower plenum  320 , respectively. The heated air stream in upper air plenum  316  is deflected by distribution ramp  328  to flow downwardly through apertures  330  as indicated by arrows  354  toward the top of conveyor assembly  308  and into toasting/cooking passageway  314 . The heated air stream in lower air plenum  320  is deflected upwardly by ramp  334  through apertures  338  as indicated by arrows  356  toward the bottom of and through conveyor assembly  308  into toasting/cooking passageway  314 .  
         [0105]     Housing  306  includes a wall  358  that separates oven cavity  302  from heating chamber  304 . A plurality of air return ducts  360 ,  362 ,  364 ,  366  and  368  are connected with wall  358  to provide fluid communication between passageway  314  and fan housing  346 . Air return ducts  360 ,  362  and  364  are disposed above conveyor assembly  308  within passageway  314  and air return ducts  366  and  368  are disposed below conveyor assembly  308  within passageway  314 . Each of the air return ducts  360 ,  362 ,  364 ,  366  and  368  includes a plurality of openings for the circulating air stream to return to fan housing  346 . For example, air return duct  362  includes openings  370  disposed on a bottom surface thereof that faces conveyor assembly  308 . After impingement upon the food product (not shown in  FIGS. 14-15 ), the heated air flow returns to heating chamber  304  via air return ducts  360 ,  362 ,  364 ,  366  and  368  under the suction action of fans  340  and  342 .  
         [0106]     In alternate embodiments, upper air plenums  316  and  318  and/or lower air plenum  320  and  322  may suitably be a single jet finger that has a length substantially along toasting/cooking passageway  314 . Alternatively, any of upper air plenums  316  or  318  or lower air plenums  320  or  322  may be a plurality of jet fingers. Apertures  332  and/or apertures  338  may have any suitable shape depending on the type of cooking to be done.  
         [0107]     Electrical heater assembly  312  includes at least one heater element  372  disposed in each lower manifold. For example, two heater elements  372  are so disposed below divider  345  in  FIG. 16 . Heater elements  372 , may be any suitable electrical heater that boosts the temperature of the air stream to lower plenums  320  and  322  relative to the temperature of the air stream to the upper plenums  320  and  322 . For example, electrical heaters  372  may be infrared or other electrical heaters. Placement of electrical heaters  372  below divider  345  augments the heat or thermal energy of the air stream so that the thermal energy delivered to the food product via lower air plenums  320  and  322  is greater than that delivered by upper air plenums  316  and  318 . This decreases the cooking time, i.e., cooking device  300 , like cooking devices  11 ,  200  and  260 , have faster cooking times than conventional air impingement ovens. Also, heater elements  372  impart crunchiness to bread products.  
         [0108]     Referring to  FIG. 17 , another alternate embodiment of the present invention is shown as a cooking device  380 . Cooking device  380  is substantially similar to cooking device  300 , except that cooking device  380  does not have electrical heater assembly  312 . Instead, a gas burner  382  is disposed in divider  345  in a manner to direct more thermal heat toward lower air plenums  320  and  322  than to upper air plenums  316  and  318 . To this end, a plurality of apertures or louvers  384  are disposed in the bottom side of divider  345  so as to allow the combustion flame to heat the air stream that is being diverted to lower plenums  320  and  322 .  
         [0109]     In an alternate embodiment, gas burner  382  can be relocated to heat the air stream in the lower part of fan housing  346  and divider  345  repositioned (for example, rotating the point counterclockwise in  FIG. 16 ) to assure that this boosted heated air be diverted below the divider to lower air plenums  320  and  322 .  
         [0110]     In an alternate embodiment of cooking device  300  or  360 , the air in the part of fan housing  346  above divider  345  can be cooled relative to the air stream to lower air plenums  320  and  322 . In this embodiment, for example, the upper air stream can be cooled by adding cooler air into the area of fan housing above divider  345 . This can augment or replace the electrical heater assembly  312  of cooking device  300  or the gas burner  382  of cooking device  380 . The cooler air, for example, can be dilution air that is diverted from passageway  314 .  
         [0111]     Referring to  FIG. 18 , a thick food product  402  and a thin food product  404  have different heights. Thick food product  402  and thin food product  404  may be any food products that have different heights, such as bakery products, pizzas, meat, poultry or fish products, vegetables, and the like. Thick food product  402  and thin food product  404  are shown, by way of example, as a thick pizza  402  and a thin pizza  404 . The difference between the two heights is represented as BTU Δ. The top of thick pizza  402  is shown as located a distance L from an air jet  406 . The top of thin pizza  404  is below the top of thick pizza  402  by the distance BTU Δ.  
         [0112]     When the distance L has been set in traditional ovens, thick pizza  402  and thin pizza  404  could be cooked only by making a change in the distance L, i.e., a vertical change in the position of the upper jet or conveyor. This resulted in a change in temperature that affected cooking times, thereby making a changeover time consuming and complicated.  
         [0113]     It has been discovered that an array of jet apertures having particular cross-section shapes and spaced to provide overlapping jets can diffuse or plume to form a blanket of heated air at the food surface of the higher food product (thick pizza  402 ). The blanket permits thick pizza  402  and thin pizza  404  to be cooked when placed adjacent one another on the conveyor without adjusting the distance L.  
         [0114]     The particular cross-sectional shapes provide a range of BTU delivery rates over the distance BTU Δ for a predetermined value of L. This range of BTU delivery rates assures that a higher BTU rate will completely cook thick pizza  402  without blowing toppings and that a lower BTU rate will cook thin pizza  404  without burning. The higher and lower BTU delivery rates will still deliver heated air at about the same temperature to both thick pizza  402  and thin pizza  404 . The BTU delivery rates within the range can be adjusted for product height variations by adjustment of air pressure (e.g., mere adjustment of fan speed) without any adjustment to the distance L. This tuning allows tuning to delivery rates in the range that will cook thick pizza  402  completely and thin pizza  404  without burning.  
         [0115]     Preferably, the cross-sectional shape includes at least one web like member that has at least one enlarged area along the length thereof. More preferably, the enlarged area is located at an end of the web like member. Even more preferably, there are enlarged portions at each end of the web like member, so as to form a dog bone shape. The enlarged portions serve to reduce velocity gradients along the length of the web like member.  
         [0116]     Other preferred cross-sectional shapes include a plurality of web like members with enlarged portions at each end that intersect with one another to form a starburst shape. For the case where the number of web members is two, the shape is a jack. More preferably, the starburst and jack also include an additional enlarged portion at the midpoints of the web like members, i.e., at the crossing point.  
         [0117]     This discovery will be described with reference to  FIGS. 19-30  for thick pizza  402  and thin pizza  404  for an example in which L=3.937 inches and BTU Δ=0.625 inch.  
         [0118]     Referring to  FIGS. 19-24 , three jet apertures  410 ,  412  and  414  are depicted as having cross-sectional shapes that are circular, rectangular and cross, respectively. With reference to  FIGS. 19 and 20 , a heat trace for jet aperture  410  shows a very narrow range of BTU delivery rates to the tops of both thick pizza  402  and thin pizza  404  of about 24 to 25.39 BTU/lbm. These delivery rates are so close together that tuning requires a combination of changing fan speed, jet fingers, finger aperture plates, adding air straighteners in the fingers or block off plates to increase static pressure or modifying return air paths. For example, vertical adjustment of the distance L would be needed to cook thick pizza  402  and thin pizza  404 .  
         [0119]     Similarly,  FIG. 22  shows a very narrow range of about 35 to 36 BTU/lbm for rectangularly shaped jet aperture  412  of  FIG. 23 . Also,  FIG. 24  shows a very narrow range of about 23 to about 25 BTU/lbm for cross shaped jet aperture  412 . Jet apertures  410 , 412  and  414  each have a noticeable drop in air velocity from the center toward circumference or the ends thereof. This means that as the food product travels across the aperture, the food product would receive unequal treatment of heat (i.e., BTU delivery rate). Also, the jet columns of air for jet apertures  412  and  414  are rather narrow and difficult to use to form a blanket of heated air at the top of the higher food product (i.e., thick pizza  402 ).  
         [0120]     Referring to  FIG. 25 , a dog bone shaped jet aperture  416  includes a web like member  418  that has enlarged portions  420  and  422  disposed at either end thereof. The enlarged portions may have any suitable shape, including, but not limited to, circular, square, rectangle and polygonal. Enlarged portions  420  and  422  serve to reduce the velocity change along the length of web like member  418 . This helps to assure a more uniform air velocity in the jet column of heated air formed by the dog bone jet aperture  416 .  
         [0121]     Referring to  FIG. 26 , the heat trace for dog bone jet aperture  416  shows a rather constant temperature of the air jet column over a wide range of BTU delivery rates throughout the BTU Δ distance. Thus, the BTU delivery rate range is about 26 to about 36 BTU/lbm. This assures a large enough range to permit tuning of the delivery rate by simple adjustment of the air speed or fan speed so as to cook both thick pizza  402  and thin pizza  404  without adjustment of the distance L. That is, the BTU delivery rate can be tuned to a pair of values in the wide range that will cook both thick pizza  402  and thin pizza  404  without adjusting the distance L.  
         [0122]     Referring to  FIG. 27 , a jack shaped jet aperture  424  includes a pair of web like members  416  arranged in crossing relationship that share another enlarged portion  426  located at the crossing point or the mid points of the two web like members. Similar to enlarged portions  420  and  422 ,enlarged portion  426  may have any suitable shape including, but not limited to, circular, square, rectangle and polygonal. Enlarged portions  420 ,  422  and  426  serve to reduce the velocity change along the length of web like member  418 . This helps to assure a more uniform air velocity in the jet column of heated air formed by the jack jet aperture  416 .  
         [0123]     Referring to  FIG. 28 , the heat trace for jack shaped jet aperture  424  shows a rather constant temperature of the air jet column over a wide range of BTU delivery rates throughout the BTU Δ distance. Thus, the BTU delivery rate range is about 25 to about 33 BTU/lbm. This assures a large enough range to permit tuning of the delivery rate by simple adjustment of the air speed or fan speed so as to cook both thick pizza  402  and thin pizza  404  without adjustment of the distance L. That is, the BTU delivery rate can be tuned to a pair of values in the wide range that will cook both thick pizza  402  and thin pizza  404  without adjusting the distance L.  
         [0124]     Referring to  FIG. 29 , a starburst shaped jet aperture  430  is similar to jack shaped aperture  424 , but includes more than a pair of dog bone shaped apertures  416  that are arranged in a crossing relationship with a central enlarged portion  426 . This helps to assure a more uniform air velocity in the jet column of heated air formed by the star burst jet aperture  416 .  
         [0125]     Referring to  FIG. 30 , the heat trace for star burst jet aperture  416  shows a rather constant temperature of the air jet column over a wide range of BTU delivery rates throughout the BTU Δ distance. Thus, the BTU delivery rate range is about 46 to about 62 BTU/lbm. This assures a large enough range to permit tuning of the delivery rate by simple adjustment of the air speed or fan speed so as to cook both thick pizza  402  and thin pizza  404  without adjustment of the distance L. That is, the BTU delivery rate can be tuned to a pair of values in the wide range that will cook both thick pizza  402  and thin pizza  404  without adjusting the distance L with the same cooking time or residence in the oven.  
         [0126]     Also, the heat traces of  FIGS. 26, 28  and  30  show that the jet columns of heated air are wide enough to allow flexibility to design a system that will form a blanket of heated air above thick pizza  402 .  
         [0127]     Referring to  FIG. 31 , a cooking device  440  includes a conveyor  442 , an upper impingement assembly  444  disposed above conveyor  442  and a lower impingement assembly  446  disposed below conveyor  442 . Conveyor  442  is operable to convey food products (not shown) along the passageway between upper impingement assembly  442  and lower impingement assembly  446 . Impingement assemblies  444  and  446  are operable to provide impingement air for cooking the food products being conveyed by conveyor  442 . Impingement assemblies  444  and  448  may be implemented in any of the cooking devices  11  ( FIGS. 1-9 ),  200  ( FIGS. 11 and 12 ),  260  ( FIG. 13 ),  300  ( FIGS. 14-17 ) and  380  ( FIG. 17 ) as well as in any impingement oven for cooking of food products.  
         [0128]     An electric heater  448  is disposed above conveyor  442  and an electric heater  450  is disposed below conveyor  442 . Electric heaters  448  and  450  may be any suitable electric heater and, preferably, are radiant heaters, such as infrared heaters. Electric heaters  448  and  450  preferably each have a heater element that weaves among the columns of impingement air in a manner that minimizes interference therewith, as shown, for example, in cooking device  200  of  FIG. 12 . Electric heaters  448  and  450  are shown as located between conveyor  442  and impingement assemblies  444  and  446 . It will be apparent to those skilled in the art that electric heaters  448  and  450  may alternatively be located within impingement assemblies  444  and  446 , respectively, as shown, for example, in  FIGS. 13 and 16 .  
         [0129]     A control unit  452  is electrically connected to electrical heaters  448  and  450 . Control unit  452  is operable to control electric heaters  448  to both be off, both be on, or one off and one on. For example, if electric heaters  448  and  450  are on and off, respectively, additional thermal energy is applied to the top of the food products, thereby imparting crunchiness thereto. On the other hand, if electric heaters  448  and  450  are off and on, respectively, additional thermal energy is applied to the bottom of the food products, thereby imparting crunchiness thereto. If both electrical heaters are on, crunchiness is imparted to both the top and bottom of the food products.  
         [0130]     It will be apparent to those skilled in the art that control unit  452  can be given additional functionality to control the energy supplied to electrical heaters  448  and  450  in a programmed fashion for various cooking procedures. This gives cooking device  440  a great amount of flexibility. It will be further apparent to those skilled in the art that the principles of cooking device  440  may be implemented in any of the embodiments shown in  FIGS. 1-30 .  
         [0131]     It will be apparent to those skilled in the art that the blanket and tuning features of the invention can be used in any of the cooking devices  11  ( FIGS. 1-9 ),  200  ( FIGS. 11 and 12 ),  260  ( FIG. 13 ),  300  ( FIGS. 14-17 ) and  380  ( FIG. 17 ) as well as in any impingement oven for cooking of food products of varying heights on a single conveyor.  
         [0132]     It will also be apparent to those skilled in the art that the ovens of the present invention achieve rapid cooking times by delivering different amounts of thermal energy to the top and bottom of the food product to match the maximum thermal absorption rate of the product being cooked. Air volumes, velocities, temperature and radiant emissions are selected to optimize thermal transfer to different thickness of product being cooked on the same conveyor belt set to the same cooking time.  
         [0133]     The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims.