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Title:
COOKING METHOD AND APPARATUS
Document Type and Number:
WIPO Patent Application WO/2003/092407
Kind Code:
A1
Abstract:
Cooking apparatus (10) comprises a pair of spaced parallel heated platens (14, 29), and a pair of endless belts (15, 32) positioned so that each passes between the platens in contact with a respective platen to be heated thereby. Food products to be cooked are conveyed between the belts (15, 32) through a cooking zone (26) between the platens (14, 29). The platens (14, 29) each form part of a respective housing (12, 27) defining a chamber (13, 28) holding gas heated by a burner (20, 35). A fan (21, 36) blows heated gas into a plenum (19, 31) extending along the respective platen (14, 29). Cooking characteristics can be varied by changing burner output, air flow, belt speed and/or platen spacing. Cooking techniques developed for cut foods include high temperature steam grilling, lower temperature continuous stir-fry and sauté and grill blanching, as well as grilling food portions using falling temperatures.

Inventors:
HLAVATY PENNY (AU)
Application Number:
PCT/AU2003/000524
Publication Date:
November 13, 2003
Filing Date:
May 02, 2003
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
HLAVATY PENNY (AU)
International Classes:
A21B1/26; A21B1/48; A47J37/04; (IPC1-7): A23L1/01; A21B1/48; A47J37/04
Foreign References:
EP0334001A11989-09-27
DE19638073A11998-03-19
EP0655215A11995-05-31
US5044264A1991-09-03
Attorney, Agent or Firm:
CULLEN & CO. (239 George Street BRISBANE, Queensland 4000, AU)
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Claims:
CLAIMS :
1. Cooking apparatus comprising a pair of spaced parallel platen members defining a cooking region there between, each platen member being heated in use, a pair of endless belts on rollers, each belt being positioned so that it passes between the platen members and in contact with a respective one of the platen members so as to be heated thereby, the belts being adapted to convey food products sandwiched between them through the cooking region and to conduct heat to the food products, characterised in that each platen member forms part of a respective housing of a chamber having gas therein, and the cooking apparatus includes a heater for heating the gas in the chamber, whereby in use, each platen member is heated by the heated gas in its associated chamber.
2. Cooking apparatus as claimed in claim 1, further comprising a plate member located within each chamber and spaced from the respective platen member to form a plenumlike cavity there between extending a major part of the length of the platen member.
3. Cooking apparatus as claimed in claim 2, wherein the heater is a gas burner located within the respective chamber.
4. Cooking apparatus as claimed in claim 3, further comprising a fan in each chamber for blowing heated gas through the respective plenumlike cavity.
5. Cooking apparatus as claimed in claim 1, wherein one of the platen members and its associated housing are positioned above the other platen member and its associated housing, further comprising a lifting mechanism for raising and lowering the upper platen member and its associated housing relative to the other platen member and its associated housing, to thereby vary the spacing between the platen members.
6. Cooking apparatus as claimed in claim 1, wherein one of the platen members and its associated housing are positioned above the other platen member and its associated housing, further comprising upturned edge formations on the lower platen member to cause the longitudinal edges of the belt in contact with the lower platen member to curl upwardly.
7. Cooking apparatus as claimed in claim 2, further comprising electric resistance heating elements in the plenumlike cavities.
8. Cooking apparatus comprising a frame, a lower assembly including a first housing defining a first chamber having gas therein, an upper portion of the first housing forming a lower platen member, heating means for heating the gas in the first chamber so that, in use, the lower platen member is heated by the gas, a first rollermounted endless belt passing over the lower platen member so as to be heated thereby, an upper assembly including a second housing defining a second chamber having gas therein, a lower portion of the second housing forming an upper platen member spaced above, and parallel to, the lower platen member to define a cooking region there between, heating means for heating the gas in the second chamber so that, in use, the upper platen member is heated by the gas, a second rollermounted endless belt passing under the upper platen member so as to be heated thereby, wherein the first and second belts are adapted to convey food products sandwiched between them through the cooking region and to conduct heat from the upper and lower platen members to the food products.
9. Cooking apparatus as claimed in claim 8, further comprising a first plate member located within the first chamber and spaced from the lower platen member to form a plenumlike cavity there between extending a major part of the length of the lower platen member, and a second plate member located within the second chamber and spaced from the upper platen member to form a plenumlike cavity there between extending a major part of the length of the upper platen member.
10. Cooking apparatus as claimed in claim 9, wherein each heating means is a gas burner.
11. Cooking apparatus as claimed in claim 10, further comprising a fan in each chamber for blowing heated gas into the associated plenumlike cavity.
12. Cooking apparatus as claimed in claim 7, further comprising a lifting mechanism for raising and lowering one of the assemblies relative to the other assembly, to thereby vary the spacing between the platen members.
13. Cooking apparatus as claimed in claim 7 wherein the first and second belts are mounted on respective sets of cantilevered rollers.
14. A method of cooking food products, comprising the steps of: providing two opposed platen members to define a cooking zone there between; heating the platen members by respective heated fluids ; locating a pair of thin endless belts so that opposed portions of the belts pass through the cooking zone in contact with a respective one of the platen members to be heated thereby; and conveying food products between opposed portions of the belts through the cooking zone; wherein the food products are subjected to a high initial temperature upon entry into the cooking zone, followed by a falling temperature profile as the food products travel through the cooking zone.
15. A method as claimed in claim 14 further comprising the step of varying the initial temperature of the platens, the speed of the belts, the flow rate of the heated fluids and/or the spacing between the platens for different food products.
16. A method as claimed in claim 14, wherein the initial temperature is over 260°C so that steam is generated quickly in the food products and raises the temperature of the mass of the food products, and further wherein the food products are maintained over 100°C for a substantial part of their transit through the cooking zone.
17. A method as claimed in claim 14 wherein the food products are cooked at an initial temperature sufficient to raise the temperature of the mass of the food products to 70°C.
18. A method as claimed in claim 14 wherein the food products are fruit, and the initial belt temperature is just sufficient to lightly grill the fruit surfaces in contact with the belts, yet sufficiently high to raise the internal temperature of the fruit to render enzymes and pathogens inactive.
19. A method as claimed in claim 14, further comprising the step of selectively using supplementary heating elements to heat one or more portions of either or both of the platens.
Description:
COOKING METHOD AND APPARATUS This invention relates to cooking method and apparatus, suitable for industrial and commercial applications, which can be used for a variety of high and low temperature short processes in addition to grilling foods. In particular, the invention is directed to belt cooking apparatus which provides automated or semi-automated cooking of a variety of foods in a controlled and variable manner.

BACKGROUND ART Belt cooking machines, commonly known as belt grills or contact grills, have been used to cook food products such as meat patties, chicken fillets and the like. Opposed endless belts of flexible, heat resistant material convey the food products between heated upper and lower parallel platens which are heated directly by conventional means, such as electric resistance heating. Each belt is mounted on a respective set of rollers, and travels along a respective platen in contact therewith, so as to be heated by the platen.

Typically, each belt is constructed of a flexible material generally with non-stick properties, such as Teflon laminated over fiberglass fabric.

The food products are cooked by heat conduction as they are conveyed between the hot platens. The food products are placed on the lower belt at an entry station, and are conveyed through a cooking zone between the two heated platens by being sandwiched between the two belts between the two platens. The belts move at the same speed, and conduct heat from the heated platens to the food products as the belts convey the food products through the cooking zone to an exit end. A typical belt grill is described in US patent no. 3646880.

Most known belt grills are designed so that the platens are heated uniformly to a constant temperature and maintained at that temperature, typically at or below 260°C. The controlled variables on known grills are platen temperature, belt speed and height between the belts. This process results in the food products having an increasing temperature profile as they travel between the platens and progressively absorb heat from the platens, which can

result in the cooked food product lacking the taste of a manually cooked equivalent food product, conventionally subjected to a variety of heat treatments. The cooking process on known grills is not easily varied to the same extent as manually cooked foods.

For proper heat treatment of food to ensure pasteurization and/or sterilization, automated cooking devices need to be operable to precise parameters chosen for microbiological safety. The necessity for such strict control has led to large, capital-intensive food cooking machines normally suited to processing very high volumes of food only.

International patent application PCT/AU94/00429 (WO95/03713) discloses a belt cooking device suitable for use in small to medium commercial applications, such as food factories and restaurants, while providing a highly controlled and predictable continuous cooking process. That apparatus uses a pair of heated metal belts to both convey and heat the food products. The belts are heated to a desired temperature just prior to the entry end of the cooking apparatus. When the food products are inserted into the cooking apparatus, they come into contact with the heated belts at or near the highest temperature of the belt. As the food products are conveyed between the heated belts, the cooking process continues at lower temperature as heat is transferred from the belts to the food products and the temperature of the belts falls.

Although the"falling temperature"profile provided by the cooking apparatus of international patent application W095/03713 provides an advantageous cooking process, it has been found that the apparatus is not readily adapted for cooking different foods or different cooking styles which may require different falling temperature profiles. The temperature profile of this known apparatus is largely dependent upon the thermal capacity of the belt and its conductivity, and as these factors are inherent properties of the belt itself, they are not easily changed. Furthermore, a substantial amount of heat energy is required to heat the metal belt : It is also known to cook food products in automated cooking processes by directing heated gas to the food products as they travel along a cooking path. However, it has been found that the direct impingement of the

hot air flow on the food products has an undesired drying effect on some foods.

It is an aim of this invention to provide an improved cooking apparatus and method which overcome or ameliorate the disadvantages of the prior art, or which at least provide a useful choice.

SUMMARY OF THE INVENTION In one broad form, the invention provides cooking apparatus of the type comprising a pair of spaced parallel platen members defining a cooking region there between, with each platen member being heated in use, and a pair of endless belts on rollers, each belt being positioned so that it passes between the platen members and in contact with a respective one of the platen members so as to be heated thereby. The belts are adapted to convey food products sandwiched between them through the cooking region and to conduct heat to the food products. Each platen member forms part of a respective housing of a chamber having gas therein (typically air), and the cooking apparatus includes a heater for heating the gas in the chamber, whereby in use, each platen member is heated by the heated gas in its associated chamber.

Preferably, the cooking apparatus includes a plate member located within each chamber and spaced from the respective platen member to form a plenum-like cavity there between extending a major part of the length of the platen member. Each platen is heated by the hot gas flowing through the associated plenum.

Each heater is typically a gas burner located within the respective chamber. Other suitable heating means may be used, such as electric resistance heating elements and inductively heated metal billets. Auxiliary electrical heating may also be provided to the plenums if desired.

Preferably, the cooking apparatus includes a fan for blowing heated gas from each chamber into the plenum-like cavity.

A lifting mechanism is suitably provided for raising and lowering one platen member and its associated housing relative to the other platen member and its associated housing, to thereby vary the spacing between the

platen members.

Advantageously, the lower platen member has upturned edge formations to cause the longitudinal edges of the belt in contact with the lower platen member to curl upwardly to contain cooking juices.

In another form, the invention provides a method of cooking food products, comprising the steps of: providing two opposed platen members to define a cooking zone there between; heating the platen members by respective heated fluids ; locating a pair of thin endless belts so that opposed portions of the belts pass through the cooking zone in contact with a respective one of the platen members to be heated thereby; and conveying food products between opposed portions of the belts through the cooking zone; wherein the food products are subjected to a high initial temperature upon entry into the cooking zone, followed by a failing temperature profile as the food products travel through the cooking zone.

In order that the invention may be more fully understood and put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic sectional elevation of cooking apparatus according to one embodiment of the invention.

Fig. 2 is an enlarged sectional elevation of a portion of the cooking apparatus of Fig. 1.

Fig. 3 is a schematic sectional end elevation of the cooking apparatus of Fig. 1.

Fig. 4 is an enlarged sectional end elevation of a side portion of the cooking apparatus of Fig. 1.

Fig. 5 is a schematic sectional elevation of cooking apparatus according to another embodiment of the invention.

Fig. 6 is an enlarged sectional elevation of a portion of the cooking apparatus of Fig. 5.

Fig. 7 is a schematic sectional end elevation of the cooking

apparatus of Fig. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in the drawings, cooking apparatus 10 comprises a frame 11 on which are mounted upper and lower assemblies. The lower assembly includes a lower housing 12 which defines a mostly closed (though not sealed) chamber 13. The housing 12 has a flat upper surface which forms a lower platen 14. The housing is typically made of stainless steel. An endless belt 15 is mounted on a series of rollers 16 and travels over the platen 14 in contact therewith. The belt 15 of the lower assembly is driven by a variable speed motor 17, and at least one of the rollers 16 is adjustable in order to vary the tension of the belt 15.

The belt 15 is typically made from thin heat-resistant flexible material such as Teflon laminated over fiberglass fabric. However, other suitable materials may be used for the belt, such as stainless steel mesh or carbon fibre composites.

An internal plate 18 is located closely under the platen 14 to define a plenum-like volume 19 (hereafter referred to simply as a"plenum") between the plate 18 and the platen 14.

A gas burner 20 is provided within the lower chamber 13, and has spaced gas nozzles extending substantially across the width of the chamber 13. A motor-driven variable-speed fan 21 in the chamber has an outlet which directs air through the burner 20 so as to be heated by the burning gas. The burner 20 may have its own air inlet (s) to provide the necessary oxygen for combustion of the gas fuel, and/or the fan may draw in air from outside the housing.

The heated air travels in the direction illustrated by the arrows in Figs. 1 and 2, into the plenum 19. As the heated air travels along the plenum 19, it heats the lower platen 14. It is to be noted that the platen is not heated directly by the burner, but principally by the heated airflow. After exiting the plenum, a large proportion of the air is re-circulated within the chamber by the fan 21.

Peg-like posts 23, or similar devices, are located in the plenum 19

and extend between the plate and the platen. These provide turbulent airflow within the plenum 19, and thereby enhance the heat transfer from the heated air to the platen 19. The posts 19 also serve to strengthen the construction of the chamber, and maintain a constant separation between the platen 14 and the internal plate 18.

A rinsing and washing station 24 is provided in the lower assembly for rinsing and washing the belt 15. The rinsing and washing station 24 may be any suitable arrangement as is known in the art.

Insulation 25 is suitably provided around the housing 12 to minimize heat loss from the chamber 13, and prevent external surfaces from becoming too hot.

The upper assembly is suspended from the frame 11 above the lower assembly. The upper assembly is generally similar to the lower assembly, but opposed thereto in orientation.

As shown in the drawings, the upper assembly comprises a housing 27 defining a mostly closed chamber 28. The housing 27 has a flat lower portion which forms an upper platen 29. The lower and upper platens 14, 29 are parallel, and define a cooking region 26 there between. An internal plate 30 in the upper chamber 28 is spaced closely above the platen 29 and defines a plenum-like volume 31 above the platen 29.

An endless belt 32 is mounted on rollers 33, and travels along the upper platen 29 in contact therewith. The belt 32 is driven by a variable speed motor 34. As in the lower assembly, at least one of the rollers 33 is adjustable in order to vary the tension in the belt 32. The belt 32 is of similar construction to the belt 15 of the lower assembly. The belt 32 passes through a washing station 39 provided in the upper assembly, as is known in the art.

A gas burner 35, similar in construction to the gas burner 20, is located in the upper chamber 28. A motor-driven variable-speed fan 36 is also located in the upper chamber 28, and directs air through the burner 35 to be heated thereby. The heated air travels in the direction shown by the arrows in Figs. 1 and 2 and passes through the plenum 31 to heat the upper platen 29.

As in the lower assembly, peg-like posts 37 are provided in the plenum 31 to

cause air turbulence and promote thermal exchange with the upper platen 29, and to strengthen the housing.

Insulation 38 is provided around the housing 27 to minimize heat loss from the chamber 28. Stainless steel covers 42 are suitably provided around the whole cooking apparatus.

As shown in Fig. 4, the lower platen 14 has upturned portions 14A along both its longitudinal edges, so that the lower belt 15 is"dished"or turned upwards at its edges to prevent juices and other liquids from the food products running over the edge of the belt. Further, a gutter 46 extends longitudinally along each outer edge of the lower platen edges 14A so that any juices or liquids spilled over the edge will be collected in the gutter 46 and suitably drained.

The upper platen 29 is provided with lateral extensions 29A which extend longitudinally along its edges. The lateral extensions 29A are located close to the lower belt 15, and assist in substantially enclosing the cooking region 26 between the upper and lower platens 29, 14. In this manner, the heat and steam generated by the cooking process is largely retained within the cooking region 26.

To further minimize loss of heat from the cooking apparatus, the lower assembly is provided with side walls 47 which extend longitudinally on both sides of the cooking space 26. The upper assembly has an angled flange section 48 extending longitudinally along both sides of the cooking region 26.

Each flange section 48 has a depending side wall which is juxtaposed with a respective side wall 47. The juxtaposed side walls assist in enclosing the cooking region, while permitting relative vertical movement between the upper and lower assemblies.

The upper assembly is suspended from the frame 11 by lifting screw jacks 40. An electronically controlled drive 41 rotates the screw jacks 40 in order to vary the height of the upper assembly, and thereby vary the spacing between the upper and lower platens 29,14. In this manner, the vertical spacing between the platens 29,14 can be controlled accurately.

Auxiliary heating, such as electric heating, may be provided to the

platens 14,29 at one or more locations along the cooking region 26. This heating may be provided by electric resistance heating elements (not shown) in the plenums.

The cooking apparatus 10 has an entry station 43 and an exit station 44. Food products placed on the bottom conveyer belt 15 at the entry station conveyed through the cooking region between the platens 29,14 by being sandwiched between the upper and lower belts 32,15.

In use, air is circulated around the upper and lower chambers 28, 13 by the respective fans 36, 21. The air heated by the gas burners 35,20 flows along the respective plenums 31,19, thereby heating the platens. The platens, in turn, heat the respective belts 32,15 with which they are in contact.

These belts conduct heat to the food products which are sandwiched between them as the food products are conveyed along the cooking region to the exit station 44.

After passing through the cooking region, the cooked food products are delivered to the exit station 44 where they typically slide directly into a aseptic or separate packaging system. The belts then pass through their respective automated washing stations 24,39 which wash and rinse both the top and bottom of the belts. The washing stations are preferably mounted on sliding cassettes for easy removal for periodic inspection and cleaning. The residual heat within the cooking apparatus dries the belts after they pass through their respective washing stations, so that each portion of the belt is clean and dry when it returns to the entry station 43.

Thermocouples (not shown) are suitably located at desired locations within the cooking apparatus to monitor temperatures at those locations. The outputs of the thermocouples can be connected to an electronic controller which automatically varies the airflow, burner output, auxiliary heating elements and/or belt speed to achieve the desired cooking profile. The automatic controller can also adjust the spacing between the platens 14,29, and hence accommodate different heights of food and/or vary the contact pressure on the food products.

An example of a method of cooking food products using the

abovedescribed apparatus will now be described. The cooking apparatus 10 is preheated in order to raise the temperature of the thin-walled plenums 19,31 slowly to avoid distortion, particularly of the platens 14,29. This is achieved by turning on the fans 21,36 to circulate air through the respective chambers, then turning on the leading auxiliary electric heating elements in each plenum, followed progressively by other auxiliary electric heating elements in the plenums to bring the temperature to around 150°C in the two chambers. The apparatus will remain preheated at this temperature, until the food products are ready to be cooked.

A desired recipe is selected via the electronic controller, which may be a personal computer, or entered manually if preferred. The cooking apparatus automatically adjusts the run time, measured in seconds, in the cooking region 26, as well as the spacing between the platens.

As soon as the recipe is selected, the auxiliary heating elements automatically turn off, and the gas burners 20,35 ignite. The specified start temperature and air flow cause the platens and the belts to be heated to the required temperature, typically within two minutes, although very high temperatures may take longer to reach in order to avoid excessive rates of increase in the temperature.

A mass of food products, such as cut vegetables, is then fed into the machine. Depending on the type of food being cooked, the food products may be processed at any desired start temperature and air velocity, and supplementary heat from one or more of the auxiliary heating elements may be applied. In this manner, a full range of surface effects can be created, and a variety of processes, including grill blanching and steam grilling (as discussed below) can be achieved. The start temperature may be selected within a wide range, from the preheat temperature of 150°C up to 450°C in the current embodiment although even higher temperatures may be used in certain applications.

The air flow of the heated gas is maintained by the fans at the desired rate. The illustrated apparatus can circulate air from 4.7 m/second to 33 m/second.

Supplementary heat may be applied in any desired pattern.

Electric elements can be turned on automatically by the electronic controller, or manually, in one or both plenums. The opposed belts and platens can be run at different temperatures or with different falling temperature profiles, e. g. to give chicken breast one gilded surface and one white surface.

The start temperature of the food is normally at a refrigerated temperature for maximum food safety and food is generally cooked to specification in one transit of the cooking chamber at the selected speed.

However, some foods may benefit from two passes, one to steam blanch and raise the internal temperature, and the second pass to cook at high heat with a chosen coating.

The temperature gain of the food products as they travel through the cooking region is governed by a combination of variables, but is usually more than 70°C, and may substantially exceed 100°C.

Unless they are to be frozen, the cooked food products will generally be packed hot to retain as much benefit as possible from the process.

However, some processes require the addition of sterilized water for rehydration. Devices for adding sterilized water to the cooked food products, or for adding sauces or syrups, may be used in conjunction with the cooking apparatus. Other cooked foods may be rapidly cooled after packaging by an ice water bath or other cooling means to which the cooked food products are delivered upon exit from the cooking region, so that the cooked food products retain the benefit of textura improvements from this rapid process.

The above described cooking apparatus and process have several advantages. First, they utilize a falling temperature cooking profile.

The platens 29,31 are relatively thin, and therefore have relatively low thermal capacity. This enables the platens to be heated quickly by the hot gas flow to a high temperature. When the food products first enter the cooking region and are sandwiched between the platens 29,14 they will be subjected initially to high temperature cooking. This sears the surfaces of the food products, sealing in moisture and juices. The heat from the platens is absorbed quickly by the food resulting in a temperature drop from the initial high temperature.

The heated air also drops in temperature as it flows through the respective plenums. The food products therefore continue to be cooked as they are conveyed along the cooking region, but with a falling temperature profile.

Since the moisture and juices are largely retained within the food products as they are cooked, the resultant cooked product retains flavour and tenderness. Most foods can be cooked in 1 to 5 minutes in a short, high temperature process, with initial temperatures from 260°C to 400°C using this belt grill. However, burning or excessive drying of the food is avoided by diminishing the heat input during transit through the cooking zone in a controlled manner.

Secondly, cooking characteristics can be easily changed. For example, the initial temperature at the leading end of the platens, governed largely by the gas temperature, can be varied by adjusting the thermal output of the gas burners 20, 35. The fatting temperature profile can be adjusted by varying the airflow through the plenums 19,31. Thus, a higher temperature drop can be obtained by reducing the airflow, or a smaller temperature drop can be maintained by increasing the airflow. The speed of the belts can also be adjusted to vary the time which the food products spend within the cooking region. In this embodiment this time is typically between 60 and 415 seconds, but the apparatus can be adjusted for slower cooking speeds for larger food items.

Auxiliary heating, such as electric resistance heating, provided to the platens 14,29 at one or more locations along the cooking region 26 enables the temperature profile to be varied. These electric heating elements can be selectively controlled to boost the air temperature at desired locations, enabling different heating curves to be obtained. For example, if all of the electric elements are turned on with a minimal hot air flow, a generally flat heating cycle will be obtained. On the other hand, if the auxiliary electric elements are not used, a steeper falling temperature profile will be achieved.

Thirdly, the above capabilities of the cooking apparatus enables it to be used for cooking different food products in different cooking processes.

For example, a high initial cooking temperature will cause some of the moisture

inside a food product to be converted to steam when the food product is subjected to the sudden rise in temperature when first sandwiched between the upper and lower platens 29,14. High initial belt temperatures quickly raise the upper and lower surface temperatures of the food products. At belt temperatures close to and over 300°C steam is generated with great speed.

The steam itself then continues to cook the food product as it travels through the cooking region. This steam mitigates the extreme temperatures at the outer surfaces of the food products, and disperses the heat efficiently in the food mass. Tight packing of the food products assists heating by conduction in addition to steam penetration. This process, hereafter referred to as"steam- grilling"is particularly suited for cut high moisture foods such as vegetables, fruits and proteins and mixtures or combinations of these with other recipe ingredients.

"Steam-grilling"is useful for raising product temperature at a rate faster than achievable by conventional belt grilling, and sustaining the high temperature throughout the process despite the deliberately created variation in belt temperature. It results in foods appropriately coloured on the contact surfaces and frequently having a naturally different colour and texture within the mass or portion. In one embodiment, chilled food products, such as sliced or diced vegetables, processed at a range of initial platen temperatures typically between 275°C and 330°C attained a temperature of over 100°C within 90 seconds and continued to be processed at above boiling point until the exit station, despite the fall in temperature profile of the platens. Higher processing and exit temperatures combined with sufficient process time and appropriate product density or height and mass improve the shelf life and food safety of products. The high initial rate of temperature increase also ensures a high death rate of any pathogenic organisms in the food products.

At lower initial temperatures, the cooking apparatus can be used for cooking"stir-fry"meats and vegetables in a continuous, batch or individual meal process which mimics the appearance and texture of foods typically cooked in woks. Food combinations may include oils, herbs, spices and marinades for authentic flavour. Where product is to be added to hot sauce to

complete pasteurization, processing speed may be as little as one minute, so productivity is high. Alternatively, the process may be run with high initial heat followed by temperatures rapidly diminishing to enable a holding temperature above 70°C to preserve crisp texture and heightened colour and for the additional food safety of product eaten or packaged without sauce. Pre-cooked rice with garnishes and flavourings may also be cooked by this method to closely resemble fried rice.

The cooking apparatus can also be used at lower temperatures for grill blanching. If initial temperatures under 200°C are used, for instance on cut fruits, novel minimally-processed products can be created which have a barely-perceptible grilled surface effect and remain very juicy. Yet, these products are processed at high enough temperatures to destroy pathogens and undesirable enzymes.

In addition, the cooking apparatus can be used for the processing of a wide variety of protein portions, kebabs, patties and like foods as well as carbohydrates and bakery products, often at very elevated initial temperatures.

Frequently the manipulation of cooking cycles through varying processing temperatures and air velocity can be used to advantage in terms of increased speed of cooking, juiciness, lowered weight loss, improved edge temperatures and heightened external coloration.

The cooking apparatus can therefore be used to grill a wide variety of food products, such as steaks, kebabs and hamburgers, as well as steam grilling or blanching a range of sauteed or stir-fried meals, vegetables and fruits.

Various surface effects can be created on the food products, e. g. by using grill formations on the upper and/or lower platens.

Fourthly, due to the falling temperature profile, the belts 15,32 have a lower average temperature than prior art belt grills, and therefore a longer life. In addition, higher initial temperatures can be used. A Teflon belt rated at 260°C can be heated initially to a higher temperature and still have an average temperature within specification.

It is also to be noted that the food products are not contacted

directly by the heated air. Accordingly, the food products are not dried out by the hot airflow.

The distance between the platens 29,14 can be adjusted accurately, not only to accommodate varying throughput of food products, but also to vary the contact pressure on the food products and thereby alter the cooking process. This distance can be changed manually or automatically.

The heated air within the chambers 13,28 is re-circulated, thereby providing thermally efficient operation.

The cooking apparatus can be made in various sizes, to suit different applications.

In modification of the above described embodiment, the platens 14,29 may be perforated so that a small amount of the heated gas passes through the platens. This not only serves to provide more direct heating of the conveyor belts 15,32 in the cooking region, but also minimizes friction between the conveyor belts and their respective platens.

In yet another modification of the invention, the internal plates 18, 30 can be omitted.

Figs. 5-7 illustrate a second embodiment of the invention. The second embodiment can be constructed as a smaller version of the embodiment of Figs. 1-4, and is particularly suitable for small food surface applications.

As shown in Figs. 5-7, cooking apparatus 50 comprises a frame 51 in which upper and lower assemblies are located. The lower assembly includes a substantially closed housing 52 which defines a chamber 53 therein.

The housing 52, which is typically made of stainless steel, has a flat upper surface which forms a lower platen 54. An endless belt 55, mounted on rollers 56 and driven by a variable drive 57, is arranged to travel along the platen 54.

Within the chamber 53, a plate 58 is spaced from the platen 54 to define a plenum-like cavity 59 there between.

A heating means, in the form of electrical resistance heating elements 60, is located in the chamber 53 to heat the air or other gas contained therein. (An inert gas, such as nitrogen, may be used in the chamber 53

instead of air). A fan 61, driven by a variable speed motor 62, is used to recirculate the gas within the chamber 53. In use, the fan 61 blows air heated by the heating elements 60 into the plenum 59, as shown by arrows in Fig. 5.

The lower belt 55 passes through a washing station which includes sprays 62 mounted on a removable cassette, as well as a rotary brush 63 and removable fibre or micro fibre pads, for cleaning the belt 55.

The upper assembly, which is mounted to the frame 51, is generally similar to the lower assembly, but opposed thereto. The upper assembly includes a housing 67 defining a chamber 68 therein. The housing 67, which is typically made of stainless steel, has a flat lower portion which forms an upper platen 69. An endless belt 70, mounted on rollers 71 and driven by a variable drive 72. is arranged to travel along the platen 69.

Within the chamber 68, a plate 73 is spaced from the platen 69, and defines a plenum-like cavity 74 there between.

Electric resistance heating elements 75 are provided in the chamber 68 to heat the air or other gas in the chamber. The heated air is recirculated by a fan 76 driven by a variable speed motor 77. The fan 76 blows the heated air into the plenum 74 as illustrated by the arrows in Fig. 5.

The belt 70 passes through a washing station having sprays 78.

The lower assembly is mounted on a jack 64 which allows the height of the lower assembly to be adjusted. In this manner, the spacing between the opposed belts between the lower and upper platens 54,69 can be varied.

In use, the air in the chambers 53,68 is heated by the respective heating elements 60,65 and directed by the fans 61,76 into the plenums 59,74. Food is placed on the lower conveyor belt 55, and is conveyed through the cooking region by being sandwiched between the upper and lower belts 70, 55.

The food conveyed between the conveyor belts will encounter an initial high temperature at the entry end of the platens 54,69 which are heated by the heated gas. The food will absorb heat from the platens and the gas as it travels through the cooking zone. As this heat is absorbed, the gas flow will

drop in temperature, creating a"falling temperature"cooking profile.

The cooking profile can be varied by altering the speed of the belts, the airflow within the respective chambers, the output of the heating elements and/or the spacing between the upper and lower platens. These variables can be changed manually, or automatically by a control panel 80 located on the cooking apparatus.

The cooking apparatus of Figs. 5-7 can be constructed in compact form, e. g. with 500mm wide belts, to provide an efficient automated cooking machine for food service applications.

A particular advantage of the cooking apparatus of the second embodiment is that the rollers 56,71 are cantilevered mounted. As shown more clearly in Fig. 7, the rollers 56 are mounted at one end to a subframe 51A of the lower assembly. The other end of each roller 56 locates in a removable bearing plate 65. The lower belt 55 can be removed simply by removing the bearing plate 65, and sliding the belt off the rollers 56. Similarly, the rollers 71 of the upper assembly are mounted at one end to the frame 51. The other end of each roller locates in a removable bearing plate 59. The upper belt 70 can be removed from the rollers 71 simply by removing the bearing plate 79, and sliding the belt off the rollers.

In a modification of this embodiment, the heated gas is replaced by another heated fluid, such as heated oil, in the chambers. (In this case, the chambers are sealed and the fans are replaced by rotary paddles).