WO2000056194A1

WO2000056194A1 - Improvements to cooking apparatus

Info

Publication number: WO2000056194A1
Application number: PCT/AU2000/000213
Authority: WO
Inventors: Gheorghe Duta; James Norman Magill; Vanessa Coufos
Original assignee: Vos Industries Limited
Priority date: 1999-03-24
Filing date: 2000-03-16
Publication date: 2000-09-28
Also published as: AUPP942099A0

Abstract

Disclosed is a cooker (10) including a cooking chamber (14) with gas venting means (21, 21a, 23, 23a). Gases and vapours from the cooking chamber (14) flow through the gas venting means (21, 21a, 23, 23a) for reducing oxygen diffusion into the cooking chamber (14). A purging gas stream, which may also be employed for moisture control, may be introduced to cooking chamber (14). A cooking method involving such moisture control is also described.

Description

IMPROVEMENTS TO COOKING APPARATUS Field of the Invention

The present invention relates to cooking apparatus and, in particular, cooking apparatus for high output processing of food items as required, for example, in the quickservice food industry. Particular methods of operating such cooking apparatus are also disclosed. Background to the Invention

A problem with cooking high throughputs of food in a quickservice operation is high consumption of oils and fats used as cooking medium for fryers. Two concerns arise in practice.

Firstly, most cooker designs result in exposure of oils and fats at high temperature to a high enough quantity of oxygen that degradation products start to form in the oil. This process may be most significant in the cooking chamber where food items are exposed to oil or fat for cooking. Key among these degradation products are free fatty acids. If an oil or fat contains over 25% total polar contaminate material it must be discarded and fresh cooking medium must replace it. Such replacement adds to the running cost or whole of life cost of the cooker.

Secondly, food items - especially more fatty food items such as chicken products - have a higher level of fat migration into the oil. Thus, there is another source of contamination of the cooking oil or fat and this needs to be addressed in a cost effective manner.

Both problems are common to all types of fryer. The spray frying art, as represented by fryers developed by the Applicant, minimises oil consumption by exposing food items to a smaller quantity of oil to achieve desired cooking than required in conventional vat fryers. Further, better thermal control may be achieved reducing oil absorption by food items, improving food quality and improving the overall economics of the fryer.

Representative of a fryer developed by the Applicant is that described in Australian Patent No. 666944. This fryer incorporates flow heaters which heat oil in the substantial absence of air for reducing oil degradation.

Substitute Sheet

This kind of fryer may be distinguished from Cπttall, British Patent No 621821 that suffers oil overheating and oil/fat wastage and US 4047476 that also suffers overheating and poor thermal efficiency.

Furthermore, known spray fryers aliow some air to enter the cooking chamber during the cooking operation through openings located at the fed and discharge ends of the cooking chamber Flaps provided in these openings do not seal the cooking chamber sufficiently to achieve acceptable free or volatile fatty acid and total polar contaminant levels over sustained periods of fryer operation. Still further, there is no means by which degraded oil products may be removed from the cooking chamber Yet further, as there may exist space constraints for many, if not most, quickservice food outlets, there is some pressure to reduce fryer unit size where oil degradation problems may become more significant.

Concentration of oil degradation products causes two problems. Firstly, such concentration may cause bad taste of the cooked product. Alternatively, or further, such concentration may expose consumers to health risks. There is no consistency in regulation of oil quality in frying. No consistent test is employed for determining when oil no longer remains good for frying. Some countries have introduced a free fatty acid ceiling of 2%. Other countries have capped frying temperature at 180°C. A few other countries mandate that the total polar contaminant material in the oil should not exceed 25-27% None of the limits alone ensures a good decision on when oil no longer remains acceptable for cooking. Summary of the Invention It is a first object of the present invention to reduce the consumption of oil or fat cooking media due to oxygen and heat induced degradation thereby increasing the profitability of cookers using such cooking media and promoting the health of consumers of product food items

It is a second object of the present invention to provide means by which degradation products may be removed from the cooking chamber of cookers

In a first aspect, the present invention provides a cooker including

Substitute Sheet (Rule 26) RO/AU (a) a cooking chamber; and

(b) at least one cooking chamber gas venting means provided for the cooking chamber wherein gases and vapours flow through the gas venting means for reducing oxygen diffusion into the cooking chamber. Broadly, the cooking chamber may be designed to discourage entry of atmospheric gases. Thus, the cooking chamber may be located within a housing with limited openings to atmosphere when in operation.

The flow of gases and vapours may be constituted at least partly by a flow of a purging gas or vapour such as nitrogen, or carbon dioxide, or another inert gas, water vapour or saturated steam which may also entrain products of oil or fat degradation such as volatile fatty acids. The balance between steam or inert gas such as nitrogen may conveniently be varied for this purpose, as well as for the purpose of moisture level control. Two benefits may be achieved by this means. Firstly, the degree of oil or fat oxidation may be reduced. Secondly, the moisture level of cooked food items may be maintained at a level acceptable to the consumer.

For example, frying of poultry - particularly chicken - may result in an overly dry cooked product. By control over the moisture level in the cooking chamber, a better quality product may be achieved. Additionally, cooking time and temperature are reduced over conventional methods.

Introduction to the cooking chamber of water vapour or steam, perhaps in admixture with an inert gas such as nitrogen, may be controlled in accordance with moisture level as sensed by a conventional moisture level probe conveniently located in the cooking chamber. Food moisture level, whether empirically or directly sensed, may also be used as a basis for moisture control. Steam or inert gas may then be introduced to the cooking chamber by opening of valves connected to a regulated pressure supply of steam or inert gas, such as nitrogen. Conventionally available steam generators may be used for supplying the steam. The degree of opening of the valves, which may be solenoid valves actuated by an electronic control unit (ECU) supervising cooker operation, may be controlled to aliow entry of the requisite quantity of steam and/or inert gas.

Substitute Sheet (Rule 26) RO/AU Generally, in accordance with this moisture control methodology, the balance of nitrogen or inert gas may be increased relative to steam balance to reduce moisture content and reduced relative to steam balance to increase moisture content. This aspect of the invention involves a method for controlling moisture level in a cooking chamber of a cooking apparatus wherein the relative proportions of steam and inert gas in a mixture introduced to the cooking chamber are controlled as a function of at least one of, food item type, food item moisture level and cooking chamber moisture level for achieving a cooked food item of acceptable moisture content. Acceptable moisture content of the food item may require to be determined qualitatively by tasting panels or other strategies.

The gas mixture may be introduced to the cooking chamber on an intermittent basis. Nitrogen or other inert gas may be introduced alone and any steam introduction may require temperature compensation by appropriate ECU control over heat exchanger output as steam presence may affect cooking chamber temperature.

Additional advantage is achieved for fryers or other cookers because hot cooking medium is contained within the housing resulting in safer operation. Cookers designed in accordance with the invention may operate in continuous or batch mode.

In a second more particular aspect, especially suitable for continuous cookers, the present invention provides a cooker including: (a) a cooking chamber having fed and discharge ends; (b) a conveyor extending between the fed and discharge ends of the cooking chamber for transporting food items to be cooked through the cooking chamber;

(c) a first opening to the cooking chamber at the fed end through which food items are fed into the cooking chamber; (d) a second opening from the cooking chamber at the discharge end through which food items are discharged from the cooking chamber; and

Substitute Sheet (Rule 26) RO/AU (e) at least one cooking chamber gas venting means provided for the cooking chamber wherein gases and vapours flow through the gas venting means for reducing oxygen diffusion into the cooking chamber.

The gas venting means may take the form of at least one gas port which may be located proximate one or both the fed and discharge ends of the cooking chamber. Plural openings may be provided as desired. The gas ports are provided separately to the first and second openings which may be provided with closures, such as flaps, gates and the like, to reduce ingress of air and oxygen into the cooking chamber. These closures may be made air- tight. This type of gas venting means is suitable for longer cooking apparatus.

Each gas venting means may include, or be integrated with, a buffer zone. The first and second openings may open into respective buffer zones located at the fed and discharge ends respectively of the cooking chamber.

Alternatively, a single buffer zone may be used for accommodating both feed and discharge of food items. Each buffer zone may be maintained at a pressure different from the operating environment in which the cooker is located, to reduce oxygen diffusion into the cooking chamber. Thus, the buffer zone may be maintained at a positive pressure relative to the atmosphere. Flow of gases and vapours through the vent means into the buffer zone(s) is indicative of the positive pressure differential. Alternatively, the buffer zone(s) may be connected to a vacuum system. Buffer zones may advantageously be provided where the cooker is shorter.

Each buffer zone may allow for sealing communication of the cooking chamber and its conveyor with infeed and output conveyors. Such conveyors, means for transporting food items, may take the form of belt conveyors, paddle conveyors, rotary conveyors and so on. The invention is not intended to be limited to any particular type or number of conveyor. The cooking chamber conveyor may comprise a number of conveyors and a longitudinally extending, flat arrangement is not the only one which may be used as will be described further below.

The gas venting means and/or buffer zone(s) may include pressure regulation means to preserve a desired pressure differential between the

Substitute Sheet (Rule 26) RO/AU cooking chamber and the buffer zone gas venting means or the cooking chamber surroundings and reduce oxygen diffusion into the cooking chamber. The term "surroundings" is used in a thermodynamic sense.

The gas venting means, buffer zones and the first and second openings may communicate with a ventilating exhaust system which allows for collection and treatment of the gases and vapours produced within the cooking chamber. Such gases and vapours should not be recycled to the cooking chamber where they may cause food contamination due to the presence of short chain hydrocarbons. The buffer zones may be provided with suitably ventilated exhaust vents for this purpose. Venting and condensate extraction may be carried out using fan forced circulation. If pressure relief valves are employed in the vents, a pressure frying operation is enabled. Gas exhausted through the vents may be treated for oxygen removal, using an oxygen selective scrubbing solution, and gas may be recycled to the buffer zone as a pressurising medium as desired.

The cooking chamber may include at least one gas inlet port for an inert gas and/or steam to be introduced for purging the cooking chamber of air. Any inert gas will be useful but nitrogen is preferred. Mixtures of such gases may be introduced to the cooking chamber The above moisture control strategy may again be applicable. Carbon dioxide may be used as an alternative. Ratio control means, for example, the ECU in association with selectively openable valves in said gas inlet port(s) may be included to control the ratio of constituent gases in a mixture thereof. Such purging may occur at start-up of the machine while it is heating up. Once the cooking chamber is at desired operating temperature and food items, typically in frozen form, are being transported through the chamber, steam will be generated within the chamber and will flow through the gas venting means. The gas inlet port(s) may be provided anywhere in the cooking chamber but may advantageously be provided generally toward the middle of the cooking chamber. Gases and vapours present within the cooking chamber will therefore comprise a large proportion of steam. In addition, where oils and fats are employed as cooking media, there may be included oil droplets and degraded

Substitute Sheet (Rule 26) RO/AU oil and fat products such as free fatty acids which may usefully be stripped out of the cooking chamber where they may detrimentally affect food quality.

The gas venting means and buffer zone(s), being typically at lower temperature than the cooking chamber, may also provide for condensation of vented steam with condensate being collected by collection means which avoid contact of the condensate with cooked or cooking food items. The collected condensate may be disposed of following suitable treatment.

The cooker type may vary incorporating vat, vacuum and pressure fryers but, advantageously, the invention is applied to spray fryers of the type developed by the Applicant. Oil and fat should be heated prior to spraying using flow heaters or the heat exchangers as described in the Applicant's co- pending International Patent Application No. PCT/AU98/00552, filed 16th July, 1998, the contents of which are hereby incorporated herein by reference. The heat exchanger and cooker generally may conveniently be operated using the methodology described in the Applicant's co-pending Australian Provisional

Patent Application No. PP 2568, filed 24th March 1998, the contents of which are hereby incorporated herein by reference. These disclosures also relate to cookers of other types, for example vat fryers, and are more widely applicable.

In the case of spray fryers, the gas venting means may intersect with the spray flowing though spray means or sprayers located proximate one or both the fed and discharge ends. To reduce entrainment of valuable oil and fat in the gas and vapour flowing through the gas venting means, deflector means may be provided which deflect oil or fat spray away from the venting means and towards the conveyor means. Such deflector means may be provided with oil collection means to collect oil impinging on the deflector means. Such collected oil may be recycled through the main storage tank of the fryer for re-use in spray frying. in a further aspect of the invention there is provided a method of reducing air ingress and oil degradation in a cooker including: (a) generating steam and/or inert gas in a cooking chamber of a cooker; and

Substitute Sheet ⁽Rule 26) RO/AU (b) inducing a flow of the steam and/or inert gas from the cooking chamber through gas venting means wherein said steam and/or inert gas reduces air ingress and causes removal of oil degradation products from the cooking chamber. Steam and inert gas may be introduced to the cooking chamber in admixture. The ratio of each may be controlled to maintain a minimal variation from a setpoint value for moisture level in the cooking chamber in accordance, for example, with the methodology above described.

In a still further embodiment, the invention provides a method of cooking food items including the step of controlling moisture level in a cooking chamber of a cooking apparatus by introducing a gas including at least one of steam and inert gas to said cooking chamber in such quantity and composition that variations from a setpoint for moisture control in said cooking chamber is minimised. The moisture level setpoint may be determined as a function of at least one of food item type and thickness.

The above method may be implemented in a cooker, and in similar manner as above described.

The method may further be supported by an oil replacement step with fresh oil being introduced in a quantity for reducing level of free fatty acids to acceptable levels. A certain proportion of oil may be dumped. Dumped oil may be treatable for free fatty acid removal with recycle possible. The ratio of fresh to recycled oil may be determined as a function of monitored fatty acid level and may be supervised by the electronic control unit supervising the operation of the cooker.

Cookers made and operated in accordance with the invention will suffer lower rates of oil degradation and will achieve better operation and economics than known cookers as oil and fat consumption required in the cooking operation may be appreciably reduced. Brief Description of the Drawings

Substitute Sheet (Rule 26) RO/AU The present invention may be more fully understood from the following description of preferred embodiments thereof made with reference to the accompanying drawings in which:

Figure 1 shows the cooking chamber of a cooker made in accordance with a first embodiment of the present invention; and

Figure 2 shows the cooking chamber of a cooker made in accordance with a second embodiment of the present invention;

Figure 3 shows the cooking chamber of a cooker made in accordance with a third embodiment of the present invention; and Figure 4 shows an elevation sectional view of a vent provided in a buffer zone of the cooker of Figure 3. Detailed Description of Preferred Embodiments

Referring now to Figure 1 , there is shown portion of a cooker 10 having a cooking chamber 14. Food items are cooked in the cooking chamber by spraying them with a stream of heated oil or fat using sprayers 30. A preferred strategy for pumping, filtering and heating oil or fat is disclosed in the

Applicant's co-pending Australian Provisional Patent Application No. PP 2568, filed 24th March, 1998, the contents of which are hereby incorporated herein by reference. The spray cooking of food items occurs while the food items are being transferred through the cooking chamber 14 by conveyor 16. The conveyor

16 may be of wire mesh type with excess oil flowing through the wire mesh to be collected in sump 40. Sprayers 30 are advantageously located both above and below conveyor 16. The conveyor 16 extends between fed end 20 and discharge end 22 of cooking chamber 14. At each end 20 and 22 are located openings 20a and

22a closed by polymer flaps 50 which provide some sealing of cooking chamber 14 from the surroundings which, having a large oxygen content, provide an undesirable source of oxygen which - when contacted with a heated oil - cause oil degradation and spoilage. The flaps 50 may conveniently be manufactured of viton or teflon backed cloth.

Substitute Sheet (Rule 26) RO/AU Flaps 50 are connected to a mounting plate 51 connected to housing 11 by nut-like spacers 52 which allow the mounting plate 51 /flap 50 assembly to be removed for cleaning. Other ways of connecting mounting plate 51 to housing 11 are possible. Flaps 50 may be substituted by gates or valves or other sealing means, the function being more important than the particular design characteristics. Such devices may prevent continuous feeding of food items.

At each end 20 and 22 of cooking chamber 14, and disposed in cooker housing 11 above openings 20a and 22a proximate fed and discharge ends 20 and 22, are gas vents 21 and 23 which take the form of passages connecting the cooking chamber 14 with the surroundings. These passages 21 and 23 may be of circular, square, rectangular or other section. The passages 21 and 23 could further be provided with one way valve means allowing communication between cooking chamber 14 and the surroundings when cooking chamber pressure exceeds a crack pressure for the valve means. Alternatively, the valve means could be of solenoid type, the opening/closing or degree of opening/closing being controlled by an electronic control unit (ECU) 100 supervising the operation of cooker 10.

As shown in Figure 2, two or more such vents or passages 21a and 23a may be formed in housing 11 at the fed and discharge ends 20 and 22 of cooking chamber 14. This is a matter of design choice, though the choice may be dictated by food item throughput. Usually, frozen food items would be fed into cooking chamber 14. On entering the cooking chamber 14 steam will be generated. As steam make increases, more ports may be required to provide adequate flow of steam from the cooking chamber 14.

It may be understood from the above description that it is desired to minimise oxygen levels in cooking chamber 14. Still further it is desired to minimise oxygen diffusion into the cooking chamber 14 due to convection currents created at openings 20a and 22a. The objective of sealing is further promoted by location of baffles 26 at each end of the cooking chamber 14.

It may be understood from consideration of Figures 1 and 2 that oil sprayed through sprayers 30a proximate ends 20 and 22 of the cooking

Substitute Sheet (Rule 26) RO/AU chamber 14 has a path that could intersect with the vents 21 , 21a, 23 and 23a. Accordingly, deflector plates 60 are located proximate the vents 21 , 21a, 23 and 23a to prevent oil passing into these vents and being lost from the cooking chamber 14. The deflector plates are of thin metal sheet, optionally of the same metal used for construction of the cooker 10. Where plural vents are provided, as shown in Figure 2, deflector plates 60 require to be of greater area.

At the bottom of each deflector plate 60, shown in Figure 2, disposed inwardly of the cooking chamber 14, is located a collection channel 61 which collects oil trapped by the deflector plate 60. The channel 61 may have a disposition that facilitates draining of oil toward sump 40 for collection into the oil handling system. Otherwise the channels 61 may communicate with ductwork (not shown) communicating with the oil handling system.

On the outward side of the cooking chamber 14, steam passing through vents 21 , 21a, 23 and 23a may partially condense as it encounters the cooler environment of the surroundings. Condensate collection means may be provided such that condensate does not trickle down the cooking chamber wall 14a and on to food items being transported out of cooking chamber 14. If such is not prevented, food quality (as measured, for example, by taste) will suffer due to contamination by short chain hydrocarbons and food wastage, being an operating cost penalty, is undesirable. It is highly unlikely that condensate will be suitable for treatment to recover oil for the cooker 10. Egress steam, gases or vapours should not be recycled to cooking chamber 14. Cooking chamber 14 may optionally be provided with an inlet port 160 connected to a nitrogen supply for introducing nitrogen to the cooking chamber 14, and an inlet port 170 connected to a steam supply for introducing steam to cooking chamber 14. Each port 160 and 170 may incorporate a solenoid valve which may selectively open to requisite degree under control of cooker 10 ECU 100. The nitrogen supply may be a bottled gas or other supply having pressure regulated to desired level. The steam supply may be a steam generator of conventionally available type.

Substitute Sheet. (Rule 26) RO/AU Ports 160 and 170 are opened to introduce nitrogen and/or steam respectively in such proportion as to maintain a desired moisture level in cooking chamber 14. The moisture level of cooking chamber 14 may be sensed by a moisture level probe 180 of conventional type. If the sensed moisture level varies from a predetermined level, which may be calculated having regard to food item type or moisture content, then ECU 100 may open one or both inlet ports 160 and 170 to allow an appropriate balance of nitrogen and steam to be admitted to cooking chamber 14. Generally, a greater balance of nitrogen relative to steam will have a drying influence. A greater balance of steam to nitrogen will have a humidifying influence. The moisture control strategy may advantageously be employed in the case of poultry products such as chicken products, the nature and thickness of which may be used as inputs to the control strategy.

It may be noted that the ports 160 and 170 could be integrated. Steam and nitrogen, or other inert gas, could be mixed in a mixing chamber separate from cooking chamber 14 prior to introduction of gas or gas mixture thereto.

ECU 100 may be programmed with gas mixture ratios and moisture levels for various types of food product. Such look up maps may conveniently be used in a moisture control strategy. The operation of the cooker 10, portion of which is shown in Figures 1 and 2, may be described as follows. The cooker 10 is switched on and the heating of oil commences. On sensed oil temperature reaching its setpoint, ECU 100 starts conveyor 16 and the food item infeed system, such that frozen food items may be in comparison transferred into the cooking chamber 14 for cooking. Steam is generated at a rate related to the food item thoughput and pressure in the cooking chamber 14 rises establishing a flow of steam through the vents 21 , 21a, 23 and 23a, as described above, to the surroundings which are at lower pressure. This flow of steam achieves four things.

Firstly, the steam flow purges air and oxygen from the cooking chamber 14 to the surroundings. Secondly, and associated with the first, steam flow due to positive pressure in cooking chamber 14 prevents ingress of atmospheric air. Thirdly, the steam acts as a stripping gas which removes oil

Substitute Sheet (Rule 26) RO/AU degradation products from the cooking chamber 14. These degradation products may take the form of free fatty acids. Fourthly, steam may be introduced in such quantity as necessary to maintain a desired moisture level in cooking chamber 14 as sensed by moisture level probe 180. Introduction of an inert gas/steam mixture, for example, a steam/nitrogen mixture with the ratio of the constituents being appropriately controlled may enhance moisture level control. Use of an inert gas alone may be used to further dry the cooking chamber 14 atmosphere.

Efficacy of the design for cookers of relatively long length may be established by measurement of free fatty acid levels in oil contained in the oil handling system. If the fraction of free fatty acids exceeds acceptable limits, oil replacement is indicated. Such oil replacement is an operating cost penalty though to some extent unavoidable. Using the embodiment of the invention shown in Figures 1 and 2, the time for free fatty acid levels to exceed the unacceptable threshold may be significantly extended with operating cost benefits. For example, it is possible to achieve two times longer oil life and minimise oil replacement rate in comparison with spray cookers of other design.

Figure 1 illustratively includes a main oil tank 150 with an oil dump valve 152. The oil dump valve 152 may be solenoid operated and opened for time sufficient to allow dumping of the requisite quantity of oil under control of ECU100. The dumped quantity of oil may be related to the opening time of oil dump valve 152. Then oil supply valve 154 connected to a fresh oil supply may then open for sufficient time to enable the required replacement quantity of oil to be introduced to main tank 150. Recycle oil 156 is filtered, heated and returned to sprayers 30.

Alternatively, as oil level in main tank 150 falls, perhaps as measured by the level sensor of the Applicant's co-pending International Patent Application No. PCT/AU99/00073, the contents of which are hereby incorporated herein by reference. Valve 154 may be opened to allow fresh oil to flow into main tank 150 until the required level is again achieved in main

Substitute Sheet ⁽Rule 26) RO/AU tank 150. There are two mostly used methods of removing the free fatty acids found in oil refineries:

1) Chemical neutralisation with sodium hydroxide;

2) Gas stripping using steam and more recently, nitrogen. Other methods may be used.

Now may be described a further embodiment of the invention made with reference to Figure 3. This embodiment though applicable to many cooker lengths is especially suitable for relatively short length cookers, such as those described in the Applicant's co-pending Australian Provisional Patent Application No. PP 5623, filed 1st September, 1998, the contents of which are hereby incorporated herein by reference, though this does not confine its application. In the description that follows, the items described above will be prefixed with the numeral "1".

Once again, cooking chamber 114 has fed and discharge ends 120 and 122. Food items are transported through cooking chamber 114 by conveyor 116 for cooking by heated oil sprayed through sprayers 130 advantageously located both above and below conveyor 116.

Food items are transported into cooking chamber 114 by infeed conveyor system 115 which drops food items onto inclined plate 115a to slide onto the conveyor 116. After leaving cooking chamber 114, food items drop from conveyor 116 onto inclined plate 117a to slide onto transfer conveyor system 117. Both the infeed conveyor system 115 and transfer conveyor system 116 are designed to minimise air ingress into the cooking chamber by providing housings 115a and 117a respectively having sealing engagement with paddles 115b and 117b forming part of the conveying means 115c and 117c of each conveyor system.

Infeed and transfer conveyor systems 115 and 117 may be disposed at an angle to the cooking chamber 114.

The foregoing description is specific to a paddle conveyor embodiment. Other conveyor types could be used bearing in mind the requirement that such be designed to include a seal between the oxygen rich environment of the

Substitute Sheet (Rule 26) RO/AU surroundings and the relatively oxygen deficient environment of the cooking chamber 114.

The infeed conveyor system 115 may be connected with food item storage means such as hoppers though manual feeding is not precluded. The conveying means 115c discharges food items onto conveyor 116 in a first buffer zone 180. The transfer conveyor system 117 receives food items discharged from conveyor 116 in a second buffer zone 185.

Each buffer zone 180 and 185 is located proximate each end 120 and 122 of cooking chamber 114 and communicated therewith by flap openings 120a and 122a in which flaps 50 are located as well as vents 121 and 123. The vent system operates in the same way as described for the embodiments of Figures 1 and 2.

The handling of condensing steam is somewhat different. Each buffer zone 180 and 185 will induce some condensation of steam and condensate collection systems 181 and 186 are provided in which condensate is collected into pipes 181a and 186a communicating with sumps 181b and 186b. Pipes 181a and 186a should be arranged to discharge below the liquid level in respective sumps 181b and 186b. These sumps 181b and 186b may be communicated with a common disposal system which may also collect condensate from other parts of cooker 110 as will be described further below. Once again, it is highly unlikely that such condensate may act as a source of recoverable oil for use in cooker 110.

At the upper portions 180a and 185a of buffer zones 180 and 185 may be located exhaust vents 180b and 185b of substantially rectangular section in the embodiment shown. These vents 180b and 185b may be provided with flaps 180ba, fixed by fastening(s) having a medial axis 188, shown in dashed outline in Figure 4 which may blow open at the positive pressure (relative to that of cooker 110 surroundings) of buffer zones 180 and 185. The flaps 180ba may not fully close vents 180b and 185b leaving an aperture 180bc and 185bc about 1 mm wide. Provision of such apertures prevents collapse of the flaps 180ba under negative pressure. Normally, pressure of buffer zones 180

Substitute Sheet ⁽Rule 26) RO/AU and 185 will be positive, preventing air ingress but they could be set up under vacuum.

Vents 180b and 185b are ventilated by exhaust hoods 182 and 186 with discharge gases from the cooker being treated by a scrubbing system prior to discharge to atmosphere. Vents 180b and 185b have sloped surfaces 180bd and 185bd such that condensate may flow into collection channels 183 and 187 which communicate with a condensate handling and disposal system, possibly through a duct system at the back of the cooker 110.

In a modification to the embodiments described above, there may be provided means to purge the cooking chamber 14 or 114 with an inert gas such as nitrogen or carbon dioxide. The latter may be relatively more reactive than nitrogen. Particularly at the commencement of operation, introduction of a purging flow of nitrogen may be used to eliminate air. Such purging may be particularly useful for products which require a long shelf life such as like crisps and nuts where oil re-coating may be avoided by use of a purge. Similarly, inert gas purging may be desirable for products subject to relatively high levels of fat migration into the oil such as chicken products. Use of such purging gas flow may also be used, as described above, with reference to Figures 1 and 2, and especially in association with steam introduction for moisture control in a cooking method especially suited to cooking of poultry products such as chicken products.

The gas introduction point may conveniently be located in the lower portion and toward the middle of the cooking chamber, the cool gas diffusing from the bottom. One or more gas inlet ports may be provided which communicate through ducts and gas regulator to bottle storage of the inert gas. Bottled nitrogen may be suitable for this application. Other gas storage or gas generators may be employed. Where steam is introduced, a conventionally available steam generator may be used for the purpose of steam generation. Modifications and variations to the cookers of the present invention may be made by the skilled reader of the specification. Such modifications and variations are deemed within the scope of the present invention. For example,

Substitute Sheet (Rule 26) RO/AU buffer zones 180 and 185 may be retrofitted to cookers 110 or may be integrated with cookers on delivery. Further, the cookers shown in Figures 1 to 3 may be operated in batch mode. In that case, loaded conveyor 16 or 116 moves into the cooking chamber 14 or 114 and stops when loaded food items are entirely located within the cooking chamber. After cooking a batch, conveyor 16 or 116 is re-started to transport cooked food items out of cooking chamber 14 or 114. Fresh food items may be re-loaded into the cooking chamber at this time. All cookers may include an oil replacement strategy as described for Figure 1.

Substitute Sheet (Rule 26) RO/AU

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1 . A cooker including:

(a) a cooking chamber; and

(b) at least one cooking chamber gas venting means provided for the cooking chamber wherein gases and vapours flow through the gas venting means for reducing oxygen diffusion into the cooking chamber.

2. A cooker including:

(a) a cooking chamber having fed and discharge ends;

(b) a conveyor extending between the fed and discharge ends of the cooking chamber for transporting food items to be cooked through the cooking chamber.

(c) a first opening to the cooking chamber at the fed end through which food items are fed into the cooking chamber;

(d) a second opening from the cooking chamber at the discharge end through which food items are discharged from the cooking chamber; and

(e) at least one cooking chamber gas venting means provided for the cooking chamber, wherein gases and vapours flow through the gas venting means for reducing oxygen diffusion into the cooking chamber.

3. The cooker of claim 1 or 2, wherein said gas venting means is at least one gas port located proximate a feed or discharge end of the cooking chamber.

4. The cooker of claim 3, wherein said at least one gas port is separate to said first or second opening.

5. The cooker of any one of claims 1 to 4, wherein said gas venting means includes a buffer zone located at at least one of said fed and discharge ends of the cooking chamber.

Substitute Sheet ⁽Rule 26) RO/AU

6. The cooker of claim 5 wherein said buffer zone has a pressure different from an operating environment in which the cooker is located to reduce oxygen diffusion into the cooking chamber.

7. The cooker of claim 5 or 6 having feed and output conveyors wherein said buffer zone allows for sealing communication of the cooking chamber and cooking chamber conveyor with infeed and output conveyors.

8. The cooker of any one of claims 5 to 7, wherein said buffer zone or said gas venting means includes pressure regulation means to preserve a pressure differential between said cooking chamber and said buffer zone or said gas venting means.

9. The cooker of any one of claims 5 to 8, wherein said gas venting means or said buffer zone communicates with a ventilating exhaust system which allows for collection and treatment of gases and vapours produced within said cooking chamber.

10. The cooker of any one of the preceding claims, wherein said cooking chamber includes at least one gas inlet port communicated to a gas supply for introducing to said cooking chamber a gas selected from the group consisting of steam, water vapour, nitrogen, carbon dioxide, inert gas and mixtures thereof.

11. The cooker of claim 10, including ratio control means for controlling the ratio of constituent gases in a mixture thereof which is introduced to the cooking chamber through said at least one gas inlet port.

12. The cooker of any one of claims 5 to 11 , wherein said gas venting means or said buffer zone include condensate collection means.

Substitute Sheet (Rule 26) RO/AU

13. The cooker of any one of the preceding claims being a spray fryer including deflector means for deflecting oil or fat away from said gas venting means.

14. The cooker of claim 13, wherein said deflector means include oil collection means to collect oil or fat infringing on said deflector means.

15. A method of reducing air ingress and oil degradation in a cooking apparatus including:

(a) generating steam and/or inert gas in a cooking chamber of a cooker; and

(b) inducing a flow of steam and/or inert gas from the cooking chamber through gas venting means wherein said steam and/or inert gas reduces inert gas reduces air ingress and causes removal of oil degradation products from the cooking chamber.

16. The method of claim 15 wherein steam and inert gas are generated in admixture, the ratio of each being controlled to maintain a minimal variation from a setpoint value for moisture level in the cooking chamber.

17. A method of cooking food items including the steps of controlling moisture level in a cooking chamber or a cooking apparatus by introducing a gas including at least one of steam and inert gas to said cooking chamber in such quantity and composition that variation from a setpoint for moisture level in said cooking chamber is minimised.

18. The method of claim 17 wherein said moisture level setpoint is determined as a function of at least one of food item type and thickness.

Substitute Sheet ⁽Rule 26) RO/AU

19. A method for controlling moisture level in a cooking chamber of a cooking apparatus wherein the relative proportions of steam and inert gas in a mixture introduced to the cooking chamber are controlled as a function of at least one of, food item type, food item moisture level and cooking chamber moisture level for achieving a cooked food item of acceptable moisture content.

20. The method of any one of claims 15 to 19 further including the step of replacing a certain proportion of oil to maintain volatile fatty acids content below an acceptable level.

Substitute Sheet RO AU