EP1109459A1 - Air impingement oven - Google Patents

Abstract

An apparatus and method for cooking foodstuffs is described. A conveyor (10) supports a series of moulds (12) each having a batter contained therein. The moulds are advanced in the direction of arrow (14). The base of the conveyor is subjected to heat from a series of transverse gas burners (16). Two heater units (22, 23) direct hot air on to the upwardly facing surface of the product in the moulds to toast or brown the surface of the product.

Description

AIR IMPINGEMENT OVEN

The present invention relates to food processing apparatus, a method of processing food and to a food product when produced by such a food process. The invention is particularly, although not exclusively, applicable to the even toasting or browning of the surface of baked goods such as crumpets and scotch pancakes.

Background and Prior Art Baked aerated products such as crumpets and scotch pancakes are produced on a commercial scale by depositing batter into a set of carrier rings which are positioned on top of a moving slat or band which is heated from beneath as it travels down the heating system.

At the end of the traveling band and within the oven, or separate therefrom, there is usually a radiant heater or contact hot box or both, which is used to give a cooked, evenly browned, top crust to the product after the internal structure has been fully or partly cooked and the desired height of the product has been achieved. Usually this top heating (or toasting/grilling) stage of the cooking process takes place for less than 25% of the total bake time and uses high temperature heat sources (>250°C) in order to impart the desired energy delivery in the required time.

This final cooking process has a number of known problems: 1. Radiant heaters always have a high temperature heating source which provides a rapid rise of product surface temperature. This rate of rise is dependent not only on the power, temperature and distance of this source from the product, but also on the thermal diffusion properties of the food product. The properties of the cooked surface therefore vary, depending on product height, recipe and aeration, or combinations thereof;

2. The use of radiant heaters gives rise to particular problems with products which have aerated internal structure and contain ingredients which readily brown by caramelisation and other mechanisms. Any bubbles or blisters on the product surface will rapidly rise in temperature due to their low thermal mass giving highly coloured or burnt spots on the product. This burnt appearance is unappealing to the consumer;

3. Any products which do not have an even or regular upper surface will be only part-cooked, as heat diffusion will be irregular.

4. Hot box heaters which cook the product by conduction via surface contact can only work after the top surface of the product has been cooked, otherwise the top surface will stick to the heater;

5. The contact hot box tends to squash the baked product, reducing its height, making it look small, and also increasing the density. There are also engineering problems which can be attributed to the use of contact heating, which usually means lowering a heated plate to make contact with the top of the produce each time that the hotplate is stopped. Some of these problems are:

1. A mechanism is required to lower the plate which is heated at the back by ribbon gas burners, necessitating a flexible gas pipe;

2. The plate can distort and may not always make even contact with the product;

3. Temperature control of the plate is difficult and usually non-existent ;

4. Contact with the product can cause charred pieces to adhere to the plate and be transferred to other products;

5. The back of the plate is uninsulated and gives off a great deal of heat as do the flames from the burners.

The resultant heat loss means that it is inefficient;

6. A canopy over the plate collects only some of the exhaust gases from the gas burners .

There are also problems which can be attributed to the use of gas fired infra-red heaters which operate in the long to medium wave band (650°-900°C) . The control of product temperature is poor since it is difficult to modulate the temperature whilst maintaining the desired infra-red wavelength. The slow response of these units also makes pulsed on/off control difficult to effect. In addition, the operation of such units leads to a hostile environment surrounding the unit due to the very high radiation temperature and consequent heat loss, with attendant inefficiencies. As with gas fired hot plates described above, there is heat loss into the environment, which leads to inefficiency and hot working conditions.

Solutions to the problems have been proposed using high speed quartz emitters which operate in the medium to short wavelength band (1200°-2000°C) but these have safety problems should the glass element or any protective ceramic cover break or splinter.

All previously proposed systems operate within narrow limits - there are very tight control parameters which must be constantly monitored.

It is an object of the present invention to attempt to overcome at least some of the above disadvantages.

The Present Invention It has been discovered that one solution to the problems described is to use a lower temperature heat source with high velocity convective air (hence a high heat transfer coefficient) directed on the surface of the product in order to achieve the desired energy delivery in the required time and simultaneously prevent parts of the product surface with low thermal mass, such as bubbles or blisters, reaching unacceptably high temperatures and becoming scorched. According to one aspect of the present invention, a food processing apparatus comprises hot air supply means and outlet means arranged to direct hot air at the upwardly facing surface of a food product .

The hot air supply means may be arranged to supply air at a velocity of greater than 10 m/s, preferably greater than 20 m/s, most preferably in the region of 30 m/s-50 m/s. The hot air supply means may be arranged to supply air at a temperature greater than 100° or greater than 140°, or in the region of 170°C, or less than 350°C or less than 250°C or less than 200°C. The temperature will depend upon the browning requirement and the nature of the product. The temperature will generally be between 100 and 300°C. The hot air supply means may be arranged to supply air at greater than atmospheric pressure, or greater than 20 or greater than 30 or greater than 40 or in the region of 55 mm water gauge at 20°C.

It is preferred on certain products that the air flow onto the top of the bakery products is such that the top surface only of the product is heated, whilst heat delivery to the side walls of the product is minimised.

The products to be cooked may be arranged in moulds, rings or trays, or placed directly on the belt. In certain cases the product will be constrained by another belt.

The outlet means may comprise at least one jet or nozzle. Preferably, a plurality of nozzles may be provided for each product. The area of the outlet of the nozzle or nozzles for each product relative to the upwardly facing surface of that product may be arranged to be in a ratio greater than 1:4, 1:5 or 1:6 or in the region of 1:7, or less than 1:10, or 1 : 9 or 1:8.

The clearance between the outlet means and the food product may be arranged to be less than 100 mm, eg less than 60 mm, preferably less than 40 mm most preferably in the region of 25 mm.

The apparatus may also include at least one gas burner located beneath the outlet means with the gas burner being arranged to direct a flame upwardly. The outlet means and the gas burner may be arranged to be offset from each other whereby gas exiting the outlet means does not impinge directly on the source of the flame.

The outlet means may include more than one outlet and at least two of the outlets may be arranged to emit air supplied from a different supply region. Each supply region may be arranged to have air supplied from a common source.

The outlet means may be arranged to conform generally to the shape of the upwardly facing surface of the food product to be processed.

The apparatus may include a conveyor arranged to transport a product past the outlet means. The conveyor may be arranged to cause successive products to be moved past the outlet means either in a stepwise fashion or in a continuous movement. The conveyor may be arranged to have a plurality of products extending in a row across a conveyor and those products in that row may be arranged to be spaced from each other. The outlet means may be arranged to direct air at each product in the row but not at locations between the products in the row. The conveyor may be a series of linked slats or may be a solid form. Alternatively, a double conveyor made of two wire mesh belts can be provided to encase the food product.

The apparatus may include a plurality of outlet means that are arranged to successively direct air at the same product. Each outlet means may be as herein described.

Alternatively, the apparatus may be separate from the conveyor, and can be moved over an already existing conveyor. The heaters can be used in modular form. Thus different modules can operate at different temperatures or moisture levels. A heater module could be adapted to emit chilled air onto a food product.

The apparatus may be arranged to have air removed from around the outlet means or from the complete periphery of the outlet means. That air may be removed in an upwards direction. The air may be removed by using a pressure differential. The apparatus may include means for recycling at least part of the air that has been removed to the outlet means .

In a preferred arrangement of the apparatus according to the present invention, two heater units are supplied which can be fitted around a conveyor belt in an existing bakery line.

The first toaster unit may be used to form a skin on the top surface of the product. The partially cooked product enters this unit with a cool top surface (<50-80°C for example) and emerges from this unit with a warm top surface (95-110°C in the case of sweet batters, and 110-220°C in the case of non-sweet batters) . This process drys the top surface and forms a thin, semi -plastic crust. The second toaster unit is used to form colour on the top surface of the product . The product enters this unit with a warm top surface (85-100°C for example) and emerges from this unit with a moderately hot top surface (110- 160°C in the case of sweet batters, and 160-250°C in the case of non-sweet batters) . This process evenly colours the top surface and forms a baked top crust.

In the present invention where the term "air" is used it will be appreciated that any gas, and not just air is covered. Moist, warm air can be supplied to a heater according to the present invention, which can be used to prove pre-cooked bakery goods, for example yeast raised doughs.

Only the top surface will be impinged by the heated air when the wish is to retain unbrowned sides. However, all sides could be treated and browned by the hot air.

According to another aspect of the present invention a method of processing food comprises directing hot air at the upwardly facing surface of a food product.

The method may comprise directing air at the surface of the food product greater than 10 m/s, preferably greater than 20 m/s, most preferably in the region of 30 m/s-50 m/s. The method may comprise pressurising air in order to direct air at the surface of a food product . The pressures may be as previously described in relation to the hot air supply means.

The method may comprise directing air from a plurality of jets or outlets at the upwardly facing surface of the food product .

The method may comprise directing air from outlets that have a ratio of outlet area to product area, over the extent of the product, of greater than 1:4 or 1:5 or 1:6 or in the region of 1:7 or less than 1:10 or less than 1:9 or within the region of 1:8.

The method may comprise directing air at the food product with the air that is so directed conforming to the shape of the food product. The method may comprise directing air at a spaced row of food products with air being directed at each food product but not, to any substantial extent, in the spaces between the food products.

The method may comprise removing air that has been directed at the surface of the food product, for instance by causing a pressure of less than that of the air that is directed at the food product to take that air away subsequently. The method may comprise removing air from around substantially the complete periphery of the food product . The method may comprise recycling at least some of the air that has been removed to direct it again at the food product .

The method may comprise moving the food product relative to hot air that is able to be directed in order to cause the food product to have different regions of hot air directed at it. Those regions of air may be arranged to be sequentially directed at the food product .

The food product may be arranged to be stationary during at least part of the time that hot air is directed at the food product .

The method may comprise passing the food product through at least two streams of hot air that are directed towards the upwardly facing surface of the food product with at least one of those streams of hot air having at least a partial cooking effect on the product.

The method may comprise browning or toasting the surface of a food product with the downwardly directed hot air. The method may comprise controlling the hot air to vary the amount of browning or toasting of a product, or to maintain the same browning or toasting of the product.

The present invention further relates to a method of baking and browning a bakery product wherein hot air in a first apparatus is used to form a skin on the top surface of a product. The partially cooked product enters this unit with a cool top surface (<50-80°C for example) and emerges from this unit with a warm top surface (95-110°C in the case of sweet batters, and 110~220°C in the case of non-sweet batters) . This process drys the top surface and forms a thin, semi-plastic crust. The method then utilises second hot air apparatus to form colour on the top surface of the product. The product enters this unit with a warm top surface (85-100°C for example) and emerges from this unit with a moderately hot top surface (110-160°C in the case of sweet batters, and 160-250°C in the case of non-sweet batters) . The temperatures exemplified can be +10°C. This process evenly colours the top surface and forms a baked top crust .

The method also relates to a method for the production of thin baked products, such as poppadums. In the manufacture of poppadums, high pressure jets of air are directed at the upper and lower surfaces of the product. Product texture is improved. Wire mesh cages in the form of double mesh conveyors may be required to retain the product on the conveyor. The two conveyors hold and restrain the food product, and substantially prevent bending and warping of the product as it cooks. A preferred temperature is of 300°C supplied for from 10-15 sees. The product poppadum has bubbles and blisters, but these are not charred. This is in contrast to other methodologies in the art, e.g. infra-red heating.

The present invention also includes a food product when produced by a method as herein referred to.

Detailed Description and Figures The present invention can be carried into practice in various ways but one embodiment will now be described, by way of example, and with reference to the accompanying drawings in which:

Figure 1 is a schematic sideways view of part of a food processing arrangement incorporating two heater units; Figure 2 is a schematic perspective view of the apparatus shown in Figure 1 ;

Figure 3 is a side view of a heater unit;

Figure 4 is an underneath view of a heater unit;

Figure 5 is a schematic end view of the heater unit of Figure 2;

Figure 6 is a side view of the heater unit of Figure 4;

Figure 7 is a view of a section across Figure 4; and

Figure 8 is a schematic representation of the flow system for the air of a heater unit.

Figure 1 shows a food processing arrangement which includes a conveyor belt 10 which supports a series of disc shaped moulds 12. Each mould has had batter poured into the centre of the mould at an upstream location (not shown) so that the batter flows out from the centre of the base of the mould to the surrounding cylindrical wall.

Now turning to Figure 2 , as the moulds are advanced in the direction of arrow 14, the base of the conveyor is heated by a series of transverse gas burners 16. Each burner 16 directs flames upwardly to the conveyor. The burners 16 direct flames from nozzles 18, that may be ribbon nozzles. Each burner is supplied with gas from a common supply pipe 20 running to the side of and beneath the conveyor 10. The heat is conducted through the moulds to heat the moulds and to gradually cook the batter as the conveyor advances. However, this is only part of the cooking .

At the location of the conveyor shown in Figures 1 and 2, two heater units 22, 23 are shown in series with each other but spaced slightly apart in the direction of travel. The effect of each heater unit 22, 23 is to direct heat onto the upwardly facing surface of the product . Heat is forced onto the upper surface of the product, thus toasting or browning the upper surface of the product. The hot airstream can also partly cook the batter.

The first toaster unit 22 is used to form a skin on the top surface of the product. The partially cooked product enters this unit with a cool top surface (<50-80°C for example) and emerges from this unit with a warm top surface (95-110°C in the case of sweet batters, and 110-220°C in the case of non-sweet batters) . This process drys the top surface and forms a thin semi-plastic crust. The second toaster unit 23 is used to form colour on the top surface of the product. The product enters this unit with a warm top surface (85-100°C for example) and emerges from this unit with a moderately hot top surface (110- 160°C in the case of sweet batters, and 160-250°C in the case of non-sweet batters) . This process evenly colours the top surface and forms a baked top crust .

The product moulds may be arranged in rows of five or six across the conveyor. The conveyor may be advanced in indexed or step-wise fashion, with the conveyor being stationary when one or more of the rows are filled, the conveyor being moved forward after each filling step. Whilst the conveyor is stationary, the product within the heater units 22, 23 is subject to the greatest intensity of heat against the upper surface of the product. The duration of the stationary period is from 1 to 2 seconds, preferably about 1.5 seconds.

It can be seen that the moulds 12 can be removed on a separate system 15 from the main conveyor belt 10. As shown in Figure 1, the moulds are removed after the first overhead heating stage at heater 22. The cooked product 25 is left on the conveyor belt.

The structure of both heater units 22, 23 are the same. Accordingly, one of these units will now be described in relation to the accompanying figures.

In Figure 3, a sideways view of the heater is shown. The conveyor belt 10 has been omitted for simplicity of description. The moulds 12 pass underneath the heater 22. Hot air is supplied to the outlets of the heater by a gas burner

60. Hot air from the burner passes through an offset fan 62 and through ducting 64 into the hot air chamber 66. This hot air chamber 66 is surrounded by an insulating body 67. The heater unit 22 is mounted above the conveyor, allowing the unit to straddle the complete width of the conveyor. The fan 62 drives the hot air from the burner 60 at an above atmospheric pressure into the chamber 66. The hot air leaves the chamber 66 at the desired set point temperature through outlets 26 arranged in bars 24. These outlets are provided as a group of jets or nozzles which direct the hot air substantially onto the surface of the cooked product 25. These are described in more detail below.

In Figure 4, the underneath of each bar 24 can be seen. It is the underneath of the bars that faces downwardly onto the upwardly facing surface of the product .

The bars 24 are arranged with their length perpendicular to the direction of travel indicated by the arrow 14. Each bar includes a cluster of holes 26 which, in use, comprise nozzles through which hot air is directed down on the product. For the sake of clarity, only one bar is shown with these holes. Each cluster is generally of a circular configuration corresponding to the surface area of the product whereby air is directed at substantially the complete top surface of a circular product accurately aligned beneath the cluster but air is not blasted down between adjacent products in the row or from in front of or behind the products. This is efficient as air is only directed at the product to be browned or toasted at least whilst the conveyor is stationary. Also, only the top surface receives the jet of hot air, not the sides.

The centre of each air bar 24 is spaced apart from the centre of an adjacent air bar by the same distance as the centre of a mould or a product left on the conveyor in adjacent rows. Accordingly during the "stop" part of the step-wise advancement of the conveyor, a mould with product, or product released from mould, will be accurately aligned beneath each cluster.

The burners 16 are arranged centrally beneath each air bar in the case where cooking and heating occur in the same system. If the air was blasted directly down from a hole 26 onto a nozzle 18 then the flame from that nozzle, or the series of nozzles may be blown out. Accordingly, no holes 26 are on the centre line 28 of the bars 24 and thus, when the conveyor is advancing and there is a gap between the air bars and the burners, that gap is not such that air from an opening can blow a burner out .

The heater unit 22 is mounted above the conveyor on four legs 30, one at each corner, that extend down to allow the unit to straddle the conveyor.

Hot air is supplied through an inlet duct 32 figuratively shown in Figure 8 (equivalent to duct 64 in Figure 3) . This air is divided by a horizontal wall 34. Half of the air is provided to a forward chamber 36 that is in communication with the holes on the three upstream bars and the remainder is fed to the four downstream air bars through a chamber 38. The air temperature is sensed by a thermocouple 39 and the temperature of the air can be controlled in dependence of the desired temperature with the sensed temperature. For example, the heater 22 can be programmed to provide a gas outlet temperature of 160°C-170°C, and the heater 23 can be programmed to provide a gas outlet temperature of 250°C. Chambers 36 and 38 are equivalent to chamber 66 in Figure 3.

The chambers 36 and 38 are also in communication with a ledge 40 that surrounds the air bars. This is shown in Figure 4. The ledge 40 includes a series of openings 42 along its extent through which bolts pass to secure the nozzle sheet to the plenum chamber. Air is removed evenly from around the periphery of the ledges 40 by a cavity 44 that completely surrounds the ledge 40 and which extends upwardly to a chamber 46 located on top of the air bar chambers 36 and 38. Reduced pressure in the region of 100 Pa is induced in the chamber 46 via a suction force or fan drawing air through an outlet 48. That outlet 48 may remove air from the edge of the chamber. Alternatively or additionally a conduit may extend into the chamber 46 such that air enters the conduit through an opening that extends, in plan, more towards one side than the other and then towards the other side as the opening approaches a middle region of the chamber. For simplicity, this alternative is not shown in the figures. Exhaust air can also be removed from between the air bars .

Although the air bars are closely spaced from each other, there is a small gap between each air bar. A wall 54 prevents air from being blasted from the chambers 36 and 38 through that gap. The wall also constrains air beneath the chambers to flow along the underside of those walls to the cavity 44 at the sides.

Returning to Figure 3, hot air passes up through the ducting 64 forced by the fan 62, and is expelled through the jet outlets 26. The outlet 26 can, as described, be arranged such that exhausted air is returned to the inside of the casing 67. This air, together with a small amount of other air can be recirculated. This has the advantage of ensuring that the temperature of the environment surrounding the heater 22 does not rise too much. Figure 8 is a schematic representation of the flow system for the air. The air enters the chambers 36 and 38 via the inlet duct 32, then enters the cavity 44 before leaving through the outlet 48. The air is drawn through the outlet by a fan 56 and then has heat added to it by direct gas firing 58, or indirect gas, oil or electricity. Then a fan 62 drives the gas under pressure to the inlet 32. The fans and gas firing may be located beneath the conveyor. Some air may be exhausted from the system.

The air is directed, by forced convection, downwardly onto the surface of the product. Crumpets, scotch pancakes and farinaceous products are particularly suited to this convection heating as it causes effective, even browning or toasting of the product without any significant presence of black spots on the surface of the product. Furthermore, with products that are intended to rise when being heated, it has been found that the direct impingement of the air causes the product to rise more than in conventional methods. Consequently, for a given rise in product, less material has to be used with the forced convection of the present invention than in the previous methods used. The product is not squashed and the end texture is lighter.

If the product becomes too brown or toasted, or if the browning or toasting is desired to be reduced, then either the velocity of the air exiting the nozzles can be reduced, for instance by decreasing the drive from the fan, or the temperature of the air can be reduced by altering the gas burner temperature, or the conveyor at rest duration can be shortened, or any combination thereof could be used. Any or all of these parameters can also be increased if the product was not browned or toasted enough or if the browning or toasting were to be increased.

Air is arranged to leave each opening 26 m the region of 30-50 m/s .

The clearance of each hole 26 (or the underside of the air bars) from the top of the product is m the region of 25 mm.

Although the present invention has been described as operating m a step-wise fashion it would be possible for the conveyor to move continuously. For continuous movement of the conveyor the moulds would probably be filled by a station that moved the nozzle when filling the moulds.

The pressure of the air within the chambers 36 and 38 is m the region of 55 mm of a water gauge at 20°C. The pressure m the cavity 44 may be m the region of atmospheric pressure or slightly less.

The diameter of each hole 26 m the air bars is 4-6 mm. The diameter of the pancake or crumpet is m the region of 75 mm. Accordingly, the ratio of the area of the 22 holes of each cluster to the area of product experiencing forced convection is 1:7.

In a variation of the invention, air ets are directed at the upper and lower surfaces of the product. This is particularly useful m cooking thin products such as poppadums For cooking poppadums, no initial cooking is carried out by burners, only by the air jets, operating at a temperature of about 300°C. The conveyor is stopped to allow each row of product to cook. Alternatively the conveyor can keep movi g. The total time of exposure to the heated air should not exceed 10-15 seconds, either through indexed motion or continuous movement.

Claims

1. A method of processing food comprising directing hot air at the upwardly facing surface of a food product .

2. A method as claimed in Claim 1 comprising directing air at the surface of the food product at greater than 10 m/s.

3. A method as claimed in Claim 1 or Claim 2 comprising pressurising air in order to direct air at the surface of a food product .

4. A method as claimed in any preceding claim wherein the temperature of the air is between 100┬░ and 300┬░C.

5. A method as claimed in any preceding claim comprising directing air from a plurality of outlets at the upwardly facing surface of the food product .

6. A method as claimed in any preceding claim comprising directing air at the food product with the air that is so directed conforming to the shape of the food product .

7. A method as claimed in any preceding claim comprising moving the food product relative to hot air that is able to be directed in order to cause the food product to have different regions of hot air directed at it.

8. A method as claimed in any preceding claim in which the food product is stationary during at least part of the time that hot air is directed at the food product.

9. A method as claimed in any preceding claim comprising passing the food product through at least two streams of hot air that are directed towards the upwardly facing surface of the product with at least one of those streams of hot air having at least a partial cooking effect on the product.

10. A method as claimed in any preceding claim comprising browning or toasting the surface of the food product with the downwardly directed hot air.

11. A method as claimed in Claim 10 comprising controlling the hot air to vary the amount of browning or toasting of a product or to maintain the same browning or toasting of the product .

12. A method as claimed in any preceding claim wherein hot air is also directed at the undersurface of the food product.

13. A food product that has been processed by a method as claimed in any one of Claims 1 to 12.

14. Food processing apparatus comprising hot air supply means and outlet means arranged to direct hot air at the upwardly facing surface of the food product .

15. Apparatus as claimed in Claim 14 in which the hot air supply means is arranged to supply air at a velocity greater than 10 m/s.

16. Apparatus as claimed in Claim 14 or Claim 15 in which the temperature is arranged to be between 140┬░C and 300┬░C.

17. Apparatus as claimed in any one of Claims 14 to 16 in which the hot air supply means is arranged to supply air at greater than atmospheric pressure.

18. Apparatus as claimed in any one of Claims 14 to 17 in which the outlet means comprises at least one nozzle.

19. Apparatus as claimed in Claim 18 in which the area of the outlet of the nozzle or nozzles for each product relative to the upwardly facing surface of that product is arranged to be in a ratio greater than 1:4.

20. Apparatus as claimed in any one of Claims 14 to 19 wherein the clearance between the air outlet means and the upwardly facing surface of the food product is less than 100 mm.

21. Apparatus as claimed in any one of Claims 14 to 20 including at least one gas burner located underneath the outlet means with the gas burner being arranged to direct a flame upwardly .

22. Apparatus as claimed in Claim 21 in which the outlet means are arranged to be offset from the or each gas burner located beneath the outlet means whereby gas exiting the outlet means does not impinge directly on the or each gas burner located beneath the outlet means.

23. Apparatus as claimed in any one of Claims 14 to 22 in which the outlet means is arranged to conform generally to the shape of the upwardly facing surface of a food product to be processed.

24. Apparatus as claimed in any one of Claims 14 to 23 including a conveyor arranged to cause movement of a product past the outlet means.

25. Apparatus as claimed in Claim 24 in which the conveyor is arranged to cause successive products to be moved past the outlet means.

26. Apparatus as claimed in Claim 25 in which the movement is arranged to be in a stepwise fashion.

27. Apparatus as claimed in Claim 26 in which the movement is arranged to be a continuous movement.

28. Apparatus as claimed in any one of Claims 14 to 27 to have air removed from the outlet means.

29. Apparatus as claimed in Claim 28 including means for recycling at least part of the air that has been removed from the outlet means again.

30. Apparatus as claimed in Claim 14 further comprising means to direct hot air supply at the downwardly facing surface of the food product .