WO2012131333A2

WO2012131333A2 - Oven for baking bread products

Info

Publication number: WO2012131333A2
Application number: PCT/GB2012/050640
Authority: WO
Inventors: Daniel Sebastian Chadwick; Guy De Warrenne Bruce Adams
Original assignee: Daniel Sebastian Chadwick; Guy De Warrenne Bruce Adams
Priority date: 2011-03-25
Filing date: 2012-03-22
Publication date: 2012-10-04
Also published as: GB2489421A; GB2489421B; GB201105053D0; WO2012131333A3; EP2689190A2

Abstract

An oven (10) for baking bread products has the following elements: a platen (3) for receiving a bread product on an upper face; a lower cavity below the platen (3) and an upper cavity above the platen (3); a heat shield (4) below the platen; and an inlet (11) and an outlet (12) for an air flow for heating the platen (3) and the upper cavity. The oven (10) is configured such that the air flow is substantially unrestricted by turbulent flow between the inlet (11) and the outlet (12). A main part of the air flow enters the lower cavity through the inlet (11), is deflected by the heat shield (4), passes through at least one aperture to the side of the platen (3) into the upper cavity, and then passes across the upper face of the platen (3) to the outlet (12). The outlet (12) is disposed in a side wall of the upper cavity and lower than the roof. A method of baking bread products is also described.

Description

OVEN FOR BAKING BREAD PRODUCTS

Field of Invention

The invention relates to an oven for baking bread products. Embodiments of the invention are particularly suitable for the baking of pizzas and other flatbreads and topped flatbreads.

Background of Invention

The basic operating principle of an oven is to heat air, which in turn heats a foodstuff within the oven, both directly and by heating any support in contact with the foodstuff. Some ovens are simply enclosed spaces with limited venting, whereas other ovens are designed with a circulation (for example, fan-assisted ovens) or with elements of the air flow defined.

Pizzas are typically cooked in large purpose-built brick or stone ovens designed to reach very high temperatures. The cooking chamber needs to reach a high temperature - preferably greater than 500°C - for the pizza to be cooked effectively, and this temperature needs to be provided evenly over the whole area of the pizza to prevent localized burning or

undercooking. In addition the pizza needs to be cooked from the underside and this cooking surface needs to be made from a porous material to absorb a proportion of the water content and thus to prevent excessive steaming of the dough. The cooking time also needs to be relatively short, as otherwise burning will occur.

It would be desirable to cook pizzas and other flatbreads effectively without such a large oven. Portable pizza ovens have therefore been constructed, including modified barbecues and stovetop ovens. Examples of these oven types are briefly described below.

Examples of a barbecue-type oven are described in French Patents Nos. 2635258 and 2819708. Both these designs use an iron hotplate for cooking, and use a large firebox to heat the hot air. In each case hot air is deflected away from the underside of the hotplate and passes behind it into an upper oven region from which it vents. High temperatures can be reached in designs of this type if sufficient fuel is provided, but temperature across the cooking region will be relatively uncontrolled.

Other free-standing ovens are described in US 2009/0064985, US 5492055 and US 6425388. These all provide for heating from below, with one or more heat shields deflecting heat away from the underside of the platen. Heated air passes around the platen to heat the upper region of the oven before venting. Auxiliary heating of the upper oven (US 2009/0064985 and US 5492055) or venting of the lower oven (US 6425388) are used to attempt to balance temperatures more effectively in the cooking region. Examples of a stovetop oven are US 3053568, US 3270740, US 5365833 and US

2008/0135037. Again, these provide for heating from below with paths to allow heated air around the side of a cooking platen to heat an upper oven and then vent. These designs will generally not reach satisfactory temperatures for effective cooking of pizzas in particular, and have generally not resulted in successful commercial products. The present applicants have produced an earlier design of this general type - this is described in WO 201 1/027096.

All these types of oven have general difficulties. Most examples share a set of elements: a platen holding the foodstuff to be cooked, a hot air flow from underneath the platen, a heat shield deflecting the hot air flow from the underside of the platen, a passage to allow the hot air flow to pass above the platen and vent. In each case, it has proved difficult to both reach a sufficiently high temperature to bake a pizza effectively and to provide heat uniformly over the pizza so that it cooks evenly without burning or undercooking. These elements therefore do not seem sufficient in themselves to provide an effective solution. Many of the ovens described augment these basic elements by additional heaters or complex heat shield and platen design, but without fundamental improvement.

It would therefore be desirable to provide a pizza oven in a portable form - for example a stovetop or a barbecue-style oven - which was capable of producing pizzas cooked evenly at a high temperature.

Summary of Invention

Accordingly, in one aspect the invention provides an oven for baking bread products, the oven having: a platen for receiving a bread product on an upper face; a lower cavity below the platen and an upper cavity above the platen; a heat shield below the platen; and an inlet and an outlet for an air flow for heating the platen and upper cavity, wherein the oven is configured such that the air flow is substantially unrestricted by turbulent flow between the inlet and the outlet, whereby a main part of the air flow enters the lower cavity through the inlet, is deflected by the heat shield, passes through at least one aperture to the side of the platen into the upper cavity, and then passes across the upper face of the platen to the outlet, and wherein the outlet is disposed in a side wall of the upper cavity and lower than a roof.

This approach enables the provision of a high temperature in the cooking zone of the oven in a reliable and effective manner. In embodiments, the invention provides a stovetop oven which allows baking of pizzas evenly at high temperatures using a conventional heating supply (such as a gas stove using mains gas). Providing a flow of gas which is substantially unrestricted by turbulent flow (there will of course be some turbulence at flow edges - however, the main body of the flow will not be turbulent in its passage through the oven) is found to be effective to obtain very high operating temperatures in the oven. Placing the outlet below the roof of the oven, and so forcing the air flow (through its inertia) down towards the upper surface of the platen is particularly effective to ensure that the cooking zone where the foodstuff is located, rather than any other region of the oven, experiences the desired high temperatures.

Advantageously, the outlet is disposed substantially at the level of the platen - and so substantially at the level of the foodstuff which is cooking. This ensures that the hot air flow is effective to heat the foodstuff. Preferably, an area of the inlet is matched to an area of the outlet - this prevents restriction in the air flow (and hence turbulence) and also prevents entrainment of cold air from outside the oven at either the inlet or the outlet (particularly the outlet, which is adjacent to the cooking foodstuff). It is also preferred that an area of the at least one aperture, cumulatively, is matched to the area of the inlet and the area of the outlet, so that this aperture does not restrict the flow.

Advantageously, the oven also comprises a throttling means at the inlet to control an air flow. This allows the inlet area to be matched to the size of the incoming hot air flow. The incoming air flow may comprise an air flow heated by one or more gas burners. If the gas burners are some distance from the inlet, then the oven may further comprise a guide passage between the one or more gas burners and the inlet.

In another arrangement, the oven may comprise a fan and an electrical heating means, wherein an incoming air flow is drawn in to the inlet by the fan and heated by the electrical heating means. This electrical heating means may comprise one or more elements arranged such that an incoming air flow passing through the electrical heating means is prevented from taking a direct path therethrough without diversion around at least one element. This ensures that the air flow is effectively heated on entry into the oven.

Preferably, the platen is formed of a refractory ceramic material.

In a preferred arrangement, the roof of the oven comprises a fixed roof part and a moveable roof part, wherein the moveable roof part has a hinged connection to allow it to be moved to allow access to the platen. This allows for a simple roof design which allows easy loading and unloading of the platen. Alternatively, the whole roof may simply be hinged to a base part.

In such an arrangement, the roof may have a splitter mounted thereon in the upper cavity so that a portion of the air flow is diverted above the splitter, and wherein the splitter has a radiative surface facing the platen. This can be added without the addition of substantial turbulence, and may consequently be used to further increase heating in the cooking zone by adding radiation from the splitter surface as a further heat source. In one type of embodiment, the oven is substantially elliptical in a vertical cross-section extending through the inlet and the outlet. Preferably in this arrangement, there is a fixed roof part which comprises a highest part of the roof. A simple and effective construction of such an embodiment is possible if the oven comprises a support ring to which a base part, the heat shield and a roof part are mounted, and the support ring forming a seat for the platen.

In another type of embodiment, the oven has a base, roof and lateral sides, with curved front and back sides, wherein the at least one aperture between the lower cavity and the upper cavity are adjacent to the back side and wherein the outlet is formed in the front side. In the arrangement it is preferable if the platen is substantially quadrilateral in its major dimensions. The base, roof and lateral sides may all be substantially flat.

In a further aspect, the invention provides a method of baking bread products, comprising: placing a bread product for baking on a platen, wherein the platen is located above a first, lower cavity and below a second, upper cavity of an oven, wherein a heat shield is located below the platen in the lower cavity; and passing a heated air flow in to the lower cavity through an inlet, through one or more apertures into the upper cavity, and across a surface of the platen, wherein a main part of the air flow passes across the upper face of the platen to an outlet substantially at a same height as the bread product, and wherein the air flow is substantially unrestricted by turbulent flow between the inlet and the outlet.

Brief Description of Drawings

Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:

Figure 1 shows an isometric view from above of a first embodiment of a stovetop oven;

Figure 2 shows an exploded view of the stovetop oven of Figure 1 ;

Figure 3 shows an isometric view from below of the stovetop oven of Figure 1 ;

Figure 4 shows a vertical section through the stovetop oven of Figure 1 ;

Figures 5a and 5b are based on the sectional view of Figure 4 with arrows to illustrate the airflow through the oven;

Figures 6a and 6b provide plan views of the interior of the stovetop oven of Figure 1 from above with and without the platen in place;

Figure 7 provides an isometric view from below of the elements of the lower part of the stovetop oven of Figure 1 ; Figures 8a and 8b illustrate a throttling arrangement for use in embodiments of the invention illustrated with respect to the stovetop oven of Figure 1 ;

Figure 9 shows an isometric view from above of a second embodiment of a stovetop oven; Figure 10 shows an isometric view from below of the stovetop oven of Figure 9;

Figure 1 1 shows an exploded view of the stovetop oven of Figure 9;

Figure 12 shows an adaptation for embodiments of the invention for use when an input gas flow is located at some distance from the oven; and

Figures 13a, 13b and 13c show an adapted inlet region for embodiments of the invention where electrical heating is used to heat the air flow.

Description of Specific Embodiments

A first embodiment of a stovetop oven is illustrated with reference to Figures 1 to 7. This design of oven is particularly suitable for use with a conventional gas stove. The basic structure of the stovetop oven of this embodiment is shown in Figures 1 to 3, with the individual elements of the oven shown in particular in the exploded view of Figure 2. The stovetop oven 10 is broadly circular in plan view, and has the shape of an ellipse from the side view flattened from below. The stovetop oven 10 comprises a base part 1 with an inlet aperture 1 1 for a hot air flow to enter, a support frame 2 which sits over the base part 1 and has handles 21 and a ring part 22, a platen 3 which is supported in the ring part 22, a heat shield 4 which is supported on the ring part 22 and which is located underneath the platen 3 to protect it from at least the greater part of the hot air flow, a fixed roof 5 sitting over the ring part 22 and a moveable roof part 6 connected to the fixed roof 5 by a hinge arrangement 24. This hinge arrangement 24 allows the moveable roof part 6 to be pivoted, using handle 26, to allow access to the platen 3.

The hot air flow vents from the oven 10 through an outlet aperture 12 formed between the ring part 22 and the moveable roof part 6. This outlet aperture 12 lies substantially at the level of the platen 3, or in practice at the level of a foodstuff placed on the platen 3. The flow of hot air through the oven 10 is discussed in more detail below.

The parts of the oven 10 and their structural interaction will now be described in more detail with reference to Figures 1 to 4, 6 and 7. Most elements of the oven 10 may be constructed out of any appropriate material - that is, any material with appropriate properties to allow the element to be formed, and to maintain the necessary structural integrity under the conditions of operation of the oven. In order to retain heat in the oven 10, it is desirable to use outward facing components with a low emissivity. In most cases, the most convenient appropriate material will be a suitable metal finished with bright nickel, though as discussed below, a different materials choice may be made for the platen 3. Other metals, such as aluminium and aluminium alloys, may also be suitable choices, and treatments such as enamelling may also be used for elements such as the base part 1 and the roof parts 5, 6, though these will tend to increase the heat input required as this will lead to greater emissivity. Corrosion may also be an issue for some materials at high temperature use (for example, oxidation of steels) - this can be addressed by cleaning or by providing a greater heat input.

In vertical section (as seen in Figure 4), the base part 1 has the shape of a half ellipse (bisected by the line joining the two foci). The half ellipse is cropped by the inlet aperture 1 1 to form a base on which the oven 10 can rest. Not shown in Figure 2 (but shown in Figures 8a and 8b discussed further below) is a web 15. This has no role in the flow of hot air through the oven 10, but provides a more extended base structure to allow the oven to sit in position over a gas burner. The base part 4 may be formed by press forming, or by any other appropriate manufacturing technique to produce this structure from an appropriate material with sufficient structural integrity.

Above the base part 1 but below the platen 3 is the heat shield 4, which may again be made of an appropriate steel, aluminium or another such suitable material. The heat shield is bowl shaped, formed with a shallow curve shallowest at its lowest point and steeper (though still shallow) where the heat shield 4 attaches to the ring part 22 of the support frame 2. As can be seen from Figures 4 and 7, the heat shield 4 extends across the full width of the platen 3, but not across the full width of the support frame 2. The heat shield 4 has an upper surface 43 which is radiative, and provides heat to the platen 3 - as is discussed below, this is a significant source of heating for the platen 3. The heat shield 4 serves to divert the main part of the hot air flow around the outside of the platen 3 and through the support frame 2 (as discussed below), but a heat shield aperture 41 allows some air to pass in - and out - of the region 42 between the heat shield 4 and the lower part of the platen 3. This assists in allowing the platen 3 to be maintained at an appropriate cooking temperature. The distance between the lowest part of the heat shield 4 and the plane of the inlet aperture 1 1 (and hence the distance from the heat shield 4 to the burner flame) is significant in determining the heat flow to the platen 3, as it affects the radiative heat flow to the underside of the platen 3. An effective value of this distance in typical embodiments is 15-20mm. Figure 7 illustrates not only the heat shield aperture 41 but also rear vents 25a and 25b formed in the ring part 22 of the support frame 2. Support frame 2 is again suitably a metal structure, and may for example be cut from steel plate to the shape illustrated in the Figures. Rear vents 25a and 25b are sized comparably to the inlet aperture 1 1 so that the hot air flow passing in through the inlet aperture 1 1 is able to pass substantially without turbulence through the apertures formed by rear vents 25a and 25b, as will be described further below. The support frame 2 engages with the base part 1 , the heat shield 4 and the fixed roof part 5, all of which are supported by it - all these engagements may be made by forming suitable protrusions on the relevant part, with each of these protrusions engaged with a suitable aperture on the support frame 2.

Platen 3 is a disc located in a seat formed by the heat shield 4 and the ring part 22 of the support frame 2. While the platen 3 may be formed of metal, a particularly suitable choice is a refractory ceramic material. The foodstuff to be cooked is placed on the upper surface of the platen 3. Preferably, substantially the whole of the upper surface of the platen will be suitable for this purpose as a result of the design of the oven 10 as a whole.

A lower part (lower cavity) of the oven 10 is defined by the base part 1 , the support frame 2 and the platen 3, with the heat shield 4 also being located in this lower part. An upper part (upper cavity) of the oven is defined by the fixed roof part 5, the moveable roof part 6, the platen 3 and the support frame 2. The foodstuff to be cooked is of course also located in the upper part of the oven, though the temperature of the platen 3 is also influenced by conditions in the lower part of the oven.

The fixed roof part 5 forms a complementary half ellipse to the base part, with a segment removed (the segment being terminated by a plane forming an angle of approximately 30 degrees with the platen) such that the fixed roof part 5 extends over the greater part of the platen. The fixed roof part 5 extends across the whole of the rear part of the oven 10, and thus extends over all of both rear vents 25a and 25b. The moveable roof part 6 is connected by hinge arrangement 24 so that it can be rotated between two positions. In one position, the moveable roof part 6 closes off all of the opening left by the fixed roof part 5 except for an aperture at the front of the oven 10. This aperture is the outlet aperture 12 for the oven 12, and the moveable roof part 6 is moved to this closed position in use. The outlet aperture 12 is located in a side wall of the oven 10, significantly below the highest part of the roof formed by the fixed roof part 5 and the moveable roof part 6 - it is located substantially in the region of the edge of the platen 3, and overall it is disposed substantially at the height of a foodstuff being cooked (when used for a flat bread product such as a pizza or a flatbread). The area of the outlet aperture 12 complements that of the inlet aperture 1 1 and the combined area of the rear vents 25a and 25b - this contributes to achieving a flow of hot air through the oven 10 that takes place without substantial turbulence.

In the other position, the moveable roof part 6 is rotated upwards to open a substantially larger opening. This enables easy access to the platen 3, so that foodstuffs can be placed on or removed from the platen 3. As can be seen from the Figures, the platen 3 is arranged within the oven 10 so that a foodstuff can be placed or slid on to the platen 3 as convenient or appropriate.

Alternative arrangements may be made to achieve an equivalent effect. For example, the whole roof may be hinged to the base 1 at the support frame 2.

The air flow through the oven 10 will now be described in more detail with reference to Figure 5a. The arrows in this Figure show the main flow of hot air through the oven 10. This air flow is carefully arranged to heat the oven to effective cooking temperatures of 500° C and above when a conventional domestic gas burner providing 3KW heating is used, and to provide these temperatures evenly throughout the cooking region. For lower temperatures, the heat supply could simply be reduced by turning down the gas burner.

The main hot air flow follows the route indicated by the arrows: through the inlet aperture 1 1 ; deflected by the heat shield 4 to the back of the lower oven and passing through the rear vents 25a and 25b into the upper oven; then up to the fixed roof part 5 of the oven and brought down by the curve of the roof parts 5, 6 and the inertia of the air flow maintains flow out through the outlet aperture 12. While there are some minor regions of turbulence (for example, at the edges of the vents 25a, 25b) and some minor losses from the flow (for example the weak flows of air into the other part of the lower oven and in to - and out of - the region between the platen and the heat shield), substantially the major part of the hot air flow is laminar rather than turbulent and passes along this route. This air flow is also substantially unrestricted - the relative sizing of the inlet aperture 1 1 , rear vents 25a and 25b, and outlet aperture 12 is such that none of these poses a significant restriction to the flow of hot air through the oven. The relative sizing of the inlet aperture 1 1 and outlet aperture 12 in particular prevents cold air from being brought into the inside of the oven, as would happen if there was a significant disparity between them (in particular if the outlet aperture 12 was significantly larger than the inlet aperture 1 1 ). The inlet aperture 1 1 should also be sized so as to prevent overspill of hot air, to prevent wastage of heat - this is particularly important when the gas burner needs to run at full capacity to operate the oven effectively. Conversely, it should also be noted that a gas burner may simply be turned down to reduce the heat flow into the oven if required.

The sizes (areas) of the inlet aperture 1 1 , the rear vents 25a and 25b and the outlet aperture 12 are thus matched to each other. This does not mean that these areas are the same. In the region of the inlet aperture 1 1 , the air flow is in close proximity to the flame, and will be at a higher temperature than it will be downstream. This will lead to an expansion in volume of the air in the air flow. When the air flow enters the oven 10 and is deflected by the heat shield 4, its temperature will drop and the volume of air will contract. This lower volume will pass through the rear vents 25a and 25b and with a slight further reduction through further cooling through outlet aperture 12. A typical ratio of apertures for inlet:vents:outlet may be 130:75:70, though it will be appreciated that this ratio may be varied significantly without affecting the oven function (for example, the vents and the outlet may have the same area without significant effect on the function of the oven.

This approach means that there is little loss of speed in the air flow between the inlet aperture 1 1 and the outlet aperture 12, so the overall time that hot air remains in the oven 10 is lower than for conventional arrangements. This contributes directly to provision of high

temperatures and effective use of the heating source - the heat provided by the source is accepted and used by the oven, whereas interruption to the hot air flow would lead to rejection of some hot air. Another factor that contributes to provision of high temperatures specifically at the cooking zone (the region of the upper oven in the vicinity of the platen 3) is the combination of the curvature of the roof parts 5, 6 and the location of the outlet aperture 12. This combination forces the air flow downwards from the roof parts and across the cooking zone, ensuring a high temperature in this region, but without the creation of significant turbulence. High temperatures are thus not only created in the oven 10, but are created specifically in the region of the oven 10 where they are specifically needed - at the upper surface of the platen 3. It should be noted that the platen 3 is not itself at as high a temperature as the hot air flow - it will typically reach a lower cooking temperature in the 250-350 °C region. The provision of heat to the platen 3 (and hence to the foodstuff) is discussed in more detail below.

This design also prevents a common problem associated with pizza oven designs - loss of heat in the platen preventing effective rapid reuse. In this design, this problem does not arise, because there are two heating sources. The primary heating source for the platen 3 is by radiation and thermal convection/conduction from the upper surface 43 of the heat shield 4 onto the underside of the platen 3. This provides a heat source effective even when the top surface is covered with foodstuff. The secondary heating source is from the hot air flow above the platen 3, which is effective to heat the platen when there is no foodstuff in the oven. This design of oven is thus suitable for rapid sequential production of pizzas (or other such products), as little time is needed to bring the oven 10 (and specifically the platen 3) back to cooking condition after a pizza has been removed.

A typical use cycle for a thin freshly made pizza might be 12 minutes pre-heat, followed by 2 minutes cooking time. Repeat cooking can be immediate for the first few cycles because of the thermal mass of the platen 3. The number of these cycles is subject to many variables, such as the dough moisture - however, once a slight cooling of the stone is detected, then a recovery period between cooking of approximately the same time as the cooking time restores the platen temperature as the loss and recovery cycles are similar.

If further control of the air flow is needed, throttling mechanisms may be provided. This may be necessary in particular to adapt the oven 10 to different burner sizes. Figure 8a shows the use of a throttling ring 17 over the web 15, for use with a smaller burner size to prevent cold air from being entrained in by the hot air flow through an aperture oversized for the burner. For a larger size of burner, this throttling ring would be removed as shown in Figure 8b. Other throttling and airflow control measures may be used at other parts of the oven 10, most critically at the other potential restriction points: the rear vents 25a and 25b and the outlet aperture 12. The outlet aperture may for example be throttled to some degree by partial opening of the moveable roof part 6, or more precisely by a mechanism explicitly to vary the size of the outlet aperture 12 itself. The rear vents 25a and 25b may be provided with a throttling mechanism to vary the aperture sizes - another possibility is the creation of a passage through the support part 2 to provide a small air flow from the outside - this may allow a small amount of air to be entrained in from the outside to balance the air flow if needed. This passage could then be arranged to be sealed when not required. Such throttling and airflow control measures may be used in an automatic control mechanism to regulate the operation of the oven 10.

Other refinements may be used to create further increases in temperature. A splitter (shown in Figure 5b) may be attached to the roof (in this case, fixed roof part 5) just below the roof itself - this may be designed to present a knife-edge shape in the direction of the air flow, thereby causing minimal disruption to the flow beyond splitting a small part of it off to pass over the top of the splitter. A lower face of the splitter, facing towards the platen 3, could have been prepared as a highly radiative surface. This would provide an extra source of heat to a foodstuff on the upper surface of the platen 3, increasing the temperature in the cooking zone. Figures 9, 10 and 11 show a second embodiment of a stove top oven 10a. While broadly similar to the first embodiment in vertical section and with a similar hot air flow, the second embodiment uses a square platen 3a and has a generally cuboid shape. The base part, support ring and fixed roof part of the first embodiment are replaced by a body part 7 and two side walls 8 and 9. The side walls 8 and 9 support handles 21a on the outside and platen 3a and heat shield 4a on the inside but otherwise simply serve to bound the flow. The heat shield 4a is pyramidal, and so serves to deflect the hot air flow as a sheet to a linearly extending gap (not shown) extending between the platen 3a as supported and an inner face fo the body part 7. The body part 7 is in the form of a sheet curved up at the front to support the platen 3a and to define the lower part of the outlet aperture 12a, the sheet then extending downwards to form a base with the inlet aperture 11a extending through it, the sheet then curving up and around the platen 3a at the back (leaving the indicated gap) and then forming another flat roof surface parallel to the base. A moveable roof part 6a - another sheet, initially flat and then curving towards the outlet aperture 12a - is hinged to the body part 7 or to the side walls 8 and 9 so that it may move between two positions as for the first embodiment. The same operating principles apply for the second embodiment as for the first embodiment, and modifications that may be made to the first embodiment may be made also to the second embodiment with compensatory changes for the different geometry of the two ovens. Figure 12 shows a further modification for use when a stove top oven of the type described above is used with gas burners that are relatively remote from the inlet region, as would be the case for a typical gas barbecue design. A remote burner pipe 121 is connected by a wedge shaped guide 122 to a ring 123 on which the inlet aperture 1 1 can be seated. This prevents turbulence and entrainment of cold air to take place between the burner and the oven inlet aperture, thus allowing the same operating principles to apply even when remote burners are used.

In other embodiments, other heat sources can be employed without deviating from the basic principles described above. Figures 13a, 13b and 13c shows an inlet region 131 modified for an electric heat source. The heat source is an electric heating element 132 arranged so that air passes over the element in a tortuous path to ensure that the air is effectively heated as a whole, and does not contain a significant unheated part to the flow. Fan 133 is provided to drive the air flow through the oven 10, as the heating source is at the inlet region 131 of the oven rather than external to the oven. The vertical member 134 around the heating element enables a slight positive pressure to be maintained on its outside due to the fan and thus an even flow of air under the heating element is provided through the holes 135 at the bottom. The distance of the heating element below the heat shield 4 will determine the amount of heating via radiation of this element. The oven 10 as a whole may otherwise be essentially as for the first or second embodiment, for example, with the air flow driven to pass through the oven in the same way as for these embodiments.

As the person skilled in the art will appreciate, the embodiments described here are exemplary only, and modifications and variations to these embodiments and also new embodiments may be devised while remaining within the spirit and scope of the invention.

Claims

1. An oven for baking bread products, the oven having: a platen for receiving a bread product on an upper face, a lower cavity below the platen and an upper cavity above the platen, a heat shield below the platen, and an inlet and an outlet for an air flow for heating the platen and upper cavity, wherein the oven is configured such that the air flow is substantially unrestricted by turbulent flow between the inlet and the outlet, whereby a main part of the air flow enters the lower cavity through the inlet, is deflected by the heat shield, passes through at least one aperture to the side of the platen into the upper cavity, and then passes across the upper face of the platen to the outlet, and wherein the outlet is disposed in a side wall of the upper cavity and lower than a roof.

2. An oven as claimed in claim 1 , wherein the outlet is disposed substantially at the level of the platen.

3. An oven as claimed in claim 1 or claim 2, wherein an area of the inlet is matched to an area of the outlet.

4. An oven as claimed in claim 3, wherein an area of the at least one aperture, cumulatively, is matched to the area of the inlet and the area of the outlet.

5. An oven as claimed in claim 3 or claim 4, wherein the area of the outlet is adapted so as substantially to prevent cold air from entering the outlet.

6. An oven as claimed in any preceding claim, further comprising a throttling means at the inlet to control an air flow.

7. An oven as claimed in any preceding claim, wherein an incoming air flow comprises an air flow heated by one or more gas burners.

8. An oven as claimed in claim 7, further comprising a guide passage between the one or more gas burners and the inlet.

9. An oven as claimed in any of claims 1 to 6, comprising a fan and an electrical heating means, wherein an incoming air flow is drawn in to the inlet by the fan and heated by the electrical heating means.

10. An oven as claimed in claim 8, wherein the electrical heating means comprises one or more elements arranged such that an incoming air flow passing through the electrical heating means is prevented from taking a direct path therethrough without diversion around at least one element.

1 1. An oven as claimed in any preceding claim, wherein the heat shield is adapted for radiative heating of the platen.

12. An oven as claimed in any preceding claim, wherein the platen is formed of a refractory ceramic material.

13. An oven as claimed in any preceding claim, wherein the roof of the oven comprises a fixed roof part and a moveable roof part, wherein the moveable roof part has a hinged connection to allow it to be moved to allow access to the platen.

14. An oven as claimed in claim 13, wherein the fixed roof part comprises a highest part of the roof.

15. An oven as claimed in any of claims 1 to 13, wherein the roof of the oven has a hinged connection to a base part.

16. An oven as claimed in any preceding claim, wherein the roof has a splitter mounted thereon in the upper cavity so that a portion of the air flow is diverted above the splitter, and wherein the splitter has a radiative surface facing the platen.

17. An oven as claimed in any preceding claim, wherein the oven is substantially elliptical in a vertical cross-section extending through the inlet and the outlet.

18. An oven as claimed in claim 17, wherein the oven comprises a support ring to which a base part, the heat shield and a roof part are mounted, and which forms a seat for the platen.

19. An oven as claimed in any of claims 1 to 16, wherein the oven has a base, roof and lateral sides, with curved front and back sides, wherein the at least one aperture between the lower cavity and the upper cavity are adjacent to the back side and wherein the outlet is formed in the front side.

20. An oven as claimed in claim 19, wherein the base, roof and lateral sides are all substantially flat.

21. An oven as claimed in claim 19 or claim 20, wherein the platen is substantially quadrilateral in its major dimensions.

22. A method of baking bread products, comprising:

placing a bread product for baking on a platen, wherein the platen is located above a first, lower cavity and below a second, upper cavity of an oven, wherein a heat shield is located below the platen in the lower cavity;

passing a heated air flow in to the lower cavity through an inlet, through one or more apertures into the upper cavity, and across a surface of the platen, wherein a main part of the air flow passes across the upper face of the platen to an outlet substantially at a same height as the bread product, and wherein the air flow is substantially unrestricted by turbulent flow between the inlet and the outlet.