GB2147788A - Biscuit manufacture - Google Patents

Abstract

A biscuit oven or oven stage has near infrared radiation sources 15 providing radiation having maximum intensity in the wavelength range 0.72 to 2.00 mu m and a conveyor belt 6. To reduce emission of secondary radiation of wavelength between 2 mu m and 6 mu m, the oven walls are cooled by air sucked into a duct formed by outer walls 30,32,34 by a fan 36. The reduction of secondary radiation emission results in an improved biscuit with an appropriate inner structure and also reduces the tendency for baked biscuits to break spontaneously when stored after baking. After exposure to infrared radiation in said oven or oven stage, the biscuits may be exposed to similar radiation in a further oven stage in which the oven walls are not cooled, whereby secondary radiation emitted from the wells effects browning of the biscuits. <IMAGE>

Description

SPECIFICATION Biscuit manufacture The invention relates to the baking of biscuits and in particular to biscuit baking by exposure to infrared radiation.

Biscuits baked by being conveyed through a baking oven enter the oven as shapes of raw dough.

During the baking process the dough shapes experience lifting which occurs predominantly in the preliminary phase of the process, moisture extraction or drying which occurs predominantly in the middle phase, and colour acquisition or browning which predominantly takes place in the final phase.

Finally, the baked biscuits are carried out of the oven for cooling and packaging. It is desirable to complete the baking process in the shortest possible time, but the energy input must be controlled to maintain the quality of product. The invention is accordingly concerned with the provision of a method of and an apparatus for biscuit manufacture providing optimised energy input into the biscuit shapes undergoing baking.

According to the invention, there is provided a method of and an apparatus for baking biscuits in which the biscuits are conveyed through an oven for exposure to infrared radiation with an intensity peak in the wavelength range of 0.72 to 2.00 Fm, and in which radiation at undesirable wavelengths due to heating of the oven wall is eliminated or reduced from at least part of the oven wall. In accordance with the invention therefore measures are employed to prevent the build up of sensible heat in the oven wall which would cause transmission from the inner surface of the wall of radiation at the undesired wavelengths.

To obtain the shortest baking times consistent with a satisfactory product, the radiation sources employed operate with energy peaks in the near infrared, in the wavelength range of 0.72 to 2.00 $m. Such radiation will penetrate biscuit dough to the depth of several millimetres, affording fast baking. The penetration of the radiation also reduces the difference in moisture content between the centre and the outer rim of the biscuit which is present in conventionally baked biscuits. The reduction in this moisture gradient is sufficient to prevent the spontaneous breakage, or checking, of the biscuits during subsequent storage. However the temperature then generated at the oven walls tendsto be such that secondary radiation in the range of 2 Fm to 6 pm is emitted from the reflective linings of the walls.Radiation in this wavelength range has a largely surface heating effect on the product. This is not necessarily unacceptable in the final stage of the baking process as it promotes browning but it is undesirable in the initial stages as the resulting biscuit outer structure inhibits the formation of an appropriate inner structure.

Accordingly, the invention is carried into effect by providing for the cooling of at least part of the oven wall so that the undesired secondary radiation is substantially eliminated or is emitted at an acceptably low intensity. The cooling can be achieved in any suitable way, conveniently by a flow of air or other cooling medium over the oven wall. The cooling effect can be limited to the upstream portion of the oven and can be confined to the top wall of the oven or to the top and at least part of the side walls. An outer casing to the oven can be provided to guide the air flow which can be obtained by convection or by a fan which may be controlled in response to the temperature of the part of the oven to be controlled. The outer casing contributes also to safe operation of the oven as its own cooler outer surface shields the otherwise hot outer surface of the oven.

The invention will be more fully understood from the following illustrative description and the accompanying drawings, in which: Figure 1 is a schematic plan view of a baking oven for biscuit manufacture in accordance with the invention; and Figure 2 is a cross-sectional view, partially schematic and on a larger scale, of the baking oven of Figure 1, on the line ll-ll of Figure 1.

The illustrated baking oven 1 comprises three adjacent oven sections 2,3,4 through which biscuits, initially biscuit shapes of a raw dough, are consecutively conveyed on a conyeyor having a belt 6 or baking band of which only the upper run is shown in Figure 1. The biscuit shapes 5 are deposited on the upper run of the belt 6 by a dough forming machine (not shown) located directly upstream of the oven. The baked biscuits emerging at a high temperature at the downstream end of the oven are conveyed to packaging machinery (also not shown) after cooling.

The three baking oven sections 2, 3, 4 are generally similar and each comprises an elongate rectangular oven housing 11. The housing 11 can be of sheet steel coated internally with a suitable reflecting material for example aluminium. The upper run of the belt 6 is supported within the housing 11 by suitable support means. Conveniently, as shown in Figure 2, rollers 12 are mounted on the housing side walls at appropriately spaced positions. The oven housing is supported on a base 14 in which further rollers 12 are similarly mounted for supporting the lower or return run of the belt 6.

For heating, the baking oven 1 employs an elongate tubular near infrared radiators 15 which are mounted to extend transversely of the belt 6, both above and below the upper run carrying the biscuits or biscuit shapes 5. The number of the radiators 15 above the belt upper run is suitably about twice the number per unit length of the oven below. The radiators 15 each comprise an elongate radiating element 16 backed by an appropriately shaped reflector 18, the element and the reflector being received within an outer protective housing 19 of material transparent to the radiation emitted by the elements.

Any other suitable form of radiator can be employed for example one comprising an elongate radiating element in a suitably transparent tubular housing, part of the surface of the housing being externally coated with a thin layer of suitably re flective material for example gold to reflect the radiation from the element back through the uncoated part of the housing. Alternatively, the elongate radiating elements within the transparent housings can be backed by appropriately shaped reflectors, for example of aluminium, supported within the oven.

The ends of the radiators at which the electrical connections to the elements 16 are made require to be cooled, and these ends are received in a duct 20 into which ambient air is blown for cooling purposes by a blower 21. A certain volume of this cooling air may enter the oven interior and this volume can be controlled to modify conditions therein, but this cooling air could be excluded or substantially excluded from the oven interior, the conditions therein being controlled by a separate system.

Each radiator 15 in the upstream, central and downstream oven sections is capable of emitting radiation with its intensity peak in the near infrared wavelength range of 0.72 to 2.00 Am. The belt 6 is an open grid, or is otherwise such as to be substantially transparent to near infrared radiation, and as the radiators 15 are positioned above and below the upper run, both major surfaces of the draw biscuit shapes 5 are exposed to the radiation.

Instead of a belt transparent to near infrared radiation, use can be made of a continuous steel belt or a belt of closely woven wire mesh. With such belts, much the greater part of the energy is applied from above, but some underbelt heating is required. Whatever kind of belt is used, the number and positioning of the radiators 15, and the speed at which the belt is driven are so co-ordinated with the nature of the biscuit dough that the biscuits are fully baked at the downstream end of the oven section.

To promote uniformity of the baking process within the oven 1, electric motors 22 are carried externally of the upper and lower walls of the oven housing 11 to drive fans 24 within it so that turbulence is created if and as requiredthin the oven, Moist air can be extracted from the oven through located central outlets in the upper wall leading through ducting 26 to an extractor fan (not shown), the outlets and the upper fans 22 being shielded by a baffle 28.

In accordance with the invention, the baking oven 1 incorporates cooling means by which the emission of secondary radiation, in the range in particular of 2 Fm to 6 Fm, by the inner surfaces of the walls of the housing 11 is reduced or substantially eliminated. Accordingly, an outer casing is provided to guide a cooling air flow over the outer surfaces of the oven housing. The outer casing has a top wall 30 spaced from the oven housing upper wall and provided with a central air outlet or exhaust duct 31, and side walls 32 extending downwardly to below the oven floor to a lower wall 34.

The lower wall 34 has a central air inlet duct 35 for air to be sucked in the outer casing by a fan 36 from an inlet 37 located at a height at which relatively cool air can be drawn in. This cool air then flows beneath the oven structure floor to either side, upwardly over the oven structure walls and then over its top wall to the duct 31. The cooling air flow may be due to convection, instead of to the fan 36, or an extractor fan can be located in the duct 31. Such an extractor fan, like the fan 36, can be controlled in response to the temperature of the oven housing 11, as sensed for example by a device located on its upper wall.

In the description so far reference has been made to the upstream oven section 2. The downstream oven sections 3,4 can be of like construction but in as far as the.browning effect of the secondary radiation from the inner surfaces of the housing 11 is less disadvantageous in the final stage of the baking process, the cooling arrangements constituted by the outer casing 30 can be omitted from at least the downstream section 4.

The cooling arrangements can in any event be operated to maintain different oven wall temperatures in different sections along the oven, and the temperature of the oven housing can be modified in different sections by external insulation of the housing wall.

The near infrared radiators 15 are of course arranged and operated to so provide a baking or power density profile, along the oven which is appropriate t9 the biscuit dough being baked. The baking process can be monitored by appropriate sensors located in canopies 38,39 located between adjacent oven sections and control of the baking conditions in the oven sections effected accordingly.

Claims (16)

1. A biscuit baking oven or oven stage comprising source means of radiation having maximum intensity in the wavelength range of 0.72 lim to 2.00 Wm and means for cooling at least one portion of the walls of the oven.

2. An oven or oven stage according to claim 1 including means for sensing the temperature of the oven wall or wall portion(s) cooled by the cooling means and control means for the cooling means, the control means being responsive to the sensed temperature to control the temperature of the cooled wall or wall portion(s).

3. An oven or oven stage according to claim 1, in which the cooling means comprises means for directing a flow of cooling medium over the cooled wall or wall portion(s).

4. An oven or oven stage according to claim 3, in which the cooling means comprises an outer casing and is arranged for cooling air to be directed between the outer casing and the outer surfaces of the cooled wall or wall portion(s).

5. An oven or oven stage according to claim 3 or 4, in which the cooling means comprises fan means for creating a flow of cooling air over the cooled wall or wall portion(s).

6. An oven or oven stage according to any preceding claim, including conveyor means for carrying biscuit shapes of raw dough and biscuits through the oven or oven stage.

7. An oven or oven stage according to claim 6, in which the conveyor means is substantially transparent to the radiation emitted by the source means which comprises portions above and below the conveyor means.

8. An oven comprising at least one oven stage according to claim 6 or 7, the conveyor means being arranged to carry biscuits through the or each oven stage to a further downstream oven stage having conveyor means for carrying biscuits therethough, source means of radiation having maximum intensity in the wavelength range of 0.72 Fm to 2.00 Fm but no means for cooling its walls.

9. An oven according to claim 8, in which the said conveyor means are constituted by a single run extending through the said oven stages in succession.

10. A method of baking biscuits, the method comprising the step of esposing biscuit dough in an oven or oven stage to infrared radiation having a maximum intensity in the wavelength range of 0.72 Fm to 2.00 Am whilst cooling at least a portion of the walls of the oven or oven stage in order to reduce or eliminate the emission of secondary radiation from the said part of the walls.

11. A method according to claim 10, in which the cooling is effected by cooling air flowing over the outer surface(s) of the cooled wall or wall portion(s).

12. A method according to claim 10 or 11, including the further step of exposing the biscuits to infrared radiation having a maximum intensity in the wavelength range of 0.72 lim, to 2.00 Am in a further oven stage of which the walls are not cooled, whereby secondary radiation emitted from the walls has a browning effect. on the baked biscuits.

13. A method according to claim 12, in which the final stage of biscuit baking takes place in the further oven stage.

14. A biscuit baking ove, the oven being substantially as hereinbefore described with reference to the drawings.

15. A method of baking biscuits, the method being substantially as hereinbefore described with reference to the drawings.

16. A biscuit baked by the method of any one of claims 10 to 13 and 15.