GB2147789A - Biscuit manufacture - Google Patents

Abstract

Biscuits are baked by exposure to near infrared radiation having a maximum intensity at a wavelength at which the radiation is not preferentially absorbed by water. The preferred wavelength is in the range 0.8 mu m to 1.5 mu m and most preferably at or close to 1.0 mu m. Baking of biscuits may take place on belt 6 in an oven 11 having infrared radiators 15 and fans 24 for creating turbulence in the oven during the baking process. <IMAGE>

Description

SPECIFICATION Biscuit manufacture The invention relates to biscuit manufacture and in particular to biscuit manufacture including baking by infrared radiation.

It is known that infrared radiation can be employed for the heating of food products with advantages, as regards speed of cooking for example, over conventional methods, and proposals have been made for the baking of bread by infrared radiation. In connection with bread baking proposals, it has been recognised that shortened baking times can be achieved due to the greater penetration of infrared radiation into the bread dough which in general increases with decreasing wavelength of the radiation. Not only the transmissivity of the bread dough but also the reflectivity of its surface has to be taken into account; also problems arise in connection with the need to provide the baked loaves with a suitable crust.Thus apparatus is proposed in US Patent 3 249 741 to Mills for baking bread primarily by ultralong wavelength infrared radiation, with wavelengths in the range of 30 to 400 pvm, with additional exposure to short wavelength radiation, with wavelengths in the range of 0.8 to 30 im, the latter being provided to effect surface browning. US Patent 2 340 354 to Wells proposes an apparatus for baking bread by infrared rays mainly in the wavelength range between 8,000 and 20,000 Angstrom units, followed by subjecting the product to baking heat substantially free from such rays.

It has been suggested that similar techniques can be applied to the baking of biscuits, but many of the factors which then become relevant are quite different from those which apply to the baking of loaves. The doughs employed for example are differently constituted from those used for making bread. Also, the product is of a substantially different shape, being in general in the form of a disc of which the thickness is very small compared with the other dimensions, whereas loaves, even when of elongate form, have substantial transverse dimensions. It is consequently not possible to obtain the potential benefits of the use of infrared radiation in biscuit manufacture simply by employing the prior art techniques proposed for heating food products generally or for the baking of bread in particular.

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 obtain an acceptable 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 by exposure to near infrared radiation in which the sources of the near infrared radiation are operated so as to have maximum intensity at a wavelength at which the radiation is not preferentially absorbed by water.

Because much of the baking process consists in the removal of moisture from the dough, it would appear that the shortest baking times could be achieved by use of near infrared radiation at a wavelength preferentially strongly absorbed by water to ensure maximum energy absorbtion by the dough. However the rate of energy transfer from the oven to the dough must not exceed a certain upper limit or the biscuit will exhibit internal cavities and external blisters.

Moreover early crusting of the dough shapes will result in increased reflectivity, so that heating of the biscuit is retarded. Accordingly, the wavelength at which the radiation sources operate with maximum intensity in accordance with the invention is selected so as to lie within the range of 0.8 Fm to 1.5 lim, preferably within the range of 1.0 Fm to 1.2 Fm, and for example at 1.0 Wm. By this means optimum baking of typical biscuit doughs can be obtained.

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 conveyor having a baking band or belt 6 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 housings 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 in 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 baking belt 6.

For heating, the baking oven 1 employs 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 reflective 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 Itm. 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 raw 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 4.

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 required within 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 24 being shielded by a baffle 28.

The near infrared radiators 15 are operated so as to emit radiation with a peak wavelength which is shorter than the wavelength at which radiation is preferentially strongly absorbed by the moisture in the biscuit shapes and preferably at or close to 1.0 Fm.

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 to the biscuit dough being baked. The baking process can be monitored by appropriate sensors located in canopies 3,39 located respectively between adjacent oven sections and control of the baking conditions in the oven sections effected accordingly.

Claims (13)

1. A method of baking biscuits by exposure to near infrared radiation having a maximum intensity at a wavelength at which the radiation is not preferentially absorbed by water.

2. A method according to claim 1, in which the maximum intensity lies in the range of 0.8 lim to 1.5 slum.

3. A method according to claim 2, in which the maximum intensity lies in the range of 1.0 Fm and 1.2 lim.

4. A method according to claim 3, in which the maximum intensity is at or close to 1.0 lim.

5. A method according to any one of claims 1 to 4, in which the baking takes place in an oven in which air turbulence is created during baking.

6. An apparatus for baking biscuits by exposure to near infrared radiation, the apparatus including source means of radiation having a maximum intensity at a wavelength at which the radiation is not preferentially absorbed by water.

7. An apparatus according to claim 6, in which the source means has a maximum intensity in the range of 0.8 m to 1.5 Fm.

8. An apparatus according to claim 7, in which the source means has a maximum intensity in the range of 1.0 Fm to 1.2 Fm.

9. An apparatus according to claim 8, in which the source means has a maximum intensity at or close to 1.0 Clam.

10. An apparatus according to any one of claims 6 to 9, including means for creating air turbulence in the biscuit-baking region.

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

12. An apparatus for baking biscuits, the apparatus being substantially as hereinbefore described with reference to the drawings.

13. A biscuit baked by the method of any one of claims 1 to 5 and 11.