Heating food articles

Food articles tending to exclude fat are heated in cooking apparatus provided with a floor removable for cleaning and of double-walled construction so that cooling air can be blown through to reduce or eliminate the risk that fat collected on the floor will ignite. The air flow is controlled so as to occur only when the floor temperature is above a predetermined level.

BACKGROUND OF THE INVENTION 
The invention relates to the heating of food articles. 
Cooking apparatus for foodstuffs which exude fat is subject to what is 
known as "flaming", that is, ignition of the exuded fat, which occurs when 
the temperature of the exuded fat rises to a certain level. For example, 
during the cooking of hamburgers the exudate is liable to ignite at a 
temperature typically of the order of 370.degree.-380.degree. C. Flaming 
can of course be prevented by the use of cooking temperatures below the 
flaming level, and it is advantageous to use near infrared heating sources 
because the surface temperature of the radiators need be no more than 
about 250.degree. C. However, there are circumstances in which high 
temperature heat sources are employed, and when short cooking times are 
required, heat of considerable intensity has to be applied, even though 
infrared radiation sources are used, so that flaming occurs because of the 
temperature reached by parts of the cooking chamber on which fat has 
accumulated. 
The invention accordingly has as an object the provision of a food heating 
method and apparatus whereby flaming is reduced or eliminated. 
SUMMARY OF THE INVENTION 
The invention accordingly provides a food heating method and apparatus in 
which the lower region of a food heating chamber is arranged to be swept 
on its underside by a cooling airflow. 
Fats exuded by food articles being heated in a heating chamber necessarily 
collect on the floor or lower part of the chamber, so this floor or lower 
part is cooled to a temperature below the flaming temperature in 
accordance with the invention. The airflow can be guided between the floor 
and a lower floor of the apparatus or an underfloor on which the apparatus 
stands, but the floor is conveniently the upper wall of a double walled 
drip-collecting tray, the airflow being confined between the walls. The 
air cooled floor is preferably inclined or shaped so that the fats, hot 
enough to be liquid, flow into a collecting region or sump, not 
necesssarily incorporated in the wall, to facilitate removal. 
The floor is advantageously readily removable and replaceable for cleaning. 
Where the floor is provided by a double walled structure, the whole 
structure is preferably removable, as otherwise a seal must be 
re-established around the entire periphery of the floor when it is 
replaced whereas the double walled structure needs merely to be 
re-connected to the cooling air supply. 
The cooling air flow can be induced in any suitable way and can be directed 
also to the cooling of other parts of the apparatus which are liable to 
reach excessive temperatures at which "flaming" could occur. For example, 
if the apparatus includes a conveyor on which food items are carried 
beneath or between radiant heaters, cooling air can be applied to the 
conveyor at a positon immediately downstream of that at which the cooked 
food items are discharged or to the guide surfaces by which the conveyor 
is guided between its upper and lower runs. If the apparatus incorporates 
heating elements such as infra-red heating tubes, the ends of which 
require to be cooled by an air flow when the tubes are in operation, the 
source of the air flow can be employed to provide cooling air also for 
such other parts of the apparatus. 
If the air flow is provided by an impeller, driven for example by an 
electric motor, the motor is preferably located remotely from the floor to 
minimise heat transfer between the motor and the cooking chamber. It is of 
course uneconomic to remove heat from the cooking chamber whatever its 
temperature and preferably the airflow is operative only when a 
predetermined temperature, near to the "flaming" temperature, is reached. 
The flow can thus be associated with a temperature sensing means 
controlling operation of the impeller through a thermostat. If near 
infra-red heating sources are used, the cooling air must be supplied to 
these regardless of the cooking chamber temperature so it is convenient to 
provide two separately operable cooling systems.

Referring now to the drawings, the illustrated cooking apparatus comprises 
a frame including tubular support pillars, for example, of stainless 
steel. The frame has two front pillars 2 and two rear pillars 4. At the 
upper part of the apparatus, side panels define a heating chamber through 
which runs a hamburger conveyor with a belt 5. The belt 5 is of ladder 
construction, that is, it comprises transversely extending bars joined to 
flexible links at their ends, the links forming a chain engaged by 
sprockets 8 at the front and the rear of the apparatus between which upper 
and lower runs of the belt extend horizontally through the frame. Between 
each pair of sprockets 8, a guide element presents a profiled surface over 
which the transverse bars of the belt 5 are guided. The rear sprockets 8 
are on a common spindle 10 driven by an electric motor 12 located at the 
base of the frame through a chain drive. At the rear of the apparatus, a 
doctor blade 14 is lightly biassed against the belt 5 to guide cooked 
hamburgers which have been passed through the apparatus on the upper run 
of the belt onto a delivery shelf 15. 
The cooking of hamburgers on the upper run of the conveyor belt 5 is 
effected by an upper bank of near infrared radiation sources above the 
upper run and by a lower bank of like sources located beneath the upper 
run, between it and the lower run. Each source comprises an elongate 
envelope or tube 20 of quartz containing a resistive element capable of 
emitting radiation preferably concentrated in the near infrared wavelength 
range for example between 1.5 .mu.m to 0.72 .mu.m. The two banks of the 
tubes 20 are mounted in respective racks 21 and 22, so that the tubes 
extend longitudinally of the path of travel of the hamburgers on the 
conveyor. Each bank of the tubes 20 is backed by a reflector 24, of 
aluminium or other highly reflective metal surface, so that the near 
infrared radiation from the tubes is directed onto the upper runs of the 
belts. 
Below the belt 5 the frame mounts a lower conveyor with a belt 25, of a 
similar configuration to that of the belt 5, for heating bun halves. The 
belt 25 is associated with drive arrangements similar to those of the belt 
5 but is of light construction, for example, a light gauge wire web, or of 
Teflon coated glass fibre material. Above the upper run of the belt 25 is 
mounted a third rack mounting a bank of the tubes 20 for heating bun 
halves on the upper run of the belt. No initial searing of the bun halves 
is required and such searing is avoided because the material for the belt 
is such as not to retain much heat. A second shelf 26 is provided at the 
rear of the apparatus for receiving hamburger buns after they have been 
heated on the belt 25. 
Between the lower run of the belt 5 and the lowermost rack of tubes 20, the 
apparatus frame mounts a drip tray 30 for receiving fat exuded from the 
hamburgers during the cooking process, as readily occurs when the 
hamburgers are being cooked relatively quickly, for example, within a 
cooking time of two minutes. The drip tray 30 is generally rectangular and 
has an upper surface which slopes downwardly towards the rear of the 
machine for fat collection in a gulley 31 extending transversely across 
the machine at the lower rear end of the tray. To prevent ignition of fat 
collected on the tray because of the temperature to which the tray may be 
heated by the tubes 20, a cooling airflow beneath the exposed upper 
surface of the tray is provided. 
For this purpose, the tray is constructed, for example of aluminium sheet 
material, from upper and lower plates 32,34 spaced apart to provide a duct 
through which the cooling air is caused to flow. 
The upper plate 32 of the tray slopes down to the sides of the apparatus 
from a centre line, to bring the fat collected thereon beneath the tubes 
20 at the sides and thus to prevent solidification before it reaches the 
gulley. 
The lower plate 34 of the drip tray has a raised rim 35 around its edges to 
which the upper plate is secured. Spacers 36 extend between the upper and 
lower plates to maintain the spacing and to confer rigidity on the tray 
structure. The lower plate 34 is apertured at 37 and 38 at the front of 
the apparatus to receive an incoming airflow and is also apertured along 
the rear edge, as by slots or as shown by a row of small holes 39 through 
which the airflow escapes after traversing the space between the plates. 
Air under pressure enters the drip tray through the apertures 37,38 from an 
elongate plenum chamber 40 extending horizontally across the front of the 
apparatus. To permit the drip tray to be removed for cleaning, its front 
edge is releasably engaged with the plenum chamber as best shown in FIG. 
5. The chamber is generally rectangular in the cross-section and has a 
transverse slot, in the upper part of its rear wall 41, in which the drip 
tray, and the upper walls 32 is turned outwardly at the upper edge of the 
slot to provide a guide for the drip tray during replacement, and to 
resiliently engage upper plate 32 to make an adequate seal. 
The apertures 37,38 in the drip tray lower plate are thus received within 
the plenum chamber 40, into one end of which air is blown from an impeller 
45 driven by an electric motor 46 at the base of the frame by way of a 
tube 44 extending upwardly from the impeller, or by way of the interior of 
one of the pillars 2. The location of the motor prevents the transfer of 
heat from the motor to the cooking chamber. The apertures 37 and 38 are 
positioned and dimensioned so that a generally uniform flow of air from 
front to back of the drip tray is obtained or so that a desired 
distribution of the air flow is obtained for example to take into account 
different cooking operations conducted at the two sides of the apparatus. 
In the apparatus illustrated, the aperture 38 nearer the inlet end of the 
plenum chamber is of smaller area than the other. 
The electric motor 46 is preferably not operated continuously during use of 
the apparatus to avoid wasteful withdrawal of heat from the cooking 
chamber at temperatures below that at which flaming becomes a risk. Motor 
operation is therefore controlled in accordance with the temperature of 
the drip tray 30, in particular, that of the upper plate 32. Preferably, 
the motor 46 is energised only when a temperature approaching 370.degree. 
C., for example 350.degree. C. is reached. Control is effected by a 
thermostat device including an elongate probe 48 which extends through the 
upper part of the front wall of the plenum chamber 40 and into the 
interior of the drip tray through an aperture 49 in the drip tray rim 35. 
The sensitive element of the probe is at its free end, and to ensure that 
this is engaged with the under surface of the drip tray top plate, a block 
50 provided with an inclined V-shaped upper surface is secured to the drip 
tray lower plate. As will be clear from FIG. 5, the drip tray can be 
installed within the apparatus after cleaning by movement towards the 
front of the apparatus, towards the end of which movement the end of the 
probe 48 will be received in the groove of the block 50, so that when the 
movement is concluded, the probe end is brought into firm contact with the 
top plate underside. 
Alternatively, the probe 48 is permanently secured to the underside of the 
plate 32 or received in a suitable guide fitting extending through an 
aperture the plate to its upperside. The probe is then electrically 
connected to a plug also secured to the tray and receivable in a socket 
carried by the frame. 
The drip tray 30 is supported along its side edges by brackets 51 and at 
its rear edge by a bracket 52 which provides a lip 54 to restrain the drip 
tray against withdrawal movement, and over which it can be lifted when 
withdrawal is required. 
Each of the racks mounting the tubes 20 includes a duct 60 at the front and 
another at the rear, into which the ends of the tubes 20 extend. As 
schematically shown in FIG. 2, cooling air from a second cooling air 
system is passed through the ducts 60. At least the side panel 61 of the 
apparatus is of double-wall constructions, and an electrically driven 
impeller (not shown) is positioned within the side panel to draw in 
ambient air through louvres 62 at the foot of the apparatus and to impel 
it upwardly within the panel for distribution laterally through the ducts 
60. The tube 44 is accommodated within this panel 61. After passage along 
the ducts 60, the air escapes at the other side of the apparatus, having 
collected heat from the ends of the tubes 20 in particular and cooling the 
apparatus as a whole. Because the tubes 20 must always be cooled when in 
operation, the second cooling system is continuously operated as long as a 
main control switch is closed to supply power to the tubes. 
Instead of the double-wall construction for the side panel 61, this and the 
other side panels defining the heating chamber can be of single wall 
construction of aluminium panels for example, and the air supply to the 
ducts 60 is then carried through one or more of the support pillars 2,4. 
FIG. 6 of the drawing shows such a construction, in which an electrically 
driven impeller 65 of the second cooling air system impels cooling air 
into the front support pillar 2 and thence into the ducts 60. 
Additionally, provision can be made for application of cooling air to the 
outlet end region of the conveyor belt 5 at which the belt achieves its 
highest temperature. Thus, cooling air can be directed onto the portion of 
the belt 5 directly downstream of the sprockets 8 at the delivery end of 
the belt, that is, at the beginning of the lower run of the belt. Instead 
or as well air can be conveyed through the guide element for the 
transverse bars of the belt at this position, the element being 
constructed as a tube to receive an internal air flow for this purpose. 
This cooling air will enter the cooking chamber after flowing over the 
conveyor belt 5 but a small volume of air flow through the cooking chamber 
is advantageous and assists in reducing "flaming". FIG. 7 of the drawings 
shows a modified cooker in which an extension part 66 of the rear duct 60 
of the uppermost tubes 20 has an apperture 67 through which cooling air is 
directed onto the upper run of the conveyor belt 5 adjacent to its 
delivery end. The rear duct 60 of the middle bank of tubes 20 has an 
outlet 69 at each end, through which cooling air is fed to tubular lateral 
guides 68 for the transverse bars of the belt 5. A further outlet 70 
directs cooling air onto the belt at the beginning of its lower run. The 
air supply for cooling the conveyor belt 5 and/or the exterior of the the 
associated guide element can be supplied from a third supply source 
controlled by a suitably positioned thermostat or operated throughout use 
of the apparatus. Instead as shown in FIG. 8 of the drawings cooling air 
can be directed to the belt and/or guide element from the ducts 60. It may 
however be preferred to supply the cooling air to the conveyor belt and/or 
the guide element from the first system, to avoid the introduction of cool 
air into the cooking chamber before this has reached the temperature at 
which the thermostat device effects operation of the motor 46. FIG. 9 of 
the drawings shows such a construction, in which a portion of the duct 44 
extends beneath the duct 60 of the uppermost tubes 20 and has an inlet 
port 72 for air cooling the upper run of the belt 5 adjacent to its 
delivery end. 
For further particulars of the illustrated cooling apparatus, for example, 
as regards control and operations, and also for other forms of cooling 
apparatus in which the present invention can be embodied reference may be 
made to European Patent Publication No. 0 040 528 issued Nov. 26, 1981, 
the disclosure of which is incorporated herein by reference. 
It is evident that those skilled in the art may make numerous modifications 
of the specific embodiment described above without departing from the 
present inventive concepts. It is accordingly intended that the invention 
shall be construed as embracing each and every novel feature and novel 
combination of features present in or possessed by the apparatus herein 
described and that the foregoing disclosure shall be read as illustrative 
and not as limiting except to the extent set forth in the claims appended 
hereto.