GB2182234A

GB2182234A - Apparatus for roasting oil-bearing seeds such as cocoa, coffee, cereals and the like

Info

Publication number: GB2182234A
Application number: GB08625442A
Authority: GB
Inventors: Karl-Joachim Mayer-Potschak; David Newton
Original assignee: Barth Maschf G W
Current assignee: Barth Maschf G W
Priority date: 1985-10-29
Filing date: 1986-10-23
Publication date: 1987-05-13
Also published as: CH672713A5; IT1197177B; GB2182234B; IT8621617A1; DE3538352C1; GB8625442D0; IT8621617A0

Abstract

Apparatus for roasting oil-bearing seeds such as cocoa, coffee and cereals comprises a rotatable drum (10) which is heat-insulated and carries a screw (13) on its internal wall for producing continuous movement through the drum of the material to be roasted and uniform roasting. The time of the material to be roasted is adjustable by regulating the speed of rotation of the drum, to between 60 seconds and 900 seconds using rollers (11, 12) and motor (M). A longitudinal continuous infra-red radiator (15) constantly exposes the material to infra red radiation of 1.5 microns to 2.7 microns and is preferably directed at the material being lifted by the screw. The amount of seeds entering and leaving the roaster may be controlled by hoppers (23, 27) which have sensors to monitor levels (24, 25 and 28, 29). The roasted beans may be fed to cooling section (32) with conveyor (33). <IMAGE>

Description

SPECIFICATION Apparatus for roasting oil-bearing seeds such as cocoa, coffee, cereals and the like The invention relates two apparatus for roasting oilbearing seeds such as cocoa, coffee, cereals and the like, which includes a rotatable drum.

In conventional roasting processes using a rotatable drum, the seeds are almost always roasted in a dry condition, a mechanically generated flow of air or gas being used as the medium for heat transfer.

This process is referred to as forced convection, and in this process a flow of hot air is usually passed at high speed over and through the material to be roasted.

All hot bodies give off energy in the form ofelec- tromagneticwaves. In the case of convection-type roasters, the hot airflow comes into contact not only with the material to be roasted but also with other parts ofthe machine, and heats them up. Thus, part of the heat energy is transferred to the material to be roasted by radiation from the hot surfaces around the material to be roasted. However, in all hot-air roasting apparatuses, the proportion of radiant heat is very low and can be disregarded when considering the conventional roasting process.

Besides convection and radiation, there is also the transfer of heat by conduction, in which the heat is propagated within a substance, that is to say the heat is transferred from moleculeto molecule. In a roasting operation,transfer of heat by conduction occurs when the material to be roasted is in contact with a heated surface. In hot air roasting apparatus therefore, part ofthe heat energy is also transferred by heat conduction as between hot parts of the machine and the material to be roasted. However the contribution thereof to the overall balance sheet in respect of heat transfer is also negligible.

In the forced convection situation,the roasting process takes place in four phases. The first phase is pure surface evaporation with a constant discharge of moisture. The first drying phase continues for the period oftime for which water in the interior ofthe material continues to be delivered to the surface thereof by capillary action. In the second drying phase, transportation of liquid by way of the capillaries is no longer sufficient to make upforthe amount of water which has been evaporated at the surface of the material being roasted. The surface experiences partial drying-out, combined with a fall in the drying speed. In the third drying phase, which involves vapour diffusion, the drying level moves slowly into the interior of the material.The water now evaporates at the liquid surface of the capillaries and, due to the vapour pressure difference, diffuses outwardly into the drying airthrough the air-filled pores. Due to the fact that the drying level is displaced into the interiorofthe material being dried, atthe sametimethere is an enhanced diffusion resistance and accordingly the drying speed falls. In the fourth phase ofthe drying procedure, the material being roasted becomes hygroscopic. The fourth phase takes up the greatest amount of time for the drying speed decreases with increasing degree of drying.

Roasting by means of forced convection suffers from various disadvantages. As the outer core layer of the material being roasted is already beginning to dry out towards the end of the first roasting phase, the surface layer undergoes a chemical and physical change. In this situation, roasting processes are already occurring in the second roasting phase, in the outer edge layer of the core, such roasting pro cessesforming a kind of insulating layer and impeding further heat exchange. Optimum degassing of the material being roasted is therefore prevented, and this has the effect of impairing development of taste and aroma. In particular, when carrying out a roasting operation using forced convection, there is no guarantee that the respectively correct roasting temperature is attained uniformly throughout the entire core cross-section.

As German laid-open application (DE-OS) No 2831 073 shows, it is also already known for cocoa beans to be shelled by subjecting them to infra-red radiation over a period of from 30 seconds to 180 seconds, using a wavelength of from 2 microns to 6 microns for the infra-red radiation. This treatment causes the pectin adhesive between the skin and the bean to melt so that the skin can be more easily removed from the bean in a subsequent dicing method.

The problem ofthe present invention is so to improve an arrangement of the kind forth in the opening part of this specification that it is possibleto carry out an absolutely uniform roasting operation, using a small amount of energy, in which the material being roasted can be completely degassed and continuously roasted.

According to one aspect ofthis invention, there is provided apparatus for roasting oil-bearing seeds such as cocoa, coffee, cereals and the like, comprising a heat-insulated, rotatable drum which carries conveyor means on the internal periphery of the drum for producing continuous movement through the drum of the material to be roasted, means for regulating the speed of rotation ofthe drum therebyto adjustthe passage time of the material to be roasted to a value of between about 60 seconds and about 900 seconds, and a longitudinally directed continuous infra-red radiating means disposed within said drum and adapted constantly to expose the material passing through the drum to infra-red radiation of wavelength in the range offrom 1.5 microns tO about 2.7 microns.

By using the infra-red roasting operation it is pos sibletotransfera large amountof energywithin a short period of time, without damaging the material being roasted.

In this connection, use is made of the realisation that the roasting operation can be improved and accelerated, in comparison with the conventional roasting process, only when the transportation of heat into the interior of the material being roasted can be improved. With the poor capacity for heating ofthe material being roasted, that occurs only if the roasting temperature is substantially increased and operation is carried out without forced convection, as is made possible by virtue of infra-red radiation.

The operational efficiency of infra-red roasting is based on the co-operation of electromagnetic waves in the infra-red range and the convection heat which however is not supplied to the material being roasted by a mechanically produced flow of air but by virtue of the natural spread ofthe hot convection gases.

Due to the rotary movement of the drum, the mat- erial being roasted is guided in a continuous flow through the infra-red radiation field, more part icularlyforthe entire period ofthe passage movement, that is to say, while the material is passing through the arrangement, the material is continuously exposed to heat radiation and convection heat. The location ofthe infra-red radiating means within the drum permits a high level of concentration of energy in a small space, namely on to the partof the drum which is covered by the moving material being roasted.

In a preferred embodiment, this effect may be optimised by the infra-red radiating means being so arranged in the region of the axis of rotation ofthe drum that the radiation field thereof is directed into the rising leading peripheral quarter of the drum cross-section.

In one embodiment the infra-red radiating means comprise a gas burner and temperatures offrom 580 to 11 50 C may occur at the infra-red radiating means, depending on the pressure ofthe gas-air mixture.

However, it is also possible to use electrical burners and oil burnersforthe infra-red radiating means.

Preferably, in order to be able to set the bestdirection forthe radiation field and the optimum roasting temperature,the infra-red radiating means is displaceable radially and/or on a circular path around the axis of rotation ofthe drum.

Preferably, uniform axial transportation of the material being roasted is provided by conveyor means in the form of a conveyor screw connected to the internal wall ofthe drum.

Preferably, so as to preventthe roasting gases produced from having a marked adverse effect on the aroma and taste of the material being roasted, the apparatus includes suction conduits communicating with the inlet and outlet ofthe drum, the conduits leading to a motor-driven fan which sucks away the roasting gases.

Regarding continuous movement of the roasting material through the drum, an advantageous embodiment is characterised in that the material to be roasted is fed to the drum from an upstream con tainer by means of a vibratory channel and a feed channel andthatthe roasted material leaving the drum can be passed into a downstream container from which it can beefed to a cooling belt by way of a vibratory channel. In that case, the material to be roasted is also supplied and removed in a continuousfashion, in a simple manner.

In orderto be able to operate at sufficiently high roasting temperatures, a preferred embodiment provides thatthe temperature in the drum can be regulated to upto about2200 by means ofatemperature regulator.

Byway of example only the invention will now be described in greater detail by means of an embodiment illustrated in the drawings in which: Figure lisa view in longitudinal section of an arrangementfor infra-red roasting, and Figure2 is a diagrammaticviewincross-section through the drum of the arrangement shown in Figure 1.

As the view in section through the arrangement in Figure 1 shows, the material to be roasted is introduced into an upstream or reserve container 23 in which level measuring means 24 and 25 monitora minimum and a maximum level of material.The vibratory channel 21 which is driven by the motor 22 passes the material to be roasted by way of the feed channel 20 in a uniform flow to the heat-insulated drum 10. The drum 10is caused to rotate about the axis of rotation 14 by way ofthe motor-driven rollertype drive means with rollers 11 and 12. A conveyor screw 13 acting as a conveyor means is mounted on the internal wall ofthe drum 10 so thatthe material to be roasted is transported axially in the same direction in the drum 10 to the outlet 26.The speed of rotation of the drum 10is adjustabie so thatthe passage time of the material being roasted can be from about 60 seconds to about 900 seconds.

The roasting gas is sucked away bywayofthesuc- tion conduits39 atthe openings40 and 41 inthe drum, more specifically by way of the motor-driven fan 43 which is connected to the suction conduit 39 byway of the branch conduit 42. The discharge con duit44 can pass the roasting gas which has been sucked away, for example to a heat exchanger in orderto remove the heat therein in a recuperation process.

The material being roasted passes by way of the outlet 26 ofthe drum 10 into the downstream con trainer 27 in which the level of material is again monitore to provide minimum and maximum values, by the level measuring means 28 and 29. The roasted hot material leaving the downstream container 27 passes by way of the vibratory channel 30 which is driven by means ofthe motor 31 ,to the cooling belt 33 which is disposed in the closed housing 32. The cooling belt is driven by the motor 34. Air is sucked through the housing 32 by means ofthe motordriven fan 35, by way of the air suction intake filter 38. The cooled roasted material is discharged atthe outlet of the housing 32. The fan 35 passes the hot air which has been sucked away, to the cyclone separator 36 with the catch or trap container 37.

The temperature in the drum 30 is maintained at a predetermined roasting temperature at the material being roasted, by means of a temperature measuring and regulating device 19. The roasting temperature can be adjusted at up to 220 C.

The material being roasted is heated by way of the infra-red radiating means 15 which extends overthe entire length of the drum 10. Reference numeral 16 indicates the burner unit of the infra-red radiating means 15, if it is for example a gas burner,to which the combustion air is fed by way of the conduit 17 and the fan 18. Instead ofthe gas burner, it is also possible to use an electrical or oil burner. The only important consideration is that the infra-red radiating means 15 reaches the necessary temperature of from 580 to 1150 C over its entire length, in orderto produce radiation with the desired wavelength of from about 1.5 to about 2.7 microns.

As shown by the sectional view th rough the drum 10 in Figure 2, the infra-red radiating means 15 is arranged outside the axis of rotation 14 of the drum in the lower cross-sectional quarter which leads in the direction of rotation 46 of the drum, and as the arrows 47 and 48 show, it is adjustable on a circular path around the axis of rotation 14 and radially with respect to the internal wall ofthe drum in orderto cause the radiation field 45to be directed on to the material being roasted, in the optimum fashion. The material being roasted is conveyed upwardly by the conveyorscrew 13to a position ataboutthe horizontal diameter of the drum 10 and it then falls in the direction ofthe lower-most point of the cross-section of the drum. In that case, the material being roasted passes through the radiation field 45 and is exposed to the infra-red radiation.In addition, the material being roasted performs a rolling movement as it is lifted up on the internal wall ofthe drum so thatthe material being roasted is moved and mixed intensively as it passes through the drum 10. That results in a uniform and regular roasting procedure, as was not achieved hitherto in any known roasting process.

Displacement of the infra-red radiating means 15 in the directions indicated by the arrows 47 and 48 can be initiated from outside the drum 10, with the rotary movement of the drum 10 being unaffected.

This novel arrangement makes it possible to en- sure that the material-to be roasted passes through the drum 10 in an absolutely regularfashion, with the material being continuously mixed and exposed to intensive infra-red radiation in order to perm it the above-discussed roasting phases to be carried out in the optimum fashion.

In the above described embodiment, the crucial consideration is that the infra-red radiating means extends over the entire length ofthe drum and that the speed of rotation ofthe drum predetermines the correct residence time for the material being roasted, for its movement through the drum. The rotary movement ofthe drum provides that the material being roasted is held exactly in the radiation field of the infra-red radiating means, in a rolling movement which also promotes mixing ofthe material,which moreover is also caused by axial transportation of the material through the drum.

The action ofthe infra-red rays is based on the transmissivity to radiation of organic materials, which is proportional to the wavelength ofthe rays penetrating thereinto, transmissivity increasing with wavelength. Such materials absorb rays with wavelengths of from 1.8 to 3.4 microns.

The radiation which is produced by the infra-red radiating means, with a wavelength of from 1.5 to 4 microns, at a burnertemperature of from 580 to 1150 C, lies precisely in the above-indicated most advantageous absorption range. That makes it pos siblefora large amount of energyto betransported into the interior of the material being roasted in a short period oftime, and forthe material to be cor respondingly quickly heated up.

In the described arrangement, the effect of convection heat is superimposed on the above-indicated action of the infra-red radiating means. The hot convection gases impinge on the material being roasted at low speed. Therefore, surface evaporation occurs with a constant discharge of moisture and the material being roasted remains moist as long as water is being supplied to the surface of the material from the interior thereof, through the pores. The energy necessary for the evaporation effect draws the water from the ambient air. This produces evaporation col dnesswhich cools the material down and holds the temperature at a fixed value just below the boiling point.

Capillarytransportation of the core water to the surface does not break down with the convection heat. At the end of the moisture-extraction phase, water no longer sufficiently evaporates at the surface of the material being roasted, to keep it cool and moist. The temperature of the material rises rapidly.

As however the material does not have a fast hot flow of air passing therearound,the surface ofthe material being roasted does nottakeon a hardened aspect with fissures and craters therein, in spite of the high temperature. Added to that also is the fact that the material to be roasted is being continuously mixed upandisonlyeverintheuppermostlayerof material for a shorttime.

Without encapsulation of the outer layers due to the surface taking on a hardened aspect as indicated above, the heat can penetrate rapidly into the interior ofthe material through the open pores thereof. The open pores play an important part in the absorption of heat as porous capillary material absorbs more energy than closely packed material with closed pores. Heat which penetrates into the capillaries is almost completely absorbed, more specifically by multiple reflection at the walls of the capillaries.

Claims

1. Apparatus for roasting oil-bearing seeds such as cocoa, coffee, cereals and the like, comprising a heat-insulated, rotatable drum which carries conveyor means on the internal periphery ofthe drum for producing continuous movement through the drum ofthe material to be roasted, meansforre- gulating the speed of rotation ofthe drum therebyto adjustthe passage time ofthe material to be roasted to a value of between about 60 seconds and about 900 seconds, and a longitudinally directed continuous infra-red radiating means disposed within said drum and adapted constantly to expose the material passing through the drum to infra-red radiation of wavelength in the rangeoffrom 1.5 micronsto about 2.7 microns.

2. Apparatus according to claim 1 wherein the infra-red radiating means is so arranged in there gion in the axis of rotation of the drum that its field of radiation is directed into the rising, leading peripheral quarter ofthe drum cross-section.

3. Apparatus according to claim 1 orclaim2 wherein the infra-red radiating means is displaceable radially and/or on a circular path around the axis of rotation of the drum.

4. Apparatus according to any one of claims 1 tq 3 wherein the conveyor means are in the form of a conveyor screw which is connected to the internal wall of the drum.

5. Apparatus according to any one of claims 1 to 4wherein respective suction conduits communicate with the inlet and outlet ofthe drum, the suction conduits leading to a motor-driven fan which sucks away the roasting gases.

6. Apparatus according to any one of claims 1 to Swherein the material to be roasted is fed to the drum from an upstream container by means of a vibratory channel and a feed channel and the roasted material leaving the drum can be passed into a downstream container from which it can be fed to a cooling belt byway of a vibratory channel.

7. Apparatus according to any one of claims 1 to 6 wherein the temperature in the drum can be regulated to up to about 220"C by means of a temperature regulator.

8. A method of roasting oil-bearing seeds such as cocoa, coffee, cereals and the like which comprises exposing the material to be roasted to infra-red radiation of wavelength in the range of from about 1.5 micron to about 2.7 microns for a period of between 60 seconds and 900 seconds.

9. Apparatusfor roasting oil-bearing seedssuch as cocoa, coffee, cereals and the like, substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of roasting oil-bearing seeds such as cocoa, coffee, cereals and the like, substantially as hereinbefore described with reference to the accompanying drawings.

11. Any and ali features and combinations thereof disclosed therein.