Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR ROASTING COFFEE
Background of the Invention
The present invention relates to a method and apparatus for roasting
coffee.
Three operations are needed to convert the green coffee beans into
consumable beverage: ( 1 ) roasting, (2) grinding and (3) brewing. The
characteristic flavour and aroma of coffee is developed only by roasting.
Roasting is a time-temperature dependent process, where chemical
and a physical changes are caused in the green coffee beans accompanied
by loss of dry matter primarily such as gaseous carbon dioxide and water
and other volatile products of the pyrolysis. Roasting is normally carried out
under atmospheric conditions with hot gases and excess air as primary
heating agents. Heat also may be provided by contact with hot metal
surfaces, usually as a supplement to convection from the hot gases. The
degree of roast plays a major part in determining the flavour characteristic
of extracts eventually brewed from roasted coffee, whatever the type.
In general, roasters have been designed and are available based on
different mechanical principles as summarized below.
Horizontal rotating drum - solid or perforated wall
Vertical static drum with blades
Vertical rotating bowl
Fluidized bed roaster
Pressure roaster
All roasters must also provide a cooling facility to bring the roasted
coffee to ambient temperatures after the desired level of roast, usually by
contact with cold air.
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The known roasters use either "once through" flow of hot air or they
recirculate the hot gases developed by roasting. The disadvantage of the
first type is a high energy consumption since the incoming air has to be
constantly heated to the required temperature. The second type is
considered disadvantageous as it is difficult to properly control the roasting
cycle. Another disadvantage of the circulated flow of air is in the danger of
tar deposits formation on the roasted beans impairing the quality of the final
product. The known roasters utilize the clocking of the roast time from the
beginning of the process to its end. This is disadvantageous as when only
one of many variables of the roasting process or conditions changes, the
result is not uniform even for the same type. The changes in variables
governing the roasting are inevitable. Every roast, even of the same type, is
slightly different from another because of variables such as temperature or
moisture.
In a coffee roasting operation, the original moisture present in green
coffee beans is first removed. Then the roasting itself starts at a
temperature of about 200°C after which through, exothermic reactions,
escalation of the roasting process occurs which requires considerable
control of the roasting for a given degree of roast. Reaction in green arabica
coffee may start as low as 160°C. The reaction peaks at about
210°C and
falls off at about 250°C.
The most obvious physical change to occur is the external color
which ranges from light brown to almost black. This change is accompanied
by exudation of oil to the surface with increased severity of roasts. Swelling
of beans also progressively occurs.
Summary of the Invention
It is an object of the present invention to improve the roasting
methods and apparatuses such as to avoid or at least reduce the above
disadvantages and to provide an improved uniformity of the coffee roasting
3fl process.
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The invention utilizes, in its one preferred application, the
phenomenon of the roasting of coffee being accompanied by the popping or
cracking of the beans leading to a considerable decrease of density as a
function of the degree of roast but also of the speed of roasting. While
different types of coffee beans behave in a different fashion during the
roast, the cracking phenomenon always occurs and has a general pattern
which is common to all types of coffee. According to the present invention,
the peculiar pattern of the popping or cracking sound is followed as a
variable which is indicative of the state of pyrolysis of the coffee beans
being roasted.
In another aspect, the invention utilizes, as a supplement or
replacement of the method mentioned in the preceding paragraph, the
pattern of changes in the temperature of the surface of the coffee beans
being roasted, or within the roasting circuit, before and after a catalytic
converter.
In general terms, the invention provides, in one aspect thereof, a
method of controlling the roasting of a batch of a type of coffee in a
roasting chamber of a roasting device, comprising the steps of:
(a) charging a batch of nonroasted coffee beans to the roasting chamber;
(b) subjecting the batch to the flow of air having the temperature
required for bringing the beans of the batch to the pyrolysis;
(c) establishing the point in time at which pyrolysis of said batch is
started by at least one of the steps of:
(i) analyzing the cracking sound generated by the beans of the
batch as the batch is being heated to the point of pyrolysis to
establish the first occurrence of the sound quality indicative of
the commencement of the pyrolysis;
(ii) measuring the temperature of the surface of the beans to
determine the first occurrence of the temperature change
indicative of the commencement of the pyrolysis;
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(d) when the commencement of the pyrolysis is established by the step
(c), initiating the operation of a clocking device preset to a
predetermined time length;
(e) upon expiry of said predetermined time length generating an output
signal for stopping the roasting operation and discharging roasted
coffee from said roasting chamber.
In another aspect, apparatus is provided for roasting a batch of a type
of coffee comprising:
(a) a roasting chamber having a bottom portion and a top portion and
operatively associated with heated air supply flowing in a direction
from said bottom portion to said top portion;
(b) a sound and/or temperature probe reaching into the roasting chamber;
(c) said sound probe being adapted to sense the pattern of noise
generated by the batch in said chamber as it is being roasted;
(d) said temperature probe being adapted to sense the pattern of
temperature increase of the surface of coffee beans in said roasting
chamber;
(e) said probe and/or probes being operatively connected to an timing
device adapted to actuate a signal upon expiry of a predetermined
time from a predetermined point of the pattern sensed by the
respective probe, a clocking device adapted to actuate a roasting
cycle ending device.
In a yet another aspect, the invention provides apparatus for roasting
coffee including a roasting chamber adapted to hold a batch of coffee beans
to be roasted by hot air, said roasting chamber being disposed within a
heated air circulation system, said heated air circulation system further
comprising:
(a) air circulation fan device disposed upstream of said roasting chamber
and having a pressure side thereof connected to an upstream end of a
hot air feeding duct, the downstream end of the hot air feeding duct
being operatively connected with a hot air inlet of said roasting
chamber at an upstream end of the chamber;
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(b) a hot air outlet system of said roasting chamber being disposed at a
downstream end of the chamber and being connected to an upstream
end of a return duct system, the downstream end of said return duct
system being disposed at a suction side of said fan device;
(c) said heated air circulation system being connected to an exhaust
conduit system for discharging to the atmosphere at least a part of air
present in said heated air circulation system;
(d) said heated air circulation system being further connected to a
downstream end of a fresh air supply conduit open at an upstream
end thereof, a fresh air valve being disposed between the
downstream and upstream ends of the fresh air supply conduit;
(e) air heating device disposed within the heated air circulation system
and adapted to maintain the temperature of the heated air in said
chamber at a predetermined roasting temperature.
Brief Description of the Drawings
The invention will now be described by way of a prototype and
preferred embodiments, with reference to the enclosed drawings wherein:
Figure 1 is a simplified diagrammatic side view of a prototype of the
roasting apparatus of the present invention, with certain parts
omitted;
Figure 2 is a front view taken from the left of Fig. 1;
Figure 3 is a perspective view of the apparatus showing the roasting
chamber in a discharge mode;
Figure 4 is a perspective view of the apparatus showing the roasting
chamber in a roasting mode;
Figure 5 is a partial perspective view of a lower portion of the environs
of the roasting chamber in an open state;
Figure 6 is a diagrammatic representation, in a side view, of the upper
portion of the roasting chamber with certain parts omitted;
Figure 7 is a partial side view showing the air circulation control of the
prototype;
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Figure 8a is a block diagram of the arrangement of a preferred
embodiment of the sound analyzing system of the apparatus of
the present invention;
Figure 8b is a diagram similar to that of Fig. 8a but showing a preferred
embodiment of the temperature analyzing system of the
apparatus of the present invention;
Figure 9 is a diagram of a modified version of heated air circulation
system for a coffee roaster in a roasting mode;
Figure 10 is a diagram of the circulation system of Figure 9 shown in a
cooling mode;
Figure 1 1 is a diagram similar to that of Figure 9 but showing another
modification of the air circulation system, in a roasting mode;
Figure 12 is a diagram of the circulation system of Figure 1 1 shown in a
cooling mode; and
Figure 13 is a diagrammatic representation of a preferred embodiment of
a catalytic converter for use in air circulation systems of the
present invention.
Detailed Description
The prototype of the roaster includes a cylindric roasting chamber 20
comprising an upper chamber 21 and a lower chamber 22. There are flanges
23, 24 with a heat resistant seal (not shown) secured to one of the flanges
23, 24 to sealingly engage the opposed flange when the upper and lower
chambers 21, 22 are aligned such as shown in Fig. 1 or Fig. 4. A locking
lever 25 (Fig. 1 ) is operatively associated with the upper chamber 21 to
press the two flanges 23, 24 to each other to secure a sealing engagement
between the two and also to sealingly press the bottom end of the lower
chamber 22 against a base plate 24a. The upper chamber 21
communicates, via a tangential inlet 26 (Fig. 3) with a cyclone separator to
be described later. The top of the upper chamber 21 is provided with a
hopper 55 shown only in Figs. 1 and 2, provided with a manually operated
knife valve 56.
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The lower end of the lower chamber 22 is pivotably secured to a
pivot 27 which permits the lower chamber 22 to assume a first position of
Fig. 1 or 4, i.e. coaxial with the upper chamber 21, and a second position of
Fig. 3 or 5, by pivoting same over an arc of about 40°.
The lower end of the chamber 22 sealingly slides on the support plate
24a which has two circular passages therein. The first passage 29 is
provided with a pattern of perforations allowing passage of air but being
smaller in size than a coffee bean. The second, discharge passage 30 has a
diameter similar to that of the first passage 29 but is of the type of a plain
bore. The first passage 29 is located on top of a pressure air chamber 31 a
at the downstream end of a lower duct 31 while the discharge passage is
located above a discharge container 32 (Fig. 2). The bottom portion of the
interior of the lower chamber 22 is provided with a truncated cone 33 the
lower end of which has the diameter corresponding to the diameter of the
passages 29, 30. Accordingly, when the lower chamber 22 is moved into
alignment with the upper chamber 21, it is also aligned with the first
passage 29. Pressurized air may then flow into the chamber 20 through the
perforated first passage 29. When the lower chamber 22 is pivoted about
the pivot 27 to a discharge position, the contents of the chamber fall
through the cone 33 into the discharge container or cooler 32.
A sampler 34 located in the wall of the lower chamber 22 serves the
purpose of visual checkup of the coffee beans treated in the chamber 22. In
principle, it is just a spoon-like element which is normally disposed inside,
but can be pulled temporarily outside of the chamber 22. The sampler is
adapted to prevent hot air and unscooped beans from escaping from the
chamber 20 as the sample of the beans is taken out of the chamber and
examined, to be later returned back into the chamber 20 by simply pushing
the sampler back to its initial, inverted closed position. The samplers of
this
type are known and therefore do not have to be described in greater detail.
As already mentioned, a tangential inlet 26 communicates the upper
chamber 21 with a top portion of a cyclone separator 35. The cyclone
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separator 35 is of a known design and operating principle. Briefly, it
separates chaff from the flow of air coming from the roasting chamber 20.
The chaff falls down, by gravity, through the tip of a cone 36 and through a
discharge tube 35a shown in Fig. 3, into a chaff collecting container 28
(omitted from some figures). The air cleaned of chaff by centrifugal force
exits at a top outlet 37 communicating with the circulation control box 38
(Fig. 7).
The circulation control box 38 has an air vent port 39 and a fresh air
inlet port 40. A lever system 41 simultaneously operates a vent flap 42 and
a fresh air control flap 43. Both flaps 42, 43 can assume a position where
they control their respective ports. Thus, in a position shown in broken line
in Fig. 7, the flap (42) closes the circulation box 38 permitting chaff free
gases from the cyclone 35 to be discharged through the outlet 37 and vent
port 39 into the atmosphere. Preferably, the discharge is effected through a
catalytic converter, not shown in Figs. 1-7, as will be described with
reference to Figs. 9-15. In an opposite extreme (solid linel, the flap 42
closes the vent port 39, forcing air coming from the cyclone 35 to flow into
the control box 38. The flap 43 of fresh air is moved simultaneously with
the flap 42. In the mode of Fig. 7, the flap (43) closes the box 38
permitting flow of fresh air through the port 40 and into an inlet 44 of an
air
heating chamber 45 having heating elements and adapted to heat the
incoming air to a predetermined temperature. Circulation fans 46 (Fig. 2, 3),
indicated only diagrammatically, force the air through the entire system. It
can thus be observed that two extreme modes can be assumed by the flaps
42, 43: (a) the circulation closed mode where the flap 42 closes the
circulation control box 38 and opens the vent 39, while the flap 43 closes
the circulation control box 38 and opens fresh air inlet 40, or (b) the
circulation mode where the flap 42 closes the vent 39 opening the
circulation box 38 while the flap 43 closes the fresh air port 40 opening the
box 38 to permit circulation of gases coming from the separator 35 to pass
again through the air heater 35. Intermediate positions with the ports 39,
and box 38 partly open can also be achieved.
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The fresh or hot air is thus forced to flow down through the heater
35, into the pressure air chamber 31 a and into the roasting chamber 20,
generating the fluidization effect on the coffee bean charge in the chamber
20 simultaneously with the roasting thereof.
Further circulation modes may be provided as will be described later.
Turning now to Figure 6, a check tube 47 reaches into the interior of
the upper chamber 21. The tube is operatively associated with a sound
analyzing device which is indicated diagrammatically in Fig. 8. Briefly, the
system 48 comprises a microphone 49 connected, via an amplifier 49a, to a
three-stage band-pass filter 50, full wave rectifier 51, low pass filter 52, a
comparator 53 and an output relay 54 which is operatively connected to a
clocking device (not shown). The clocking device, in turn, provides suitable
signal or activation of controls, to stop the instant roasting cycle. Other
known systems can be applied for the same purpose but the arrangement
shown is preferred.
The output relay 54 is adapted to cause the control of air circulation
depending on the condition of the roasted coffee as will be described. It will
be appreciated, however, that different parts or a number of various
sections of the roaster can be automatically operated utilizing the output of
the device shown in Fig. 8.
In operation of the first embodiment (Figs. 1-8), the circulation fans
of the air heater 45 draw in air from the inlet 40 (the flap 43 closes the
circulation control box 38) and discharge it in to heating chamber 45 where
is heated to a thermostat controlled temperature from about 250°C to
about 270°C. The heated air then flows (Fig. 1 ) through the lower duct
31
into the pressure air chamber 31 a and through the perforations of the first
passage 29 into the lower chamber 22.
The hot air passes through the batch of coffee beans in the roasting
chamber bringing the batch into the state of a fluidized bed. The air which
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has passed through the fluidized bed and through the upper chamber 21,
with chaff carried from the roasted beans, passes through the tangential
inlet 26 into the cyclone 35 for chaff removal. The chaff is collected at the
container 28 (Fig. 3) and the chaff free air exits through the central tube
35a and through the outlet 37 at the top of the cyclone body 35. At this
stage the flap 42 closes the vent port 39 and the flap 43 closes the inlet
port 40. The air is drawn through the circulation control chamber 38 back
into the air heater 45 and circulated to the roasting chamber 20 as
described.
Heavy smoke may develop near the end of the roasting operation
using the recirculated air. This may result in undesired deposits of tar on
the
roasted beans which negatively influence the final quality of the product. If
heavy smoke develops, the operator interrupts the circulation by activating
the lever system 41 such as to move the flap 42 to open the vent 39 and
close the circulation control chamber 38 while also opening the inlet 40 to
draw fresh air into air heater 45 and hence into the roasting system. The
hot air with smoke is vented at 39 to the atmosphere, preferably through a
catalytic converter as described hereafter, while fresh air is drawn through
the inlet port 40 and into the system. The described system of control of
the recirculation of course also permits a partial venting and a partial
circulation with a partial intake of fresh air.
The operator is guided by electronically developed activation or
signals, it being understood that the activation or signals may also be used
to operate one or more elements of the roasting circuit, for instance the
recirculation of hot air, temperature control at the heater 45 etc. The
present invention provides such activation utilizing a phenomenon which
occurs during the roasting of coffee, as will be described later.
Turning now to Figures 9 and 10, an alternative system of circulation
of air through the roaster is shown by way of simplified diagrams. While
many of the elements of this diagram have their counterpart in the first
embodiment described, some of them (for instance, the hopper for feeding
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green coffee beans into the roasting chamber or the split of the roasting
chamber into upper and lower part) are not shown for clarity. It will
therefore be more convenient to use separate reference numbers for the
elements of the system shown even though some of them have their
corresponding counterparts in the first embodiment shown.
Reference number 100 designates a roasting chamber which, in
operation, holds a batch of coffee beans to be processed. The upper end of
the roasting chamber 100 is connected, through a tangential duct 101 of a
return duct system (corresponding to duct 26) with the upper section of a
chaff separator 102 disposed within the return duct system and provided
with a central vertical tube 103 which, in turn, communicates with an air
duct 104. The air duct 104 thus forms the downstream end portion of the
return duct system. The downstream end of the duct 104 connects with a
cooler air duct 1 12. Air circulating fan device 105 is adapted to force air
flow from the cooler air duct 1 12 through an air heating chamber 106 lalso
referred to as "air heating device," provided with an air heating device
including coils 107 and with a catalytic converter 108 at a downstream end
of the chamber 106. The coils 107 are activated to provide the roasting
temperature at the roasting chamber 100 and also to maintain the
temperature of the catalytic converter 108 at an operative value.
The downstream end of the catalytic converter 108 communicates
with an upstream end of a return or hot air feeding duct 109. The
downstream end of the duct 109, in turn, communicates with the lower end
of the roasting chamber 100. There is a first control valve 1 10 disposed at
the upstream end of the air duct 104 and a second control valve 1 1 1
disposed at the downstream end of the return duct 109, just before the
lower end of the roasting chamber 100.
The cooler air duct 1 12 communicates, at its end remote from the
heating chamber 106, with a cooler 113. The cooler 1 13 is a functional
equivalent of the cooler or discharge container 32 of the prototype. A third
control valve 114 (also referred to as a fresh air valve) is adapted to
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selectively close or open communication of the cooler air duct 1 12 with the
cooler 113.
The return duct 109 also communicates with a branched-off exhaust
duct 1 15 forming a part of what is generally referred to as "exhaust conduit
system". A fourth valve 116 is arranged to selectively close or open the
communication between the return duct 109 and the exhaust duct 1 15. A
partial opening of the fourth control valve 1 16 allows partial venting of the
return duct 109. The exhaust duct 1 15 is provided with a catalytic
converter 117 disposed upstream of a discharge section 1 18 of the exhaust
duct 1 15.
The air circulation of the embodiment of Figs. 11 and 12 is as
follows. During the roasting cycle (Fig. 9), the roasting chamber 100
contains a batch of coffee beans (not shown). The circulation of air is
induced by circulation fan device 105. The air is forced to flow through the
heating chamber 106, where it is heated by heating coils 107 and then
through the catalytic converter 108 where the volume of undesired
substances is removed from the circulating air thus reducing the volume of
smoke within the system. The air heated to the desired temperature then
flows through the return duct 109 and by the second valve 1 1 1 which is
now open, into the roasting chamber 100. As in the first embodiment, the
heated air performs two basic functions: first, it brings the batch of coffee
beans into the state of a fluidized bed; second, it gradually heats the coffee
beans to the desired roasting temperature.
Downstream of the roasting chamber 100, the circulating air contains
chaff which has to be removed. This is effected by passing the chaff laden
air flow coming from the chamber 100 through the tangential duct 101 into
the cyclone chaff separator 102. The chaff is separated from air by
centrifugal force and driven down by gravity. Eventually, it passes through
the lowermost part of the conical chamber into a chaff collecting chamber
(not shown in Figs. 9, 10 but shown in Fig. 3). The chaff free air remains at
the core of the swirling air and is removed through the vertical tube 103,
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past the open first control valve 1 10 into the air duct 104 from where the
air is again drawn by the fans 105 and recirculated through the system as
described.
Inevitably, there is pressure drop across the air circulation system.
Certain vacuum exists at the suction side of the fans 105, i.e. in the air
duct 104. Excessive rise of the vacuum would impair the operation of the
cyclone 102 by drawing chaff through the vertical tube 103. Therefore,
provision is made to selectively open the third control valve 1 14 thus to
allow fresh air to be drawn to the suction side of the fans 105. This reduces
the magnitude of vacuum in the air duct 104.
The third and fourth valves 1 14, 116 are normally fully closed during
the roasting cycle so that the drive by the fans 105 results only in
circulation of the roasting air. Partial opening of the control valve 1 14,
however, will permit fresh air to flow from the cooler 113, via the cooler air
duct 1 12 into the system as described.
When the roasting is completed, the second valve 1 1 1 and the first
valve 1 10 are both closed thus interrupting the air circulation. The third
valve 1 14 and the fourth valve 1 16 are open.
The roasting chamber is moved from the position of Fig. 9 to an
offset position of Fig. 10, above the collecting chamber or cooler 1 13,
whereby the roasted batch is dumped into the cooler 113. In this state of
the valve positions, the air drawing effect of the fans 105 results in the
flow of ambient air through the discharged batch of coffee beans, then
through the cooler air duct 1 12 to the suction side of the fans 105 and
through the heating chamber 106 into the exhaust duct 1 15, then through
the catalytic converter 1 17 into the discharge section 118 and out of the
system. It can thus be appreciated that the cooler air duct 1 12 also
functions as an embodiment of a fresh air supply conduit, selectively open
or closed by the control valve 114.
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The advantage of this embodiment is in a more efficient use of the
heat generators; one, 107, in the heating chamber 106, the other ahead of
the catalytic converter 1 17, as will be described. The arrangement is also an
improvement in that the discharged air having passed through the catalytic
converter is cleaner than in the first embodiment as at least some chemical
substances brought into the circulation air by the roasting process are
burned.
When the cooling cycle is finished, the cooled coffee bean batch is
removed from the cooler 113, the valves 114, 1 16 closed, the roasting
chamber 100 brought in alignment with the upright end portion of the return
duct 109. The valves 1 10, 1 11 can now be open whereby the circulation of
heated air induced by the fans 105 is repeated as described.
The diagrams of Figs. 1 1 and 12 show a yet another, presently
preferred embodiment of the circulation system of the roaster. The roasting
mode is shown in Fig. 1 1, the cooling mode in Fig. 12. A substantial
improvement in this embodiment is in the provision of an additional, exhaust
fan device 144 whereby the need of the control of the opening and closing
of the valves, as described above, is eliminated. The control of circulation
is
provided by controlling the operation of the two fan devices. The fan
devices or systems 135, 144 are independent and have an overlapping
usage. In particular, when the roasting cycle is finished, the fan system 135
continues to run for the period (about 2 - 5 seconds) of placement of the
roasting chamber 130 over the cooler 143. The fan system 144 is started
before such displacement of the chamber 130 and runs until such time as
the fumes coming from the discharged batch, and cleaned in the converter
147, are removed. Typically, the time period of the run of the second fan
system 144 is from about 90 seconds to about 2 minutes but this may vary
from one application to another.
In the roasting mode of this embodiment, the roasting chamber 130
communicates at its top with a tangential duct 131 of a return duct system,
the downstream end of which communicates tangentially with the upper
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portion of a conical chaff separator 132 disposed within the return duct
system. As in the preceding embodiments, chaff exits at the bottom of the
cone of the cyclone 132, while clean air is removed by the vertical tube 133
and then through the air duct 134, which forms the downstream end
portion of the return duct system, to the suction side of the circulation fan
device 135, through the heating device or chamber 136 with a heating coils
137, the catalytic converter 138 and return or hot air feeding duct 139 back
to the roasting chamber 130.
The fresh air supply conduit 140 with a check valve 141, forming
another embodiment of a fresh air valve, prevents the buildup of an
excessive vacuum at a point immediately downstream of the cyclone 132 to
avoid its malfunction as described above.
When it is established that the roasting of the coffee beans is
completed (Fig. 12), the cooler fans 144 are started. With the roasting
chamber moved sideways to a position above the collector or cooler 143,
the roasted batch is dumped into the cooler 143. The cooler 143 permits
passage of air through the discharged roasted batch. The cooler is provided
with a removable container for the roasted coffee. The fans 144 draw air
through the batch in the cooler, through the check valve 158 into the
exhaust ducts 145. The catalytic converter 147 removes the undesired
substances forming the roasting smoke and the cleaned air free of chemical
residues from the roasting process is then discharged from the discharge
section 148. It will thus be appreciated that the described elements form an
embodiment of what can generally be referred to as "exhaust conduit
system."
If the heated air circulation system 130 - 139 requires exhaust of
some gases, a connecting duct 155 of the exhaust conduit system can be
used. It selectively communicates the return duct 139 with the exhaust
duct 145. The exhaust of excessive gases is accomplished by opening a
control valve 156 in the connecting duct. The pressure of the excessive
gases opens the check valve 157 and closes the check valve 158 in the
exhaust duct 145. When the desired excess of gases has been vented, the
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control valve 156 is closed and the exhaust system 145 - 148 is ready to
remove exhaust gases from the roasted batch present in the cooler 143.
It will be appreciated that the inclusion within the hot roasting air
circulation of the catalytic converter 108, 138 substantially reduces the
amount of smoke circulating within the hot air system thus improving the
quality of the roast. At the same time, the utilization of the converter 108,
138 just downstream of the respective heating coils 107, 137 presents
savings in energy as the heated air is utilized not only to roast the coffee
in
the roasting chamber 100, 130 but also to maintain the respective catalytic
converter 108, 138 at an operative temperature.
Figure 13 shows a diagram of an exemplary embodiment of the
operation of the catalytic converter 147. While described in relation to the
embodiment of Figs. 1 1 and 12, the same converter could be and is utilized
in the first two embodiments described. Since the converter system is
identical for any embodiment, it will suffice to refer in the following
description only to Figs. 1 1 and 12 as it will be understood that the
arrangement in the embodiment of Fig. 9, 10 is the same.
Disposed within the housing 149 is the converter element which, as
is well known, is a grid made of a catalyst reducing the volume of
undesirable substances to be discharged from the discharge section. The
converter requires a predetermined temperature to assure the burning of the
undesired substances in the smoke drawn from the roasted batch contained
in the cooler 143. A heating element 150 is located just upstream of the
converter element 147.
The purpose of the heating element 150 is, first, to preheat the
catalytic converter 147 to its operative range. Second, the element 150
gives a boost to the temperature of the exhaust air entering the converter.
The converter 147 has to be at operative temperature before the actual
exhaust or cooling is commenced. The air flow from the cooler 143 is most
laden with smoke at the beginning of the process of cooling and the
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temperature of hot air from the cooler alone is insufficient to maintain the
converter 147 operative.
A thermostat probe 151 in the converter housing 149 is operatively
connected to a thermostat 152 which controls, by a 24V control circuit, a
relay 154 of the circuit of the heating element 150. The heating element is
typically a 2000 W element which normally suffices to maintain the smoke
laden air flowing toward the converter 147 at a desired temperature.
Typically, the thermostat would be set to maintain the converter 147 at an
operating temperature of about 230°C to about 245°C.
As mentioned above, the advantage of the third embodiment is in
that it simplifies the control of the overall system as instead of a complex
control of the operation of the four valves, the system simply controls the
actuation of the two independent fan systems 135, 144. As already
mentioned, the two fan systems have an overlapping function.
In a coffee roasting operation, the original moisture present in green
coffee beans takes place. Then the roasting itself starts at a temperature of
about 200°C after which through exothermic reactions, escalation of the
roasting process occurs which requires considerable control of the roasting
for a given degree of roast. Reaction in green arabica coffee may start as
low as 160°C. The reaction peaks at about 210°C and falls off at
about
250°C.
The most obvious physical change to occur is the external color
which ranges from light brown to almost black. This change is accompanied
by exudation of oil to the surface with increased severity of roasts. Swelling
of beans also progressively occurs.
The invention utilizes, in its preferred application, the phenomenon of
the roasting of coffee being accompanied by the popping or cracking of the
beans leading to a considerable decrease of density as a function of the
degree of roast but also of the speed of roasting. While different types of
CA 02304324 2000-03-31
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coffee beans behave in a different fashion during the roast, the cracking
phenomenon always occurs and has a general pattern which is common to
all types of coffee. According to the present invention, the peculiar pattern
of the popping or cracking sound is followed as a variable which is
indicative of the state of pyrolysis of the coffee beans being roasted.
The inventive method will now be described by way of examples. In
one tested method, the variable of the cracking sound sensed and observed
was mainly the volume of the sound. The different qualities of the sound (in
the embodiment described, the volume) accompanying the roasting of the
coffee can be divided into three stages:
( 1 ) the level of background sound occurring at the outset of the heatup
of the batch up to the first crack sound occurring at the beginning of
pyrolysis of the beans;
(2) an interim period of a reduced level of sound following the first crack
but preceding the second crack; and
(3) an increased level of crack sound when the pyrolysis of the beans is
at its peak.
It has been established by sound analyses that, in general, the level of
the sound developed during the roasting of a batch within the roasting
chamber 20 during the first crack is higher than that observed during the
interim period. Similarly, the sound level of the second crack is always
higher than that of the interim period.
Experiments carried out in the context of the present invention point
out to a relationship between the pronouncement of differences in sound
levels at the respective stages and to the frequency measured.
Sound level spectra have been analyzed utilizing the present
invention. The following table contains representative examples of
measurements obtained with a particular type of coffee:
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Band 1 st Crack Interim 2nd Crack
Hz dB dB dB
971.63 31.5 28.6 30.0
1539.93 29.2 23.2 28.6
2053.53 32.2 32.2 29.2
2585.23 29.0 25.7 30.6
3447.46 33.5 28.6 34.6
5158.22 31.6 28.2 35.1
6493.81 25.2 21.0 29.0
9172.76 23.4 18.2 26.4
The duration of the 1 st crack may vary from about 30 sec to about
90 sec and that of the interim and the 2nd crack depends on the desired
degree of roast and on the type of coffee being roasted. It is typically from
about 3 sec to about 90 sec. The table shows that with the increased band
levels the distinction between the interim period is better pronounced and
therefore can be used for the control of the operation of the roasting. Once
the second crack occurs, the pyrolysis of the beans has reached the desired
level and the roasting should be stopped. As mentioned above, the sound
characteristics vary with different types of coffee beans but once
established, they provide a reliable value for controlling the process.
The present invention thus provides an improved and simple way of
determining the duration of the roasting of a particular type of coffee beans
by
(i) recognizing and differentiating the pattern of first and second
cracking;
(ii) providing the operator with a visual and/or sound signal that
the second cracking has started;
(iii) switching hot air to vent and open the fresh air inlet;
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(iv) starting timer to clock preset time for particular roast (light,
medium, dark, very dark) and coffee type.
The invention allows the operator to automate the roasting process
with a consistent result that cannot be achieved by prior art mentioned at
the outset, namely the clocking of the time from the beginning of the
process. The start of the clocking at the second crack, i.e. at a point when
pyrolysis is at peak, provides a united point for any type of coffee beans,
assuring consistent repeatability of the degree of roast for the particular
type.
Further experiments with the present invention reveal that the
beginning of the pyrolysis of the coffee bean batch in the roasting chamber
can also be established by another successful method. This method, which
may be additional to or a substitute of the method utilizing the analysis of
the cracking sound as described, is based on measuring the surface
temperature of beans being roasted.
A mentioned at the outset of this description, it is known to use a
thermocouple which is indicative of instant temperature within the roasting
chamber. This measurement cannot be used in accurately determining the
start of the exothermic reaction and thus the start of the time interval
required for roasting.
When green beans are in the roasting chamber, such as chamber 100
or 130, they are heated up by hot air until saturated. The saturation
temperature is independent of the temperature of the roasting chamber.
Once the thermal saturation point is achieved, the surface temperature of
the beans will remain unchanged until the exothermic reaction starts. The
start of an exothermic reaction is accompanied by further escalation of the
surface temperature of the roasted beans.
Based on the above phenomenon, we measured the surface
temperature of the beans by an infrared sensing apparatus 160 with
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_22_
accompanying board lFig. 8b) which is commercially available as a product
of Raytek Inc. and is sold under the trade name of RAYNGER STT"'. The
probe of the sensing apparatus was placed in the roasting chamber such as
chamber 100 or 130 (not shown in Figs. 9-12). The measurements showed
that, at the commencement of a roasting cycle, the surface temperature of
the roasted beans continuously increases until the saturation as referred to
above. At this point, a short interim period of about 4 to 20 sec occurs
during which there is virtually no increase in temperature. The end of the
interim period, i.e. the start of the exothermic reaction, is accompanied by
further increase of the surface temperature above the value of the interim
period.
The infrared sensor located within the roasting chamber and directed
toward the batch of the coffee beans provides accurate data of the surface
temperature of the beans rather than the overall ambient temperature within
the chamber. This is due to the fact that the infrared sensor, utilizing a
laser
beam, is generally directed against one bean at any short period of time. Of
course, the number of the beans reached by the laser of the infrared sensor,
is high due to the motion of the batch in the fluidized bed. The system used
in this method and diagrammatically shown in Fig. 8b thus comprises the
step of infrared measurements of the roasted bean temperature. The
measurement results in the production of an electrical signal which is
proportional to the bean temperature. A signal comparator 162, preceded by
a volt meter 161, compares data previously obtained from the sensor to
determine the point at which the temperature of the beans starts to increase
again after the stabilized temperature during the interim period. A counter or
timer 163 is then operative upon receipt of the signal from comparator 162,
to start a predetermined countdown, to eventually indicate by the signal
device 164 when the roasting process is to be terminated. In the prototype
of this system, a visual and audio signal was used to indicate to the
operator when to terminate the process.
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The infrared device has to be maintained at room temperature and
must therefore be protected from the heat generated in the chamber 100 or
130.
It was established that the end of the interim period occurs at the
commencement of the pyrolysis of the roasted beans. It can thus be used in
determining the beginning of a time period the end of which activates a
suitable signal or actuation means required for stopping the roasting
operation.
The sensing of the surface temperature can be used as a supplement
or as a substitute of the sound analysis described above.
Other methods based on the following of the commencement of
pyrolysis are readily conceivable. For instance, the commencement of
pyrolysis of the roasted beans can also be followed, referring, as an
example, to the embodiments of Fig. 9 or 1 1, by comparing the temperature
of the air entering the catalytic converter 108, 138 and exiting from the
converter. The volatiles released during the roasting process, seen as
smoke, are burned in the catalytic converter causing the air temperature to
rise. Pyrolysis is accompanied by a marked increase in released volatiles
which, when converted to heat, promptly indicates the beginning of the
exothermic reaction.
Such process (not shown in the drawings) would then utilize
(a) a sensor with accompanying board to measure the temperature before
the catalytic converter 108, 138 to give an electrical signal
proportional to the temperature sensed;
(b) another sensor after the catalytic converter with accompanying board to
produce an electric signal that is proportional to the temperature
downstream of the converter 108, 138;
(c) a signal comparator that would compare the temperature measurements
before and after the catalytic converter 108, 138, to indicate at
which point the temperature of the air leaving the catalytic converter
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is higher than that of the incoming stream or at least increasing in
temperature faster than the air entering the converter;
(d) a counter which, upon receiving a signal that the temperature exiting the
catalytic converter exceeds the incoming air temperature, begins a
predetermined countdown to indicate when the roasting process
should be terminated; and
(e) visual and/or audio signalling device to indicate to the operator when to
terminate the roasting process.
Preferably, the temperature sensors used in this method would be
located below the respective heating chamber 106, 136. The comparator,
sensor boards, counter and signalling device would be located in an area
convenient to the operator.
Those skilled in the art will readily appreciate that further
modifications of the roasting system and method can be made without
departing from the gist of the present invention as set forth in the
accompanying claims.
