WO2002021944A1

WO2002021944A1 - Coffee roaster

Info

Publication number: WO2002021944A1
Application number: PCT/US2001/028634
Authority: WO
Inventors: Olivier J. Ph. D. Whitfield; Sydney R. Stapleton
Original assignee: Coffee Kinetics Llc
Priority date: 2000-09-14
Filing date: 2001-09-13
Publication date: 2002-03-21
Also published as: AU2001289070A1

Abstract

The invention provides a coffee roaster (1) including a housing (2), a heater (4) arranged within the housing, and a generally cylindrical plenum chamber (6) arranged within the housing for receiving air heated by the heater. The heater air exits the plenum chamber radially outwardly and preferably passes through louvers (10) provided along the circumference of the plenum chamber. The coffee roaster further includes an air blower (14) arranged within the housing for supplying air to the heater and to the plenum chamber and for fluidizing coffee beans, and a roasting jar (16) for receiving coffee beans therein. The roasting jar is adapted to be removably placed on the housing and a surface (18) of the roasting jar interfacing the housing is porous for receiving the heated air exhausted from the louvers therethrough. The coffee roaster still further includes a temperature sensor (20) coupled to the roasting jar for measuring the temperature of the coffee beans. The temperature sensor produces a temperature signal. Finally, the coffee roaster includes a microprocessor (24) including a timer. The microprocessor is coupled to the heater, the air lower, and the temperature sensor, and is adapted to receive the temperature signal from the temperature sensor and the control the heater based on a predetermined desired slope of temperature per time until a predetermined goal temperature corresponding to a desired level of roasting is reached.

Description

COFFEE ROASTER

Field of the Invention The present invention is directed to a coffee roaster, and more particularly, to a coffee roaster including a system for achieving a predetermined slope of temperature per time during a roasting process.

Background of the Invention

Various coffee roaster devices have been proposed in the past for both industrial use and home use. In any application, the process of roasting coffee is prone to encountering various roasting anomalies due to either excessive or inadequate amounts of heat applied at various stages of the roasting process. These anomalies include, for example, "tipping" (a form of scorching), uneven roasting, and

"baking" that results from an inadequate rate of roasting. To avoid these anomalies, commercial or industrial roasters typically rely on manual intervention by highly skilled and experienced personnel. Some roasters include means for controlling roasting temperatures. For example, U.S. Patent No. 5,394,623 to Sewell describes a self-controlled coffee roaster using heated air, which monitors the temperature of the air that has passed through the beans being roasted and terminates the heating upon detection of a predetermined temperature. U.S. Patent No. 4,501,761 to Mahlmann et al. describes a method of roasting coffee using heated gas at a temperature of between 200°C and 240°C for two to ten minutes. Some home-use coffee roasters have been proposed, including an automatic system for controlling a roasting process. For example, U.S. Patent No. 4,494,314 to Gell, Jr. describes various methods of controlling a roasting process, including (1) use of a timer to operate a roaster for a preset period of time; (2) use of an optical sensor to detect the surface color of coffee beans, for determining the degree of bean carbonization as a function of the detected surface color; and (3) use of a microphone for detecting popping sounds created by roasted beans, for monitoring the progress of a roasting process.

None of the coffee roasters proposed in the past, however, is capable of consistently producing adequately roasted coffee beans, automatically and regardless of type of beans being used. This is so because green beans come in a great variety, exhibiting a full range of physical characteristics and capacity to absorb heat. Controlling a roasting process of various beans to consistently obtain an adequate final product has been extremely difficult. A need exists for a method and device for roasting coffee, which can roast coffee beans to variable darkness as desired, regardless of the type or variety of coffee beans used.

Summary of the Invention The present invention provides a coffee roaster that can automatically and consistently produce coffee beans ideally roasted to a desired degree regardless of the type of beans used. The coffee roaster includes a housing, a heater arranged within the housing, and a cylindrical plenum chamber arranged within the housing for receiving air heated by the heater. The heated air exits the plenum chamber radially outwardly. The coffee roaster further includes an air blower arranged within the housing for supplying air to the heater and also to the plenum chamber and for fluidizing coffee beans. The coffee roaster still further includes a roasting jar for receiving coffee beans therein. The roasting jar is adapted to be removably placed on the housing, and a surface of the roasting jar interfacing the housing is porous for receiving the heated air therethrough. The coffee roaster also includes a temperature sensor coupled to the roasting jar for measuring the temperature of the coffee beans. The temperature sensor produces a temperature signal. Finally, the coffee roaster includes a microprocessor including a timer. The microprocessor is coupled to the heater, the air blower, and the temperature sensor, and is adapted to receive the temperature signal from the temperature sensor and to control the heater based on a predetermined desired slope of temperature per time to achieve an ideal coffee- roasting temperature-per-time profile, until a predetermined goal temperature corresponding to a desired level of roasting is reached.

In one aspect of the present invention, the heater is formed of a gas burner and a spark igniter located adjacent the gas burner. The microprocessor controls the gas burner by turning on and off a gas valve of the gas burner. In another aspect of the present invention, the microprocessor controls the heater so that the slope of temperature per time reaches a predetermined value, or predetermined values at different phases during a roasting process, for example, three phases. By closely controlling the slope of temperature per time at these three phases during a roasting process, the present invention produces a substantially identical temperature-per-time profile (i.e., the change in temperature measured during a roasting process) during roasting a variety of coffee beans. This is the key, in accordance with the present invention, to produce ideally roasted beans at any desired level of roast, regardless of the kind of beans being roasted. In a further aspect of the present invention, when the microprocessor receives a temperature signal corresponding to a predetermined goal temperature, the heater is turned off while the air blower is left on to continue supplying air into the roasting jar to cool off the coffee beans.

In yet another aspect of the present invention, the temperature sensor is further used to provide various safety features for the coffee roaster. For example, the microprocessor may be adapted to shut off both the heater and the air blower when a temperature or temperature gradient (i.e., slope of temperature per time) outside the normal operating range is detected.

The present invention also offers a method of roasting coffee beans while controlling a slope of temperature per time. According to the method, first, coffee beans are provided. Next, the coffee beans are roasted. During the roasting, the temperature of the coffee beans is monitored. The roasting is controlled based on a predetermined desired slope of temperature per time until a predetermined goal temperature corresponding to a desired level of roasting is reached. The coffee roaster of the present invention, by controlling the slope of temperature per time during a roasting process, specifically, by controlling a heater so as to reach and maintain a predetermined slope value at each of several phases during the roasting process, achieves a substantially uniform temperature-per-time profile for a variety of coffee beans. It has been found that achieving such a uniform temperature-per-time profile during a roasting process is the key for consistently and automatically producing coffee beans that are ideally roasted at a desired level. Therefore, the coffee roaster of the present invention, and a method of coffee roasting in accordance with the present invention, are highly suited for automatically producing ideally roasted beans, regardless of the type of beans used. Brief Description of the Drawings The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: FIGURE 1 is a partially cutaway view of a coffee roaster constructed in accordance with the present invention;

FIGURE 2 is a partially cutaway view of the coffee roaster of FIGURE 1, viewed from a different angle;

FIGURES 3A illustrates temperature-per-time profiles of various roasting processes for roasting various kinds of coffee beans, respectively;

FIGURE 3B is the same chart as FIGURE 3A, further including notations of three phases included in a roasting process together with their desirable slopes of temperature per time, respectively; and

FIGURE 4 is a control panel for use in connection with the coffee roaster of FIGURE 1.

Detailed Description of the Preferred Embodiment

Referring to FIGURES 1 and 2, a coffee roaster 1 of the present invention includes a housing 2, a heater 4 arranged within the housing 2, and a generally cylindrical plenum chamber 6 arranged within the housing 2 for receiving air heated by the heater 4. The plenum chamber 6 is defined by a generally cylindrical plenum wall 7 and a generally circular top surface 8. The heated air then exits the plenum chamber 6 radially outwardly, as indicated by arrows 9a and 9b. Preferably, as in the illustrated embodiment, louvers 10 are arranged for passing the heated air exiting the plenum chamber radially outwardly (9a, 9b) to impart a swirling motion thereto, as indicated by arrows 32a and 32b. In one embodiment, the louvers 10 are formed by a plurality of leaves 12, which are arranged along the circumference of the generally circular surface 8 and bent away from the surface 8 so as to form an angle between each of the leaves 12 and the surface 8. The coffee roaster 1 further includes an air blower 14 also arranged within the housing 2 for supplying air to the heater 4 and to the plenum chamber 6, as indicated by arrows 29, 15a, and 15b, and also for fluidizing coffee beans, as more fully described below.

The coffee roaster 1 also includes a roasting jar 16 for receiving green coffee beans therein. The jar 16 is configured and adapted to be removably placed on the housing 2. A surface 18 of the jar 16 interfacing the housing 2 is porous for receiving the heated air exhausted from the louvers 10 therethrough. A temperature sensor 20 is coupled to the roasting jar 16 for measuring the temperature of the coffee beans. The illustrated temperature sensor 20 is adapted to measure the temperature of air that has passed through the coffee beans in the jar 16. This arrangement is practical since the enhanced heat transfer associated with fluidizing coffee beans during roasting ensures that a sensed temperature of air is representative of an actual coffee bean temperature. Other means for measuring the temperature of coffee beans, for example use of optical or electromagnetic temperature sensors known in the art for measuring the temperature of coffee beans directly, are also within the scope of the present invention. The temperature sensor 20 produces a temperature signal corresponding to the sensed temperature, which will then be transmitted via a line 22 (see FIGURE 2) to a microprocessor 24. The microprocessor 24 includes a timer, and is further coupled to the heater 4 and the air blower 14. The microprocessor 24 is adapted to receive the temperature signal from the temperature sensor 20 and to control the heater based on a predetermined desired slope of temperature per time (i.e., change in temperature as a function of time), until a predetermined goal temperature corresponding to a desired level of roasting is achieved.

Various components of the coffee roaster 1 are now described in detail. The housing 2, the plenum chamber 6, and the air blower 14 may be formed of any suitable material, such as steel.

In the illustrated embodiment, the heater 4 is formed of a gas burner 25 enclosed within an inner burner tube 26, which in turn is enclosed within an outer burner tube 27, together with a spark igniter 28 provided adjacent the gas burner 25. The gas burner 25 is coupled to a suitable gas source (not shown). Air from the air blower 14 not only enters the plenum chamber 6 between the inner and outer burner tubes 26 and 27 as noted by arrows 15a and 15b, but also enters the inner burner tube 26 to provide air for combustion as indicated by arrow 29. The gas burner 25 includes a controlled valve, for example a solenoid-controlled valve. The spark igniter 28 provided adjacent the gas burner 25 provides the source of ignition for the gas whenever the valve is opened. Other means of heating, such as an electric heater, may also be used as a heater, as long as the activation/deactivation of the heater can be controlled by the microprocessor 24, as more fully described below.

The plenum chamber 6 serves to complete the combustion process of the gas therein. Further, the plenum chamber 6 serves to direct the combustion gas in a downward direction as indicated by arrows 30a and 30b, where the combustion gas meets and mixes with the air moving upward along arrows 15a and 15b between the inner and outer burner tubes 26 and 27. The gas/air mixture then exits the cylindrical plenum chamber 6 radially outwardly as indicated by arrows 9a and 9b. In the present description, the term "heated air" as used to describe air exiting the plenum chamber 6 refers to the gas/air mixture.

The louvers 10 serve to complete the mixing process between the hot combustion gas and the fluidizing air from the air blower 14 by imparting a horizontal swirling motion to the gas/air mixture in a direction indicated by arrows 32a and 32b. To provide a swirling motion, the louvers 10 are arranged in a circular manner as illustrated in FIGURES 1 and 2. The gas/air mixture now moving in a swirling motion will then pass upwardly through the porous bottom surface 18 into the roasting jar 16, creating a fluidized bed for the coffee beans therein. Fluidizing coffee beans and constantly moving the beans around ensures that heat is uniformly transferred to the beans during the roasting process. The housing 2 includes a circular opening 34 located above the surface 8 of the plenum chamber 6. The circular opening 34 is defined by an annular flange 36, which is adapted to receive the removable roasting jar 16 thereon. As illustrated, the roasting jar 16 is placed on the annular flange 36 and does not enter into the housing 2 past its external surface. The housing 2 further includes a hollow first column 37a for housing the line 22 connecting the temperature sensor 20 and the microprocessor 24 therein. The housing 2 may still further include a second column 37b, which is located generally opposite from the first column 37a across the roasting jar 16. The function of the columns 37a and 37b will be more fully described below.

The roasting jar 16 generally includes a container portion 38, a lid portion 40, and a top portion 50. The container portion 38 is preferably made of glass for allowing a user to view the roasting process of green coffee beans inside. Preferably, the container portion 38 includes a grip 39 for easy grasping. The lid portion 40 includes an outer wall 42 made of, for example, aluminum, and an inner cylindrical grid 44 covered at the top with a filter screen 46, for example a metallic screen. The top portion 50 includes a vent 52 and a bracket 54 for supporting the temperature sensor 20 thereon. The top portion 50 still further includes a socket 56a (FIGURE 2), to which the line 22 from the temperature sensor 20 is directed. The socket 56a is configured to mate with the top portion 43 a of the column 37a of the housing 2 so that, when the top portion 50 is placed over the lid portion 40 sitting on the container portion 38 on the housing 2, the line 22 continuously extends from the temperature sensor 20 to the microprocessor 24.

The top portion 50 may further includes a second socket 56b (FIGURE 1). The sockets 56a and 56b of the top portion 50 are adapted to mate with the top portions 43 a and 43b of the first and second columns 37a and 37b, respectively. Lower ends 45 a and 45b of the first and second columns 37a and 37b are coupled to first and second bars 47a and 47b, respectively, both of which are in turn linked to a handle 49. The sockets 56a and 56b, the columns 37a and 37b, the bars 47a and 47b, and the handle 49 are linked such that movement of the handle 49 (for example, pulling up or down of the handle 49) causes the sockets 56a and 56b, and hence the top portion 50, to be raised and lowered with respect to the lid portion 40 and the container portion 38 of the roasting jar 16 seated on the housing 2.

In operation, a user raises the top portion 50 using the handle 49 and removes the lid portion 40 and the container portion 38 from the housing 2, and removes the lid portion 40 from the container portion 38 to load coffee beans into the container portion 38. Thereafter, the user replaces the lid portion 40 over the container portion 38, raises the top portion 50 again using the handle 49, and reinstalls the container portion 38 and the lid portion 40 on the housing 2. Thereafter, the air blower 14 and the heater 4 are activated by the microprocessor 24 to generate hot air in the plenum chamber 6. The hot air travels tlirough the louvers 10 and then through the porous bottom surface 18 of the container portion 38 into the container portion 38 to roast the coffee beans therein. The cylindrical grid 44 of the lid portion 40 serves to keep the coffee beans within the container portion 38 while allowing the hot air and chaff (the skin of coffee beans) to escape. The filter screen 46 serves to capture chaff entrained in the fluidizing air during the roasting process. (The chaff may be easily washed off the filter screen 46 when the lid portion 40 is removed from the rest of the roasting jar 16.) The hot air is eventually exhausted from the roasting jar 16 through the vent 52 provided in the top portion 50.

The temperature sensor 20 senses the temperature of the air that has passed through the coffee beans inside the container portion 38 of the roasting jar 16 and sends a temperature signal corresponding to the sensed temperature to the microprocessor 24. The microprocessor then controls the heater 4 based on a predetermined desired slope of temperature per time. Specifically, the microprocessor controls the heater 4 so as to achieve a predetermined slope of temperature per time by, for example, periodically turning on and off the heater 4, until a predetermined goal temperature corresponding to a desired level of roasting is reached. In the illustrated embodiment using a gas burner as a heater, the valve of the gas burner 25 is opened or closed, which in turn sends a signal to the spark igniter 28 to provide sufficient spark for the gas from the gas burner 25 to ignite. (After each ignition, the spark igniter 28 is turned off using, for example, a flame sensor). Other methods for controlling the heater 4 may also be used as will be apparent to those skilled in the art. For example, a valve of the gas burner 25 may be modulated to control the amount of gas supplied to the burner 25. The goal temperature may vary from low to high, so as to achieve roasted beans in light brown to dark brown with oily surfaces, as desired by a user.

FIGURE 3 A is a chart illustrating the relation between temperature (°C) sensed by the temperature sensor 20 and time measured from start of a roasting process (minutes), in one application of the present invention. It has been found that maintaining a certain roasting temperature-per-time profile is the key for ideal coffee roasting for a wide variety of green beans. FIGURE 3 A illustrates six temperature- per-time profiles obtained by using a coffee roaster of the present invention to roast six kinds of beans to a certain degree of roast: (1) Sumatra Organic #6 ("#6" refers to the degree of roast, as more fully described below); (2) Kenya AA #6; (3) Costa Rica #6; (4) Mexican Organic #6; (5) Peru Organic #6; and (6) Papua/New Guinea (PNG) #6. These various kinds of green beans exhibit a full range of physical characteristics, and yet according to the present invention their temperature-per-time profiles are successfully controlled to follow very similar patterns, as illustrated.

The temperature-per-time profiles of FIGURE 3 A are achieved according to the present invention by having the microprocessor 24 closely control the heater 4 to achieve a certain slope of temperature per time, or rate of roast, at each of various phases during the roasting process. This allows for varying amounts of heat to be applied to beans depending on their widely varying capacity to absorb heat, which was achieved by skilled manual labor prior to the present invention. FIGURE 3B illustrates the same temperature-per-time profiles as FIGURE 3A, but explicitly notes four phases (the initial phase 58, Phase I, Phase II, and Phase III) included in a roasting process together with the slope of temperature per time desired at each phase.

In the illustrated embodiment, the microprocessor 24 controls the heater 4 so that the slope of temperature per time reaches and generally maintains 100°C/minute during the initial phase 58, lasting approximately 1.25 minutes in this example, during which the moisture within the coffee beans is evaporated; 20°C/minute during Phase I that lasts approximately 2.75 minutes; 10°C/minute during Phase II lasting approximately 4.25 minutes; and 4.4°C/minute during Phase III that lasts approximately 4 minutes. It has been found that programming the microprocessor 24 to perform the following steps in each of these four phases achieves the illustrated temperature-per-time profile for a variety of coffee beans automatically and consistently:

(1) For the initial phase 58, leaving the heater 4 on until the temperature reaches 90°C; (2) For Phase I, when the temperature is above 90°C and at or below

160°C, if a 15°C rise takes longer than 60 seconds, leaving the heater 4 on until the next 15°C rise is achieved, otherwise turning off the heater 4 for 6 seconds with each 15°C temperature rise;

(3) For Phase II, when the temperature is above 160°C and at or below 205 °C, if a 7°C rise takes longer than 45 seconds, leaving the heater 4 on until the next 7°C rise is achieved, otherwise turning off the heater 4 for 6 seconds with each 7°C temperature rise; and

(4) For Phase III, when the temperature is above 205°C, if a 3°C rise takes longer than 45 seconds, leaving the heater on until the next 3°C rise is achieved, otherwise turning off the heater for 6 seconds with each 3°C temperature rise.

It should be understood that the above set of steps is merely one example of controlling a temperature-per-time profile, and other ways of controlling a profile, depending on the degree of roast desired, the type of a heater used, etc. will be readily determinable for those skilled in the art.

In any event, when a predetermined goal temperature is reached, the heater 4 is turned off while the air blower 14 may be left on to start a cooling cycle, i.e., to continue supplying air into the roasting jar 16 to cool the coffee beans. In one embodiment, the air blower 14 is left on for 7 minutes after the predetermined goal temperature is reached, or until a temperature of 35°C is reached, whichever occurs first.

FIGURE 4 illustrates a sample control panel 62 that may be placed on the exterior surface of the housing 2 and connected to the microprocessor 24 to control the operation of the coffee roaster 1. The control panel 62 includes a power switch 64 and a gas switch 66. When the power switch 64 is turned on, a "power on" indicator 67 is lit up. In the illustrated embodiment, both the power switch 64 and the gas switch 66 must be on for the coffee roaster 1 to operate. Turning the gas switch 64 off during a roasting process will manually stop the roasting process and start a cooling cycle. The control panel 62 further includes an "up" arrow key 68 and a "down" arrow key 69, which are used to select a goal temperature corresponding to a desired level of roasting. For example, the goal temperature may be set at between 199°C (degree of roast "0", light brown roast) and 235°C (degree of roast "9", dark brown roast) in 4°C increments. The selected degree of roast is displayed in an LED display area 71. Preferably, the goal temperature may be adjusted (altered) even during a roasting process, by a user pressing the "up" or "down" arrow keys 68, 69. In the illustrated embodiment, the "up" and "down" arrow keys 68 and 69 will adjust the degree of roast up and down by 1. The LED display area 71 includes a "heater-on indicator" 72, which lights up whenever the heater 4 is turned on (for example, the valve of the gas burner 25 is opened in the illustrated embodiment).

Finally, the control panel 62 includes a "start roast" button 74, which activates an automatic roasting process (followed by a cooling cycle) in accordance with the present invention. In one embodiment, after activation of the "start roast" button 74, the air blower 14 will be turned on for 5 seconds, then the heater 4 is turned on and the microprocessor 24 starts monitoring the temperature detected by the temperature sensor 20. The microprocessor 24 controls the roasting process, by controlling (activating and deactivating, for example) the heater 4, based on a predetermined desired slope of temperature per time, until a predetermined goal temperature is reached. At this point, a post-roast cooling cycle will start by turning off the heater 4 while leaving the air blower 14 on.

Preferably, the temperature sensor 20 is used to further provide various safety features for the coffee roaster 1. For example, the microprocessor 24 may be adapted to shut off both the heater 4 and the air blower 14 when the temperature sensor 20 detects a temperature outside an expected operating temperature range, such as below -50°C or above 350°C. In such a case, it is suspected that the line 22 to the temperature sensor 20 is broken or shorted. In one embodiment, this error will be displayed on the LED display area 71 as alternating "E" (error) and "1" (error code "1").

As another example, the microprocessor 24 may be further adapted to turn off the heater 4 and the air blower 14 when it determines that there is no temperature rise of 5°C within 15 seconds after the heater 4 is first turned on. This occurrence will be displayed as error code "2", and its likely causes are heater defects (lack of burner ignition, for example) and significant overload of coffee beans.

As a further example, the microprocessor 24 may be adapted to turn off the heater 4 and initiate a post-roast cooling cycle using only the air blower 14 when the heater 4 is on for longer than the time expected for green beans to reach the highest degree of roast, for example degree "9" corresponding to 350°C. This occurrence will be displayed as error code "3". In one embodiment, this time period is set as 60 minutes. As a still further example, the microprocessor 24 may be adapted to again turn off the heater 4 and initiate a post-roast cooling cycle when the temperature drops more than 15°C while the microprocessor 24 is calling for both the heater 4 and the air blower 14 to be on. This occurrence will be displayed as error code "4". Possible causes for this error are lack of gas (or other energy supply for the heater 4), stalled air blower 14, and removal of the roasting jar 16 during a roasting process.

As a final example, the microprocessor 24 may be adapted to turn off both the heater 4 and the air blower 14 when the temperature rises 5°C above a predetermined goal temperature during a post-roast cooling cycle. This occurrence will be displayed as error code "5". For this purpose, the temperature will be monitored once every second. Likely causes of this occurrence are loading only a partial batch of beans, reroasting of a previously roasted batch of beans, and combustion of beans.

In one embodiment, the microprocessor 24 is designed to scan various input and output states used in the operation of the coffee roaster 1 at a maximum of 20 cycles per second, and all scan timing is in some multiple of the 1/20* second scan rate. For example, for an "on" input to be accepted from any of the membrane switches 68, 69, and 74 (FIGURE 4), three continuous "on" scans (or 3/20 seconds of total switch activation) may be required. Similarly, three continuous "off scans may be required before another "on" can be accepted. Error code display will consist of "E" being displayed for 1 second, alternating with an error code number being displayed for 1 second. The temperature sensor 20 may be scanned four times per second, with a "1 -second rolling average filter", which works as follows:

New stored value =

(1 x most recently scanned value + 3 x last stored value)/4. (1) The roasting process setting is updated once every second. A roasting process setting includes processing of timing and temperature inputs to achieve a desired temperature-per-time profile as described above. The gas switch 66 may be scanned once every second for status, so that no error code will be generated if a roasting process is aborted by manual gas shutoff. The sensed temperature in °C may be displayed by simultaneously depressing the "up" and "down" arrows 68 and 69. The temperature is displayed in the LED display area 71 as three sequential digits of Vi second duration each followed by a ^lA second pause.

The present invention further provides a method of roasting coffee beans while controlling a slope of temperature per time during the roasting process. The method includes the initial step of providing coffee beans. Thereafter, the coffee beans are roasted. During the roasting process, the temperature of coffee beans is monitored. Further, according to the method, the roasting process is controlled based on a predetermined desired slope of temperature per time until a predetermined goal temperature corresponding to a desired level of roasting is reached. Specifically, the slope of temperature per time may be controlled to reach different values at different phases during a roasting process, for example, three phases as described above.

The coffee roaster of the present invention may be designed to roast, for example, approximately 1.25 pounds of green coffee beans to provide approximately one pound of roasted coffee. Thus sized, the coffee roaster of the present invention is suitable not only for industrial or commercial use but also for home use.

The coffee roaster of the present invention, by controlling a heater to achieve a predetermined desired slope of temperature per time at each of several phases during a roasting process, achieves a substantially uniform temperature-per-time profile for a variety of coffee beans. It has been found that achieving such a uniform temperature-per-time profile during a roasting process is the key for consistently and automatically producing coffee beans that are ideally roasted at a desired level. Thus, the coffee roaster of the present invention, and a method of coffee roasting in accordance with the present invention, are highly suited for automatically producing ideally roasted beans using a variety of coffee beans.

While the preferred embodiments of the invention have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A coffee roaster comprising: a housing; a heater arranged within the housing; a cylindrical plenum chamber arranged within the housing for receiving air heated by the heater, the heated air exiting the plenum chamber radially outwardly; an air blower arranged within the housing for supplying air to the heater and to the plenum chamber and for fluidizing coffee beans; a roasting jar for receiving coffee beans therein, the jar being adapted to be removably placed on the housing, a surface of the roasting jar interfacing the housing and being porous for receiving the heated air therethrough; a temperature sensor coupled to the roasting jar for measuring the temperature of coffee beans, the temperature sensor producing a temperature signal; and a microprocessor including a timer, the microprocessor being coupled to the heater, the air blower, and the temperature sensor; the microprocessor being adapted to receive the temperature signal from the temperature sensor and to control the heater based on a predetermined slope of temperature per time until a predetermined goal temperature corresponding to a desired level of roasting is reached.

2. The coffee roaster of Claim 1, wherein the heater comprises a gas burner.

3. The coffee roaster of Claim 1, further including louvers arranged for passing the heated air exiting the plenum chamber radially outwardly to impart a swirling motion thereto.

4. The coffee roaster of Claim 1, wherein the microprocessor controls the heater so that the slope of temperature per time reaches a predetermined value.

5. The coffee roaster of Claim 1, wherein the microprocessor controls the heater by adjusting energy supply to the heater.

6. The coffee roaster of Claim 1, wherein the microprocessor controls the heater by turning the heater on and off

7. The coffee roaster of Claim 6, wherein the microprocessor controls the heater to be pulsed on and off after the predetermined slope value is reached.

8. The coffee roaster of Claim 1, wherein the microprocessor controls the heater so that the slope of temperature per time reaches a first value in a first temperature range and a second value in a second temperature range.

9. The coffee roaster of Claim 8, wherein the microprocessor is adapted to perform the following steps:

(a) when the temperature is above 90°C and at or below 160°C, if a 15°C rise takes longer than 60 seconds, leaving the heater on until the next 15°C rise is achieved, otherwise turning off the heater for 6 seconds with each 15°C temperature rise;

(b) when the temperature is above 160°C and at or below 205°C, if a 7°C rise takes longer than 45 seconds, leaving the heater on until the next 7°C rise is achieved, otherwise turning off the heater for 6 seconds with each 7°C temperature rise; and

(c) when the temperature is above 205°C, if a 3°C rise takes longer than 45 seconds, leaving the heater on until the next 3°C rise is achieved, otherwise turning off the heater for 6 seconds with each 3°C temperature rise.

10. The coffee roaster of Claim 1, wherein the microprocessor is further adapted, upon receiving a temperature signal corresponding to the predetermined goal temperature, to turn off the heater while leaving the air blower on to continue supplying air into the roasting jar to cool off the coffee beans.

11. The coffee roaster of Claim 10, wherein the air blower is left on for 7 minutes after the predetermined goal temperature is reached or until a temperature of 35°C is reached, whichever occurs first.

12. The coffee roaster of Claim 1, wherein the predetermined goal temperature corresponding to a desired level of roasting is alterable during a roasting process.

13. The coffee roaster of Claim 1, wherein the microprocessor is adapted to turn off the heater and the air blower upon receiving a temperature signal outside a predetermined scope.

14. The coffee roaster of Claim 1, wherein the microprocessor is adapted to turn off the heater and the air blower upon determining there is no temperature rise of 5°C within 15 seconds after the heater is first turned on.

15. The coffee roaster of Claim 1, wherein the temperature sensor is arranged to measure the temperature of air that has passed through the coffee beans.

16. The coffee roaster of Claim 1, wherein the roasting jar includes a container portion, a lid portion, and a top portion, the coffee roaster further comprising a column and a handle, one end of the column being coupled to the top portion of the roasting jar, the other end of the column being coupled to the handle; the top portion, the column, and the handle being linked such that movement of the handle causes the top portion to be raised and lowered with respect to the lid portion and the container portion of the roasting jar.

17. A method of roasting coffee beans while controlling a slope of temperature per time, the method comprising the steps of:

(a) providing a coffee roaster comprising: (i) a heater;

(ii) a cylindrical plenum chamber for receiving air heated by the heater, the heated air exiting the plenum chamber radially outwardly;

(iii) an air blower for supplying air to the heater and to the plenum chamber and for fluidizing coffee beans;

(iv) a roasting jar including a porous surface for receiving the heated air therethrough;

(v) a temperature sensor; and

(vi) a microprocessor including a timer, the microprocessor being coupled to the heater, the air blower, and the temperature sensor;

(b) pouring coffee beans into the roasting jar;

(c) under control of the microprocessor, activating the heater and the air blower to start a roasting process;

(d) sensing the temperature of the beans using the temperature sensor;

(e) under control of the microprocessor, controlling the heater based on a predetermined desired slope of temperature per time until a predetermined goal temperature corresponding to a desired level of roasting is reached.

18. The method of Claim 17, wherein step (d) comprises measuring the temperature of air that has passed through the coffee beans.

19. The method of Claim 17, wherein step (e) comprises turning the heater on and off.

20. The method of Claim 17, wherein step (e) comprises adjusting energy supply to the heater.

21. The method of Claim 17, wherein step (e) comprises controlling the heater so that the slope of temperature per time reaches a predetermined value.

22. The method of Claim 21, wherein step (e) further comprises:

23. The method of Claim 17, further comprising the step of:

(f) after the predetermined goal temperature is reached, turning off the heater while leaving the air blower on to continue supplying air into the roasting jar to cool off the coffee beans.

24. A method of roasting coffee beans while controlling a predetermined slope of temperature per time, the method comprising: providing coffee beans; roasting the coffee beans; during the roasting, monitoring the temperature of the coffee beans; and controlling the roasting based on a predetermined slope of temperature per time until a predetermined goal temperature corresponding to a desired level of roasting is reached.

25. The method of Claim 24, wherein the coffee beans are roasted with heated air.

26. The method of Claim 25, wherein the temperature of the coffee beans is monitored by measuring the temperature of air used to roast the coffee beans.

27. The method of Claim 24, wherein the roasting^'is controlled so that the slope of temperature per time reaches a predetermined value.

28. The method of Claim 27, wherein the roasting is controlled in a first temperature range so that the slope of temperature per time reaches a first value, and in a second temperature range so that the slope of temperature per time reaches a second value.

29. The method of Claim 28, wherein the roasting is further controlled in a third temperature range so that the slope of temperature per time reaches a third value.

30. The method of Claim 29, wherein the step of controlling the roasting comprises: