GB2039451A - Coffee roaster - Google Patents

Abstract

A coffee roaster and method of producing roast coffee in which roasting is automatically terminated by the provision in the roaster of a temperature sensing device (8) which detects the temperature of the coffee beans during the steps of stirring and roasting and produces at a predetermined appropriate temperature a signal which is used to terminate the roasting. <IMAGE>

Description

SPECIFICATION Coffee roaster The present invention relates to an improved coffee roaster, more particularly to a coffee roaster for automatically sensing the completion of roasting.

In roasting coffee beans, it is quite difficult to judge whether suitable roasting of the coffee beans has been carried out or not. Therefore, the judgement inevitably depends on a visible inspection or perception by skilled persons. Even in such a case, several samplings are required during the course of the roasting, which results in complexity and incon venience in the system.

Alternatively, there is another roasting method wherein the time control is performed by using a timer. This method causes a difficulty in setting the timer to perform an optimum roasting since the amount of coffee beans to be roasted and humidity content contained in the coffee beans vary in each case, this causing the requirement of changing the time of roasting.

Furthermore, there is another method wherein the temperature within an exhaust duct is measured.

This method cannot directly measure the temperature of the surface of the coffee beans and tends to fail to carry out a desirable roasting due to the fact that there appears the difference between the bean temperature and the exhaust temperature resulting from the occurrence of changes in the amount of raw coffee beans, the humidity content and room temperature.

The present invention provides a coffee roaster which automatically senses the completion of roasting raw coffee beans and which is capable of providing a desirable degree of roasting by a simple operation which can be handled by any person.

According to a preferred form of the present invention, a temperature sensing device to be inserted between the coffee beans to be roasted within a drum for stirring and roasting the coffee beans is provided at a front door of the coffee roaster. The temperature sensing device detects the surface temperature of the coffee beans and puts out a sensing signal.

Referring to the drawings, an embodiment according to the present invention will be explained. In Fig.

1, there is shown a coffee roaster 1 as a preferred embodiment of the present invention, wherein a drum 2 is mounted so as to be rotatably driven through a drum axis by a motor 4. The drum 2 is formed into a cylindrical shape ortapered shape as illustrated and is provided at the side 5 thereof with a plurality of ventilation holes 6 having a dimension such that the coffee beans cannot fall down therethrough. The coffee beans are stirred by the rotation of the drum 2. Provided at the front door 7 of the coffee roaster 1 is a temperature sensing device 8 which faces the interior of the drum 2. The temperature sensing device 8 is inserted between the coffee beans within the drum 2 to directly detect the surface temperature of the coffee beans. Preferably, the device 8 is installed by pressing and fixing same using a thermal resistant rubber which belongs to a silicon system.A heater 9 used as a heating source for roasting is usually mounted at a lower portion of the drum 2. The utilization of the temperature sensing device 8 permits automatic completion of roasting. Further, cooling may be started at the time the roasting is finished, and then terminated. A construction therefor will be illustrated with reference to the drawing. The temperature sensing device 8 is connected to a thermodetector 10 connected with a switching device 11 of the heater 9 and therefore, the detecting signal from the thermodetector 10 is transmitted to the switching device 11. When the detecting signal is transmitted to the switching device 1 1,the supply of power to the heater 9 is automatically disconnected to complete the roasting.The operating point setting volume 12 of the thermodetector 10 is set so as to disconnect the power supply to the heater 9 by causing the thermodetector 10 to operate when the surface temperature of the coffee beans reaches a temperature range in which a desired degree of roasting can be obtained. By way of example, a circuit for disconnecting the heat supply is shown in Fig. 2. A fan 13 for supplying cool air is mounted within an air supplying duct 14 in which the heater 9 and the fan 13 are separated by an air flow rate adjusting plate 15 from each other. The adjusting plate 15 is driven by an air flow rate adjustor 16 connected with the switching device 11 so as to open and close the duct 14. Although the adjusting plate 15 is closed during the operation of roasting, a light air is supplied to the drum 2 through the small holes provided in the plate.The fan 13 is driven by the motor 4 which drives the drum 2. Other features of the construction are explained hereinbelow.

The head portion of the coffee roaster 1 is opened at an inlet portion 18 covered by a hood 17 which is integral with a recovery vessel 19. The recovery vessel 19, having an exhaust hole 21 at the head portion thereof, receives thin husks separated from the coffee beans within the drum 2 and are blown away through the exhaust duct 20, and this recovery vessel 19 is disconnectably mounted on the coffee roaster 1. Provided at the bottom portion of the coffee roaster 1 is a drawing-type housing vessel 22 for receiving the coffee beans supplied from the drum 2.

With reference to the above-mentioned constructions which automatically perform the completion of roasting and the start and completion of cooling, an example of the operation of each constitutional element will now be illustrated. The hood 17 is opened and the coffee beans are charged into the drum 2 from the inlet portion 18 and then the volume 12 is preset. It has been known that the temperature of beans during stirring and roasting thereof increases as the degree of roasting increases, as shown in Fig.

4. The volume 12 is set so that the thermodetector 10 operates to cause the power supply supplied to the heater 9 to disappear when the temperature reaches the range corresponding to a desirable degree of roasting. Thereafter, a power source switch is closed to rotate the motor 4, resulting in starting of the rotation of the drum 2 through the axis 3 to carry out stirring operation. At the same time, the switch of the heater 9 is actuated and the fan 13 may be rotated. The airflow rate adjusting plate 15 remains closed. Thus, the amount of supplied air is restricted and a light air is supplied to the heater 9 and then the roasting operation starts.Thereafter, upon detecting the temperature which exceeds the preset temperature by the temperature sensing device 8 inserted between the coffee beans, the detecting signal is transmitted from the thermodetector 10 to the switching device 11 to automatically disconnect the power supply to the heater 9 and to terminate roasting. Referring to Fig. 2, the above-mentioned operation is explained in detail. When the power source is actuated, the sensor circuit is present in an initial state to output a high level signal to the gate of a thyristor as in Fig. 3C. The application of the high level signal causes the thyristor to activate and the heater 9 to be ON, and then roasting begins.After starting the roasting, the surface temperature of the coffee beans increases as shown in Fig. 3A while the resistance value of the thermistor decreases as indicated in Fig. 3B and the sensor circuit outputs a low level signal at a predetermined temperature P as shown in Fig. 3C. The thyristor receives the signal to close the gate thereof, causing the heater 9 to be OFF and the roasting operation to be completed. At that time, the air flow rate adjustor 16 connected to the switching device 11 simultaneously operates to open the air flow rate adjusting plate 15 so as to increase the amount of the supplied air, thereby rapidly cooling the roasted coffee beans.The temperature sensing device 8 detects the drop in surface temperature of the coffee beans to the predetermined cooling temperature, causing the airflow rate adjustor 16 to actuate through the thermodetector 10 and the switching device 11 to close the adjusting plate 15 and the cooling operation is terminated.

Alternatively, the air flow cooling mechanism may be constructed by using a timer so that it operates during a predetermined time period, which is preset in a timer mechanism, starting from the time that a roasting completion detector outputs a command so as to control the starting and termination of the cooling operation. When the front door 7 is half opened after the completion of cooling, the roasted beans fall into the housing vessel 22. Of course, the completion of roasting may be automated while the cooling of the coffee beans may be carried out outside the coffee roaster.

The coffee beans were roasted in accordance with the embodiment of the present invention constructed as mentioned above and the results are as follows: The surface temperature of the beans: The surface temperature of the beans in a roasting operation, wherein the heating is carried out by supplying a constant power to the heater 9, changes as shown in the graph in Fig. 5 in which the abscissa indicates time and the ordinate indicates the surface temperature of the beans and P indicates the point at which the water content of the beans vaporizes and the temperature rapidly rises.Experiments confirmed the fact that the surface temperature of the beans and the degree of roasting after the completion of heating, in accordance with the roasting performed in the above-mentioned manner, does not depend on conditions such as the amount of raw beans, humidity content, and room temperature and produces a highly correlated relationship. Therefore, there is shown the change in the degree of the roasting with respect to the changes in the amount of raw beans, humidity content and room temperature, in case that the surface temperature of the beans at the termination of heating is maintained constant.

The degree of roasting: Figs. 6A, B and C indicate the changes in the degree of roasting with respect to the changes in the amount of raw beans, humidity content and room temperature, respectively, and k indicates french, u indicates fullcity, m indicates city and a indicates medium.

As shown in Fig. 6A, experiments wherein the roasting was carried out by predetermining the degree of roasting as being confirmed in that the degree of roasting becomes relatively weaker than fullcity (strong roasting) in case that the amount of raw beans varies from 100 grams to 150 grams.

However, the degree of roasting in such a case does not largely change relative to those of 50 grams and 200 grams of the raw bean amount.

Fig. 6B shows the results of experiments regarding the degree of roasting using 200 grams of raw beans of which water content varies from 6% to 12%. This confirms that the degree of roasting remains constant regardless of the change in the water content of the raw beans.

Fig. 6C shows the results of experiments regarding the degree of roasting using 200 grams of raw beans in the case where the room temperature varies from 1000 to 30"C. This result confirms that the degree of roasting also remains constant even when the room temperature changes.

Furthermore, other experiments different from the above-mentioned experiments in point of effecting inconsistant heating were carried out and it is confirmed that the relationship between the surface temperature of the beans at the completion of heating and the degree of roasting is not affected by changes in the amount of raw beans, water content, room temperature and the like. Thus, the same degree of roasting can always be reproduced.

As explained above, it is merely required in the present invention to turn the switch to ON after charging raw coffee beans into the coffee roaster and setting the volume at a desired degree of roasting. The judgement of the completion of roasting is automatically carried out without the necessity of skill since the roasting temperature of the coffee beans charged into the rotation drum is automati cally detected by the temperature sensing device.

This always permits the abtainment of the desired degree of roasting and remarkable reduces the cost of employment in the case where large amounts of beans are to be roasted. Furthermore, the operation from the completion of roasting to the starting and termination of cooling can be automatically performed.

Claims (5)

1. A coffee roaster wherein there is provided for measuring the surface temperature of coffee beans a temperature sensing device which is inserted bet ween the coffee beans during the steps of stirring and roasting to automatically detect the completion of said roasting.

2. A coffee roaster as set forth in claim 1, wherein said temperatures sensing device is a thermistor.

3. A coffee roaster substantially as hereinbefore described with reference to and as shown by the accompanying drawings.

4. A method of producing roast coffee beans in which the temperature of the beans is measured during the steps of stirring and roasting of the beans by a temperature sensing device, which produces at a preselected temperature a signal which is used to terminate the roasting of the beans.

5. A method of producing roast coffee beans substantially as hereinbefore described with reference to the accompanying drawings.