WO1992012643A1

WO1992012643A1 - A method for the drying and roasting of coffee and cocoa beans

Info

Publication number: WO1992012643A1
Application number: PCT/DK1992/000029
Authority: WO
Inventors: Søren JOHANNESSEN
Original assignee: Johannessen Soeren
Priority date: 1991-01-28
Filing date: 1992-01-28
Publication date: 1992-08-06
Also published as: AU1240992A; DK14991D0

Abstract

In order to avoid having to dry and roast coffee and cocoa beans (10) directly in flue gas in a drying furnace, the drying according to the invention takes place in a drum (6) to which air (1) is supplied, said air being heated by flue gas (5) from a burner (3) in a heat exchanger (18), and where the flue gases (5) are subsequently supplied to the exterior of the drum (6). Thus, the drying of the beans (10) in the drum (6) is performed totally cut off from the flue gases (5), thus eliminating the risk that the beans will become exposed to pollution from the flue gases. At the same time the beans (10) are heated uniformly partly from the sides of the drum and partly by the air (1) through the drum. This creates an effective and yet gentle drying and roasting at no risk of partial overheating causing the beans to be burned.

Description

A METHOD FOR THE DRYING AND ROASTING OF COFFEE AND COCOA BEANS.

Background of the invention

The invention relates to a method for the drying and roast¬ ing of coffee and cocoa beans which beans are found inside a drum in which they are heated by means of flue gases from a burner, until the required degree of drying and roasting is obtained.

Drying of such beans has the primary objective of producing a particular taste and aroma. Furthermore, the beans are made dry and crisp so that they become easier to grind and extract substances from by subsequent extraction.

Drying is normally performed in drying furnaces comprising a drying chamber in which the beans are placed. Flue gas is then added directly to the chamber from a burner causing heating of the beans inside the chamber. At the beginning of the drying process, liquid evaporates from the beans, and they may later increase their volume due to a slight vesiculation. The cellulose and sugar will gradually start to burn, and the colour of the beans will darken.

Subsequent to the drying, the beans must be cooled, after which they can be processed in a generally known manner by rolling, grinding or the like.

Thus, since drying is effected by a direct influence by hot flue gases, the beans are exposed to the detrimental ele¬ ments in the flue gases, such as soot particles, sulphur dioxide, nitric oxides, benzamines and heavy metals which are all suspected of causing abdominal cancer. The risk that these poisonous substances will deposit is particularly great in connection with coffee and cocoa beans which expand during drying, in that they immediately absorb the flue gases in their porous interiors during the cooling process.

In order to reduce this risk of polluting the beans during drying, it is known to use gas as a heat source, but the risk that the flue gases may contain health hazardous sub- stances also exists in connection with this heating source.

In order to avoid the direct contact with the detrimental flue gases, it is known from US patent no. 1,547,655 to heat the beans in a drum by supplying pure hot air to the interior of the drum. Hereby drying is effected only by the use of pure air, and the risk of pollution is eliminated.

However, this known method of roasting is encumbered with serious shortcomings and disadvantages. First of all, heat- ing of the beans in the drum takes place only by the use of hot air which is supplied to the interior of the drum, after which air is discharged through perforations in the drum. This causes the roasting to be greatest where the air is hottest, viz. at the innermost layer in the drum, and smallest at the outermost layer along the sides of the drum.

This increases the risk of burning the surface of the in¬ nermost layers which means that the drying process must be very carefully controlled in order to ensure an even and homogeneous roasting.

Add to this that the perforations of the drum may tend to clog and thus require frequent cleaning. Finally, the drying and roasting takes an excessively long time, because the heated air is only supplied to the interior of the drum. Since the temperature of the air will have dropped to about 50°C when leaving the drum, the out¬ side of the drum will serve to cool due to the great dif¬ ference in temperature between inlet and outlet air in the drum.

Advantages of the invention

By the method according to the invention where heating takes place partly directly by supplying pure hot air to the interior of the drum, and partly indirectly by supply¬ ing the hot flue gases to the exterior of the drum, a hitherto unknown homogeneous and even, viz. gentle, drying and roasting of the beans in the drum is obtained, in that they are heated both directly by the hot air as well as in¬ directly by the heating of the drum by means of the flue gases.

Since the temperature of the hot air is hereby reduced re¬ lative to the temperature applied in the known methods with direct supply of flue gases, burning of the tips and edges of the beans is completely avoided.

The drying time is at the same time reduced without re¬ quiring the same degree of supervision as do the known methods. This ensures harmless heating and drying and very homogeneous and gentle roasting of the beans.

As disclosed in claim 2, by recirculating the hot air in the drum and by heating it by means of the flue gases which heat the exterior of the drum, a considerable reduction in energy consumption is obtained while at the same time a configuration is obtained which is much more simple to produce and maintain. As disclosed in claim 3, by recirculating the flue gases and by leading them to the air intake of the burner, the heat of the flue gases is utilized by the mixing with the fresh air, whereby energy is saved while at the same time the flue gases are effectively combusted by this recircu- lation.

As disclosed in claims 4 and 5, by maintaining a compara- tively low temperature for the hot air in the drum, and a comparatively high temperature for the flue gases sur¬ rounding the drum, a fast and yet gentle drying and roasting of the beans is obtained.

Finally, it is expedient, as disclosed in claim 6, to use gas as heating source since the temperature of the flue gas thereby becomes higher than is the case with for instance oil.

The drawing

An example of an embodiment of a device for carrying out the method is shown in the drawing.

Description of the embodiment

A device for carrying out the method can, as shown in the drawing, be designed as a drying furnace with an outer jacket 2 in which a drum 6 is suspended.

In the one end wall 21 of the drum 6 an opening 22 is pro¬ vided through which the green beans can be poured into the interior of the drum through an outer inlet channel 20.

In the side wall of the drum 6 and the jacket 2 there is furthermore provided hatches 7 so as to permit access to the drum. After the drying, the drum can thus be emptied of its contents of beans 10 from without through the hatches 7.

At its ends the drum 6 is provided with an inlet and an outlet pipe mounted 8 to the jacket 2 and at their ends having connections 9 which are connected to an outer pipe 14 which can recirculate the air through the drum.

Moreover, guide vanes 19 are provided on the interior sur¬ face of the drum ensuring an effective mixing of the beans 10 during the drying and roasting.

As will be seen from the drawing, a belt drive and a motor 11 are arranged permitting the drum 6 to rotate during the drying process.

Moreover, a fan 15 is fitted on the pipe 14 forcing the air in the drum to circulate and causing the beans 10 to mix during the drying.

A separator 12 is provided on the pipe 14 for collecting dust, filming and husk, the result being that the dried product will be clean.

A venting pipe 16 with a motor-controlled valve facilitates the discharge of steam from the interior of the drum 6 and an inlet pipe 17, likewise controlled by a motor valve, provides an intake of fresh air for the cooling of the beans 10 after the drying..

The heating of the air 1 in the drum 6 takes place through a heat exchanger 18 in which the air pipe 14 extends. Hot flue gases 5 are led from a burner 3 to the heat exchanger 18 prior to being added to the interior of the jacket 2, where the exterior of the drum 6 is then heated. The method will now be described. Green beans of either coffee or cocoa are poured through the channel 20 through the opening 22 to the interior of the drum. The burner 3 is then started, and the motor 11 is started.

The temperature of the flue gases 5 is about 800°C, and the temperature when leaving to the pipe 13 will be down to about 400°C.

The heat energy is especially used for heating the exterior of the drum 6 so as to heat the beans 10.

When entering the drum, the air 1 has a temperature of about 300°C, and when leaving the drum it has a temperature of about 160°C during drying after which it will increase to about 200°C during the subsequent roasting.

The drying and roasting time will normally be about 10 minutes, and the capacity in the drum up to 240 kilos of beans.

During the rotation of the drum 6 a continuous reshuffling of the beans takes place, in that the guide vanes 19 will mix them. Heating is performed from the outside of the drum by convection as well as by air heating in the interior of the drum.

This efficient two-sided heating of the beans means that the temperature need not be higher than those mentioned, which is considerably below the temperatures applied in the usual direct flue gas heated coffee burners.

This ensures a hitherto unknown gentle drying of the beans and also that burning of the outermost parts of the beans 10 is avoided altogether. The drying and roasting obviously becomes perfect and offers an improved aroma with minimum risk of the occurrence of carbon on the beans; also, during the entire drying and roasting process the beans are com¬ pletely cut off from any contact with the flue gases from the heating source.

Once the roasting process is completed, the rotation of the drum is stopped, and the burner switched off, after which the finished beans are emptied out through the hatch 7 in the side of the drum. A new roasting process may now com- mence.

Finally, it should be noted that there is no risk of flue gases 5 entering into the drum through the access opening 22 in the end wall, the reason being that there is a posi- tive pressure inside the drum which will prevent such an ingress.

Claims

C A I M S

1. A method for the drying and roasting of coffee and cocoa beans which beans are found inside a drum in which they are heated by means of flue gases from a burner, until the re¬ quired degree of drying and roasting is obtained, c h a ¬ r a c t e r i z e d in that heating takes place partly directly by supplying pure hot air (1) to the interior of the drum (6) and partly indirectly by supplying the hot flue gases (5) to the exterior of the drum (6) .

2. A method according to claim 1, c h a r a c ¬ t e r i z e d in that the air (1) in the drum (6) is forced to circulate through a closed pipe system ( 14) and is heated by the flue gases (5) in a heat exchanger (18).

3. A method according to claims 1 and 2, c h a r a c ¬ t e r i z e d in that the flue gases (5) are forced to circulate in a closed pipe system (13) from the exterior of the drum (6) and to the air intake of the burner (3) .

4. A method according to claims 1-3, and where coffee beans are dried and roasted, c h a r a c t e r i z e d in that the temperature of the hot air (1) when entering the drum (6) is about 300°C, and about 200°C when leaving, while the temperature of the flue gases (5) is about 800°C when sup¬ plied to the exterior of the drum (6) and about 400°C when leaving.

5. A method according to claim 4, and where cocoa beans are dried and roasted, c h a r a c t e r i z e d in that all temperatures are approximately 50°C lower.

6. A method according to claims 1-5, c h a r a c t e r - i z e d in that heating takes place by means of a gas bur¬ ner (3).