Principle of Roasting Machine

A coffee roaster is a professional boiler that roasts coffee beans by mixing and stirring coffee beans to ensure uniform heating and transfer of heat energy. There are several types of specialty coffee roasters on the market today:

Classic Drum Roaster

Indirectly Heated Drum Roaster

Fluid-bed Roasters

Recirculation Roasters


The recirculation roaster pushes part of the exhaust gas after combustion to the combustion chamber for re-combustion, so as to play a combustion-supporting role in the roasting process. Roasters without off-gas refiring call it “single combustion.” Different types of coffee roasters have advantages and disadvantages. So far, no newly invented coffee roaster machine can replace the traditional drum roaster.

Classic Drum roaster

The main part of the traditional drum coffee roaster machine is a cylindrical, rotatable iron drum/steel drum, with the central axis as the fulcrum, parallel to the ground and lying horizontally in the machine, and the heating flame is at the bottom of the drum. The firepower is in direct contact with the drum wall, and its hot air is transmitted into the drum. The fan blows hot air from the combustion chamber to the beans being roasted in the iron drum, and the smoke, steam, and other residues and incineration generated during the coffee roasters coffee roasting process in the drum are discharged through the vertical chimney, or fall on the silver skin. Recycle drawer. The iron drum rolls to mix the coffee beans, so that the heat conduction and heat absorption (Conduction) between the coffee beans and the drum wall, and the heat convection and heat absorption (Convection) between the coffee beans and the hot air in the drum.

After the roasting is completed, the roaster will open the drum gate, the coffee beans will slowly fall into the cooling plate, and start to stir. The effect of cooling coffee roasters coffee beans in a short time.

The best drum roasters available today have double drums, one large and one small concentric circle, with the distance between the drum being a few millimeters wide. When heating in a double-drum roaster, the outer drum is in direct contact with the flames while the inner drum is slightly cooler.

The double-drum roaster reduces the heat conduction between the drum wall and the beans, thereby limiting the focus (Tipping) on both ends of the coffee beans during roasting, the burning of the bean surface (Scorching) at the beginning of roasting, and the burning of the bean surface at the end of roasting ( Facing) risk. If you choose a traditional roaster, it is strongly recommended to buy a double drum machine.

Advantages of the traditional drum machine: the environment in the drum without tail gas re-combustion function is relatively clean, and the heat storage effect of the drum is good, providing heat conduction and heat absorption for the beans, especially in the first few minutes of roasting.

Our coffee roasters use 316 double-layer drums of stainless steel.

Disadvantages of the traditional drum machine: If the drum is overheated, it is easy to cause burns on the surface of the bean body.

Classic drum roaster
Classic drum roaster

The picture above is a schematic diagram of a traditional drum coffee roaster machine. The brown arrow represents coffee beans, which enter the roasting drum (1) from the bean hopper (2), and after the roasting is completed, the coffee beans are introduced into the cooling plate (3). The hot air enters the drum from the combustion chamber (4), and the exhaust gas is blown to the chimney (5) and the silver skin collector (6) collects the silver skin that floats down.

single drum and double drums
single drum and double drums

The left picture above is a single drum, and the right picture above is a double drum.

Indirectly Heated Drum Roaster

It means that the hot air generated by the combustion chamber is directly sent to the roasting drum for roasting. This design prevents the surface of the beans in the drum from being burned due to direct contact with the flame with the outer drum of the roasting drum. Roasters can use this technology to roast beans with high heat to increase flavor and aroma. Like the traditional drum coffee roaster machine, the beans are mixed and stirred evenly in the drum and heated evenly. After roasting, they are poured into the cooling tray for rapid cooling.

Benefits: This technology makes the internal and external environment of roasting neat and clean, and the roasting efficiency is high because the temperature rises quickly, and it is not easy to burn the bean surface.

Cons: Indirect heating consumes a little more gas than traditional coffee roasters.

Indirectly heated drum roaster
Indirectly heated drum roaster

The picture above shows the indirect heating drum machine

Fluid-bed Roasters:

It refers to relying on the atmospheric airflow to keep the beans suspended and rotated continuously in the roasting bin. Because the density of beans is getting smaller and smaller during the roasting process, this kind of coffee machine roaster needs to increase the wind force in the early stage of roasting to make it suspend and rotate, and gradually reduce the wind force in the later stage of roasting.

Almost all fluid-bed coffee roasters are not equipped with a cooling plate; instead, when the roasting is completed, the roaster pours room temperature air into the roasting chamber for cooling, that is, the roasting chamber and the cooling chamber are in the same place. This technique is far from ideal, as the surface temperature of the inner wall of the roasting chamber is very high when you finish roasting, which will affect the cooling progress. In order to solve this problem, most users of fluid-bed coffee roasters can only buy a separate cooling plate.

Advantages: The Fluid-bed coffee roasters are cheap, reliable in performance, small in size, and the chance of burning the bean surface is extremely small.

Disadvantages: Excessive wind speed destroys the flavor of coffee roasters coffee, consumes gas, and is very cumbersome to operate, because the roaster needs to control the gas to adjust the wind speed to achieve the best flavor, and also needs to know the rotation speed of the coffee roasters coffee beans during the suspension and rotation process, very complicated.

Fluid-bed roasters
Fluid-bed roasters

When the fluid-bed coffee roaster machine roasts coffee roasters coffee beans, it basically uses convection to absorb heat (Convection). The airflow is heated in the combustion chamber (1) and sent to the roasting chamber (2) and then drifts away from the chimney, where the silverskin falls in the silverskin collector (3). The green coffee roasters coffee beans enter the roasting chamber from the hopper, float, and rotate in the roasting chamber, and the place where the beans are dropped is not shown in this picture.

Recirculation Roasters:

Unlike single-circulation coffee roasters, recirculation coffee roasters send exhaust gas that has been burned once to the combustion chamber for reheating, saving fuel (gas) during the roasting process. This coffee roaster machine technology is currently very popular because it saves energy and reduces emissions, limits bean surface burn, and provides a stable, delicate, and consistent roasting environment for coffee roasters coffee beans. Its stable baking environment is attributed to the automatic tracking and acquisition of internal roasting analysis curves in the coffee machine roaster. The fly in the ointment is that, because the exhaust gas is re-combusted, it means that the exhaust gas passes through the coffee roaster machine again and makes the coffee roasters coffee smell smoky.

Advantages: gas saving, high roasting efficiency, and low chance of bean burns. Built-in fully automatic tracking to obtain roasting curve grading data software

Cons: Smokey smell

Recirculation roasters
Recirculation roasters

The picture above shows the principle of the recirculation coffee bean roaster machine. The coffee roaster machine recycles the exhaust gas, and the exhaust gas enters the combustion chamber through the roasting chamber again. The heat absorption principle of this technology is completely heat convection. The combustion chamber is also a re-combustion chamber, and the white arrow represents the direction of the hot air flow. It is the same as the traditional drum coffee machine roaster, the green bin enters the beans, and the blue cooling plate exits the beans for cooling.

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