[Coffee Roasting] Fire damper control of roasting machine (I)| Coffee Workshop

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In the process of roasting coffee beans with most drum roasters, after the raw beans are dropped into the roaster according to the established initial parameters, the whole baking process can only be controlled by adjusting the firepower and the size of the throttle at a specific time.

So, how to distribute firepower and throttle, choose when to adjust, and even how to control the throttle to reasonably preheat the roaster between each batch of beans before baking, so as to improve the consistency of each batch of beans under the same amount of beans and the amount of beans, all these will affect the final taste of coffee.

In the process of roasting coffee, the general heat is transferred to the coffee bean through three aspects, including the heat conduction between the roaster boiler and the coffee bean, the thermal convection and infrared heat transfer between the hot air and the coffee bean in the roaster. But the proportion of infrared heat transfer is very small. Therefore, it mainly depends on the heat transfer directly through the heat conduction of the boiler wall and the thermal convection of hot air, but there will be a dominant between the two, which mainly depends on the design of the roaster.

The roaster generally uses burning gas or electric heating device as the heat source, and adjusting firepower is to control the amount of heat provided by the heat source per unit time to the roaster. The heat source of the roaster not only heats the boiler, but also heats the air pumped into the boiler by the exhaust fan around the heat source, resulting in thermal convection. In addition, the roaster boiler is a relatively airtight space, so the heating of the air in the boiler will lead to a rise in pressure and a pressure difference with the environment outside the boiler. The pressure in the boiler also has a great influence on the baking, and controlling the firepower can affect the temperature rising speed of the environment in the roaster per minute, which also affects the pressure in the roaster.

The throttle is generally achieved by adjusting the opening of a baffle at a certain position of the smoke pipe installed in front of the exhaust fan of the roaster, or some roasters are achieved by adjusting the speed of the exhaust fan. The use of the throttle is to control the air flow and velocity in the boiler. The size of the throttle will affect the effect of hot air in the boiler on the heating of coffee beans. Under the premise of sufficient heat, slightly increasing the throttle can enhance the effect of hot air on coffee beans, but if the heat is not enough or the throttle is too large, the boiler will lose temperature. Opening the throttle when necessary can more quickly remove the silver skins and particles that make the coffee smell. The size of the throttle will also affect the pressure of the boiler and the development of coffee beans.

So specific to the actual example, how to bake a satisfactory pot of coffee beans by properly adjusting the firepower and throttle at all stages of coffee roasting? The following chapters will slowly share their own experiences!

To be continued.