Many drum roasting machines share similar concepts in their design and function. Giesen machines come with unique features that aren’t offered by any other manufacturer. In general, drum roasters feature a revolving drum and an impeller that continually sucks air through the machine and through the drum itself. The air intake is usually situated near the burners of the machine and preheated roasting air is mixed inside the roasting chamber with the coffee beans and evacuated by the roasting impeller. The design of most drum roasters allows the roasting impeller to continually evacuate more air than the roasting machine is taking in. In simple terms, the roaster is always a bit out of breath. With the force of the roaster impeller, the machine collects chaff in the roasting cyclone and roasting exhaust (mostly smoke) is blown out through the exhaust stack.
Some roasting machines utilize the concept of variable airspeed. How does this impact the heat transfer? More air at higher temperatures can accelerate the heat transfer and increase the Rate of Rise (RoR). More air at lower heat input levels, will slow down the heat transfer and decrease the RoR. The impact on flavor works as follows: more airflow can accentuate the sweetness and brightness of the coffee; too much airflow can create sourness. Too little airflow will mute the acidity and potentially lead to leather-like or even smoky flavor notes. So, in theory, air speed offers positive benefits but nevertheless few roasting companies have embraced airspeed as a roasting parameter.
Giesen has taken airflow control to the next level by introducing the highly innovative concept of pressure profiling. How does it work? The control panel of basically all Giesen machines features a setting for “Pa” (which stands for Pascal), which is an expression of the underpressure in the coffee roasting system. By increasing the Pa setting, the machine will increase the rotation speed of the roasting fan to maintain the higher pressure target. During the roast, the operator can increase or reduce the Pa setting confirm the requirements of the profile. If this is done while recording the roasting profile using the Giesen roasting control software, then all the modulations can be repeated automatically with the next batch of the same profile. With the integration of Cropster, this software will also record all modifications made with the Giesen user interface, which allows for the maximum possible consistency of roasting profiles.
In my opinion, these features make Giesen roasters truly unique!
My next article about the exciting technology of pressure profiling will discuss specific roasts using the Giesen pressure profiling technology.
Willem Boot is the Giesen brand ambassador in the USA and in his column, Willem shares his insights in the wonderful world of roasting coffee.