The Art of Airflow
After two months of roasting and nearly 5 pounds of green coffee, I decided if was time to take my roaster apart and clean away any visible grime. The process itself wasn’t very notable, but seeing the internal mechanics of the roaster reminded me of how simply it all worked — applied heat, measured time and airflow was all it took to roast coffee. Up until a few weeks ago, I had only focused on heat and time with all my roasts; airflow was not something I felt I needed, nor did I understand the role it could play. For my last couple roasts of the Nano Challa coffee, I decided to experiment and record my results.
379F Degrees and Drop
The section headline largely describes the roast preference I quickly defaulted to after several experiments of really light roasts and several darker ones. When dropped below 379, I found the coffee lacked any strong flavors and anything over 385F+ was tasting of char even though the bean itself was still far from a full city roast. Without much of an idea, I suspected the density of the bean was playing a role in the final output — maybe smaller beans had a smaller margin of error?
While I may not be wrong in my density theory, I found there was another element at play happening within the roaster I was ignoring — smoke. As you start to cross 300F degrees and the coffee has dried out, it’s not uncommon for smoke to seep out from parts of the roaster and in fact, it’s normal. Could it be that smoke trapped within the roaster had coated the beans? Much like standing near a campfire, were my beans picking up a char flavor simply by being around the smoke for too long?
Adding Exhaust to the Roast Variables
In order to test my theory, I roasted a batch of my normal beans and activated the exhaust fan at the sign of smoke within the drum. This newly introduced air caused two major changes within the roaster — 1) smoke trapped within the drum was dispelled out the back through a filter and 2) the coffee inside was now roasting via convective means, not conductive. This change in heat transfer meant I needed to lower the applied heat in order to avoid spiking my temperatures.
Even though I added this new airflow, I was sure to leave my temperatures the same with the goal being to compare one method to the other. In the end, roasts that had the fan applied when smoke appeared lacked any discernible char flavors and instead had sweeter notes most speciality coffee drinkers would prefer. For me, this became my new baseline and was saved into a profile I could repeat over and over.
Finding the exhaust fan use on my roaster was like unlocking a whole new range of flavors for this Ethiopian bean I was certain I had conquered. Having experienced a wide range of roasts and brewing methods, I think it makes sense to roast the final batch with one of my favorite profiles — a slightly charred medium roast, dropped around 380F and dosed as a 17g double espresso shot. Over the next several weeks, I will be roasting two new coffees — a wet processed Kenyan and a honey processed Columbian. Stay tuned for notes and updates!
