Effects of Exhaust Fan Speed on Roast Time

About a month ago, I purchased a new coffee roaster, the Aillio Bullet R1. This roaster uses induction to heat the drum, making it much more energy efficient and one of very few coffee roasters that can handle 1 kg of coffee using a normal residential electrical outlet.

My beautiful new roaster

When I purchased my Bullet R1, I was fully expecting that I would need a ventilation system. My previous roaster, a Behmor 1600+, had a “smoke suppression” system that drastically reduced the amount of smoke emitted during roasting, but I still had to use fans and open my garage door once I was finished roasting. With the Bullet R1, I can now roast almost four times the amount of coffee, but there is no built-in smoke suppression and thus there is more smoke.

On my first seasoning roast (outdoors), the amount of smoke emitted by the roaster was much more than the Behmor, but not nearly as much as I had expected. So, I planned a ventilation system in my basement with an inline fan to suck the smoke from the machine and out a nearby window. I purchased a Vivosun fan with a speed control, and attached 4-inch flexible ducting to both sides, with one duct taped lightly to the exhaust port of the Bullet, and the other going out the window using a custom-built attachment that I can place into the window “track” or remove when the weather is cold.

Inline fan for exhaust

After my first few “real” roasts after seasoning, I realized the direct attachment of the duct to the vent on the back of the Bullet was causing some issues. My roasts were taking longer than I expected, especially based on times and recommendations I had read about on Therese Brøndsted’s site, Coffee Navigated. Plus, I noticed during preheat and during roasting that higher fan speeds for my inline exhaust fan directly affected rate of rise (ROR), causing it to drop drastically.

With this in mind, I did a roast with the exhaust fan speed on a very low setting, and found that the roast progressed much quicker than I had ever seen. Plus, my ROR curves and times were much more in line with what I was expecting based on my reading online.

Below is a roast with a higher exhaust fan speed. Note that this is a 500g sample of a Columbian coffee, using a preheat of 160 degrees C. The roast time was almost 15 minutes. First crack was harder to hear on this roast.


The roast I tried with the lower exhaust fan speed graph looks much different, with a similar 500g sample of a Guatemalan coffee, but with a preheat of 200 degrees C. The roast time here was slightly more than 9 minutes, and first crack was very audible.


Based on this information, I decided to experiment with a “hood” of sorts instead of directly attaching the exhaust vent. I was concerned that low exhaust fan speeds won’t push the smoke away from my house, and I’d like to ensure that it’s getting expelled appropriately. So, I went to Home Depot and purchased some aluminum semi-flexible ducting that can hold its shape better than the flexible ducting I was using. I positioned this over the Bullet vent in a way that doesn’t completely seal the exhaust, but still will capture the smoke coming out of the roaster.


A few days ago, I tried out my new “hood” setup using ~500g of a sample Brazilian coffee from La Bodega, and with the exhaust fan on high the entire time. The results were that my roast only took 7-8 minutes total, and first crack was very audible. The coffee is actually quite good, and there was no visible smoke during roasting. I actually had a harder time ensuring that ROR decreased throughout the roast.


I think the results are much more in line with what I’d like. The only downside is that the room smelled much more like coffee roasting smoke than before, but the smell faded after a few hours. I might experiment with other fans, but at this point, I think it’s definitely manageable.