Effect of Fan Speed


So I did a test yesterday becasue I was bored/curious…burious(?), and I wanted to see how fast the roaster can reach sustained temps 300, 400, and 500 Fahrenheit with a 1min ramp, at fan speed 60, 80, 100 and see what temp that read on my thermometer. I did not have any beans loaded so this was just to test the heat application from roaster to thermostat soley with air.

In a way it confirmed what I have seen time and agian.

Results: Basically the slower fan (60%) took much longer to reach any temp recorded on my makeshift thermostat recorded temps were 195F on the thermometer for 300F on the roaster app, 270F thermometer/400F Roaster (app) and 350F thermometer/500F Roaster (app). At sustained temp profiles 300 and 400 at 100% fan speed the thermometer would reach 5 degrees hotter. At 60% fan, temps reached and sustained at the 8min, including the 1 minute needed to ramp. 80% fan reached temps by 3mins usually, and 100% fan reached temps within a minute after the ramp except @500F and 100% fan the temp reached 467-468F/1min on the app and 325 on my thermometer and did not go any higher. I let this run and stopped at 5min and not 8 min because I did not want to overexurt the machine and the whole time the temp would no go higher. @500F and 90% fan, the temp reading on the app did reach 500 but was slightly delayed then the 1min ramp. 80% fan reached but with a similar curve/gap as 90% 500@1:30ish min mark.

What does it all mean? Loosely I’d wager that an increasing fan magnifies the heat applied and for a flat temp, this helps carry more energy to the bean and so helps keep the roasting going. A decreasing fan, decreases the heat. But I’d wager that there are points where this changes like when 60% fan at the beginning doesn’t get the beans to move or a 100% at the end and all the beans go flying out… a second guessing/ no evidence conclusion could be that instead changing the profile or temps one could simply walk into Mordor or change the fan to slightly increasing fan profile (cold weather) or slightly decreasing (hot weather). A thought for future testing…


So I’ve done a couple roasts in this cold weather and so far just increasing the fan doesn’t help much because it’s throwing off the total energy put to the roast.

My thinking is that the fan can be used as a magnifying glass helping the inlet curve of the profile come into focus.

I also tried decreasing the bean weight from the usual 55g to 45g and though (again) the attempts so far are not very extensive…with the base profile of Marshal Etheo and Marshal Etheo -1charge, it made the tastes murkier like changing the fan. So roughly like how George Howell puts each progression of the process from bean to cup are like windows. Similarly I think of roasting now like getting fitted for glasses; finding the right combination of lenses (of inlet, weight and fan) will bring the flavors into focus. But I have to remind myself constantly to play with only one variable at a time. On the up and up!


Hahaaaa yes! Some of my new favorite coffee metaphors there, Deven!


It may be the case that fruit and inner bean development is linked with high (80%~) and chocolate and outer bean development is low <75% fan.


My recent findings.
I was meant to drive the tempature up to 275C with fan speed at 86%. The roaster turned me down as follows. It seemed confusing as I had believed high heat could/should be driven by strong air flow. Then something caught my eye. The turning point of temperature seems to correspond with the drop of fan speed.
I’m even confused yet I’m glad to find a way to manipulate the tempature in high. Anybody has any idea about this?

More charts for reference.


For all roasters there is a point at which the fan speed can be so high that the heating element can’t keep up with it, and the system starts to lose heat.


makes perfect sense @jboutte88, the higher the fan speed the more hot air that will be expelled!


I disagree, there is a fault in the roaster, this has happened and happens when I try to go to 500F/250C in 1 min. But has happened during roasts at much lower temp. Best bet is to reinstall firmware and app.


interesting findings, did you resolve this issue by reinstalling the firmware?

note that several things can be going on:

  • higher fan speed will suck in more cool air which will affect the heating element upto a point that it can’t keep up anymore, but as you said it also happens at lower temps so something else must be going on
  • there can also be an energy management issue going on: high fan speed requires more energy and high heat obviously also it could be that the entire system is struggling, althoug I find this unlikely.

hence im really curious whether you’ve resolved it!