Fan speed settings

Greetings weird coffee people!

I’m new to roasting on the Bullet having roasted on a Loring S15 for five months. Anyhoo I’m finding each incremental adjustment to the fan setting has a fairly significant impact on the RoR trend. I’ve had quite a few RoR crashes due to increasing F2 to F3. I’ve had a look at a number of user roast profiles now and see that most people only use F2 and F3 and are using F3 later in the roast. I’m curious on other users view on fan speed and maybe some examples of when and why they might increase (or decrease) fan speed instead of altering the power level? Also what do people think about a slower graduation of fan speed (rpm) in relation to the fan speed setting (Fx) so that the rpm increase is a smaller across the lower fan speed settings? I think this would give us extra flexibility in fine tuning our roast profiles. It seems to me any fan setting above F4 is almost unused in most roast profiles I’ve seen. Feedback and opinions appreciated!


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Hey David -

F2-F3 has worked well for me with small 325g batches roasted on the lighter side, up to near SC. I tried constant F4 for a while, with correspondingly higher power to compensate for increased cooling, and found it easier to achieve a smooth declining RoR but the flavors in the cup were flatter. When to switch to F3 is a good variable to fine tune for each bean.

Lately I’ve been trying to learn how to roast larger 500-600g batches, which some say should be nearer to the “sweet spot” for our machines. I’m not sure if F2-F3 applies as well to these larger batches, eager to hear other’s experience.

For finer control of fan speeds, check out what your machine does with fan calibration disabled. You can see the fan speed in the Info display. On my machine the slope of the fan speed vs. fan setting curve is MUCH shallower, providing about twice as many settings to cover the lower range of speeds. The drawback is that each machine runs differently in uncalibrated mode, so comparisons and profile sharing isn’t as useful.


@bradm I probably should have clarified - I’m roasting 500g batches. With the limited amount of roasts I’ve done on the Bullet I’ve found F2 - F3 sucks away a lot of heat and momentum but would be interested in seeing how you go with an increased batch size. I’m fortunate to still be working in the coffee industry so have a lot of kit (various commercial grinders, brewing apparatuses and a high end espresso machine) to play around with. I’m really looking forward to seeing what I can get out of the Bullet, or more truthfully, what the Bullet can get out of me! Out of interest do you use the calibrated or non-calibrated fan mode?

I still think that a slower RPM graduation in the lower fan speed settings would be beneficial. I might have a go running the fan in the non-calibrated mode once I’m more versed in the nuances of roasting on the R1. I’m using some fairly cheap green at the moment while I’m learning the ropes but hope to get some tasty espresso out of it. Not much going in the way of pleasant fruity notes so strictly espresso.


Hey David,

I’m still really new to this so please take anything I suggest with a grain of salt.

Scott Rao’s book talks about how upping the fan settings can absolutely suck the heat out of the roaster and cause crashes. His first suggestion is to lower the “gas” which I interpret as induction power, and then a few seconds later up the fan. Apparently that helps smooth out the RoR and avoid fan crashes.

He also talks about the importance of modulating fan speed in an electric roaster because of the way it holds heat more indirectly. I haven’t done enough research to say if that’s different for the Bullet because it is induction vs some sort of coiling.

I’m roasting 500g batches myself and I’m planning on doing a few roasts tonight, so I’ll give it a shot and I can post my findings here if it’s not too much.

Thinking of the starter roast where Aillio ups the fan speed and drops power simultaneously at IBTS 120C. I’m thinking about dropping power, then waiting 3 seconds, then upping the fan. They also drop power at IBTS 165C, then up fan at IBTS 190C. I’m thinking of basing my fan increase more on time than temp for that second fan up.



Thanks for your input @andrewk8ov much appreciated. I haven’t read Scott Rao’s book but I have read Rob Hoos roasting manifesto and a bunch of articles by Anne Cooper. The Loring roasting machines don’t allow fan speed control, it is adjusted automatically when the gas setting is changed so I am new to using fan settings.

My understanding of most roast systems is that a majority of the heat transfer to the coffee beans is by convection (hot air). Even in a direct-heat drum roaster such as the R1 where the hottest component is the drum, the hot air (environment) in the roaster is doing the majority of the work. On the Loring heat transfer skewed towards convection as it uses hot air to indirectly heat the environment and drum.

The R1 vs a typical “direct-fire” gas roaster will behave in a similar way though I’m of the view that gas is slightly less efficient at heating the drum but will also heat up the environment (air inside the roaster) more effectively than our induction roaster. I’m a total novice on the R1 and although I did very small scale production roasting on a S15 (150kg/week) I’m still very much beginning my journey also. Fortunately I did glean a decent chunk of basic knowledge from that time which is translates across all types of roasting systems.

I do think that dropping the power and increasing the fan speed at the same time or close together will have a large effect on RoR and I would be inclined to do one or the other unless the RoR trend is rising substantially. Perhaps my approach to using fan speed to help regulate RoR is incorrect and I should just be focusing on using the charge temperature and power settings to establish, maintain and control momentum and RoR.

Afternoon :smiley:!

I think you are right about the air doing a lot of/most of the work roasting. The aillio manual & beginner’s roast talks about fan speeds 1-3 increasing convection, while F4+ starting to remove heat.

I ran a few roasts trying out the staggered fan technique with 500g batches.

I think it actually helped smooth my curve and stop my plateaus from my first roasts but I have not looked at, or tasted, enough curves to say for sure.

Here is my favourite one:

and the follow up more tea-like roast:

I think they are both much different tasting, but way less baked than my first roast that didn’t use the fan speeds as much.