IBTS... To clean or not to clean? That is the question

For Bullets with the new IBTS, is there an official recommendation as to cleaning the inside face (IBTS) of the Bullet. The IBTS is said to be self cleaning. On older machines, there is a recommendation to clean the inside every 10kg roasts. I assume that since the IBTS is self cleaning that the every 10kg cleaning recommendation no longer applies.

Is there an official recommendation. It is not clear to me in the updated manual 2.8 .

My new IBTS is still receiving coffee oil build-up and I need to clean it every 25 lbs (10-11 kg). I’m curious to see if anyone else’s new IBTS is seeing coffee oil build up?

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If you see that your FC temperatures are suddenly different then you should inspect the sensor and clean it with a cotton bud and a drop of alcohol. We are investigating why some IBTSs still have a little residue on them. One of the theories is that dust while filling the hopper travels down the side and is being sucked into the micro fan and then onto the sensor.


I also struggle with my IBTS. For the first 100kg it worked fine, but since 2 months or so I need to clean it at least every 10kg since IBTS temp drop by about 2°C.
Any help would be well appreciated.


I’ve seen the same thing. My current favorite suspicion is that we may be seeing some aging in the IR sensor as well as some accumulation of roasting ‘stuff’. ‘Stuff’ means I have never seen anything on the cotton swab after cleaning, yet cleaning makes a difference in IR levels during the roast. ‘Aging’ means that no amount of cleaning has restored the original values I saw before I realized there was a need for cleaning.

Recently I noticed that batch size changes the difference between BT & IBTS levels: a larger batch brings IBTS closer to BT values, especially at the end of the roast. Unfortunately I can’t tell if IBTS is lower or if BT is higher. This isn’t a change in IBTS behavior- it’s just that I always roast 550 gm batches till the day I tried one 800 gm batch and one 1 kg batch. The difference between IBTS vs BT was noticeably smaller. And again, there’s no clear way to tell if one or both of the sensors is different.



It makes sense that BT is higher for larger batch sizes, where the thermocouple is more fully immersed in the bean mass. I’ve been concerned about the other end of this issue: is BT temperature unreliably low for small batch sizes like 325g?

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I wonder about that as well. I started using the Bullet with 300 gm loads but finally thought “why am I doing a small batch like this? limited loads was a HotTop thing”. I can’t answer your question but as I think back I seem to recall having trouble correlating 300 gm vs. 550 gm roast profiles. I’ll see what a little digging turns up but I didn’t keep very good notes 2 years ago.


I roasted about 18 batches, including seasoning. Then I had to remove the motor to fasten the tiny wheel back onto the motor drive shaft (both of the tiny recessed screws were completely loose). While I was at it I looked at the IBTS and it looked like it had a really bad cataract, it was milky white. Kind of explains why I’ve been finishing FC quite a few degrees earlier than I expected. Also the roasts have been going pretty quick probably because I’ve been driving the temp higher than I thought I was. Guess I’ll be pulling off the front panel regularly from now on.

Try this…

Pay attention to the difference between IBTS and BT at about IBTS 320 deg F. With my 550 gm batch size, when I see that difference reduce to less that 40 F deg (a difference of say about 37 F deg) I know it’s near time to clean the front panel & IBTS. For smaller batch sizes the difference will be larger and conversely for larger batches the difference will be smaller (making it a little harder to judge). I have found that difference to be consistent from roast-to-roast and a reliable indicator for sensor maintenance.

If you’re seeing whitish deposits on the lens of the ir sensor it may suggest you’re getting smoke near the base of the pedestal for the Control Panel… that base has openings that are the air inlet for the ir sensor cooling fan. You might want to pay attention to where smoke is drifting as you finish the roast e.g. when dropping the beans. There’s often smoke above the cooling tray right after the drop that can be picked up by the ir sensor cooling fan thru the inlets at the base. If you see that happening, a strategically placed fan may help steer it away. I’ve not seen smoke in that area during a roast… just when I start cooling.

I’ve cleaned the sensor many times and have never seen anything on the cotton swab. But the temp difference will be restored as IBTS data shifts. If you don’t see a shift in temp difference (in my case from T-difference =37 to T-difference greater than 40), then it may require more passes with the alcohol-wetted swab.


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Over time I have found that the IBTS gets dirty faster and faster. I clean it almost every roast cycle now, and after just a few roasts the IBTS is distinctly off. I have turned it off and use the Bean Probe in order to avoid being tripped up by the gradual change as it gets dirty. The Bean Probe may be less accurate, but it is less accurate in a very consistent way, which makes it spot on. The ever changing nature of the IBTS reading may be a defect of my specific machine, or perhaps the way I am cleaning it (alcohol and q tip). Some of what I see on this thread is really interesting though. food for thought.

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It’s a pain/nuisance to keep the IBTS clean if you turn out a lot roasts like you do (!!). Just remember that the IR sensor of the IBTS determines your Preheat temp. The probe isn’t involved in setting preheat except to confirm stability (IBTS = Set Point AND B-RoR < 1°/min).

Fyi- I was having more trouble with the IR sensor getting dirty before I went to fw 606. Have you tried that version yet? It may help. Just be aware that you won’t be able to downgrade to what you use now if you find some other issue (currently you can up-/down-grade 605 ↔ 606). With 606 I’ve been able to go long enough that now I have an issue with the exhaust fan getting too dirty which has affected the roast profile of reliable recipes… ‘there is no free lunch!’ (I roast pretty dark which exaggerates maintenance tasks)

And I agree that the bean probe is very repeatable (at least for my purposes) once the face plate gets heated by a couple roasts.



Hi Jacob -
Has there been any update on this? I’m having the same issue as [nanelle.QBeC] describes below. My BT and IBTS lines are crossing before FC after just two 800g roasts, IBTS appears to be then completely innaccurate (e.g. BT at 220C and IBTS still lagging at 210C) and then IBTS completely caked when I go to clean it. It doesn’t seem reasonable to be able to rely on IBTS going forward because I would like to do more than two roasts per session. I’m fine with even weekly cleaning the IBTS after for example 10kg roasted, but such a timeline is wildly different than the recommendations from aillio on how often it should need to be cleaned.

If your IBTS gets dirty so quickly then there could be another issue with the sensor housing not being seated correctly. You can take off the front and take some pictures and make sure the plastic pegs holding the parts together are completely pushed into the silicone (for this you will need to remove the control board and plastic housing as well)
Another recommendation is to use firmware 606 which runs the exhaust fan during pre-heating. This has been shown to lower the amount of dirt buildup.

Just two things quickly.

Also, you must have noticed that with lower preheat the lines cross sooner. To me, 260c seems pretty low for 800g. If you look at smaller batches, you’ll also see that BT goes much lower than IBTS. As bradm mentions above, I’d call BT unrealiably low for smaller batches. If you look at all your roasts, which I’ve done, you’ll see that the 350g ones have IBTS higher and 800g ones have BT higher. It’s just the way it works.

P. S. If you do a quick roast where FC happens between 7 to 8 minutes, the lines won’t even cross, no matter what batch size you’re using.

Thanks Jacob. Not exactly sure though what is requested. I’d like to try the other things first before updating the firmware due to other people’s issues they had when updating firmware. Here is what I could find on removing the control board, but beyond that, I’m not sure which plastic pegs you’re referencing: youtube.com/watch?v=TJzGPMt-TnY. Are you asking me to check the electrical connectors, or is there another layer behind the control board shown in the video where there are plastic pegs associated with the IBTS that you’d like me to look at/ take pictures of?

Upon cleaning the IBTS again, it was not caked over this time, seemed clean but I swabbed it nonetheless. Just a slight hazy layer, but I could still see my reflection (unlike last time where it was covered in chaff dust). Would this possibly indicate issues with my roasting environment or venting set up? Found some other related posts that possibly the back plug was slightly open during roasting (this is possible, it seems worn out and doesn’t like to stay fully sealed) or that my venting set up could be causing smoke to come back into the roaster (I use a passive system with air gap between piping and bullet; vent pipe about 1.5m long that goes out an open window).

Final update, today upon roasting, first 800g batch successful and everything seemed normal, but upon preheating again from bAC mode, i received ErC 0004 (posted also here: Erc 004), so I cooled and shut down the roaster. Happy to have a look into what you mention above but I require more guidance on how to access the parts you are referencing.

Thank you!