IBTS unreliable

My IBTS get’s dirty all the time after 10 roasts. Have to clean it regularly. As the preheating depends on the IBTS, it means that the start temperature isn’nt always the same, due to the degree of polution of the sensor. The IBTS is installed properly (no gap), so that’s not the problem. But it might be the fan that is situated behind the sensor. If the fan is not rotating I can imagine the smoke isn’t blown away correctly. Can anyone tell me how I can see if the fan is working? Can I check this by the software?

Is anyone else having issues with cleaning the IBTS? I was wondering if it would help to raise the “F”. Normally I roast on F3, but wouldn’t it be better to roast at a higher F-speed so the smoke can’t reach the eye of the IBTS?

I had a problem with the IBTS fan which caused my Bullet to shutdown power. The Info panel in RT displays the fan rpm.

When new, my fan had been running at just over 6,000 RPM and was slowing progressively till it eventually dropped under 5,000 RPM after a few months. It was about that time Aillio changed the f/w to look for a minimum speed of 5,000 RPM which rendered my Bullet dead. The replacement fan runs at just over 16,000 RPM once the roaster is warmed up; cold it’s over 15,000 RPM.

My fan was spotless when I opened up the control panel. But I’ve seen photos of another IBTS fan that was replaced about the same time which was covered in white dust (smoke residue?). My guess is that fan had been working fine till the residue got so bad it killed it; my fan (running at 1/3 speed) was spotless.

Edit- Also, I have to clean the IBTS lens frequently as well. Not sure what’s going on, but the lens seems susceptible to contamination. If you want to use IBTS to manage the roast, that seems to be what we have to deal with. I’ve also noticed that simply swabbing the lens with alcohol won’t necessarily remove the contamination (whatever it is… I see nothing on the swab!). I’ve had occasions where I have to do it twice to see the data shift all the way back to “normal”. It’s easy to see by looking at the displacement between the IBTS data and Bean Temp.

There’s some thought that there may be smoke residue being picked up through the air inlet at the base of the control panel pedestal. If you roast dark a lot (I do), there may be a chance for smoke to rise from the beans when they are dropped. If not sucked down to the cooling fan they may rise up to the base of the pedestal and get pulled in and lead to the IBTS cooling fan. Frankly I haven’t been able to see smoke rising from the tray like that… everything seems to be going down thru the beans into the cooling fan.

That said, when I wipe my hand across the perforated cover over the power boards (bottom of the Bullet), I come away with white residue. That’s fixable to some extent by rotating the cooling tray about 90° clockwise to redirect the exhaust (the cooling tray power cable limits what you can do). I don’t know if there’s a flow path thru the power board cover to the inlet of the IBTS fan but I doubt it.


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Hi Bruce,

Thank you for the reply. Lots of information to study about! I’am going to read it carefully. As soon as I can see what’s the speed of my IBTS fan, I’ll let you know.


I have the V2 and also have to clean my IBTS lens after 10-15 roasts. As mentioned above, it’s a thin white residue. I’ve verified that my fan rpm tends to stay around 15,000.

At this point, I’ve accepted it as a monthly maintenance task.


Bruce, thanks for the input.

I did not know about the fan readout in RT.

I recently cleaned my IBTS for the first time after a year of use. I also found it clean on visual inspection and on the alcohol swab.

What I am curious about is your comment on data shift back to normal. Do you mean the difference from the temperature probe or the start of first crack?

On my Bullet, the temperature difference between the IBTS and the probe is about 30C. Sometimes at the end of the roast it will get closer. I have no idea how normal that may be, but seems a lot.

Also, I am one of those who cannot easily hear first crack. Once is a while, yes, but most times no. I have relied on others who say first crack starts around 203 C to judge time to end of roast. However, when I do hear first crack it is usually around 208 C. I do not know if that is really the start of first crack or the beginning of the rolling part.

Any comments?



re: Data shift… take a look at the IBTS and the Bean Temp. They run fairly parallel, drawing a little closer to one another as the roast progresses (till FC when they tend to move very close together). It’s the simultaneous difference between IBTS & BT that I was referring to. The difference tends to get smaller as the IBTS gets dirty.

These 2 screenshots were taken with the mouse at about 3:00 minutes into the roast. Check the data at the upper right of each. Bean Temp is approximately the same value in each, but Drum Temp (IBTS) is about 9F° less in the lower shot.

The 1st screenshot was taken 9 roasts before the 2nd shot. In just 10 roasts the IBTS/Drum Temp indicates 9° less. If left uncleaned, the contamination keeps building till Drum Temp is less than Bean Temp at the end of the roast.

If you don’t want to deal with cleaning the IBTS lens (the clear ‘glass’ over the sensor), then you can use Bean Temp exclusively for managing the roast and ignore IBTS. But that presents a problem during Preheat. Since Preheat set point is determined by IBTS value alone, that means a roaster with a dirty IBTS as actually Preheating to a higher temp than the same roaster with a clean IBTS. You will have to guesstimate what adjustment you have to make to keep Preheat where you want it otherwise the starting temp when you charge the beans will get progressively higher and higher.

re: hearing FC & SC… I’ve got that problem too. I wear hearing aids and I’m not sure if that helps or hinders. The issue, of course, is the crashing sound of the beans obscuring the sound of the crack. For a given variety of green beans, FC is fairly repeatable. I find I can make out the crack if I watch the temp… I convince myself that the sound is a little different. I don’t try to pick out the very first cracks, but once it gets going a little I’m pretty sure I’m getting it right.

You can also pick out FC to some extent by watching RoR- the beans change from an exothermic reaction to an endothermic reaction (giving off more heat than they are absorbing) which causes the increase in RoR. I can see it clearly in hindsight (it’s very obvious with the profile I use), but I’ve never trusted myself to identify it properly without sound for confirmation.

As an alternate to direct listening, one Bullet owner here devised a ‘listening tool’ using a mechanic’s stethoscope. It’s intended to help a mechanic listen to the sound of an auto engine while it’s running. He replaced the long thin probe with a short length of metal tube and some hose that fit that tube. The metal tube was sized to fit the trier opening. He said it worked great for his purposes: just removed the trier and inserted the stethoscope adapter into the trier and listened for the crack. Do some digging with search and you should find his post with a photo.


How are you guys venting your bullets? We suspect that this could have something to do with the IBTS becoming dirty.

Inline extraction fan with an air gap. In another week I’ll be back outside to roast with venting to atmosphere. I have the same issue with IBTS needing to be cleaned both indoors & outside.


please explain more


Thanks for the detailed response.

I have read and tried many of the suggestions for better hearing first crack, including a medical stethoscope, but not the modified one in the tryer hole. All suffered from what you call the crashing sound of the beans obscuring the sound of the crack. I, too, looking at temperature and color am able to sometimes make at the steady sound of cracking, not the first few. I have adjusted to this, even if I am not happy about it. I really like the Bullet, except for this. Maybe I’ll give the modified stethoscope a try.

I do not have the problem that your two graphs show with a dirty IBTS. As I said in my original post, I just cleaned the IBTS for the first time after one year of use, and have done my first roast since. I compared the 3 minute point like you did with the clean IBTS and prior roasts. They are the same.

I am reading your two roasts correctly? It seems that the FC temp and times are about the same. I am assuming power and fan settings are the same. So, the dirty IBTS temperature difference hasn’t carried over to the FC point.

I mentioned that the difference between IBTS and bean probe in my roaster is over 30 C. See below.


Same to me. Made a kind of venthood so the smoke can poor out freely. No smoke in the room where I roast my beans so there’s no obstruction or what so ever. This should not be the problem.

The charts are different beans (the first a multi-origin blend; the second is single origin); temps are different at FC. The numbers shown upper right are at the mouse position. Yes, you can guesstimate the temps for FC using the grid (if I hadn’t cropped the scale!), but I don’t imagine they’re any closer than say 5°. Since these profiles for power setting were so similar, I just went to the same Bean Temp for both and that happened to be at about 3:00 min for both roasts; similarities slide later in the roasts. Doesn’t always work out this way as ambient room temp, bean density and a few other things affect the time axis even though the same power setting might be used.

That said, I expect FC to happen (depending on the bean) about 400°F and to finish about 425°F using IBTS data. Just how close they are to 400°/425° depends on how recently the IBTS was cleaned, but for sequential roasts it’s pretty close.


Checked my info panel in RT (finally found it…). The IBTS fanspeed was about 15000 rpm, so there is nothing wrong with that. The IBTS gets poluted and once in a while you have to clean it. We have to deal with that. If so, the IBTS is not giving the temperature correctly all the time . A clean IBTS gives a temperature about 25C higher then my probe, a dirty IBTS 5C lower. This means you can’t rely on the IBTS. Is my conclusion wright?

From now on I am going to focus on the probe again. That’s a pity as a clean IBTS sensor is giving a better indication of the temperature, but a dirty one isn’t.

Apparently not everyone is having a problem with the IBTS getting dirty. Not sure what that’s about… I guess we’re just special! :slight_smile:


My v2 IBTS needs regular cleaning. Like Purduecarter, I just do mine every dozen roasts or so. I have a vent pipe adapter but am not vented. I roast under a 1200cfm exhaust hood with approximately 18 inch gap in distance and have no issue with smoke. I also have issues relying on IBTS as my FC and SC temps have drifted since new from198 - 202 and 224 to 228. So is the IBTS accurate but not consistent and the bean probe is not accurate but is reliable?

Yes! That’s the best description for now: the ibts is accurate but not consistent, the bean probe is not accurate but reliable.

I’m using a metal kazoo to help hear first crack.

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Has your child missed it yet?! :smile: How well does it work?


My kids are all grown and the kazoo was ordered from Amazon. It makes enough of a difference to be able to hear first crack if you listen closely, but it’s still hard to hear so I put the kazoo in just before I expect first crack and listen up.

Well, you may have gotten your kazoo the same way I would have had to get one, but I like the story about stealing your kids toy so much that’s probably how I’ll repeat it! :slight_smile: