Bean Temp Difference RoasTime vs Display


I’m on my ninth roast and definitely getting the hang of it. I noticed that on my third roast (without unplugging the Bullet), I will get a much higher bean temp on the display as opposed to the RoasTime software. The software appears to be correct and I tend to do things based on sight, smell, sound, and time. So, not a huge deal.

First two roast always go fine. I also allow the box to enter the shutdown cycle and cool a bit prior to taking care of the chaff, etc. From there, I fire up Preheat. I use a combination of the manual controls and the application controls.

Thanks for any pointers!



Hi Douglas-

I see no difference between RT data display and what is displayed on the Control Panel other than having no fractional display on the Control Panel.

That said, there are times that IBTS and Bean Temp are swapped on the Control Panel:

  • IBTS data being displayed as Bean Temp and
  • Bean Temp displayed as Drum Temp (IBTS).

Like you I pay attention to RT so I haven’t bothered to work out what causes the values to be swapped (it’s probably in the manual, but I haven’t been bothered enough to pursue it).



Turns out, I am an Idiot. I decided to hit the “A” button and the bean temp displayed (agreeing with RT.) I’m guessing that hitting “B” puts the drum temp there (did not want to go nuts on buttons in the middle of a roast.) The display labeled “Drum Temp” seems to show the ROR (and agrees with RT.)

Bottom line is I’m getting all the info I need in both places.

Thanks a lot for the reply. I appreciate it!


however… all this said. I’ve been observing that the IBTS temperatures aren’t actually that accurate. There’s always about a 40 degree F spread between the IBTS and the drum temp during the roast, and myself and 3 other pro roasters all agree that the IBTS isn’t accurate. We think the actual bean temp is somewhere close to the middle of the two sensors.(15-20º F cooler) I was all excited to have this super accurate tool of the IBTS and I’m not sure its super accurate yet. Still working on it. And Yes- It would be super cool, if in the software display, the readings were organized to reflect the curves.


Not sure what is meant by 40°F spread between IBTS and the drum temp - they’re the same measurement. Did you mean drum temp vs. bean temp? That would be comparing the IBTS (drum temp) to the thermocouple (bean temp) mounted on the inside of the face plate. Depending on where I am in the roast, and with a clean IBTS, I see about 50F° difference after RoR starts registering. That difference shrinks by about 50% over ~2 min period after start of 1st crack and stays pretty constant into the start of 2nd crack.

In the past I’ve had the impression IBTS is pretty accurate when the sensor lens is clean. After a dozen or more roasts the difference between IBTS/drum temp and bean temp would diminish indicating the IBTS lens was getting dirty. It turned out that for the first 11 months of using the Bullet I had a defective IBTS fan (the related ErC was introduced in Nov 2019 with FW 540), so I’m not sure anymore how quickly the IBTS lens will get dirty now that it has proper air flow.

Btw, bean temp readings at rest (pre-charge) are less before starting the first roast than what you will see at rest after the first roast. The face plate & thermocouple don’t get heat-soaked without beans in the drum. Bean temp readings are pretty consistent after the first roast of the day.



Unless your IBTS is dirty, it is far more accurate than the traditional bean probe. You will see huge temperature differences in smaller batches because 300g of beans will not heat the old bean probe up very quickly. This means you might see first crack temperatures of about 170C on the old probe. But if you try a 1kg roast of the same bean, that traditional bean probe temperature will be closer to 200C at first crack. Are the beans really cracking at different temperatures? No. They aren’t. This temperature spread is just due to the limitations of the traditional probe. The IBTS solves this problem, and if you look at the IBTS for these two different batch sizes, the first crack temperature will be at about 200C for both roasts.


Wow! interesting you had a defective probe. dang… nothing like figuring that one out! Thanks for the 50º spread info. I’m also unsure how fast it would get dirty. I’m only about 20 roasts in. I need to ck the calibration on the fans as I have WAY too much airflow, even on F1 right now. I never even get off of of F1. We roasted about 6 times in one go, and the spread stayed quite consistent, and we all agreed that the “real” bean temp was somewhere between the 2 probes. I found that to be similar up to 600g also. Yes. I understand the logic with the larger the charge, the more accurate and close the two probes would be. I was just hoping the IBTS would sort out the smaller loads more accurately. So far… not-so-much. BUT… its all just “fun” info, if a person is still watching the Bean itself. Thanks guys.
Bruce… I’ll go back tomorrow and review my 6 roasts and see if I have much diff between first and last roast on probe temps at pre-charge phase.


The IBTS sensor was fine. It was the fan that was defective. The fan keeps debris from entering the viewport for the IR sensor. Without sufficient airflow the sensor is prone to contamination.

Calibration is a 5 minute operation. No biggy and it’s done in OFF mode, so no need to connect it to a roast session.