With a 550 gm batch I expect to see about 43F° difference between I-Temp and B-Temp at about I-Temp = 250-300°F. That difference diminishes to about 12F° at 2Cs. E.g. on this roast from a few days ago…
Hi @owntom.k2NH,
This can happen when the Fan Calibration is off. Could you share your Serial Number with us? We can take a look at your roast profiles. If you feel that the information is too sensitive to share publicly, you can send us a ticket through [email protected].
Best regards,
Kevin
I’m wondering about this too, since on even a 9:20 roast that ends with IBTS at 440F shows a bean temp of 420F and the 16.6% wait loss and color seems to match more of a 420 end temp from what I’ve seen on previous roasters.
In my experience a 440 should be past Full City+ towards Vienna and I’m seeing more of a Full City which seems to be somewhere halfway like actually 430F.
This is on a 350g batch though but I was hoping smaller batches would be more accurate than this.
Maybe I need fan cal but I thought the fan calibration was no longer required on the newer models?
I have SN 009795
Thanks!
Your fan RPM is pretty standard. In most cases, the Bean Temp at first crack differs slightly depending on your batch size. This has something to do with the nature of the Bean Probe. The beans transfer heat/energy to the Bean Probe during roasting, so fewer beans means less energy transferred. This is why you usually see inconsistency in Bean Temp at first crack across different batch sizes. Of course, with the same batch size, the Bean Temp at first crack should be relatively consistent.
Here’s an article on the Bean Probe and IBTS Module for more information:
https://aillio.medium.com/the-start-of-something-39aa01d08fa9
Best regards,
Kevin
How many grams was that roast?
I am having this issue too, and have noticed that the difference in probe temps is further exacerbated on smaller roast sizes. <300gm
Did you resolve your problem?
What you are seeing is expected. At full capacity (1 kg for my V1.5) the difference between I-Temp and B-Temp is minimal by the end of the roast but about 10-15F° with my usual 550 gm batch size.
Room ambient affects the difference as well, especially noticeable in the summer heat of my uncontrolled shop temp here in SE Arizona.
Bruce
Thanks Bruce,
So it sounds like the bottom line is that the IBTS is giving the truest readings and the bean probe is inaccurate on smaller batches especially. With large batches the bean probe becomes more accurate due to the larger bean mass and better heat transfer since there is less air which doesn’t transfer heat to the probe as well. I have been doing mostly small 454g or less batches and have been ignoring the B-probe temp pretty much from day one. I guess I was more interested in if the IBTS accuracy and exactly what that was. I’m finding the more roasts I do now that it’s very consistent and probably more accurate then what I was used to. So I think my expectations were that I would see similar temps on the Bullet when in fact the ones that I was used to are probably off by about >10F .
Thanks again,
Bill
The bean probe as a measuring instrument is accurate within some spec and very consistent. The issue has more to do with the bean-action inside the drum, i.e. there are fewer beans and less force of contact with the probe when roasting a small batch compared to filling the drum with as many beans as the drum can hold. Which is only ‘gee whiz’ information in terms of your case where you are roasting a range of batch sizes.
There are nuances you can view with the bean probe during a roast but the reality is for roasting a range of batch sizes it sounds like the IBTS will best serve your needs (unless you do mental gymnastics to compensate for batch size).
Just keep in mind that you may have to do a little more maintenance on the IR sensor in order to have the displayed I-Temp be consistent. I see the reading creep lower over a time as the sensor picks up some roasting smut. It’s much better these days, however, since the recent f/w mod (615?) related to the fan (it’s now set to F1 during PH).
Also some of my issue is roasting dark… that causes the IR sensor to get dirty faster than the vast majority of Bullet users. So you may wonder ‘what’s this guy worrying about?!’ What happens is the drop temp displayed is a little lower after a lot of roasts. I have to confirm with audible sounds… all cuz a little of the IR is blocked from getting to the sensor after 15-20 lbs of greens.
Too much info!
Me
IBTS is only accurate for the exterior temperature of the beans. To get a better sense of how the heat is being transferred to the middle of the bean, you want to also reference bean probe and air flow temperatures.
Never too much information and thanks for your tip on cleaning.
Bill
Ps wondering where exactly the bean probe is mounted. Is it spinning on a slip ring or something or how do they do that?
I will have to keep that in mind about IR and surface temperatures for sure. Makes a lot of sense when I see people roasting 800+g where the IBTS and the BT eventually meet up it seems. As far as air flow temps go I’m not sure how I would measure that. Though I think I will try putting a thermocouple wire in alongside the trier next time and see what the air is and if it matches the BT and another on the exhaust just for grins. I’m not sure where the actual BT probe in the bullet is located.
Thanks,
Bill
You’ll see it when you remove the faceplate for cleaning. It’s the little silver stick. next to the glass window.
Ah ok got it. I will look for it when I do a cleaning.
Thanks,
Bill
That is correct. I roast either 1lb or 1.1kg batches. With 1kg batches the BT and IBTS will “merge” as you get to FC and sometimes crosses (which is ok). I switch to the BT readings once I get to FC on my larger batches, I find this gives me more accurate results. For my 1lb batches I solely use the IBTS reading.
Good to know, thanks!