This is my first post, so please be gentle with me. lol
I had a Hottop with probably close to 700 roasts on it with Artisan.
I have had the Bullet now for about 2 weeks and have 27 roasts fo far. I started out with smaller batches to experiment with the settings and controls.
I just ran 2 batches at 2 lbs each. (906g) and noticed that the IBTS stopped rising and the BT curve kept rising and passed the IBTS. If I had waited for the IBTS to get to my target temperature, I would have started a fire.
I am assuming that the IBTS gets covered by the beans as they expand and then the IBTS no longer can read accuratly. I ended up dropping when the BT reached 405.
(One of my pet peeves with the Hottop was that the probe temps lagged by about 20 degrees. Once you accept that, you can adjust your profile mentally. You just canāt talk to pros with larger machines and tell them that you are dropping at 380.)
Very familiar with HotTop roasting and using Artisan.
Using the Bullet, and assuming you have an IBTS cooling fan that is working properly (use the āinfoā button on the Roast page)ā¦
IBTS & BT shouldnāt cross. The ir sensor of your IBTS has roasting residue on it, i.e. itās dirty. Looking at the sensor lens (the flat glass covering) using fibre optics most often tells you nothing. Just follow the instructions mentioned here on R.W and in the Bullet manual for cleaning IBTS.
It will take several passes with the cotton swab + alcohol and you probably wonāt see anything on the swab. Be sure to start by cleaning the walls of the rubber view port so that ugly stuff doesnāt end up on the sensor lens when you finish.
Besides the issue that the roast will be taken to a higher-than-wanted temp at the end, one of the issues with the IBTS sensor being dirty is the IBTS is used to determine Preheat temp. If the sensor is dirty, some of the ir radiation is being blocked from reaching the sensor creating an error in that reading- the sensor reads low. The effect is that the drum is being heated to a higher temp than the sensor and ultimately the f/w think it is. In this case Iāll make a wild guess at 30CĀ°.
The beans are not blocking the ir from reaching the ir sensor. The beans are the source of the ir. More beans, more ir sources. If anything a larger batch size will improve ir accuracy provided the ir can reach the sensor.
Bruce
Edit- small-batch profiles donāt directly translate to large-batch profiles by simply raising the power. Additionally the ratio of BT:IBTS readings change because of the bean mass. From what little Iāve seen I believe the 2 readings come closer together as batch size increases. I canāt offer guidanceā¦ like the one-trick-pony I keep doing the same thing using just 550g batches. But there are folks here that do both small-batch and large-batch roasts . Hopefully one of them will step in here.
Iāve been reading much on the forum and appreciate all of the helpful comments from you and others.
I have already cleaned the IR sensor. (as an aside: I used to repair industrial robots for a living. I know my way around mechanical, electrical and electronic systems)
If you go to the Roast Discover tab and filter the results to a minumum Green weight of 900, You will find that 99% of the profiles have the BT and IBTS curves crossing.
For my smaller weight roasts, everything is as expected. When I use the overlay or playback feature, my curves match the sample profile that I select and the drop temp is just like the template that I am using. That kind of rules out the IBTS being dirty.
Different subject:
One of the other things that I noticed with the large batch is that a lot more smoke was created. I donāt believe that this is related to the BT/IBTS curves. I am going to try to conrtrol the heat by adding more fan earlier on rather than turning down the power. Hopefully that will help push much of the chaff out of the roasting chamber. I am thinking that maybe there is so much chaff in the drum that it is smoldering.
I keep everything very clean. I take out the chaff basket and wash it in the sink with dish detergent and keep it sparkly and un-clogged after each roasting session. I vaccum out the chaff chamber after every roast using the trap door and temporarily removing the bean filler plug. I get about 80% of the chaff out that way. Without removing the plug, I only get around 40-50%.
Iāve definitely found that even though the sensor looks clear and shiny, a few aggressive swabs with alcohol+cotton makes a big difference. I need to do this about every 15 roasts, I think.
That is very interesting. I looked at your roasts.There was a big difference.
I cleaned the IBTS very carefully and ran the roast that I ran last night. It came out about the same. It still crossed, but it did it a little bit later. (about half a minute, later)
I agree with what Bruce and Damon that the BT and IBTS curve crossing can be a way to identify that IR sensor maybe need to be cleaned. But it is also truth if the batch size of the green bean are larger the gap between of BT and IBTS becomes smaller. I have noticed it somewhat related to the charge temp that I am using. The higher charge temp the larger that gap. It is also related to the induction power that applied to. Higher power can maintain the IBTS higher than the BT.
However, I have also experienced that same as bill.milagrokfoc mentioned here. Because the way I apply power is much less than what Damon demonstrated and because of my personal roasting preference I will always encounter this symptom that the BT and IBTS will be crossing each other if the batch size is larger than 800g.
I will use most of the time a smaller batch size to roast (less than 600g) to avoid that crossing.
Youāre welcome and best of luck! Itās been a long time since I did 900g on a regular basis. I tend to do 500 and 800. When my lines cross, I fix it by cleaning.
Maybe like @fred0823 says, Iām avoiding some weird curves by roasting 800 or less.
This is an interesting conundrum.
I am going to dig out my old thermocouple thermometer and modify the probe length so that I can get it into the bean mass through the bean charging plug. Then I should be able to map out the differences between the BT and the IBTS and see what the temperatures actually are in the bean mass.
I had to do the same thing to my Hottop. Once I knew that 382F was actually 400F on my Hottop, I stopped worrying about it and adjusted my profiles.
As I am writing this, I am thinking that I might be able to set up a second computer with Artisan and compare the Bean Temp with a more sensitive thermocouple and the resulting ROR and see if it matches RoasTime. Oh Boy! a new rabbit hole to fall into. lol
Sometimes I look at some of the pictures of people local to the coffee farms roasting coffee on a steel skillet over a wood fire. I donāt think that they are concerned with Raoās ROR.
I would suggest you try to raise that charge temp up to around 290C or above for a 2lb (900g) of roasting. See if starts to create a gap in between. Or at least it cross over after the FC. (make sure the IR sensor is cleaned)
Hello billc - Digging way back in the archives here, but did you ever end up coming to a conclusion on BT crossing IBTS? Iām beginning to roast 900g batches and finding that BT is ending up ~12 degrees F when Iām ready to drop. As you pointed out, seems like this is common across larger batch sizes and Iām curious if you were able to solve this riddle? I saw you mention in another post that you begin using BT once it has crossed IBTS.
I really havenāt come up with an answer that I feel is accurate.
I never reported back about experiment that I mentioned above.
I did build a new thermal probe that I could get into the bean mass and that the probe tip was exposed so that it should have reacted faster to the change in temperature. Unfortunately, that wasnāt the case. there was still too much lag in updating the temperature.
The lines donāt seem to cross when the amount of beans that you are roasting is less than 700g. The larger the weight, the sooner the cross happens.
I have reduced the size of my roasts to ~550g. Iām not selling coffee and 550g leaves me with a pound of roast beans after the weight loss of the moisture in the beans.
When I was doing larger batches, if the Bean Temp crossed and became larger than the IBTS, I would start using it for determining drop temp. I donāt know if the BT probe is accurately reading the temperature of the bean mass.
In the final analysis the numbers from whichever probe you use will give you data that you can use to determine when to drop. I donāt rely on the temperature as much as I do the sound of the first and second cracks. For some of the beans that I roast, I will drop at the end of first crack. That is usually a safe dropping point. It will usually be past the vegetal flavors. Depending upon the results, the next time that I roast that bean I may drop it a little earlier if I feel that I can get away with it and want more fruity flavors.
These are things that work for me. Your mileage may vary.
Thanks for the insight! Youāre right - sticking with one and using that as the baseline seems like the best approach. Out of curiosity, did the readings from your thermal probe mirror what you were getting on the bean probe?
I went down a rabbit hole with ChatGPT and thought it provided some interesting arguments as to why this might be happening. One theory that seemed to make some sense:
When the infrared temperature dips below the bean probe temperature, the internal heat of the beans is becoming more aligned with the air temperature in the roaster. The bean probe now more accurately reflects how much heat is inside the beans, as it measures the air temperature thatās been warmed by the beansā internal heat.
The infrared sensor, which only measures the surface temperature, might show a slower rise in temperature or even plateau once moisture is evaporating from the beans, as moisture tends to cool the surface during evaporation. This means that even though the beans are absorbing heat, the surface may not get much hotter for a while.
The comment from ChatGPT is partially true; both sensors in the Bullet are accurate in their own way.
When there are beans inside the Drum, the Bean Probe reads the temperature by absorbing the heat from the beans (as opposed to reading the air inside the Drum), while the IBTS Module directly reads the infrared light emitted from the beans when they heat up, working like a non-contact infrared thermometer.
The IBTS Module does a better job of reading the real-time surface temperature in comparison to the Bean Probe; with a well-maintained IBTS Module, you should see First Crack at 195Ā°C-205Ā°C, and it should be consistent across different batch sizes.
The Bean Probe temp curve varies in different batch sizes. you should anticipate the First Crack ranging from 180Ā°C to 205Ā°C depending on your batch size, reaching closer to 200Ā°C with a relatively larger batch (800g to 1000g). Of course, the readings should also be consistent when you stick to a constant batch size and bean species. This means that the Bean Probe gives you an idea of how much energy is going into the beans. If the curve is getting too different from what youāre expecting, somethingās up and you might need to make some Settings changes accordingly (i.e., Fan calibration has gone off, causing the Bean Probe temp to be lower than it should) during your roast, and then attempt to rectify whatever issues you may be having.
Circling back to the crossing point, the IBTS Lens is prone to read lower whenever itās dirty, but the crossover will happen when the roast reaches First Crack. As long as the IBTS First Crack Temp is between 195Ā°C to 205Ā°C, the crossover does not reflect an issue. Instead, this means that the Bean Probe has picked up momentum in absorbing the heat and continued to absorb more.
To conclude, there isnāt a superior or āmore accurateā sensor when you compare them. We usually recommend that users play with the Bullet and familiarize themselves with the readings. While the crossover will eventually happen especially in bigger batches, it does not reflect a maintenance issue unless the IBTS First Crack Temp is lower than 195Ā°C.
Please feel free to let us know if you have further questions.
Edit: @kevin added a post while I was writing my post.
Thanks Kevin. Great insights
My probe matched the Bulletās probe. It just was a little faster getting there. The lag wasnāt quite as bad as the bullet probe.
I love rabbit holesā¦
This is a very plausible theory. The crossing usually happens around or slightly after the start of first crack when steam is being released by the beans.
Another idea that might be related and has been floating around but is seldom talked about is: internal scorching. People are defining it as: the interior of the bean is darker than the outside layer.
one of the takeaways that I got was from someone who commented on a comment that Rob Hoos had made:
āThen I watched a YouTube video of Rob Hoos (I believe it was RH) where he said he didnāt believe it was internal scorching but simply the higher concentration of sugars in the interior of the coffee bean caramelizing to a darker color compared to the outer most part of the coffee bean which contains less sugars. Iām paraphrasing big time but that was the gist of it.ā
Here is the link to that video. It is well worth watching:
The link didnāt work, so here is a picture of the the screen in YouTube.
I donāt worry about internal scorching too much. However, after I drop a batch of beans and they have cooled, I will sometimes bite one open and look at the color. I am more interested in seeing that the outside is not scorched and to get an idea of what flavor I am going to end up with.
@deaddriftcoffeeroast I can speak to my experience with 1kg batches and what @da-kevin wrote above confirms my experience.
It is very consistent for me that I get FC in the range Kevin mentioned with the IBTS reading. And here is when I switch to using the Bean probe to read the temps of my bean for the rest of the roast. When I started to roast 1kg batches I was trying to target a drop temp of 430 to 435F and at the time I was exclusively using IBTS reading. As Iām also a sensory based roaster I was noticing that the beans were getting to the color and aroma I wanted before getting to 430-435F IBTS. When I look back at the BP temp at drop I noticed that the BP temp was pass those temps. Once I started to realize what is going on I made the conscious switch to read off the BP after FC for all of my 1kg batches. This gave me a lot more consistent results. It did take me many batches of 1kg to figure this out. My BP and IBTS lines often cross or overlap (after a cleaning of the IBTS) around FC or shortly after FC of the 1kg batches.
At larger batches 800g and above, with the beans having expanded quite a bit and there is enough mass to provide the BP with contact with the beans, my theory is that it would be more accurate for what I want to achieve.
That said when I roast a 1lb or 500g batch I use IBTS only. There is not enough bean mass contact with the BP to give me as consistent a reading as with the larger batches.
I will run a roast with 1000g of the beads after washing and taking all precautions with the beads. Probably preheat the beads a little to make sure that they donāt experience thermal shock and break. The beads may remove some of the āseasoningā from the drum. I can always re-season the drum.
By using the ceramic beads, we take the moisture variable out of the equation. It will be interesting to see if the curves cross without the organic factor. Also no expansion.
I will definitely give this a look - thanks for sharing!
The crosscut image is interesting. Reminds me of a youtube video I was watching recently of the German roasting champion who spoke to biting open his coffee beans to get a sense of how well they were roasted. He mentioned he personally tries to target a consistent color throughout the entire bean and too light or dark on the inside might suggest under or over roasting ā pretty good listen!
Yes, I watched that video with Andre Kirberg. I found it very interesting.
I also watched the one with Daniel Coe. Also very good.
Thompson Owens of Sweet Mariaās also bites his beans open.
I got the beads and tried to use them but the Bullet did not like them at all. A lot of loud bad noises. I dropped the beads and everything looks okay.
I think that the problem was caused by the size of the beads, I thought that they were supposed to be 8mm, but they were 10mm.
I ordered some more beads that are 6mm (about 1/4 of and inch) they should be here in a day or two and I will try again.
