Bean Temp vs IBTS with larger batch sizes

Hey RoastWorld Community,

Hoping some of you can share some insights as it relates to increasing your batch sizes on the Bullet and the interplay between IBTS and Bean Temp.

Up to this point, I’d been roasting 500g batches PH at 260C and kicking off a Power Level of 8, gradually decreasing to 3, and have been getting some wonderful roasts. With these the difference between my drop IBTS and Bean temp tended to be around 5-6C at a final bean temp of 204C.

Today I decided to move up to 800g batches. I’ve played around with both PH time (ranging from 260-285C) and initial Power Level (ranging from 7-9) at all combos (high PH, low power, high-high, low-high) but in all these situations my IBTS and Bean Temp were identical at the time of Drop. Another concern here is that post first crack, to hit a ~25% development time, my Bean Temp hits 209.

how have you successfully navigated larger batch sizes on the Bullet? Please feel free to direct me to similar posts as well or other sources of literature!

Today’s batches are still to-be-tasted, which I know is the ultimate test.

My only batch size is 1KG and I haven’t done smaller batch sizes, so, cannot talk about the latter. With the former, the IBTS and BT come very close together and even converge with the BT going higher, especially while roasting dark - SC and beyond.

Though I prefer lighter roasts, roasting for cafes mostly, it is dark most of the time. I use both DTR and DT as a measure of roast level along with Drop Temp but also factor in the time it takes to reach those. With a 1KG batch size, following a solely decreasing ROR, it takes too long to reach the threshold of SC (about 225 - 230℃), so, I follow a decreasing ROR till about 5-8% DTR and then a rising one to reach a DT of about 20℃ DT, 20 DTR and Drop Temp of about 215℃ for medium, +5 for medium dark and a further +5 for dark.

My PH is 300℃ btw.

What’s “DTR” and “DT” stand for? Sorry for the ignorant question as I don’t think I’ve come across those abbreviations before…

Will take a peek at your profiles for 1kg. Mostly roasting at 500g (from 350g) right now and looking to scale up to 750/800g at some point. I may do some extrapolation between your 1kg profiles and my 500g and experiment with that :slight_smile:

“Development” is the final phase of roasting (drying/maillard/development)

DT = Development Time (time from first crack to drop) (edit: oh, he meant ∆°C, my mistake!)
DTR = Development Time Ratio (what % of the total roast time was DT ?)

Scott Rao writes a lot about it in his books/blog.
Development Time Ratio — Scott Rao


Thanks … I don’t read Rao :slight_smile:

By DT, I meant the Delta Temperature or the increase in temperature from FC temperature.

Don’t worry too much about dtr or bean temp. Drop when it is the color you’re looking for. Once you find the right color with a profile that brings out the desired flavors, then go back and look at the other variables (dtr and bean temp can be useful for repeating results at this point). Furthermore, the IBTS reading should be close to the same as your smaller batches, whereas the bean probe will read quite differently since it is reading a smaller mass and not covered as often and as fully as with the larger batches. This is typical for most any roaster