Hey ! Sorry for the late reply, I’ve been experimenting and have found drum speeds to be a useful tool in creating flavour experiences in the cup.
Every Bullet is different, for instance my D5 is 42 RPM and that’s about as low as I’d recommend anyone go on the Bullet, at least in my experience roasting 910gram batches. My journey down this particular rabbit hole started with a rather troublesome washed colombian that I just found to be far too acidic for my tastes. What started as an attempt to attenuate the acidity using a more “conductive” approach led to me discovering how slow drum speeds in the bullet can increase body and mouthfeel in the cup without necessarily making things “roasty”. I managed to avoid scorching everything surprisingly, and in combination with my lower pre-heat (aiming for a 72-75 degree Turn using a 30 second soak at P0 straight to P9), I was blown away at the rich juicy cups I was able to obtain. Seriously crushable stuff. Don’t let the long Drying times dissuade you, 6-7 minutes in my cases…it’s what happens after that I find is most important anyway.
Couple of things I have noted using a very slow drum speed:
- You definitely want to soak it to help avoid scorching.
- Long yellow times have tasted awesome! Like 5, or 5:15, and I’m calling Yellow after no longer being able to detect any green, usually around 170-173 IBTS. Now you might be thinking this is where the body comes from, spending so much time in yellow. Well, even spending 3:15-4:00 minutes in yellow the cup had an undeniable boost in body from the drum speed. But because I was afraid of scorching on D5 I didn’t want to spend too much time roasting after FC when things got real hot…so I tried to push for maximum flavor development in yellow. Conductive heat transfer is less efficient so that’s perhaps why it worked going long?
- Going much longer than 1:40 after FC will definitely result in some roastyness espcially if RoR “flicks” back up, but still, surprinsingly, nothing unpleasingly burnt tasting to my basic pallet, just not ideal. The best cups we’re anywhere between 50 seconds (longest yellow times) and 2 minutes (4-4:30 yellows) with no roasty flicks to be seen.
Also how’s this for interesting: when brewing with Third Wave water, I compared a Guatemalan I roasted using only D9 with one only using D5. Both we’re very nice, the D9 having nice clarity and beautiful flavors although much less body than the D5. The D5 had such lovely texture and was crushable, no bitterness despite being little bit less clear. It was toss up, both we’re great but different, no clear winner. However when brewing both coffees using basic filter water (I have an Aquagear filter jug thingy) the D5 coffee won hands down! The flavor still managed to punch through while the D9 fell flat. So this was quite interesting as most people drinking my roasts don’t go through the trouble of using Third Wave or water treated specifically for coffee. Very interesting how this approach results in coffee that is perhaps more accessible to your average consumer? I definitely plan on tasting the same coffees now using both Third Wave and regular filter water in the future.
Currently I’m experimenting with a graduated drum speed approach, starting at D5 and hitting D9 before yellow to try and capture the best of both worlds:
texture, juicyness, creaminess with articulated clear flavors. So far so good, but I’m still working that out.
This roast here was particularly tasty, multiple people telling me it was the best coffee they ever had. Higher air and the slow drum speed seems to add a lovely new dimension to the sweetness.