This is good information and helpful to me. It makes sense that a p3 setting works for 1kg roasts, since the objective of a soak is to balance the bean temp. with drum temp. at heat charge. A pre-roast soak is critical to me, precisely because I chose the conductive-roast bullet over a convective (fluidized bed/air) roaster for many “flavor” reasons. But it’s also very easy for conductive roasting methods to trigger the exterior of the coffee beans to start roast expansion while the bean interior is still green/hard (baking) and resistant to roast expansion. The result in coffee flavor is a kind of chemical acidity that is all too prevalent in coffee from conductive commercial roasters nowadays. Through a pre-soak where I can verify uniform temperature in the bean bed and the drum, I have the ability to more easily control uniform expansiion and ROR, whether I choose a faster roast at higher roasts temps, or a slower roast at moderate temps. Keep me in this loop, please. I’d like to see what you all develop using a pre-roast soak stage. Regards
I am glad to hear you were happy with the roasting.
I do increase Power during drying stage. But I always decrease heat after yellowing by increasing drum or fan, decreasing power. I have never tried increasing Power after yellowing before. Would you mind give more detail about this?
I’m very interested in trying this pre-soak method as I’ve noted baked notes in many of my roasts and this could be why. Would you mind sharing a representative roast profile to help solidify in at least my mind how your adjustments through that first stage are being done? I was going to go search through the online profiles, but last time I checked one has to scroll through hundreds of profiles to find the user of interest.
I was able to upgrade from a V1 power board to a V2 power board at the end of June. With that change I can now control drum speed for the first time in 1.5 years. I’m like a kid with a new toy and can’t seem to leave drum speed alone!
Bruce have you noticed that your tryer is less effective at catching beans with lower drum speeds? Using D6 with a 450g batch I had trouble getting more than 2 or 3 beans into the tryer in say 10 seconds.
Now that I have working drum speed control I have so far been increasing drum speed as the roast progresses. By the time I think to use the tryer it’s higher than D6 and I have been able to catch a few beans ok. I picture the beans falling away from the upper rotation path earlier since there’s lower centrifugal force at lower drum rotation speeds. I’ll try to pay attention to that next time out, but what you describe makes sense to me.
Well isn’t that a pain in the butt! At D3 thru D6 not a single bean caught by the tryer. Needs higher rotation speed to throw the beans far enough to reach it. Not useful till I’ve increased drum speed to D7/D8 toward the end of the roast.
@bab, I just found the same that I can’t catch beans without a higher drum speed.
There is some worthy summaries and reading over at Coffee Roasting Navigated on drum speed: Roasting coffee basics - CoffeeNavigated.net
One part discusses centrifugal force potentially having the potential to increase wall sticking above D8. I don’t think that is a major issue, but there could be some small percentage of beans that spend time stuck in a corner or low agitation point.
Thank you for that link… interesting analysis. Apparently the poster is in Europe… ?? Lots to read there. I have the impression they are working with a Bullet but some of the images are Probat. Need to dig into it tomorrow and answer my own questions! Bottom line, though, is that the tryer will only be useful at D8/D9.
On the recent Rob Hoos online class he shared an anecdote from roasting at a bigger shop where they had cleaned down a Probat and when reassembling, had reversed the gears driving the drum, the net result being it spun way too quick. They didn’t notice the error until they loaded the beans and instead of hearing them tumble, nothing, silence. When they opened the bean drop chute and looked in they saw their mistake. All the beans were stuck to the outside of the drum like carnival riders on the Wall of Death I don’t think the Bullet has anytning approaching that speed…
Ah yes… the Wall of Death. Been there; done that; never again! Taught me all I’ll ever want to know about personally experiencing centrifugal force. That 360 seconds (or whatever it was) seemed to last hours!! I’m fairly certain you’re right that the Bullet won’t reach those speeds.
I was trying to remember the name of that carnival ride just the other day…didn’t have to do with roasting, but now you have me thinking of each bean as a carnival rider!
Tilt-a-whirl!
Yeah I don’t think the bullet drum speed can get that so high as to create that effect for all the beans. Even at 9 it seems like the bean pile is pretty stable and settling in the bottom left side of the drum. I was hoping that there would be a little more loft in the rotation.
An ImageJ analysis on the size of the bean pile for a 500g green bean batch at variable drum speeds would be interesting. Have anyone seen such an image analysis?
Some people have measured D9 around 77 RPM. Rao generally recommends 70-80 RPM for a 1-2 kg roaster. Lower RPM for larger roasters (ie. 60-70 RPM for 5-7kg & down to 50-54 RPM for 15k kg roasters).
I don’t think the Bullet has anytning approaching that speed…