Drum Speed

[rojo]

The primary result is effecting all others : Control.
The increased drum speed and air early on gives me a quicker ramp rate that I can reduce or increase with the burner. Taking that, I can range from 12 to however long minutes roasting 50 Kg or so. Before I had to really decrease the charge to have control. So....Yeah,

In terms of slowing the drum, I'm able to tend to the development better, leading to a more even appearance on the beans which was a problem at the constant speed that also lead to inconsistencies in the cups' cleanliness. So, it's all pluses so far, keeping in mind drum speed manipulation may be a prerequisite for my set up given the substantial modifications and the fact that I got a steel drum with iron faceplate and very little insulation underneath to create radiant heat with.

Thanks for the post originally though...Because of your inquiry, I did this experiment in the first place and learned more about what other folks' drum are at for RPM's. It's turning out better coffee in the long run and will help us with roast profile development..!

[Thompson Owen]

I run all my roasters (we have barrels on top of barrels here, too many to count) at roughly 103 to 122 RPM after finding that coffee quality increases in a linear relationship to rotation, adjusting for the lunar cycle. Okay, I am exaggerating, we don't adjust for the lunar cycle. But Marty is right, taking one metric of a roast system (system, see, system) out of context is like saying all great coffee comes from 1600+ meters. Everyone knows it's actually 1533, accounting for distance from the equator and, yes, the lunar cycle. Anyway, it is reductive logic and can do more harm than good. Okay, I have not really tested RPM difference in my roasters, but I am actually doing it right now as I write, because the new secret prototype Behmor home roaster has a variable speed drum motor. But in this system, we are talking gobs of convective heat from a radiant (halogen) source and open mesh drum, akin to the most perforated drum on a shop roaster that could possibly exist. In that context, RPM means something quite different than any other context. Each roaster is, to some degree, a singularity, a lonely star in the night sky, sad, yet noble.

Respect

[AndrewT]

My head is spinning with all the potenial options that could be addressed before deciding to adjust drum speed. After reading the posts and thinking about it i have two questions. First how does drum speed effect coffee development independent of other variables like changing batch size, adjusting exhaust temp / flame and airflow? Second if there is an important effect (and i do believe there is), independent of these other variable, then shouldn't the drum speed be variable based on bean density and mass as it changes in the roaster, as "rojo" suggests, not static? just a few thoughts...

[AndrewT]

i think it is exciting you are getting such distinct results with drum speed adjustments. We can play with it on our sample roaster i look forward to trying it out. any suggestions?

[rojo]

shouldn't the drum speed be variable based on bean density and mass as it changes in the roaster, ...

I found this to be true a little in my machine. Brazilian coffees being soft tended to roast more evenly and I eliminated occassional scorches and stuff by slowing the drum by like 2 rpms....
Also, I'm kind of doing that in general with the profile... Starting a a higher speed that I slow around the first crack, so as weight and density goes, so slows the drum, as it were. Actually, if I didn't do this on my machine and kept it high as I do early on, it would get away from me and come out uneven with facing and other craziness. So I don't even know if moving the drum speed is wise unless you can adjust it throughout the process like this.

I think I might prefer a static, easier, more dialed in system, but, ya know, "love the one your'e with" and all that... I'm learning a lot trying to turn out better coffee and I think it's working whether or not it works for others... It's a challenge roasting everything trying to consider burner, air and drum speed on every individual coffee and blend and be consistent at the same time. I've got a mess of data, then the rain comes and it's twenty degrees colder and 50% more humid for a week and I"m in a "WTF?!" phase for a day or so...time will tell.