[Homeroast] Drum rotation > Jimma > PID iRoast

Edward Bourgeois edbourgeois at gmail.com
Sat Oct 9 10:19:15 CDT 2010

Pro roaster design has been tweaked for many years. Much effort, r&d,
$$$ has gone into fin/vane design and adjusting to the proper speed
for the design. I'm very happy with my hybrid homebuilt but got a
Behmor (thank you John) early after it's release to play around with.
There's much to like about it. But as most 1st models it has some
design issues that can be improved upon. Drum speed it certainly one.
Agitation is very important for quality of roast along with
efficiency. Increasing drum speed has allowed for improvements in both
these areas(I'm running 50rpm but also have a 30rpm I could try and
compare). I still haven't had a chance to really test the chaff issue
Tom mentioned but in the few roasts I've done it didn't start a chaff
issue that was bad enough for me to notice. I've thought about trying
to lower the floor a bit  and redesign the chaff tray but just haven't
gotten around to it. For anyone who didn't see my recent mod. post you
can check out my blog below.

On Thu, Sep 30, 2010 at 12:20 PM, miKe mcKoffee <mcKona at comcast.net> wrote:
> First I'll say I'm not a roaster designer or manufacturer so can't say
> exactly how specific drum rotation speeds are chosen for different roasters.
> Before his passing Ron did a fair amount of testing for various drums and
> drum diameters to determine how fast was too fast for his Q drums. IE at
> what speed would the beans not loft but instead have centrifugal force push
> them against the wall. IRC the HotTop drum rotation is ~30rpm (checked it
> but that was almost 3 years ago so memory fades), USRC 3k ~65rpm, Behmor
> very slow ~6rpm. Observation of other commercial drum roasters and their
> observed bean loft means using similar speeds to measured (counted) USRC
> drum speed.
> A common mistake is thinking the drum itself is the primary heat source for
> drum roasted beans. Modern drum roasters convection accounts for about 80%
> of the roast energy, air roasters even more. While the specific pre-heat of
> the drum and roaster IS VERY important at the beginning of the roast, it's
> importance is it's stored energy which is applied primarily via convection
> and radiation not conduction. With a bit of understanding of the types of
> heat in the roast process and observation of various roasters it becomes
> clear constant loft of the beans by the drum is the goal. Convection is the
> primary heat transfer in all modern roasters.  (See a good article by Terry
> Davis, originally written for Roast Magazine IIRC
> http://www.ambexroasters.com/information/read/heat_transfer.html )
> If the beans aren't vigorously tumbling convection can't occur for the
> majority of the beans stuck in a barely moving mass. This leaves conduction
> and radiation as the more predominant roast energies, which is the problem
> with the stock Behmor. Radiant energy primarily from the heater and
> pre-heated roast chamber primarily affecting the beans on the outside of the
> mass and conduction later in the roast bean to bean. At the same time I
> split out the heater for variac control Alchemist John put in a faster drum
> motor, with marked improved results. (We both had/have first production run
> Behmors from Joe) I never got a roast I was satisfied with just by directly
> controlling radiant heat, ie the heater. Some "ok" roasts to be sure, but
> nothing as good as Caffe Rosto profiled roasts or later CCR HotTop roasts.
> Convection or lack thereof was the apparent difference.
> IF a faster drum rotation causes problems with the Behmor Alchemist can
> chime in since fairly certain he's been using IIRC ~45rpm drum motors for
> close to 3 years.
> It's easy to turn beans brown, it's a lifetime Journey learning how to make
> beans sing. IMO (and that of many others) a huge part of the process is
> learning how to effectively control your particular roaster.
> Slave to the Bean  miKe mcKoffee
> www.CompassCoffeeRoasting.com
> URL to Rosto mods, FrankenFormer, some recipes etc:
> http://www.mckoffee.com/
> Ultimately the quest for Koffee Nirvana is a solitary path. To know I must
> first not know. And in knowing know I know not. Each Personal enlightenment
> found exploring the many divergent foot steps of Those who have gone before.
> Sweet Maria's List - Searchable Archives
> http://themeyers.org/HomeRoast/
>> -----Original Message-----
>> From: homeroast-bounces at lists.sweetmariascoffee.com
>> [mailto:homeroast-bounces at lists.sweetmariascoffee.com] On
>> Behalf Of Jim Couch
>> Sent: Thursday, September 30, 2010 7:49 AM
>> Believe I saw some comments from Tom cautioning about the "dangers" of
>> spinning a Behmor drum too fast, something about it causing
>> chaff collection
>> problems and messing with the ability of the beans to
>> transfer heat to each
>> other perhaps problems would be a better word than dangers..........
>> On Thu, Sep 30, 2010 at 8:36 AM, Robert Yoder
>> <robotyonder at hotmail.com>wrote:
>> >
>> > Hi MiKe,
>> >
>> >
>> > Thanks for your posts!  So much to learn!
>> >
>> > >
>> >   Even directly controlling the heater via variac
>> > > didn't help enough because drum rotation was so slow yielding poor
>> > > convection. If I hadn't acquired a CCR HotTop so soon
>> after the Behmor
>> > > likely would have mod'd it further with faster drum and bean temp
>> > probemaking it a decent roaster.
>> >
>> >
>> >
>> > Can you clarify the drum-rotation/poor convection comment?
>> Is there a
>> > typical shop-roaster drum-rotation speed?  How is that chosen?
>> >
>> > Happy Roasting,
>> >
>> > robert yoder
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Ed Bourgeois aka farmroast
Amherst MA.

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