[Homeroast] Drum rotation > Jimma > PID iRoast
robotyonder at hotmail.com
Thu Sep 30 16:04:20 CDT 2010
> From: mcKona at comcast.net
> To: homeroast at lists.sweetmariascoffee.com
> Date: Thu, 30 Sep 2010 09:20:45 -0700
> Subject: Re: [Homeroast] Drum rotation > Jimma > PID iRoast
> 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
> URL to Rosto mods, FrankenFormer, some recipes etc:
> 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
> > -----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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