[Homeroast] Drum rotation > Jimma > PID iRoast

Edward Bourgeois edbourgeois at gmail.com
Sat Oct 9 10:33:39 CDT 2010

One thing that has baffled me is why all the profiles end with a 100%
power. This goes against what the beans need after 1st crack and adds
to the chaff singeing issue.

On Sat, Oct 9, 2010 at 11:19 AM, Edward Bourgeois <edbourgeois at gmail.com> wrote:
> 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.
> http://coffee-roasting.blogspot.com/

Ed Bourgeois aka farmroast
Amherst MA.

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