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Date: 26 Apr 2007 21:10:43
From: Scott Sellers
Subject: roast exothermy
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I've read in a few places that at some point, coffee beans in the
roasting process become exothermic. Is this a combustion
process, like burning wood? Any thoughts will be appreciated.
I'm trying to achieve profile control in my HGDB roasting
sessions, and it would be nice to know at what point I might ease
heat application without the roast itself going into a tailspin.
HGDB note: Using the 650F (vs the 1000F) setting on my Harbor
Freight heatgun and giving slightly more distance between nozzle
and bean mass, I was able to delay first crack until (at least) 5
and 6.5 minutes in successive 4 oz roasts. At least! And I'm
thinking now I could have gone all day. But in each case, I grew
restive with thoughts of inadequacy, and so cranked the gun up to
1000F, thereby achieving a robust first in short order.
cheers,
Scott S
--
Scott Sellers
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Date: 01 May 2007 14:42:58
From: Flasherly
Subject: Re: roast exothermy
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On May 1, 2:43 am, Scott Sellers <scottsell...@mindspring.com >
>
> I think I have room to slow my roasts down simply by applying
> less heat, while using the sensory cues to maintain as even a
> ramp as possible. At the same time, with this batch size, I've
> got more on-demand heating capacity than I'd probably want to
> apply.
>
I built a "sock" last night for an air roaster. Regular screen door
3' wide roll. Cut off 2', wrapped and stapled into a "sock" assembly
to filter spare chaff and better contain the process under a
rangehood. Did a pound plus. The sock makes it a little hotter now,
but looks like I can work within it. Past first crack, second isn't
much longer. I've also a cool fan-only cycle to the roaster that
helps bring down the heat quickly. Be nice to have on a heat gun or
keep an extra fan for that purpose. Added help also comes from the
colander. As the roasted bean mass builds, immediately stirring in
subsequent hot batches disperses retained heat well. Now and then I
let one get away and go into a darker roast to spice things up a bit -
though at a medium roast and close but not hitting second crack isn't
hard to maintain.
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Date: 02 May 2007 15:06:49
From: Scott Sellers
Subject: Re: roast exothermy
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Flasherly <gjerrell@ij.net >:
>On May 1, 2:43 am, Scott Sellers <scottsell...@mindspring.com>
>>
>> I think I have room to slow my roasts down simply by applying
>> less heat, while using the sensory cues to maintain as even a
>> ramp as possible. At the same time, with this batch size,
>> I've got more on-demand heating capacity than I'd probably
>> want to apply.
>>
>I built a "sock" last night for an air roaster. Regular screen
>door 3' wide roll. Cut off 2', wrapped and stapled into a
>"sock" assembly to filter spare chaff and better contain the
>process under a rangehood. Did a pound plus. The sock makes it
>a little hotter now, but looks like I can work within it. Past
>first crack, second isn't much longer. I've also a cool
>fan-only cycle to the roaster that helps bring down the heat
>quickly. Be nice to have on a heat gun or keep an extra fan for
>that purpose. Added help also comes from the colander. As the
>roasted bean mass builds, immediately stirring in subsequent hot
>batches disperses retained heat well. Now and then I let one
>get away and go into a darker roast to spice things up a bit -
>though at a medium roast and close but not hitting second crack
>isn't hard to maintain.
I'm roasting outdoors. Chafe disperses and is not heard from.
For cooling, I dump the roast into a stainless mesh strainer,
which fits into a short length of sonotube I had on hand
(essentially a large cardboard tube, used as a concrete form),
which is zip-tied to a small but powerful fan in an upright
orientation. With some stirring, the roast is cooled in short
order.
cheers,
Scott S
--
Scott Sellers
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Date: 27 Apr 2007 14:58:15
From:
Subject: Re: roast exothermy
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On Apr 26, 2:10 pm, Scott Sellers <scottsell...@mindspring.com > wrote:
at what point I might ease
> heat application without the roast itself going into a tailspin.
Some clues to HG/DB exothermy-- you can start to smell smoke, but not
necessarily see it. I wait until 1st c. is underway, starting to
peak, and begin to ease off without losing the trajectory of increased
heat. You can follow that increase on your stirring hand and face.
It's interesting. Watch for it. IMO, that's one of the advantages of
HG/DB.
>
> HGDB note: Using the 650F (vs the 1000F) setting on my Harbor
> Freight heatgun and giving slightly more distance between nozzle
> and bean mass, I was able to delay first crack until (at least) 5
> and 6.5 minutes in successive 4 oz roasts.
There's something about each batch-size/bowl-size pairing that seems
to "want" to hit 1st and other markers at it's own determined time.
We can alter that, but it takes concentration and room for error
increases. 4 oz "wants" a short roast. Optimally, select coffees that
do well with a quick air roast. Not to say that you can't "delay,"
but with so little bean mass the roast quality becomes more
challenging.
> thinking now I could have gone all day. But in each case, I grew
> restive with thoughts of inadequacy, and so cranked the gun up to
> 1000F, thereby achieving a robust first in short order.
>
Yes. For the longest time, I was preoccupied with "stalling" ---
which is certainly possible, but was always more of a concern during
roasting than something that was evidenced in the cup. I'm now more
comfortable and patient. Keep an eye on the timer. If you go more
than maybe 2.5 minutes (at that batch size) lower the HG. But likely
you are overly concerned.
Martin
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Date: 01 May 2007 06:43:03
From: Scott Sellers
Subject: Re: roast exothermy
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coffeeemail@gmail.com <coffeeemail@gmail.com >:
>On Apr 26, 2:10 pm, Scott Sellers <scottsell...@mindspring.com> wrote:
> at what point I might ease
[...]
>> HGDB note: Using the 650F (vs the 1000F) setting on my Harbor
>> Freight heatgun and giving slightly more distance between nozzle
>> and bean mass, I was able to delay first crack until (at least) 5
>> and 6.5 minutes in successive 4 oz roasts.
>There's something about each batch-size/bowl-size pairing that
>seems to "want" to hit 1st and other markers at it's own
>determined time. We can alter that, but it takes concentration
>and room for error increases. 4 oz "wants" a short roast.
>Optimally, select coffees that do well with a quick air roast.
>Not to say that you can't "delay," but with so little bean mass
>the roast quality becomes more challenging.
I'd do larger batches, but I'd end up with more roasted coffee
than I'm drinking. Perhaps a 6 oz roast would be more optimal
for my setup.
I think I have room to slow my roasts down simply by applying
less heat, while using the sensory cues to maintain as even a
ramp as possible. At the same time, with this batch size, I've
got more on-demand heating capacity than I'd probably want to
apply.
I think the main task is learning what a desirable roast profile
is, and what it looks/smells/feels like.
>> thinking now I could have gone all day. But in each case, I
>> grew restive with thoughts of inadequacy, and so cranked the
>> gun up to 1000F, thereby achieving a robust first in short
>> order.
>>
>Yes. For the longest time, I was preoccupied with "stalling"
>--- which is certainly possible, but was always more of a
>concern during roasting than something that was evidenced in the
>cup. I'm now more comfortable and patient. Keep an eye on the
>timer. If you go more than maybe 2.5 minutes (at that batch
>size) lower the HG. But likely you are overly concerned.
I think so.
cheers,
Scott S
--
Scott Sellers
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Date: 27 Apr 2007 13:29:41
From: Ed Needham
Subject: Re: roast exothermy
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There's quite a bit of flammable 'fuel' in coffee beans. As in most things,
there is a 'bell curve' for beginnings and endings of reactions. I'd be
surprised if there wasn't a tiny degree of heat generated by roasting beans
near, during or after second crack (never been there to see the third option
yet).
--
*********************
Ed Needham®
"to absurdity and beyond!"
http://www.homeroaster.com
(include [FRIEND] in subject line to get through my SPAM filters)
*********************
"Scott Sellers" <scottsellers@mindspring.com > wrote in message
news:f0r4gj$43l$1@news.datemas.de...
> I've read in a few places that at some point, coffee beans in the
> roasting process become exothermic. Is this a combustion
> process, like burning wood? Any thoughts will be appreciated.
<SNIP >
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Date: 26 Apr 2007 18:49:43
From: Dan Bollinger
Subject: Re: roast exothermy
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> I've read in a few places that at some point, coffee beans in the
> roasting process become exothermic. Is this a combustion
> process, like burning wood? Any thoughts will be appreciated.
It seems to be a contentious subject for some, but not for me. I know coffee
goes exothermic. Check this out:
http://www.claycritters.com/coffee/calorimetric_study_of_coffee.htm
Dan
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Date: 27 Apr 2007 20:58:42
From: Scott Sellers
Subject: Re: roast exothermy
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Dan Bollinger <danNObollinger@insightSPAMbb.com >:
>> I've read in a few places that at some point, coffee beans in the
>> roasting process become exothermic. Is this a combustion
>> process, like burning wood? Any thoughts will be appreciated.
>It seems to be a contentious subject for some, but not for me. I
>know coffee goes exothermic. Check this out:
>http://www.claycritters.com/coffee/calorimetric_study_of_coffee.htm
Thanks. It looks like the exothermic effect measured here kicks
in around 165C (329F), and peaks at around 210C (410F). These
correspond roughly to the "early yellow" and "first crack
underway" phases (degree of roast pictorial @ sweetmarias.com).
In my experience, "first crack underway" is when a roast tends to
start getting out of control.
My thinking: while there is water in the green coffee, much
energy is absorbed in the phase change from liquid to gas, but
much is also released as steam. Once this liquid water is out of
the way (first crack?), heat is captured in the remaining bean
matrix, and not easily dissipated.
I think I will try easing off the heatgun considerably at rolling
first crack in my next roast, to see if I can slow things down.
cheers,
Scott S
--
Scott Sellers
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Date: 27 Apr 2007 18:35:15
From: Ed Needham
Subject: Re: roast exothermy
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My guess is that anything you could measure with a dial thermometer is not
exothermic in nature, but better described by the things you mentioned...
bean to roaster temp differential, moist roaster air vs. dry roaster air
affecting temp measurement, less mass and moisture in the bean itself to
absorb roaster heat.
Whatever exothermic reaction there might be would be so minutely small, it
would take controlled highly precision experiments to measure it.
Now if the beans actually became hotter than the roaster temps, that might
be a pretty credible reason to vote for exothermy.
--
*********************
Ed Needham®
"to absurdity and beyond!"
http://www.homeroaster.com
(include [FRIEND] in subject line to get through my SPAM filters)
*********************
"Scott Sellers" < > wrote in message news:f0to62$hho$1@news.datemas.de...
> Thanks. It looks like the exothermic effect measured here kicks
> in around 165C (329F), and peaks at around 210C (410F). These
> correspond roughly to the "early yellow" and "first crack
> underway" phases (degree of roast pictorial @ sweetmarias.com).
>
> In my experience, "first crack underway" is when a roast tends to
> start getting out of control.
>
> My thinking: while there is water in the green coffee, much
> energy is absorbed in the phase change from liquid to gas, but
> much is also released as steam. Once this liquid water is out of
> the way (first crack?), heat is captured in the remaining bean
> matrix, and not easily dissipated.
>
> I think I will try easing off the heatgun considerably at rolling
> first crack in my next roast, to see if I can slow things down.
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Date: 27 Apr 2007 14:45:42
From: I->Ian
Subject: Re: roast exothermy
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On Fri, 27 Apr 2007 20:58:42 +0000 (UTC), Scott Sellers
<scottsellers@mindspring.com > wrote:
>I think I will try easing off the heatgun considerably at rolling
>first crack in my next roast, to see if I can slow things down.
You may want to begin a bit earlier, say 385-395°F and gently lower
the 'power input' so you are at about 50% around 405-415°F
"Make haste slowly"
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Date: 01 May 2007 06:43:04
From: Scott Sellers
Subject: Re: roast exothermy
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I- >Ian <someone@nowhere.com>:
>On Fri, 27 Apr 2007 20:58:42 +0000 (UTC), Scott Sellers
><scottsellers@mindspring.com> wrote:
>>I think I will try easing off the heatgun considerably at rolling
>>first crack in my next roast, to see if I can slow things down.
>You may want to begin a bit earlier, say 385-395°F and gently lower
>the 'power input' so you are at about 50% around 405-415°F
I'll try it. Actually, the temperature band between first and
second crack isn't very wide -- I probably want to slow the
entire roast down.
cheers,
Scott S
--
Scott Sellers
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