HomeRoast Digest

Topic: Roasting Energies (11 msgs / 246 lines)
1) From: Dan Bollinger
The article I mentioned has arrived, in English!  It was written by the
Germans Hobbie and Eggers for the French 19th ASIC conference. "The
Influence of Endothermic and Exothermic Energies on the Temperature Field of
Coffee Beans during the Roasting process."  Whew!
Two things struck me.  First they say during the roasting process, "At
higher temperatures above 175C (350F)additional heat is being generated by
exothermic chemical reactions which start if the temperature is high enough
to reach the activation energy of the roasting reactions (Raemy and
Lambelet, 1982). The exothermic energies lead to a further increase of the
bean temperature without additional heat applied from the roast gas."
Kinda puts a lid on that discussion, doesn't it?  I'm going to check at the
U's Food Service Library and see if they have the Raemy and Lambelet
Second, they performed an FET thermal analysis of roasting by modeling a
single bean.  The result was something very startling for me.  I'd always
assumed the bean was being heated from the outside in and that at every
roasting step the interior of the bean is cooler than the exterior. Not
according to this!
Because of the exothermic reactions, at about 230C (445F), the center of
the bean is hotter!  As best as I can tell, this happens during the second
I scanned the article, converted it to pdf, and post it on the web for you
to read or print.http://www.claycritters.com/coffee/hobbie-eggers1.pdfDan
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2) From: floyd burton
Think the bottom line of the below is this-roasting to get best results is
an art and science-just modified my HWP by removing the washer from the
bottom of the thingy in the center of the roasting chamber-really extends
the roasting time between first and second crack-have been underroasting-got
to learn where to stop the modified HWP.  Thanks to whomever made this
suggestion-it does make a difference.

3) From: Simpson
Thanks, Dan... and I like the critters too!
*********** REPLY SEPARATOR  ***********
On 10/6/2002 at 9:35 AM Dan Bollinger wrote:
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4) From: Dan Bollinger
A number of us have independently discovered this.  On my HWP the machine
would roast for 9:15m for Full City.  Without washer, 14:15m.  Cupping
showed that the roast was mellow, but the origin was lost.  So, I use a 1/2"
washer for 12m roasts and I like this a lot.  So do my friends who notice
the difference.  Dan
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5) From: Dan Bollinger
Thanks!  It pays for the greens!  Dan
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6) From: Dan Bollinger
" the washer from the bottom of the thingy in the center of the roasting
fyi:   We HWP operators call that the 'dispersion rod.   ;)
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7) From: Ed Needham
Way to go, Dan!  You 'do' love a challenge.
This is 'hard science', and explains quite a bit about what goes on during
the roasting process.  Not easily adaptable to a Hearthware Precision, or a
wok, but since some here are interested in roaster design, it is great
'foundation' information to build upon.

8) From: Irene and Lubos Palounek
Thank you, Dan, for scanning and making available the article "The Influence
of Endothermic and Exothermic Energies on the Temperature Field of Coffee
Beans during the Roasting process" by M. Hobbie and R. Eggers.  Although I
am not quite sure why, I plan to read it. For now, it is on my large list of
things to read; not even on the top.
I have some difficulties reading the numbers in the small legends on the
sides of individual parts of Figure 2.  Are they easy to read in the
original?  If yes, could you, Dan, at your convenience, re-scan Figure 2 at
higher resolution and post it as a separate file?
As I remember, some time ago, somebody on this list, I do not remember who,
posted many messages looking for scientific data about exothermic reactions
during coffee roasting. This article shows that at about 230C (445F), the
center of the bean is hotter than the surface - to me a clear indication of
the exothermic reactions for me. I am curious to know whether that person is
satisfied by the data in this article. In what way have those data helped?
If the data in this article are not satisfactory, why not?
Regards, Lubos.
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9) From: Dan Bollinger
Thanks, Ed and Lubos!  Even though I might not use this information per se,
I like knowing what's going on when I'm roasting. The idea the the bean
roasts from the inside out during the 2nd crack is pretty 'hot' if you know
what I mean.
Lubos, I'll scan figure 2 and add it to the pdf file. Good idea.  Dan
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10) From: AlChemist John
Sometime around 07:35 10/6/02, Dan Bollinger typed:
Thank you for taking the time and effort to track that down Dan.
It is greatly appreciated and very informative.  Now I have to find time to 
digest it.
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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11) From: Dan Bollinger
Thanks, John!  I've added the larger diagram in the pdf.  Dan

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