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Topic: Pyrolysis is generally accepted by the industry (6 msgs / 257 lines)
1) From: Kevin DuPre
A search on Google using the terms "pyrolysis coffee
bean roasting" produces 97 results with a concensus
that pyrolysis is generally what is going on inside
the bean during roasting at and beyond 1st crack...
Oregon Coffee Roaster:
The roasting of green coffee beans develops the coffee
aromas and flavors. Roasting is the process of heating
the coffee beans uniformly, first to remove the
moisture (about 12%) then to cause pyrolysis of the
sugar in the bean cells, which means that the sugars
break down to caramel, water, carbon dioxide, and many
aldehydes and ketones which characterize the aroma and
taste of fresh coffee.
Coffee Bean Corral:
Start your roaster and the beans start to move, but
that's about all you can see for awhile. Inside the
beans, however, the water is beginning to evaporate
and the chemical decomposition of the sugars
(pyrolysis) is occurring. The beans get brighter, then
turn yellowish and emit a wonderful smell. Don't stop
here unless you like drinking straw or lawn clippings.
Lucid Cafe:
The air temperature inside the drum is usually
controlled at about 500 degrees F; the precise
temperature depends on the intentions and philosophy
of the operator. Eventually, the deep "bound" moisture
is forced out, expanding the bean and producing a
snapping or crackling noise. Then, when the interior
temperature of the bean reaches about 400 degrees F,
the oil suddenly begins developing. This process is
called pyrolysis, and it is marked by darkening in the
color of the bean.
This is the moment of truth for the coffee roaster,
because the pyrolysis, or volatilization, of the
coffee essence must be stopped at precisely the right
moment to obtain the flavor and roast desired. They
are quickly dumped into a metal box, where pyrolysis
continues until the beans are quenched with either
cold air or a light spray of cold water. 
 Roasting a coffee bean increases its size by over
50%, but reduces its weight up to 20%.
The chemical changes that occur to coffee during
roasting are called "pyrolysis."  With pyrolysis, the
coffee develops chemical compounds resulting in the
aroma, flavor, and body of the coffee.
In the next step the temperature rises from 205 °C to
approximately 220 °C, the color changes from light
brown to medium brown (Agtron # 60-50), and a weight
loss of approximately 13% occurs (Davids, Roasting,
68).  The resulting chemical process is called
pyrolysis and is characterized by a change in the
chemical composition of the bean as well as a release
of CO2.
The second step is followed by a short endothermic
period, which is followed by another exothermic (beans
release heat) step called the second crack.  This
second pyrolysis occurs between 225-230°C, and the
roast color is defined as medium-dark brown (Agtron
#50-45) (Davids, Roasting, 68).  
When the beans reach an internal temperature of at
least 302° F they swell and double in size. At an
internal temperature of 400 F, the beans' cell walls
begin breaking down and the polysaccharides within are
converted to starches and sugars. This stage is called
pyrolysis. Moisture is drawn out and the bean fibers
expand and break open, producing a cracking or
snapping sound. The sugars caramelize, causing the
beans to darken. Pyrolysis releases the volatile oils
that give coffee its distinctive flavor and aroma and
creates new compounds not found in green coffee beans.
All the while our roastmaster is keenly aware of the
color and shape of the bean and the sound of the
process. As this “first pop” (as the roastmaster
refers to it) occurs, “pyrolysis” also takes place.
This is a term that refers to all the chemical changes
that occur when the interior of the bean produces its
own heat and the beans raw components are broken down
to form over 800 new aromatic, volatile compounds.
Some of these compounds include chemicals that give
wine and most foods their flavors.
Pyrolysis A chemical reaction that occurs during
roasting when the bean cell’s temperature approaches
400 degrees F. This leads to the development of most
flavor compounds.
This oil is called coffee essence or caffeol. The
chemical reaction of the heat and coffee essence is
called pyrolysis, and is what produces the flavor and
aroma of coffee. A second "pop" occurs about three to
five minutes later and signals that the bean is fully
Many thermal and chemical reactions occur during the
roasting process: decarboxylation, dehydration of
quinic acid moiety, fractionization, isomerization,
polymerization, and complex sugar reactions. The
principal thermally reactive components are
monosaccharides and sucrose, chlorogenic acids, free
amino acids, and trigonelline. Both aravinose and
calactose of polysaccharides are splitoff and the
basic sulfur containing and hydroxyamino acids
decompose. Carbohydrates both polymerize and degrade,
liberating thermally unstable monosaccharides
decomposing 20-30% of the polysaccharides, depending
on the degree of roast....The best cup characteristic
are produced when the ratio of the degradation of
trigonelline to the derivation of Nicotinic Acid
remains linear. The control model of this reaction
ratio is a time/temperature/energy relationship. The
environment temperature (ET) establishes the pyrolysis
region for the desired chemical reactions while the
energy value (BTU) and system transfer efficiency
(STE) determines the rate of reaction propagation and
linearity of Nicotinic Acid derivation to degradation
of trigonelline. Because green bean density varies
dramatically, under any given ET / BTU / STE format,
the reaction distribution will vary. it takes longer
to obtain comparable uniformity for a higher density
And the list goes on and on.  While we can sit here
and debate whether or not pyrolysis is actually
occurring, the specialty coffee industry has generally
accepted it as so, and in fact goes to great lengths
to explain it as the following URL on Sweet Maria's
Kevin DuPre
obxwindsurfhttp://profiles.yahoo.com/obxwindsurf"The real voyage of discovery consists not in seeking new landscapes but in having new eyes -- Marcel Proust"
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2) From: Ed Needham
Many times those in an industry quote an 'expert' in a point and make it
'fact' in their conversation and talk about their product as if it was true.
That is not science.  The 'expert' could have loosely used the word, or
erroneously misused the word, but because they said it, it 'becomes' true.
I don't care if it is an industry standard (I really don't believe it is
though).  I don't care if a hundred people in the industry say it's true.  If
it is not backed up with hard scientific research, then all those people
could be wrong.
Ed Needhamhttp://www.homeroaster.comed

3) From: Gary Zimmerman
Kevin DuPre wrote:
Forgive me, because I've only been skimming the thermodynamics messages 
(they're interesting, but a little too much for me).  I thought the debate 
was about whether the beans actually go "exothermic" and whether that term 
implies they are generating heat or just radiating out the heat they've 
taken in.
"Pyrolysis" (I think) is just a structural or chemical breakdown due to 
heat - pyro meaning fire, and lysis meaning breaking apart.  It doesn't 
really imply endo or exothermy, just a heat-induced breakdown, which is 
clearly going on when coffee is roasted or anything is cooked.
-- garyZ
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4) From: Dan Bollinger
It happens a lot!  A misconception or mistruth taking on the guise of fact.
Take infant circumcision, for example. No good medical necessity, no medical
association recommends it, yet half of American parents insist on cutting
off a perfectly good part of their baby's body and tossing it in the trash.
Just plain weird!  Same could be true of 'exothermic reaction' in coffee
roasting; everyone believes it because they've heard it so often. What's
next?  Someone trying to tell us the earth is round?  ;)  Dan
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5) From: EskWIRED
What indication do you have that that is the case WRT the use of pyrolysis
and exothermic?
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6) From: Ed Needham
David.  I am challenging the use of the term 'exothermic' in relation to
coffee roasting because I see it used over and over and over again, but I
cannot find even one tiny speck of research that shows it's existence.  I
have no personal interest in it either way.  It won't change my life one
iota, but for the sake of factualness, I choose to not accept the accepted
UNTIL there is some proof that it is happening.  Proof is NOT Illy, Davids or
Sivetz saying it is so.
Ed Needhamhttp://www.homeroaster.comed

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