HomeRoast Digest


Topic: Exothermic and envirnoment vs bean (6 msgs / 190 lines)
1) From: Ed Needham
The chemical process of turning sugars to carbon emits energy in the form of 
heat.  Basic science.
The browning of the beans is caused by two things, a heat reaction with the 
sugars, caramelizing and ultimately carbonizing if taken far enough into the 
roast, and a heat reaction with amino acids, otherwise known as the Maillard 
browning reaction.
*********************
Ed Needham
"to absurdity and beyond!"http://www.homeroaster.com*********************

2) From: miKe mcKoffee
Nothing wrong with questioning etc. But as far as exothermic reactions in
coffee roasting goes it's seems pointless to argue semantics or definitions
when it's been observed, accepted, and the term as it applies to the
roasting bean is commonly used by roasting professionals. Whether the "roast
system" itself is exothermic or not has never been a point of discussion or
contention. A "Roast Master" (which I am not) does not need to be a Chemist
to know how the coffee bean behaves during the roast. If a Roast Master also
happens to be a Chemist then they may intelligently discuss with other
Chemists what is happening at the molecular level. Generally there seems no
need for a Roast Master to discuss molecular chemistry specifics but rather
discuss how the bean behaves during a roast.
Pacific Northwest Gathering VIhttp://www.mcKonaKoffee.comURL 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">http://home.comcast.net/~mckona/PNWGVI.htmKona Konnaisseur miKe mcKoffeehttp://www.mcKonaKoffee.comURL 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.
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3) From: Ed Needham
A general definition of exothermy is just 'heat exiting'.  An exothermic 
reaction is where fuels are combusting and creating heat as a byproduct.
There are fuels inside a coffee bean (mainly oils and sugars) that begin the 
combustion process as heat is added to them.  Combustible gasses are 
released in the conversion of sugars to carbons (think hydrogen).  It's a 
bell curve phenomenon, that ends in flames, charring, and ultimately 
depletion of combustible fuels.
Hopefully only Starbucks roasts that far.
At the beginning point of the bell curve, the combustion would only be 
measurable with 'rocket science' sensitive measurement devices, in a 
contained environment.  As more and more of the tiny combustion reactions 
take place, it literally begins to feed on itself and put out more heat than 
is put in.
Just taking a guess, I would expect this to begin as the color of the bean 
begins to change, and 'after' much of the moisture has dissipated.  I would 
also expect that the roast would be pulled at second crack somewhere in the 
beginning tail of the bell curve, never really getting to the point where 
significant heat is generated.  When the mass of beans is greater, this 
phenomenon becomes problematic.  Large roasters, that roast 600 pounds at a 
time are seriously concerned with exothermic reactions near the end of a 
roast.
*********************
Ed Needham
"to absurdity and beyond!"http://www.homeroaster.com*********************

4) From: Rich
Its not chemistry, its thermodynamics.  Entropy and enthalpy.  The 
energy released from the system is from the breakdown of the 
hydrocarbons, in this case carbohydrates.  The system in this case is 
the batch of beans.
Floyd Lozano wrote:
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5) From: Tom Ulmer
One system is the roaster and the other would be the beans. The discussion
is focused on the exchange of heat from the roaster to the bean.
<Snip>
system to the bean (endothermic) to a point where that energy is released
(exothermic).

6) From: Tom Ulmer
Ambient with reference to the human controller...


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