HomeRoast Digest


Topic: As a practical matter... (6 msgs / 103 lines)
1) From: EskWIRED
Is there really any good reason to doubt that first crack is the result of
an exothermic reaction?  The gurus seem to all agree, and coffee roasting is
something that has been extensively studied.  There seems to be no
disagreement among those who have performed careful studies, but much
skepticism among us, who have not done careful studies.
I pretty much assume that when the experts *all* agree, and when it is not a
very complicated issue, and when the reactions and mechanisms are
non-exotic, then the universal agreement of the experts is usually correct.
This ain't theoretical physics; we're talking simple chemistry.  The
measurements can be performed in a high school chem lab.  Could Illy and
Seivitz and Davids all be wrong on such a simple and basic point?
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2) From: Dan Bollinger
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It seems most of us agree, it's just that no one has been able to prove it!
Not even one solid citation of a scientific article.  Not yet, anyway.
Still, I'm with you, it seems to be exothermic at 1st and 2nd crack. Hell,
when a popcorn kernel explodes it is exothermic!  The sudden release of
steam is the giving off of heat leaving the kernel cooler than before.  Yet
this still doesn't prove that this is true for a coffee bean, too.  So, I'm
still digging and in the process I'm learning a lot more about coffee
roasting which I think is a very good thing.  :)  Dan
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3) From: Dan Bollinger
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Aha!  I didn't say it was an exothermic reaction, I said it was an
exothermic event!  Anytime something gives up heat it is exothermic, at
least that's what my reading is saying.  This may be part of the problem we
are dealing with, definition of terms.  Dan
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4) From: dewardh
Dan:
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steam is the giving off of heat leaving the kernel cooler than before.
Um, no, that's not what "exothermic" means.  Popping popcorn is the effect of 
the sudden expansion of steam when the containment ruptures . . . no heat 
producing (exothermic) chemical reaction is involved.  Coffee beans, on the 
other hand, are porous . . . they lose moisture continuously (by diffusion) 
during the drying phase and do not "pop" because of a sudden release of steam 
pressure.  Their expansion is a  result of some other "state change" within the 
bean, almost certainly related to the rapid release of heat (exothermic 
reaction) which occurs at the same time.
Deward
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5) From: Ed Needham
Definition of terms is why this thread started off in this direction.  I felt
the 'experts' were tossing around terms that were not accurate in describing
the events and chemical changes within coffee roasting.  Using the terms more
accurately will help all of us improve the language of roasting.
Ed Needhamhttp://www.homeroaster.comed
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6) From: Ken Mary
First crack seems endothermic to me. I have a roaster equipped with manual
temp control for slow roasts of 10 to 20 minutes. I have to "add heat"
during first to maintain my desired constant temp rise.
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