HomeRoast Digest


Topic: To Crack or Not to Crack [was Re: + Replacement Alp adventures] (4 msgs / 89 lines)
1) From: Michael Vanecek
I guess it's the point where the pressure inside the bean overwhelm the
structural resistence to change and we have a sudden pop. Perhaps
popcorn and coffee have more in common than the WB? The outer shell of
the coffee can't expand as fast as the internal body of the bean and
several sources have indicated that's where the audible pop comes from.
With that pop, the high-pressure steam is released and the beans
internal structure is made porus. In retrospect, the chaff would indeed
be the silver-skin and surely not the source of the audible crack, but a
result of the sudden expansion of the bean shedding a flimsy outer coat
that is sometimes left on coffee depending on the process. Sorry if I
got confused there for a second. 
To me, the second crack is a little more ambiguous. Visibly, little
chips fly off the surface of the bean. It's kinda neat to watch if
you're using a HWP or similar roaster. If you examine a bean that had
been taken into second crack, more often than not you'll find a little
circular area where a chip had popped off. I'm not sure of the mechanics
of this - perhaps the chemical changes create a layer of carbon dioxide
immediately under the surface that get's trapped and pops off a chip of
the surface of the bean when the pressure gets too great? In any case,
at this point another process is taking place as well and oils are
starting to not only build up in the cavities created by the first
crack, but to migrate towards the surface. Without the damage created by
the first crack, I doubt this would be possible. 
In any case, IMHO, the cracks are absolutely necessary, or better yet, a
reliable indicator of a proper roast. If the cracks are not there, the
internal structure of the coffee isn't opened up and damaged
sufficiently for the good stuff to be released and collect in the
cavities - after all, the porus nature of roasted coffee allows hot
water to go in and collect all this good stuff and give us the pleasure
we work so hard to get, right? Grinding the coffee only reduces the
distance the water has to travel to get to the good stuff and makes
extraction easier. If it wasn't porus and opened up then it'd be like
brewing sand. A test of properly roasted coffee is crunching it between
your thumb and forfinger. If the structure wasn't opened up and damaged
then you might as well try crunch a dried green bean. So, not only do we
create chemical changes when we roast coffee, we also create structural
changes too that facilitate the ability to extract the results of the
chemical changes. 
Disclaimer - the above is only my personal understanding based on
various sources of information and casual observation. I'm not a PhD -
only a coffee fanatic. If I'm wrong, then I welcome correction...
Cheers,
Mike
Kathleen Tinkel wrote:
<Snip>

2) From: Angelo
I've noticed that no matter how dark the beans are roasted by a commercial
roaster there aren't any of those little "craters". Has anyone had that same
observation? Anyone care to venture a guess as to why that might be? I do
have to say I have not bought much commercially roasted coffee......
Ciao,
Angelo
<Snip>

3) From: drg
Angelo wrote:
<Snip>
I believe the "craters" are due to fast roasting into the second crack stage.
I rarely get craters roasting in the wok or over a open fire with the fireplace
popcorn popper and never get them when i finish a roast slowly.
   Jim Gundlach

4) From: Jeff Wikstrom
True, I've hardly ever gotten craters on the stove top popper, usually just
in the popcorn pumper.


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