[Homeroast] Heat Gun method (was List Traffic at Zero)

raymanowen at gmail.com raymanowen at gmail.com
Wed Oct 20 04:29:12 CDT 2010


For sure, the ambient temperature has an effect on coffee roatsing.
Everything comes together when it's 0° C with a little breeze and I have a
pound of greens stirring in the bread machine. As pointed out, it's easy to
control the rosat in cool ambient air.

Even easier to stop the roast on a dime and get a few cents change when
using a large furnace blower with a screen mesh colander in an intake
venturi. Still good results in Needles or Bakersfield, Ca a few days ago.
120°F ambient is still way below roast temperatures

I have no inclination to do any adiabatic/ calorimetric bomb testing to gong
the imagined exothermic properties of coffee roasting. Just like when
popping corn, you're heating the sample a little irregularly. The whole mass
is within a few tenths of a degree of the target temperature.

When the first one cracks, a hundred others are at temperature, maybe 0.1° -
1.0° behind it. Has anyone ever blown up a roaster because all the beans
cracked at once? My girls (33 - 39 yrs old) still have an aversion to
popping corn- "Watch out they don't all pop at once- you'll blow up the
popper!"

Same thing happens when boiling water in a Pyrex bowl. If you watch, the
boiling starts at the heated surface and the bubbles immediately condense
until the whole mass reaches the bp. In a microwave, the whole water mass is
being heated evenly.

Almost every molecule can reach the bp together. The magnetron is generating
about a horsepower in radio frequency energy and the water mass is acting
like a big spring until it hits the transition temperature. An invisible
trigger is pulled when a large fraction of the molecules hit the boiling
point together and turn to steam. Is it exothermic?

It might seem to be, but the transition is highly endothermic and absorbs a
lot of energy. It's pretty vigorous, not explosive.

The transition takes place at an precise temperature that depends only on
the barometric pressure. Land is nearly all above sea level, so the actual
bp is lower than 212° F. Of course, in the mine lunch room/ safety chamber,
they'd cook the heck out of their Chile-mac if they boiled it at 216°(+) F.


Cheers, Mabuhay -RayO, aka Opa!

"The difference between a violin and a viola is that a viola burns longer. "
 - - Victor Borge


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