So there is an effect! When I was entertaining going
into the coffee business and having discussions with a
roaster here, he was taking ambient temp, relative
humidity, atmospheric pressure and (to a lesser
degree), dew point and compensating the cycling of his
gas burner due to a phenomenon called
It seems that with varying values of APPARENT air
density, gas burners burn hotter or cooler due to the
density of oxygen present in a given volume of air
over time. Makes sense to me. I could never get a
definitive answer whether there is an effect on an
electric heat hot air roaster, though, but the
argument about the density of the air pushing through
the beans is what gets them to turn in the roasting
chamber also makes sense. I don't think that an
electric heater burns any hotter or cooler with
changes in DA - at least in my locale to make a
A pilot's calculator will have this computation built
in. I have a pilot's calculator for the Palm platform
I bought just for the purpose of logging this although
I don't have enough roast data to determine the effect
of DA changes on the roast, though. The one I have
allows you to enter temperature, pressure (from a
calibrated barometric pressure instrument), field
altitude (of the place you're at), and will calculate
density altitude (apparent altitude given the above
We are at 660 ft above mean sea level. Not really
anything to appreciate in the altitude world really.
However, with the changes in atmospheric pressure
going from a barometer at 29.something to 30.5 gives
me DA readings which vary from 1800-2000 ft down to
around the 660 actual with the barometer recording a
high. That is a BIG swing, relatively speaking. It's
like going from Michigan lowlands to most places in
the Appalachian chain.
It turns out that my watch has both a digital
thermometer, barometer which has been calibrated with
a known pressure, and altimeter calibrated at mean sea
level, in it for when I'm hiking in the mountains. I
use that in combination with a topo map and GPS to
somewhat precisely locate position.
It also turns out that I can take my watch off, leave
it in the roasting area for about 15 minutes before I
start and get both temperature and barometric pressure
readings and knowing the altitude, get a DA value
which I log when I roast.
I was always looking at time of roast with respect to
DA. Maybe I also need to look at how well the beans
are tumbling as well. Although I have noticed that
beans which start out tumbling sluggishly are having
no problem halfway between start and 1st crack, maybe
due to moisture loss.
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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