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Topic: questions about using thermometer (11 msgs / 244 lines)
1) From: David Martin
I included a thermometer in my last SM order a few weeks ago - the
digital kind with the thermocouple probe. I've tried it with 4 or 5
HGDB roasts, using a variety of beans, but I'm not sure I'm using it
right.
Basically the thermometer seems to work properly, to the extent that I
can see the increase/decrease in temperature as I roast, and it gives
accurate results when testing against room temperature and boiling
water; but the numbers I'm seeing while roasting are much lower than
expected. When I hit 1st crack it usually shows just over 300F, which,
unless I'm mistaken, is over 100F lower than the numbers for 1st crack
which I've seen described on this list and on the SM web site.
Here is my setup:
I'm using a heat gun, with the beans in a wire mesh colander which is
set inside a stainless steel pot. I typically roast either 1 lb or 1/2
lb batches. I snake the temperature probe underneath the colander, and
poke the tip through one of the holes in the mesh, the idea being for
the probe to always be in contact with the roasting coffee.
My roasts are fine, by the way. Even without the thermometer, I'm
easily able to control the speed of the ramp-up to 1st crack and
beyond.  Also, even though my temperature readings are so much lower
than I expected, the thermometer is definitely useful for getting a
better idea of what's going on heat-wise. (In particular, I now have a
better understanding of what it means for the beans to go endothermic,
during late stage of darker roasts.)
However, it's bugging me that my readings are so different from what
I've seen described elsewhere.
Am I using it wrong? Should I try a different type of probe? Or is it
normal to get temperatures in this range when using this type of
roasting configuration and this type of thermometer?
Any insight or advice is greatly appreciated.
Thanks,
-Dave
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2) From: Paul Helbert
My first guess is that maybe the mesh basket is conducting heat away
from the probe. Try advancing the tip a bit (maybe 3/8") farther into
the bean mass and see if the indicated temperature rises. If it does
it would lend credibility to my hunch. If not, then I guess it's just
another bad guess; and you'll know something it's not.
-- 
Paul Helbert
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3) From: David Martin
Maybe. I did try poking it through the mesh about half an inch, so
presumably it was within the bean mass, but maybe it was getting
pushed down and touching the mesh anyway. Part of my problem is that I
need to stir the beans, and the wire gets in the way.
How do other HGDBers do it? Should I try just periodically sticking
the probe into the bean mass from up above?
On Thu, Jul 3, 2008 at 7:01 PM, Paul Helbert  wrote:
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4) From: Edward Bourgeois
To test, How about using an assistant and one keep the normal stirring
process going while the other fishes around the bean mass for a spot
reading around 400f at first crack. Then work from that info.
On Thu, Jul 3, 2008 at 11:07 PM, David Martin  wrote:
<Snip>
-- 
Ed Bourgeois aka farmroast
Amherst MA.http://www.aginclassroom.org/Homeroast mailing list">http://coffee-roasting.blogspot.com/ Co-President- Ma. Agriculture in the Classroomhttp://www.aginclassroom.org/Homeroast mailing list
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5) From: David Martin
No sooner said than done. I just roasted a pound of Oaxaca Decaf,
sticking the probe into the beans from up above instead of through the
mesh, and guess what - the thermometer was around 400F at first crack.
I think your theory about heat conduction may be on the mark. Either
that, or it has to do with my setup, with the colander hanging in the
pot, and the probe tip being underneath, but not immersed in, the
beans.
On Thu, Jul 3, 2008 at 8:07 PM, David Martin  wrote:
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6) From: David Martin
Per my other message, I just tried this, except without the assistant,
and yes indeed I hit 1C at around 400F. I would have benefited from an
assistant, though. Probe kept falling out, so I wasn't able to really
observe the temperature changes. I guess a workable solution will be
to fasten the wire to the edge of the mesh, such that it remains
immersed in the beans without interfering with the stirring.
Anyway, many thanks to you and Paul for your suggestions.
-Dave
On Thu, Jul 3, 2008 at 8:20 PM, Edward Bourgeois  wrote:
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7) From: Bill
David,
couple months ago I switched to a BM from the DB.  I can't think of a way to
make the DB work with a TC except in ways that you've described.  The BM, on
the other hand, agitates at the same place every time, so you simply put a
TC above the paddle.  Seems like it should work just fine...
thanks for the info in your roasting.
bill in wyo
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8) From: Paul Helbert
I'd be looking around for some sort of support. A piece of bakelite
tube or fired clay, maybe. Perhaps form something out of a high
temperature adhesive.
Epoxy putty is easily fabricated, but I'd have to looksee what
temperature it will withstand without breaking down. Some epoxys won't
stand much heat.
Have a potter close by? Ceramics will stand the heat.
Looks like you are on the right track now.
-- 
Paul Helbert
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9) From: raymanowen
"My roasts are fine, by the way."
And you're doing it all, without a sphygmomanometer? Why not add drama to
your perfectly functional roasting process. If you want to incorporate
failure potential, narrow your field of observation to data that is only
partially indicative of the degree of roast and yields variable readings.
"...not sure I'm using it right." Using the HG/ DB roasting method takes
both hands and feet, for me to hold the bowl in position while I heat and
stir the beans. No grip for the meter and thermocouple that's more like a
wet noodle. If the thermocouple is not physically stable, you might as well
read the temperature on Mars.
Cheers, Mabuhay, iechyd da -RayO, aka Opa!
Your roasts are fine- enjoy, don't fix...
On Thu, Jul 3, 2008 at 4:50 PM, David Martin  wrote:
<Snip>
-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the Mighty
Wichita (ex- NYC Paramount) WurliTzer- 1976
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10) From: David Martin
On Fri, Jul 4, 2008 at 10:00 AM,   wrote:
<Snip>
A sphygmomanometer? To detect 1st & 2nd crack? Of course I'm using
one, I just didn't mention it because I didn't think it was relevant
to the subject. :-P
Sarcasm aside, I agree that a thermometer is unnecessary. I'm using it
to improve my understanding of the roasting process, and because it's
fun.
-Dave
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11) From: Brian Kamnetz
David,
Thank you very much for this line of inquiry. I use a very similar
set-up, and have a thermocouple (I think I am using the term right -
at any rate, the digital thermometer) that I perchased from Sweet
Maria. However, I couldn't figure out where to start and so have yet
to try the thermocouple. I do have an infrared thermometer that gives
me some idea of temps at various stages, but I use one hand for the
heat gun and one hand to stir, so until I evolve into a life form with
three hands it's difficult to get readings. Anyway, I read your
initial post and all responses with great interest.
I agree with you that it is fun to get data and otherwise fiddle
around with gadgets. In spite of his cautionary comments, I personally
think that no one on the list enjoys gadetry more than Ray, and I
always enjoy the gadget-related info he shares with the list.
Brian
On Fri, Jul 4, 2008 at 5:51 PM, David Martin  wrote:
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