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Topic: Measuring Bean Temperature in a Drum (was +sour coffee) (7 msgs / 142 lines)
1) From: Bob Hazen
Thanks Eddie.  I admit, I'm feeling a little foolish.  It never occurred to 
me to put the probe on the axis of rotation!  I was only thinking of getting 
my thermocouple wire wrapped all around the drum.  I also thought of 
inserting a dial thermometer into the drum and letting it rotate with the 
drum, but I figured the "dial end" wouldn't survive the roasting process.
Reading some of the comments at the link you provided and other stuff  I've 
read, makes me wonder if it is actually useful to measure bean temperature. 
I've seen quite a bit of literature that specifies internal bean temps for a 
give degree of roast.  As I recall Tom's webpage also specifies 
temperatures.  With the uncertainty resulting from measuring the bean mass 
(not internal temp and poor thermal conductivity to the bean surface), I 
wonder if it means anything at all.

2) From: Ken Mary
To me the bean temperature is vital. Without it, control of the profile is
hopeless. Yes, you can "make do" with time and heat input, but when those
odd beans or odd environment conditions appear it is too easy to ruin a
roast. If I had no way to measure bean temperature, it is very likely that I
would not be roasting coffee today.
Measuring bean temperature is easy if you build a drum but a little more
difficult when you have to modify someone else's design.
My drum has an internal support for the spit rod which removes that task
from the end cap. This support is a metal strap passing through the drum
walls and fastened at both ends. There is a round hole in the center of the
strap through which the spit rod can pass. The hole is a snug fit on the rod
so there is no wobble. The spit rod extends through a 1 inch opening in the
end cap. I have a thermocouple wire mounted in a bracket on the inside oven
wall close to this drum opening. The wire is formed into an arc so that when
the drum is in place the bead is immersed into the bean mass. The drum is
moveable on the spit rod so the drum opening can be threaded over the fixed
thermocouple wire and allows the spit rod to be inserted into the drive
without disturbing the wire. The wire is angled so the rotating mass of
beans keeps the bead covered at all times.

3) From: Mejia, Carlos
Ken... thanks for the detailed description!  For those of us who are
more visual learners, would you post some pictures to go with the words?
That would be loverly!   ~carlos

4) From: Homeroaster
Ken, do you have a picture of this posted somewhere?
Ed Needham
"to absurdity and beyond!"http://www.homeroaster.com*********************

5) From: Ken Mary
Sorry I made no pictures during assembly. Since the internal support is not
visible in the finished drum, there is no point in making any pictures. The
drum is nonperforated sheet metal.
If you build your own drum, just think about the task and make a cardboard
model to test your design.
Another option for the Behmor may be an infrared thermometer. If there is
any access opening other than the door, it may be possible that an IR unit
can "see" enough of the beans through the screen drum to give a reading
suitable for profile control.

6) From: Aaron
Ken I dont think the IR thermometer idea would work,  the beam tends to 
be fairly large on those.  People get these IR thermometers and see the 
neat tiny little point of the laser beam and think they are getting a 
'pinpoint' spot temp reading, however the aperture for the IR sensor is 
really about an inch in diameter.  That just kind of shows you the 
'general location' of where you are reading.   Also, IR tends to be 
highly reflective, it will reflect off glass, metals, I believe water 
too, or get absorbed... anyways.... you probably wont be able to get the 
beam through the drum prefs to get a good temp read on the beans itll 
keep bouncing of and being reflected everywhere but where you want.
Keep on thinking though, that's how new things are invented!!

7) From: Ken Mary
I mentioned in a previous thread that I can measure roasting peanuts in my
screen drum with an IR. Peanuts (shelled spanish) do not seem to be bothered
by my opening the oven door for a quick shot with the IR thermometer.
The cheaper units with a 6 to 1 distance to spot ratio may not be able to
focus on the beans without seeing other sources in the oven. With any unit,
flat metal surfaces will reflect the heater and give very high readings. A
fine wire mesh (window screen) seems non-reflecting and transparent to the
IR and only minor errors can be expected.
I formerly used an IR setup on a popper with good results.

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