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Topic: Some results measuring the FR's exhaust temperature (13 msgs / 521 lines)
1) From: Jim Schulman
I've given up on getting consistent readings with 
a TC in the bean mass; so I took some readings of 
the exhaust air. 
The TC is mounted in the Freshroast's lower lid, 
wrapped around one of the bars of the chaff 
catcher cage, with the probe sticking out towards 
the middle of the roast chamber diameter. I did 
this very roughly on two lids, the upper lid still 
sits properly as the TC wire is thin enough to 
I've done 10 roasts and have gotten consistent 
readings with Brazil, Kenya, Indian Pearl Mountain 
Peaberry, Yauco Selecto, and Mocha beans. The 
first crack started at 360F and ended at 410F, the 
first pops of the second start at 440F, and one 
gets a "rolling second" at 450F.  Decaf roasts 
read about 5F higher at each stage.
Altering the input air temperature with my variac 
affected the readings initially, but they 
stabilized at close to the same level as the 
previous settings (takes about 20 seconds). I 
would guess the readings are some average of 80% 
to 85% bean temperature, 15% to 20% inflow air, 
and some constant for the ambient. 
In any case, the readings correspond fairly well 
with the standard crack temperatures, and they 
remained consistent roast to roast. It was much 
easier controlling the roast profile between the 
cracks with this temperature reading than by 
judging the bean color.
Is this a peculiarity of my roaster, or the FRs; 
or is exhaust air a good measuring point for 
airroasters in general? Anyone willing to try this 
on theirs?
Jim Schulman
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2) From: Ben Treichel
Actually I have the little dial thermometer in the beans on my FR and 
seem to get repeatable results. My readings may be lower because of the 
bean temp being cooler than the air temp. I variac also, with my fan 
driven off a 12 volt wall transformer. Also, the consistency of the 
reading is important, not the actual reading. However, it does seem that 
miKe McCoffee and me do seem to agree about temperature points.
Jim Schulman wrote:
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3) From: dewardh
or is exhaust air a good measuring point for
airroasters in general?
That's a dandy question . . . and I think that there's not going to be a simple 
answer.  In the FR there just aren't any beans that are not "in the airstream" 
.. . . so measuring bean temperature alone (by any method other than IR) is 
always going to be difficult (if not impossible).  It may be that the exhaust 
air is close enough to equilibrium with the beans to be accurate enough . . . 
and if the air input temperature and air flow are constant it should be 
reproducible regardless accuracy and that gives what we're looking for anyway . 
.. . a consistent way to determine state of roast.
For my next round of Rosto experiments I'll look at exhaust temperature too, 
and see how that tracks with what I see at the beans (in the Rosto the beans at 
the outside wall of the roast chamber are pretty much out of the airflow, so 
maybe, just maybe, I'm actually measuring mostly the beans there).  There is a 
potential opportunity for the Z&D in this regard . . . since there is so little 
airflow to worry about a probe at the top of the bean mass could be assumed to 
be seeing pretty much all bean . . . which would make it relatively easy for 
them to incorporate *real* endpoint control (instead of just a timer) in the 
next iteration of their machine.  That, and something to accelerate the 
"quench", would dramatically improve the Z&D machine.
easier controlling the roast profile between the
cracks with this temperature reading than by
judging the bean color.
I think one has to acquire quite a body of experience, with roaster, with bean, 
in general, to master that without temperature.  I often cannot hear second 
crack until it's too late (if I hear it at all) . . . and color is, as you 
note, "uncertain".  I can stop . . . I *always* stop . . . at the first hint of 
oil, but even that varies from bean to bean and is itself open to 
interpretation . . . ("sheen"? "spots"? "darn it's getting dark but it still 
looks dry?") . . . and often leaves me with something other than the roast I 
set out to produce.  It's always a problem with my (unistrumented) HWP.  It's 
sure hard to "profile" that first-to-second transition when I don't know when 
second is going to happen, or how close the end is.  With my Rosto I've come to 
depend on the thermometer more than anything else, and my roasts have improved 
considerably for it.
One cannot control what one cannot measure . . .
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4) From: floyd burton
Finished my gas grill roaster last night and did 3 roasts.  The thing has a
very high quality temperature gauge in the top of the grilling chamber which
is just above the roasting drum-it very accurately measures the boiling
point of water.  I recorded the time and temps of the three roasts.  Now
since I have horrible hearing I could not hear the first crack and so kept
on roasting the first roast till what I thought was the first crack was
actually a screaming second crack.  Took the drum out and emptied it at 21.5
minutes and the final temp was 500F-well when I opened the grill top to pull
out the drum-smoke and more smoke and the beans were covered with shiny oil.
Next roast I stopped at stopped at 17.5 minutes and 480F.  Beans looked
great and the coffee was very good-had the smooth full flavor I like-beans
are el cheapo col supremo-cost $2.50 /#.  Batch #3 I stopped at 16.5 minutes
and 460F.  This one looks like it was just getting into the second crack.
Again I am measuring the temperature above the drum and the temp in the drum
maybe a bit less-not much though since the drum occupies a signifigant bit
of the space inside the grill.  Each batch was about 1.5#.  Cold tested a
10# batch-beans were agitated very well and should be no problem to roast
10# or maybe more beans at one batch.  Also no scorch or burn marks on beans
from batch 2 & 3.  The first batch was universally over roasted-beautiful
black shiny beans and what smoke.
Again I am just getting started but also think the below numbers you have
seem to agree with what is going on with my roaster.  I am going to build
another drum-this one built so that I can hopefully insert a remote
temperature sensing device in the drum.  Will do this by suspending the drum
on the axel a few inches inside the roaster and making the hole in the end
of the roaster for the axel a bit bigger to permit the insertion of a
temperature sensing device.  Any suggestions as to what kind of remote temp
sensing device.  Sources and brands would be helpful. Will also try to
develop a means of using a bean thief to pull some beans out during the
roasting process-that too appears to be possible.
Ah roasting-what fun and am now getting coffee I really like-spresso maybe

5) From: Ed Needham
I would think that measuring exhaust air would be a good indicator of roast
progress.  If it was compared to input air, a clearer picture of bean temp
would be possible.  At first, assuming the input temperature is constant, the
output air should be quite a bit cooler than input air, since the cool beans
are absorbing heat quickly.  As their temperature becomes closer to the
surrounding air, I would assume that the output air and input air would be
very similar.  A plot of the difference between the two should give a clear
indication of bean temp change.  I realize there will be heat loss to the
roaster itself and loss through the glass, but that loss would be fairly
constant after the parts all heat up.
Ed Needhamhttp://www.homeroaster.comed

6) From: Tom & Maria
My .02 cents: as other people have concluded, IR is going to be the 
only way to get accurate readings in a rapid air flow, but that 
doesnt mean readings arent useful. Figuring out a good place to mount 
it and get consistent readings. like you did, is very useful, even if 
the numbers don't indicate empirical data about all coffee in all 
roasters (but your crack temps look accurate anyway). In my Diedrich, 
i NEVER got "correct" temperature readings for bean temp, and I 
drilled quite a few holes in that poor thing to reposition the probe. 
But I did get consistent readings, logged them, and found them very 
useful for optimizing the results from that roaster (the 12 kilo with 
IR burners). The Coffee Kinetics roaster uses an RTD probe in the 
exit air as its only data for turning the gas burner on and off to 
moderate the heat. It works well because in a sense it accounts for a 
change in airflow due to a greater charge of coffee in the roaster 
.... if you overload the roaster with coffee, the initial RTD readings 
are too low and the roaster shuts off with an error code.
                   "Great coffee comes from tiny roasters"
            Sweet Maria's Home Coffee Roasting  -  Tom & Maria
		1455 64th Street Emeryville CA 94608
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7) From: john kangas
It works for me, with my popper. The temp may not be the exact bean temp, 
and may not agree with someone elses, but it's very consistant. That's what 
really helps, having another reliable reference to consult. It is important 
to keep the thermometer in the same place, moving it somewhere else in my 
own popper results in a different, and unfamiliar reliable indicator of 
roast temps!
It's also helped to fine tune my nose to degree of roast.
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8) From: dewardh
Ain't that just the way it is . . . my thermometer is teaching me how to roast 
without a thermometer . . .
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9) From: jim gundlach
I ended up doing this the other way.  My nose taught me what the 
thermometer means at different readings so I can now have my son-in-law 
roast by thermometer because he insists that he can't smell the 
    Jim Gundlach
On Thursday, January 16, 2003, at 11:28 PM, dewardh wrote:
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10) From: Jim Schulman
To all:
Thanks for all the information. I guess there's 
lots of right ways to measure temperature 
consistently (along with all the wrong ways I've 
discovered). I'm glad I finally got one that works 
for me.
I think a thermocouple is fine, although a more 
expensive RTD won't have to be replaced as often 
(TC sensors cost about $10, and mine seem to last 
about a year before the insulation goes. Maybe if 
they're dedicated to one use, they'll last 
longer). This link has been posted before, it 
seems to be a reliable and very cheap K-type TC 
reader with one probe:
Perhaps you could attach the TC (its a long wire 
with the sensing at the end) to an L shaped rod 
with some wire wrapping, and adjust the position 
until it's in the bean mass. However, i'm hardly 
the person to give anyone mechanical instructions.
I tried the inflow/exhaust temperature system. But 
with switching between TCs, and tweaking the 
variac, all the while setting up the next roast 
batch and cooling the last, my brain overloaded. 
I'll stick to one temperature until I get graceful 
with it. Then I'll try this extra wrinkle again.
Steve Ackman of Two Loons recently started a 
thread related to this on alt.coffee (just in case 
you missed it)
I'd be interested to hear comparisons between 
exhaust and bean mass measurements on the Rosto. 
The latter seems to work well on it, so it would 
give some idea what sort of discepancies are 
introduced by measuring at the  exhaust.
Jim Schulman
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11) From: floyd burton
Thanks for the info Jim.  Dan Nathan sent me info on a TC and it is called
Atkins #39658K and his company has had their unit for 7 years-will get
details and post it on AC or here or both and get input.
Hope u enjoy the party-is it this weekend-having to make that trip alone-oh
I drive so much and another 10 hours in my car is more than my mind can
take-anyway thanks again.

12) From: dewardh
roast by thermometer because he insists that he can't smell the
   I guess that's my point . . . that temperature is the most consistent and 
conveyable measure of state-of-roast.  It's the least "subjective", and is 
relatively invariant across variety of bean and (properly measured) across 
method of roast.  Once temperature is established it is relatively easy to 
learn the associated "non-instrumental" clues . . . (and how they vary from 
variety to variety).  Over time he may well "learn" which changes in smell to 
"notice" (that correspond to the temperatures you provide).
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13) From: David Westebbe
I have two holes drilled in my Popcorn Pumper, and I used two thermometers
as an informal experiment the other day.  No data logging, just seat of the
pants stuff.
My initial indications are that you are exactly correct.
I want to try some experiments with no beans, to see if position of the
thermometer affects the measured air temp significantly, and to reverse the
two thermometer's position to see if they are calibrated equally.
But with one thermometer immersed in beans, and the other somewhat above the
beans, I got the results you predicted.
I have a cheapo thermocouple thermometer on order, so my next stage is to
use three at once, to monitor coil temp, bean temp and exhaust temp.
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