HomeRoast Digest


Topic: roasting temp (31 msgs / 714 lines)
1) From: Roy Gordon
What are the usual and c ustomary roasting temperatures?
I use the turbo oven/stir crazy combo.  I can set the temperature on the 
turbo oven up to 500 degrees.  I have no idea how accurate or stable the 
setting is.  When the stir crazy is on that adds to the temp.  But it's 
not a great effect.
I tend to roast beans with body at a somewhat lower temp than bright 
ones.  Obviously a lot of experimentation is called for to establish 
roast profiles, but I'd like to know if there are customary roast 
temperatures for various types of beans.
I assume in commercial roasters the temperature can be controlled.  (Is 
this true?)
-- Roy
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2) From: Ken Mary
<Snip>
Ken Davids' book "Home Coffee Roasting" gives a table of (bean environment?)
temps and corresponding degrees of roast. Others who use the "combo" will
have a better feel for the temp settings required. You could check the list
archives for previous posts. Especially with the "combo", there is no
substitute for trial and error.
--
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3) From: Dan Bollinger
Here is what I have, I don't know the source.
Cinnamon <400
New England 400
American 400-415
City 415-435
Full City 435-445
Vienna 445-455
French 455-465
Italian 465-475
Spanish 480

4) From: David Westebbe
<Snip>
It is hard for me to imagine coffee beans at such high temperatures.  Why
don't they burst into flames?  What is the flashpoint for coffee oils?
Doesn't cellulose burn at around 450 or so?
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5) From: Ed Needham
I think it was Fahrenheit 451, right?
Ed Needhamhttp://www.homeroaster.comed
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6) From: dewardh
Roy:
This portion of the list Dan posted:
<Snip>
corresponds well to the bean temperatures that I see with an IR thermometer. 
 Roast chamber (roast air) temperatures need to be a bit higher  to "move the 
roast along" (depending on how rapidly you want to move into 2nd crack), but 
not by much.  475F (oven temp) should be plenty (unless you really like "black 
beans").
The beginning of the roast (drying phase) is not particularly temperature 
sensitive . . . it responds primarily to power (heat) getting into and 
evaporating moisture from the beans.  Once dry (250-300 F bean temp) the roast 
becomes more temperature sensitive (and time sensitive . . . both in the sense 
that it proceeds more rapidly and in the sense that you *do not* want to leave 
the beans "sitting" at or near their endpoint temperature, they will rapidly 
lose any "interesting" flavors).  Go for steady ramp up in bean temperature 
after the beginning of first crack, followed by the most rapid cooling you can 
manage when your desired endpoint is reached.  The goal is to cause temperature 
initiated chemical reactions to occur in the beans, and then trap ("freeze") 
the mostly volatile products of those reactions (the "flavors") in the bean 
before they can escape.  "Profiling" the roast is the art of subtly adjusting 
the rate at which bean temperature rises at various points in the (primarily 
post "first crack") roast, to change the balance of the various flavors.
Deward
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7) From: Dan Bollinger
<Snip>
I'm not sure the temperature, but 480 is getting close!  Fires are a
definite hazard in a roasting operation. Dan
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8) From: jim gundlach
On Saturday, December 7, 2002, at 12:03 PM, Ed Needham wrote:
<Snip>
That is always how I remembered it.
    Jim Gundlach
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9) From: Tom Gramila
On Sat, 7 Dec 2002, dewardh wrote:
<Snip>
Deward,
	Cal you tell us a bit more about your infrared thermometer?  It
would seem to me to be a good way to measure real bean temperature,
especially in fluid bed roasters.  But I have been a bit worried about the
bean emissivity changing as it roasts.
	I vaguely remembering that a real Agtron roast analyzer ( the
expensive machine, not the colored tiles) relies on changes in the IR
absorbance of various IR bands in order to determine the degree of roast.  
This has always concerned me as regards IR thermometry, since changes in
absorbance go hand in hand with changes in emmisivity.  If the emissivity
varies during the roast, then an IR thermometer will measure a "false"
temperature, at least during parts of the roasting....
	Does it turn out that this is not a problem?  I would love to know 
if you (or someone else .....) has considered the accuracy of an IR 
approach to bean temperatures.  
Tom G.
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10) From: dewardh
Tom:
<Snip>
would seem to me to be a good way to measure real bean temperature,
especially in fluid bed roasters.  But I have been a bit worried about the
bean emissivity changing as it roasts.
I'm using a Raytek "MiniTemp" handheld (forget what I paid . . . under $100). 
 As the roast nears completion I pop off the lid of the Rosto and shoot down at 
the bean mass, replacing the lid if I want to continue the roast.  Since the IR 
sensor itself cannot stand the heat (but still has to be fairly close to the 
beans because of "field of view") it all has to be done fairly quickly.  I 
don't see any reason to even suspect a significant change in IR emissivity over 
the temperature range (or color change) in question.  It's effectively Boltzman 
by then.
<Snip>
measure a "false"
temperature, at least during parts of the roasting....
<Snip>
It does not seem to be an issue at all . . . I believe it's looking at the 
relative intensity of two spectral ranges, so unless there's some spectral 
filtering by the sample emissivity is corrected for, at least over a reasonably 
useful range.  Despite the "error window" of the Raytek I am at least as 
confident of its readings as I am of "immersed" probes, which read surrounding 
air temperature as well as bean temperature in a mix of uncertain proportion, 
and suffer lag as well.  The Raytek is at least reading only the beans.  If 
anything I "calibrate" the position of my fixed probe to conform with the IR 
readings .  Ideally (and maybe someday ) I'd use a fixed IR sensor behind 
an IR window . . . but that's a much more expensive proposition, and poses the 
additional complication of keeping the window clean so the sensor sees through 
it and isn't "confused" by hot oils on the window itself.  Mostly now I use the 
IR only to confirm endpoint temperature . . .
Deward
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11) From: David Westebbe
<Snip>
Despite the "error window" of the Raytek I am
<Snip>
One of these days I'm going to turn the air off at several points during a
roast to see whether the indicated temperature changes significantly.  My
guess is that it will.
There's really two lags at play in my setup:  The lag of the beans as they
slowly attain the air temp, and the lag of the thermometer as it attains the
beans' temp.
Supposedly, in a true fluid bed, all parts of the mass are at the same
temperature.  I kind of doubt that is the case in my roaster.
But if I turn off the air and wait for the temp to stabilize, I'll see
whether there's a big difference between the bean temp and what the
thermometer says.
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12) From: dewardh
David:
<Snip>
roast to see whether the indicated temperature changes significantly.
It's particularly difficult because one doesn't really much care about 
temperatures until after 1st crack (except as a matter of curiosity, of course) 
.. . . and after 1st things are changing so fast it's hard to tell what's 
happening . . . and as Jim S. has already noted if you stop the air (and heat) 
during one of the exothermic phases the bean mass will increase in temperature 
all on its own . . . confounding everything . . .
I'm getting up to my shop in Washington next week, after a year long absense 
dealing with family things . . . I'm going to bring back several thermocouple 
probes currently just sitting up there and start seriously poking into things 
.  I've come to believe that controlling the roaster is the least of the 
roasting "problems" (it's easy enough to do "by hand" with a variac or an 
airflow damper) . . . knowing what's happening (what you're controlling for) is 
really the key.
Deward
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13) From: Rick Farris
Deward wrote:
<Snip>
Hear hear!
-- Rick
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14) From: Wendy Austin & Thomas Oswin
Now, that was a good movie!
Wendy
On 7/12/02 22:03, "Ed Needham"  wrote:
<Snip>
Wendy Austin & Thomas Oswin
Coastal Road
Pomponette
Mauritius Island
Tel/ans/fax  (230) 6257399
Mobile  (230) 2560182   
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15) From: Dan Bollinger
Yeh, and I've been in love with Julie Christie ever since!
Now, that was a good movie!
Wendy
On 7/12/02 22:03, "Ed Needham"  wrote:
<Snip>
Wendy Austin & Thomas Oswin
Coastal Road
Pomponette
Mauritius Island
Tel/ans/fax  (230) 6257399
Mobile  (230) 2560182   .
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16) From: Tom Gramila
On Sat, 7 Dec 2002, dewardh wrote:
<Snip>
	As someone who is still really learning the ropes, I have to say
that I very much agree with this.  I have a pretty well computer
controlled rig, but "knowing what is happenning" is still a bit elusive.  
I have extremely good control and repeatability in the measured
temperatures of both the air entering the roast chamber, and of the
thermometer in the roast chamber.  But what I am controlling for is
primarily repeatability in the roasted beans, so that I can make changes
in how I roast, and then try to evaluate what I have done.  If things are
not repeatable in the beans, evaluation is impossible.
	I believe that the most uncertain MEASUREMENT element for me is
the bean temperature.  -- Thus my interest in the IR approach.  Perhaps
you will permit me to ask the question again, since I think my concern may
not have been clear.
	The IR thermometer you have (raytek mini) measures incident
radiation between 7 and 14microns, and assumes an emissivity of 95%.  
(this is a pretty good "greybody", its really hard to make an ideal
blackbody).  It does not do a "two color" comparison measurement, which I
think is only available in multi-thousand dollar pyrometers. (this is from
raytek's web pages)
	An emissivity different from 95% will mean the readout temperature 
differs from the objects temperature.  If the emissivity were 50% for 
example, the temperature would be wrong by (.5/.95)**.25 = .851, or a 15% 
error.  this can be significant.
	The reason that I worry that the emisssivity is not .95, (or close
to boltzmann)  is that the agtron measures changes in REFLECTIVITY in the
IR.  Anytime you have reflectivity, the emissivity is altered.  Usually by
alot....
	So....  I worry whether it is possible to really measure an
accurate temperature of coffee beans with an IR thermometer, because the
emissivity in the 7 to 14 micron band may significantly change with the
bean "chemistry" during roasting. Does anyone know whaere to find coffee
bean emissivity versus wavelength???
	I dont know, maybe you can think of a comparison measurement which
could rule this out.  Please keep us posted about your poking around!
(I'll have a look in my infra-red handbook for a suitable window material
that might be useful, but is better than CaF.  Glass appears to be really
bad!)
Tom G.
<Snip>
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17) From: Tom Gramila
Deward,
	
	Perhaps this can be addressed simply.  This IR thermometer can 
measure at room temperature, yes?  So...  How about measuring the temperature 
of unroasted beans at room temperature, and that of roasted beans cooled 
to the same temperature.  If they are the same real temperature, any 
difference in measured temperature directly reflects emissivity 
differences in the measurement band between the two, no?  
	Tom G.
On Sun, 8 Dec 2002, Tom Gramila wrote:
<Snip>
<Snip>
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18) From: Jack Berry
This discussion is way over my head but I'm at home with asking basic
questions so here goes. If I understand correctly the IR measurement is of
the color temperature of the roasted bean, not the sensible temperature. If
that's correct then does the error go down with ground rather than whole
beans?

19) From: dewardh
Tom:
<Snip>
the bean temperature.
This is my sense as well, coupled with the sense that bean temperature is, far 
and away, the most important element . . .
 > Perhaps you will permit me to ask the question again, since I think my 
concern may
not have been clear.
Your concern was clear, perhaps it was my answer which was not.  It may be that 
there is something in the Agtron material that would change my mind on this, 
but I still do not see any reason to suspect a significant change in bean 
emissivity over the temperature range in question (essentially 200-235 C), and 
certainly not a change from 50% to 90-95%.  Granted I'm (or the engineer in me 
is) comforted by the fact that the numbers I see agree quite well with those 
widely reported "in the trade" . . . (and acknowledge the "not-goodness" of 
that . . . I recognize that being happy because one sees the numbers one wants 
to see is *not* the formula for "good science" ) . . . enough so that I 
haven't undertaken "confirming" experiments (except also to note that if I keep 
my "bean probe" well away from the hot air inlets it agrees with the IR 
reasonably well).  I'll have to put "establish measurement conformance" on my 
"things to do" list.  At the moment, for me, acceptable accuracy from the IR 
readings is a not-blindly-accepted but also not a thouroughly tested assumption 
.. . . it's not "certifiable" by any standard  (other than that it seems to 
work).
Deward
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20) From: dewardh
Tom:
	
<Snip>
measure at room temperature, yes?  So...  How about measuring the temperature
of unroasted beans at room temperature, and that of roasted beans cooled
to the same temperature.  If they are the same real temperature, any
difference in measured temperature directly reflects emissivity
differences in the measurement band between the two, no?
Sounds reasonable . . . although I'd compare a "light City" with a "dark Full 
City" . . . (or "beginning of first, ending of second", since that's the 
"important" range for determining roast endpoint).  And, perhaps, a couple of 
different beans, including a decaf.  Shall we assume the 20C/200C difference in 
validation temp to be non-significant?
Deward
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21) From: Ken Mary
<Snip>
I made a measurement of green vs. roasted at near room temperature. Samples
were placed in saucers and left on the countertop overnight. There is no
difference within 1 degree F. The coffee reads the same as the saucers
holding the samples and also the countertop. I would have expected this
based on experience reading widely different objects at the same
temperature. Where IR thermometers have large errors is bare metal, shiny or
not. I have an AZ model 8869, 0 to 788 F, .95 emissivity. I never heard of
this brand but it was on sale, I think about $60.00.
IR thermometers are useful elsewhere also. The emissivity of water is .95
(cold) to .96 (hot) so you can measure brew temperature at the liquid
surface instantly (avoid the foam). I scanned the ceiling of my house and
found several cold spots where I presume the insulation has lifted letting
cold air in. Stuff in the fridge reads 38 to 40 F and the freezer 2 to 5 F.
Another neat gadget to play with.  8^)
--
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22) From: Dan Bollinger
<Snip>
Cool! Sounds like a fun toy, I'll have to get work to buy one!  Where did
you buy yours?  Here is the mfgr: http://www.az-instrument.com.tw/  Dan
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23) From: AlChemist John
Sometime around 04:36 12/9/02, Dan Bollinger typed:
<Snip>
Nice, although a  bit of a hyper energy web site.  Makes we wonder about 
two items.  I saw there was a RH% instrument and wonder if someone is 
trying to "fully and reproducibly" control a roast if this would be good 
data to work with.
Also, I am going to attempt to make a dial thermometer work for my drum 
roaster.  Problem is the length of the probe is not sufficient.  I seem to 
recall a discussion about lengthening one.  Can anyone suggest a way to do 
this and still maintain the responsiveness of the probe (not that it is 
instantaneous or anything).
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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24) From: Ken Mary
<Snip>http://www.mcmelectronics.comEnter part number 72-6797 in the search box, it is now $79.95. Search
thermometer for the complete list. There may be other suppliers so shop
around.
--
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25) From: Tom Gramila
Ken,
	Well, with your and Dewards results on this, I have to say that 
my emissivity concerns seem to have been disproven.   Count me among the 
converted....
	I poked around a bit more, and from what I saw, the chemistry
chamges that are measured in the agtron appear to be in the near-IR. These
thermometers measure from 7 microns to 18 microns, which is not near IR.  
Pretty much most stuff seems to be black-body like in this band, other
than metals, as you point out.  Even wood has emissivity somewhere between
..9 and .95!  
The best tables that I found were:http://www.selbybiolab.com.au/aus/index.htmlThese list  list frequency dependences.">http://www.selbybiolab.com.au/Product%20and%20Technical%20Information/Infrared%20site/Theoris%20of%20Infrared/Table%203.htmland related tables, which are listed in:  http://www.selbybiolab.com.au/aus/index.htmlThese list  list frequency dependences.
	It looks like the tricky part for using these things is going to 
be finding a suitable window material. 
	Thanks for the info.    -- Tom G.
On Mon, 9 Dec 2002, Ken Mary 
wrote:
<Snip>
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26) From: Ken Mary
<Snip>
I plan on mounting mine to look down onto the top of the beans in the open
roast chamber. I had problems holding it by hand and erratic readings over
long duration exposure. And of course chaff blowing in my face. I need a
window vent or similar setup to pull the hot air away from the thermometer.
If continued exposure to the roast temperature (radiant heat) causes
drifting, I may use a shutter and just take intermittent readings.
--
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27) From: dewardh
All:
Here are three places that currently list the Raytek MT4 at or under $70.00 
(shipping will effect final price).  They are currently $99.99 at Graingers.  I 
got mine at officeshops.com about a year ago . . .http://www.officeshops.com/hobby/raytek.htmhttp://www.bradystools.com/thergunminte1.htmlDeward">http://www.infrared-usa.com/Product.asp?Param1YMT4&Param2"http://www.officeshops.com/hobby/raytek.htmhttp://www.bradystools.com/thergunminte1.htmlDeward
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28) From: dewardh
<Snip>
From:	Ken Mary [SMTP:kdmary]
<Snip>
roast chamber. I had problems holding it by hand and erratic readings over
long duration exposure. And of course chaff blowing in my face. I need a
window vent or similar setup to pull the hot air away from the thermometer.
If continued exposure to the roast temperature (radiant heat) causes
drifting, I may use a shutter and just take intermittent readings.
When I checked (near a year ago) Raytek sold sheets of an IR window material 
(that would withstand roasting temperatures) for about $200 . . . I forget 
whether that was for a 2x2 or 4x4 (inch) piece.  More than I wanted to spend 
then, but I'd go in for a quarter sheet  . . . (won't be able to reply to 
e-mail until next Monday, though).
It is *necessary* to keep the face of the IR sensor cool . . . both for 
accuracy in readings and because the plastic window on the inexpensive devices 
melts at a relatively low temp, permanently damaging the device.  I thought 
about trying to establish an air curtain (with a little "muffin" fan and some 
ducting), but it started to get too complicated even in the contemplating of it 
.
Deward
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29) From: Angelo
Disclaimer: I know nothing about these devices, except what I read here. 
With that said, would it be possible to mount a mirror over the beans, and 
take a reading in that manner? Just an idea...
Ciao,
Angelo
<Snip>
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30) From: Ken Mary
<Snip>
You would sense the temperature of the mirror's surface plus a small
reflectance effect. I just did a quick check with a rear surface mirror
after *turning off* the laser pointer. The mirror's glass surface read room
temp. But I warmed an element on the stove to about 400 F and read a higher
temp (about 110 to 120 F) as the element was reflected into the sensor.
Shifting the mirror returned the reading to room temp as it reflected the
stovetop beside the element.
This may be a source of error in IR measurements. Will coffee beans show a
higher temp by reflecting the higher temp roast chamber wall? I just did a
quick test duplicating the mirror test but with a piece of white paper.
Similar results, the paper rose from room temp to near 90 F but showed a
heating effect by falling to near 75 F, room temp is 65 F. Other experiments
with coffee and a roaster are planned for later. Stay tuned.
--
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31) From: Tom Gramila
 On Tue, 10 Dec 2002, Ken Mary wrote:
<Snip>
I agree that this result make sense.  The glass is a pretty good
blackbody, so it absorbs and emits IR on its own.  The IR from the heater
will likely never see the rear surface reflector, but the fact that glass
has a different index of refraction from air will cause it to have some
front surface reflection.  I am guessing that this front surface
reflection is where the temp incerease came from.  You really need a true
front surface reflector to do this well.
I had another idea for using the IR thermometer, but not having one, I
cannot test it.  My reading says that ordinary polyetheylene is not bad in
this band as a possible window material.  If it is thin enough, the loss
it introduces is primarily due to reflection.  a 4 mil plastic bag should
have 85 or 90% transmission.  The idea would be to have a tube at the
roast chamber, with the plastic seal at the end (far enough away from the
chamber that it doesnt melt) and then the IR gismo outside the seal that
the plastic sheet makes.  I'm hoping that it could be possible to keep the
sheet from melting with some approach like this.
This would be a cheap, replacable window, but one which would require a 
correction factor to the measured temperature.
If you are interested in testing this, you'll need your 400F measured
source, and then measure the temperature with a .004" polyethylene sheet
(often available as vapor barrier) between the thermometer and the source.  
If  88% transmission is right, the measured temperature should become
379 degrees.  The change should be calculable for other temperatures....
There has to be a way to incorporate an IR sensor safely into the roast 
system.....
<Snip>
						Can't wait!
							Tom G.
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