HomeRoast Digest

Topic: thermometer (22 msgs / 407 lines)
1) From: Glen Sutherland
Does anyone use an instant read digital thermometer that they like? 
What brand?
ICQ 34239611
Drago Dormiens Nunquam Titillandus 
Abit BX 6r2 1.8v | PIII 700 | Alpha PAL-6035

2) From: Hugh Solaas
Unless you specifically need a digital thermometer ( in which case I
recommend a probe hooked to your multimeter), I would use a commercial grade
thermometer from Marshall Instruments.  You can order any dial size and
whatever probe length you like.
Unlike all of the cheap digitals and many analog thermometers, these
beauties hold up to the rigors of vibration and high temperatures of home
roasting.  You can find them at:http://www.marshallinstruments.com/And, they are precisely calibrated.  I own two of them, and they both read

3) From: Ken Mary
I have a cheap digital multimeter with a t/c readout that I bought from MCM
Electronics. It reads only Celsius degrees, has 1/2 inch 3 1/2 digit
display, and uses a standard type K fine wire thermocouple. This may be a
discontinued item, but call MCM at 800-543-4330 to inquire. Ask for part
number 72-6344, cost was $11.43 in catalog 42A. The t/c part number is
72-2061, was less than $10.00. They have better grade multimeters with t/c
capability and a dual input digital thermometer part number 72-2065. They
have an online catalog but I have not checked it lately.http://www.i-mcm.com/welcome.jhtmlThe fine wire t/c reads temperature changes almost instantly and is good for
measuring air or surface temps (by contact). In actual use for measuring
bean temperatures, the fast response gives unpredictable results,
alternately sensing the hot air and bean surface which may be 10 to 15
degrees different. I use mine to measure the inlet hot air temperature. But
the outlet air temp may also be useful as an indicator of roast completion.
Ken Mary - Aromaroast & Popper - whirlyblade - decanter

4) From: kstevens
I am using an Omega TPD-39. (www.omega.com)
    8" Stainless probe. (Awesome for poppers)
    Easy readout up to 500+ deg
    Had a problem after 1 month with first unit, but
    omega was very good about sending out a replacement.
I would recommend that others consider other members of the TPD
series as the digits on this model read vertically. I think the
TPD37 reads horizontally.

5) From: Robert Cantor
I just bought an infrared thermometer.  It seems to read my oven walls
accurately, but bean temps are much lower than I expected.  The alp drum is
at the temps I used to think my beans were at when I used a PII and analog
thermometer, but the beans themselves are 20-35 degrees cooler.  I don't
really know what to make of it yet.  Anyone with any comments?
Bob C.

6) From: Paul Goelz
At 10:04 PM 11/20/2000 -0600, you wrote:
What kind of thermometer did you get, and is it adjustable for emissivity?
Do you know how big the target spot is at the actual distance to the beans?  
This is the age old problem with infrared.... properly applied, it is quite
accurate, and often flies in the face of what you thought the temperature
was.  But you have to make sure that the target completely fills the
sensing spot area, and you have to have the correct emissivity set.  I'm
guessing, but something like 0.9 might be a good starting point for the
emissivity of the beans.  
If you are reading cooler beans compared to the drum, that sounds
reasonable to me.
Paul Goelz
Rochester Hills, MI
pgoelz at eaglequest dot com
Videoastronomy. electric helicopter and music web site:http://www.eaglequest.com/~pgoelz

7) From: Paul Goelz
Just looked it up.... I'm guessing that coffee beans are similar to wood in
emissivity, and wood is listed as 0.85 to 1.00 at 8-14 microns (the
wavelength where I think your thermometer operates).  
Paul Goelz
Rochester Hills, MI
pgoelz at eaglequest dot com
Videoastronomy, model helicopter and music (UnFest) web site:http://www.eaglequest.com/~pgoelz

8) From: Matt Worner
I would suspect that emissivity of the beans would also shift as the
composition/color changed as well.  My own inclination would be to spray
a dot of flat black on the  outside of the roaster as a target, and use
an emissivity near one.  A few roasts would be enough to get a
temperature/roast profile correlation that would work.
I use heathware(s) and roast fairly dark.  Just let her rip til the
beans are "spit shined". YMMV
 But you have to make sure that the target completely fills the
Pam, Matt and Darrell Worner
1975 31' Sovereign, 2000 F-350 PSD, Hensley Arrow

9) From: Paul Goelz
At 07:27 PM 11/21/2000 -0500, you wrote:
It would be an interesting research project!  But I still suspect that
especially at the longer wavelength where the low temperature sensors
operate, the emissivity does not change much with roast level and/or color.
 And even if it does to a small extent, we are really interested in
reproducability more than absolute accuracy.  
The biggest hurdle is simply keeping the lens clean!  Although in the Alp,
the fan may be able to pull smoke away from a sensor if it includes a small
air bleed around it.  
Paul Goelz
Rochester Hills, MI
pgoelz at eaglequest dot com
Videoastronomy. electric helicopter and music web site:http://www.eaglequest.com/~pgoelz

10) From: Robert Cantor
Brown coffee beans should be at 95, which is the default of the gun.  It has
a target spot so I can fill it with beans.
Bob C.

11) From: Steven Dover

12) From: Glenn R. Holmes
Hi Steve. 
I have a thermometer in my HW Gourmet. I cannot control the temperature
but I do use the readings as an extra guide to tell me the stage my
roast is at. It is not infallible of course but it is a help in that
For a beginner who is unused to determining the first and second cracks,
it may be quite a help. 
Your point is certainly irrefutable, I just thought I'd toss in a reason
to support the use of one.
Steven Dover wrote:
homeroast mailing listhttp://lists.sweetmarias.com/mailman/listinfo/homeroast

13) From: Rick Farris
I just finished modifying my HIP so that I can get a thermometer down into
the beans, but now I find that my 5" thermometer (0 - 550) sits right in
the exhaust air.  I seem to recall someone mentioning an 8" version lately.
If you know where to find one would you post it, please?
-- Rick
homeroast mailing listhttp://lists.sweetmarias.com/mailman/listinfo/homeroast

14) From: Nick Trubov
Here is my SECOND question.
I have not, yet, purchased one of Tom's thermometers to measure bean or
chamber temperature. But, I DO have an IR thermometer that reads up to about
six or seven hundred degrees F. Does anyone out there use one of these? How
accurate are they at determining temperature in a batch of roasting beans?
Nick Trubov
and all the little Trubovs
Lorree, Eupie & Corbin

15) From: Steven Van Dyke
And on your second question, there are folks that use the IR thermometers
but they're not suitable for a lot of roasters - glass is generally IR
opaque, remember, so you wind up just reading it's temperature rather than
that of the beans.
I managed to score one of Tom's $30 digital wonders - works great!  Flexible
thermocouple you can snake into almost anything.
Steve :->
http://www.svandyke.com<- my simple home page
http://www.cafeshops.com/stevespics<- my little store of Impressionist &
Special Events Photography stuff)

16) From: MS
I found in my drawer a dial thermometer on a "stem" of slightly longer than 4 inches.  It looks like the one at Sweet Marias.   However, mine gives me 200 degress as the highest temperature, with the word next to it (or close to the temperature) "poultry".  I assume therefore that this must be 200 degrees celsius, which is equal to 392 F. accourding to one online site I went to.  If I let the thermometer temperature go beyond the 200 degree mark, will the thermometer be damaged?  I can figure on just slightly more to get me to the 450 degrees I want to roast my beans at.  Or is 200 C close enough for the top temperature of good roasts?
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17) From: Brett Mason
It's a meat thermometer - and it's Fahrenheit...
On Wed, 8 Dec 2004 22:09:46 -0800 (PST), MS  wrote:
Brett Mason
   _(( )_  Please don't spill the coffee!

18) From: Gary Townsend
You can use the thermometer, but you can't use it for roasting coffee.
You need to read temperatures  up to 500F. Turkey fryer thermometers
work pretty good, most have ranges up to 700F. (maybe when you hit 3rd
crack, you'll see this thermometer pegged.)
Remember, when we assume, you make an *ss out of u and me.
MS  wrote:

19) From: Edward Spiegel
At 4:21 PM -0600 12/09/04, John N. Alegre wrote:
If you have a bead thermocouple and it is embedded well in the bean mass, you will be measuring the temperature of the beans not the air temp. It won't be the internal bean temp, but if the roast profile is reasonable (i.e. if you aren't roasting too quickly) the internal and external temp should be pretty close once the roast really gets going. The bead type thermocouples are great because they are being heated up by what they are in contact with and the surface area is pretty small so they aren't exposed to a lot of air. The 'wand' type thermocouples and dial thermometers are more influenced by air temp since a higher percentage because less of the surface is actually in contact with the beans.
Just my .02,

20) From: Deward Hastings
you will be measuring the temperature of the beans not the air temp
Um . . . maybe . . .
That supposes that the TC "bead" is always in contact with a bean, over =
of its surface than it is in contact with air (plus additional =
about the relative thermal conductivity and heat capacity of beans and =
and a whole lot of other things ).  A lot depends on the placement of =
sensor . . . if it's in an airflow "backwater" the stagnant air around =
beans will equilibrate with the beans rather quickly, so you'll see a =
approximation of the actual bean temp.  If the bead is in the airflow =
(of an
air roaster) . . . well, try it, it's an easy experiment.  Switch the =
off and on (with a long enough interval to let the heating element/air
stream cool) and see how much (how quickly) your "bean temperature" =
varies (it's especially effective if you also monitor inlet air temp,
especially with a fast bead).  It's a good way to test sensor locations.

21) From: Edward Spiegel
At 7:14 PM -0800 12/09/04, Deward Hastings wrote:
I agree. Placement is important and easy to test and adjust. When I use the thermometer (which is pretty infrequent nowadays unless I am going for something between City and Full City, I always mess with the thermocouple placement for a couple of seconds. It is pretty obvious whether the placement is right because if it isn't right the temp will be way out in front of the roast. So, if it is reading 400 degrees before the roast is even close to first crack, I know that the thermocouple (which I have wrapped around a bamboo skewer to keep it from moving around too much) has to be moved. After the first couple of uses placement wasn't an issue as I quickly learned the 'bad spots'.

22) From: Ken Mary
In my experience, a small exposed bead t/c will read mostly the hot air
temp. I had way too many faulty unpredictable readings with the t/c in the
beans. By moving it above the beans near the top of the roast chamber, I was
able to get steady readings but still unpredictable from roast to roast.
Then I bought an IR thermometer and found by comparison that the t/c
readings (either in or above the beans) were way off, sometimes as much as
50C from the IR sensed bean surface temp. So I no longer use a t/c.
You can use a t/c in a well (or a dial thermometer) to even out the
fluctuations. Use the readings as an indicator of roast progress, not as a
measure of the actual bean temperature.

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