HomeRoast Digest


Topic: more on Pumper roasting: thermometer placement (54 lines)
1) From: Johnny Kent
At 11:19 AM 1/4/2004 -0700, peter zulkowski wrote:
<Snip>
Hi Peter,
have you calibrated your Cooper?
they mention that instructions for doing so come with it:http://www.sweetmarias.com/thermo.how.to.install.htmlAs Ron said, no way to get even first crack at 300F. 
But all is not lost. You obviously got there so it must have been hotter
than what it read. You can use any old kind of temperature sensor that can
take the heat and responds to changes fast enough. What's needed is to use
the sensor for lots of roasts and compare temps read against your results
and then keep that setup. Then you can translate temps read to roast stages
and thats what its all about, the actual temps don't , in general,  matter
so much as does how they correlate to the point the roast has proceeded to.
You could always mark the face of your thermometer with ranges for 1st and
2nd crack. The numbers just don't matter as much.
You'll get different results depending on what sensor you use. Using a WBII
and a metal probe thermometer like a Cooper, through the lid vertically
down into the beans, my experience is similar to Ron's as regards temps for
1st and 2nd crack but your results may not be exactly the same. 
For location the best place is largely a matter of experimentation. The tip
needs to be in the beans and preferably in them from the start. You need a
good amount of the tip in there also. It may be that going in straight from
the side messes up the thermometer reading as not enough of the stem may be
in the beans, not knowing what the minimum is. Research what others have
done by looking at the various setups from the links athttp://www.sweetmarias.com/reading.htmlThe folks around here will probably
offer further also...
A thermocouple will give different results and react at a different speed.
I have had wildly different readings using a thermocouple depending on
where its placed in the lofted beans. A dangling thermocouple can give
varying readings as it moves to different places within the beans so its
better to have it fixed onto something to keep the point of measurement
stable. As before, remember that what you are trying to do is monitor the
roast. Temperature is just one way of doing that and the absolute temp is
not as important as the correlation between your temperature sensor reading
and the stage of the roast. Some prefer an infrared temp sensor.
Whatever setup you end up with be careful to keep it as stable as possible.
Changing parts can mess up the 'calibrated' or perhaps 'correlated' state
you had, causing your system to drift and your roast results with it.
Let us know how you get on.
Respectfully,
Johnny


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