HomeRoast Digest


Topic: Rosto mod pic's (11 msgs / 279 lines)
1) From: R.N.Kyle
<Snip>
I have one of these babies, and they are rugged, I use at work, and have =
even dropped off 10 foot ladder a couple of times, and it still keep =
ticking , been using it for 6 months now.
Ron Kyle
Anderson SC
rnkyle

2) From: Mike McGinness
Finished modifying my other Caffe' Rosto. Went MUCH faster! Separated the
heater from the dial, connected through the Rosto on/off switch. Just pic's,
no step by step directions yet. I'll add text directions later.http://home.attbi.com/~mdmint/coffee/Rosto_mod.htmMM;-) aka Kona Konnaisseur miKe mcKoffee
Dual Variable Transformer Rosto Roasting
Rocky grindin' - Miss Silvia brewin'
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3) From: Rick Farris
Oh Mike!  I'm so jealous of your 19.2 Volt tool!  How about a couple of
pictures from a few feet back so we can see the whole thing, and how about a
detail on how you mounted the thermometer on your Rosto.  SM has them back
in stock, so the next check I get I'll be getting mine.
-- Rick
Mike wrote:

4) From: Mike McGinness

5) From: Mike McGinness
Oops, if I double click reply the second click is send! Follows real
reply...

6) From: Rick Farris
Mike wrote:
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Whoops.  When I said they had "them" in stock, I meant the Caffe Rosto.
I think that I'll use a thermocouple to measure temperature.  My dial
thermometer is plenty accurate, but where I roast I have to crane my neck to
see it.  With the digital, I can lay it on the stove and watch it more
easily.
I'm going to get a piece of stainless tubing like Deward recommended and
instead of filling the far end with boy butter and crimping it, I'm going to
thread the thermocouple bead until it sits just inside the far end, and then
use heat-resistant RTV at the near end to hold it in place.  That way I get
some mechanical shielding from the tubing, but still almost the same
sensitivity of a naked bead.
Thanks for the instructions on where to drill the hole!
-- Rick
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7) From: dewardh
Rick:
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instead of filling the far end with boy butter and crimping it, I'm going to
thread the thermocouple bead until it sits just inside the far end, and then
use heat-resistant RTV at the near end to hold it in place.  That way I get
some mechanical shielding from the tubing, but still almost the same
sensitivity of a naked bead.
That's what I did for my air temperature sensor (except it projects just beyond 
the end of the tubing, into the airflow), but I chose to fully protect the bead 
from the battering beans for the bean temperature task (and to give a little 
more surface area for the beans to contact).  If you fully recess the bead into 
the tubing *without* heat sink grease you probably slow its response, not speed 
it, because of the air barrier around the bead.
An alternate mounting location for the bean probe (the one that I use) is 
through a hole drilled in the side wall of the roast chamber right where it 
abuts the plastic front housing (to which the probe is then clamped).  That 
puts the tip of the probe a little further from the hot air, and gives, I 
think, a bit more "bean temp" and less "air temp" in the roast chamber.  I 
"scouted around" for position with a "regular" SS handheld probe, and found 
that position seemed to work best. An advantage of the thermocouple-in-tubing 
is that you can bend it to place the tip wherever you want . . .
I put my air probe inside the dome so it sees the roast air just before it gets 
to the beans.
Deward
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8) From: Rick Farris
Deward wrote:
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I don't have battering beans, I have civilized beans. ;-)
What I'd really like to do is get one of those probes with the cage on the
end for sampling gases.  I'm betting that the air in the bean mass is
probably pretty close to the temperature of the beans.  I'm pretty sure that
a stainless steel probe in the bean mass is measuring the same air
temperature, just a little more slowly.
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I don't actually have my Rosto yet, so I'm having a little trouble
visualizing this, but I'm going to save your article.
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Got any pictures?
-- Rick
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9) From: dewardh
Rick:
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probably pretty close to the temperature of the beans.  I'm pretty sure that
a stainless steel probe in the bean mass is measuring the same air
temperature, just a little more slowly.
One of the "problems" with measuring things in a hot air roaster is that the 
air has to be hotter than the beans, or it wouldn't be heating them (worst 
case, start of roast. air at inlet maybe 260C, beans 25-30C).  In practice that 
means you want to be measuring the bean temperature as far from the hot air 
inlet as possible, and with something that maximizes physical contact with the 
beans (for conductive transfer).  There is no "perfect" solution (apart from 
IR) or "perfect" probe position, but a sensor that is mechanically shielded 
from the beans and reads *only* the air is going to read high . . . how much 
high depends on its position in the bean mass, and how well the air is 
circulating in that mass (how "fluidized" it really is).
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Not yet . . . well . . . some, but haven't even started on editing or the 
how-to-post-them front.  Same with the temperature graphs from the data logger. 
 So much to learn, so much to do, so little time . . . .  And I've taken a 
bit of a break from the Rosto to play with a Z&D . . . (and to "tidy up" the 
Rosto for "presentation").
Deward
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10) From: Rick Farris
Deward wrote:
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Yeah, ideally I'd want the probe to be just where the air left the beans,
near the exhaust.
I still maintain, though, that your stainless steel probe is measuring more
air than beans...  Look at the relative contact areas, and the fact that the
air is moving.
-- Rick
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11) From: dewardh
Rick:
<Snip>
near the exhaust.
The Rosto makes that difficult . . . the air enters from the sides of the 
center "tower", swirls horizontally accelerating the beans as it does, and 
"exits" from the entire top of the bean mass (and thence to the exhaust port). 
 The furthest you can get the probe from the incoming air is the outside wall 
of the roast chamber, where one can at least hope that the beans and the air 
have (more or less) equilibrated in temperature.
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air than beans...
It surely is still measuring some air . . . but just as surely it is measuring 
more bean than a probe with no bean contact at all.
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It certainly is complicated . . . too complicated for me to model or to address 
analytically.  Conduction trumps convection (by a lot) . . . but there is more 
of the convective medium.  But that convective medium has (relatively) low heat 
capacity and thermal conductivity.  Too many variables, too many uncertainties. 
 The answer will be had not by thinking about it, but by running some tests . . 
.. and I'm not going to have time for more of that for a while.  Maybe by the 
end of the month . . .
In the meantime I'm going with the theory that the more bean *contact* with the 
temperature probe the better (and the further from the hot air the better, too) 
.. . . .
Deward
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