Piston Rod Temperature Probe - Page 4

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drgary (original poster)
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#31: Post by drgary (original poster) »

Jon,

You can test such variations. I'm not going to do so, since there's no breeze inside my house and room temperature is fairly consistent now that we have the air conditioner running again.
Gary
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drgary (original poster)
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#32: Post by drgary (original poster) »

Chert wrote:I practice short preinfusion times when the group is relatively cold and longer preinfusion times when the group is relatively warm.

My thinking is that my actually extraction temperature might still be hot in a relatively cool group by short preinfusion. And might come down more toward the 90-96C sweet zone by longer preinfusion with the warmer group.

Does your experience or any of these measurements bear that out?
Flint:

I just tested this idea and the piston thermowell with a challenging coffee, Heart's Stereo Blend. Heart roasts in the Nordic style. If it's not pulled hot enough, it's a sour shot. I watched my outside the group thermometer and thermowell probe readings while pre-infusing. It took a bit longer than expected to get the piston temperature up to about 205F, which of course slightly lags the the temperature in the brew chamber. The external group temp had soared to above 210F and I was no longer watching that. The thermowell temp was more accurate and pulled a shot that was a degree or two above ideal, but still not burnt. It will help me tune actual brew temperature more easily though, because in this case I would have underestimated the pre-infusion time needed.

I've to a "personal choice" response to the question about whether to modify this further with a tip insulated at the very end of the piston. My barista skills will be sufficient to work with a probe inside the piston. Doing that further mod has the potential to create several maintenance issues. The seal can easily leak under pressure. It would be hard to keep clean. Changing it out if the thermometer or probe fails could require a complex re-installation.

Added: I just pulled a beautifully tuned shot of Stereo Blend by starting with piston temp at 202.5F with about a 5 sec pre-infusion, and starting with Robert Pavlis's method of locking in right after releasing some steam and drips from the group.
Gary
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Chert
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#33: Post by Chert »

Quite interesting. What was your bell temp when the piston probe read 202.5F? What does the piston temperature do relative to a bell temperature while ramikin - cooling? I've never started a shot with the bell above 92C. I might have to try it.
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drgary (original poster)
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#34: Post by drgary (original poster) »

Bell temp may have been 5 F higher. But I do other things than only cool the outside of the group. On two shots this morning I toggled off power and let the machine cool for a couple of minutes.

Back on topic for this thread, though, I believe measuring temp in the piston is an improvement over measuring outside group temp. I don't think measurement is the only way to control shot quality, but it makes it easier.
Gary
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Javier
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#35: Post by Javier »

This modification for measuring temperatures reminds me of "Alchemist" modification for measuring pressure - First ever lever pull pressure mod
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drgary (original poster)
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#36: Post by drgary (original poster) »

Pulling shots yesterday on my 3rd generation Europiccola with a temperature probe in the piston rod, I was getting less helpful readings than with a probe on the outside of the group. My particular version has no hole drilled in the brass piston, so I'm measuring piston temperature. naked-portfilter's version measures temperature at the bottom of the piston, although I wonder if that is sufficiently isolated from the brass the surrounds the tip of the probe.

Here's what happened. My piston temperature was reading over 220 degrees F when I knew from experience the overall group had cooled sufficiently to pull a shot. I wasn't measuring temperature on the outside of the group, but the shot was not overheated. I believe the piston stays heater longer than the outside of the group, which is exposed to air.
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jonr
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#37: Post by jonr »

My guess is that temperature measured as the water leaves the grounds would have the highest correlation to taste. It's also an easy place to measure. OTOH, it's only a post brew measurement, which isn't what the typical Europiccola owner needs.

Best correlation before handle lift would probably be some combination of boiler temperature and the temperatures of the surrounding brass (piston and group). In theory, a temperature controller could measure all of these and adjust the boiler to compensate to get the right average temp - but there would still be effects on the temp profile.

A hot boiler and cold group should result in a declining temp profile - more contact time -> more heat taken from the fixed volume of water under the piston.

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