Adding Thermometry to a La Pavoni Europiccola - Page 20

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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drgary (original poster)
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#191: Post by drgary (original poster) »

I no longer have a second generation machine to play with, but measurement at the coffee cake is easily done by punching a small hole in a filter basket and inserting a thin wire thermocouple. The coffee we're describing isn't being brewed in steam. I can measure this on my first generation Europiccola if you'd like that. Perhaps one source of the difference is that the portafilter and coffee I'm locking in aren't nearly at boiling temperature.
Gary
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mathof
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#192: Post by mathof replying to drgary »

Recently, I've been measuring the brew temperature with a thin thermocouple kapton-taped to the bottom of the shower screen:



Amazingly this seems to make no difference to the pour or the taste. I find that if I lift the lever when the side of the group measures around 75C, and hold the preinfusion (usually 12-15 seconds) until the shower screen reading is around 94C, the shower screen temperature rises about 1.5C during the pull and then drops back to around 94C at the end of the shot. (I use a heat radiator on the group; if I remove it, the rise is about a degree greater).

Matt

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mathof
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#193: Post by mathof »

I just lifted the lever for a shot when the group read 72C. After 10 seconds of pre-infusion, the shower screen temperature (which I take to be a good proxy for the brew temp) was 93.4C. I pulled the shot and saw a declining profile which ended at 91.5C. The resulting shot was creamy and full of flavour, with a brew ratio of 52%. Thermometry on the shower screen seems to allow one to use pre-infusion time to achieve a more-or-less precise initial brew temperature.

jonr
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#194: Post by jonr »

Measuring post room temperature coffee typically yields initial temperatures noticeably lower than when measured above (the usual standard when people talk about "brew temp"). Ie, it tends to show a strongly rising profile on a machine that would normally be (mis-)characterized as having a "flat temperature profile". So if you had a declining profile measured below the coffee, then above the coffee was probably seeing an even steeper decline. I'm curious about what could cause this - ie, where is the cooler water coming from?

Are you able to graph the results?

mathof
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#195: Post by mathof replying to jonr »

I guess I wasn't clear about what I am doing. I was, in point of fact, measuring "above the coffee". The thermocouple is attached to the bottom of the shower screen: it is thus measuring the temperature of the screen and the water that passes through it. The coffee swells to enclose the thermocouple wire and tip, as can be seen by looking at the dry puck afterwards. This sandwiches the thermocouple between the top of the puck and the shower head. The cooler water is a result of the heat sink characteristics of the group head.

(Unfortunately, I don't have a digital thermometer that outputs its results to a computer for graphing.)

Matt

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

I have the digital thermometer and ability to do the graphing but no second generation La Pavoni. (Oh poor me, I think I'm well set for levers.) Maybe someone watching this has that combo? I simply adapted the setup I use for doing roast profiles via Artisan, two thermocouples and an Amprobe TMD-56 data logging thermometer.
Gary
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jonr
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#197: Post by jonr »

I guess I wasn't clear about what I am doing
My bad, you were clear. I'm still curious where the cooler water is coming from. In my case, anything coming from the boiler (the usual source of cooler water in HX and small boiler machines) is much hotter than water already in the group.

My guess - there is enough thermal mass (water and brass) in the group prior to pre-infusion that one gets a pretty much flat temperate profile. Small drops of ~2C might come from differences in temperature within the group.

PS - my initial results from turning on the machine, waiting for a ~75C group temp and then pulling the shot are good. Thanks for the info.

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mathof
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#198: Post by mathof »

mathof wrote:I guess I wasn't clear about what I am doing. I was, in point of fact, measuring "above the coffee". The thermocouple is attached to the bottom of the shower screen: it is thus measuring the temperature of the screen and the water that passes through it. The coffee swells to enclose the thermocouple wire and tip, as can be seen by looking at the dry puck afterwards. This sandwiches the thermocouple between the top of the puck and the shower head. The cooler water is a result of the heat sink characteristics of the group head.

(Unfortunately, I don't have a digital thermometer that outputs its results to a computer for graphing.)

Matt
Absent the ability to graph, I have made a video of the declining temperature profile on my modified LP Europiccola. First, a photo of the setup; then a video that shows the temperature when I first raised the lever, followed by pre-infusion during which the temperature declines to ~94C, at which time I pull the lever.



http://youtu.be/kwQnqYYmgEA

Note: If I remove the heat dissipator from the group, the temp profile goes up rather than down.

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

Talk about temperature control -- I must admit I enjoyed seeing that machine much more with the heat dissipator and reinvented base. It's Mad Max's Europiccola!
Gary
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mathof
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#200: Post by mathof replying to drgary »

In addition to the pleasure of seeing the numbers go in the intended direction, I find the taste of espresso is softer and less harsh as compared to shots pulled without the dissipator.

Matt