Déjà vu. Just as two years ago with the Moka Pot (https://vimeo.com/112675264). A four channel temp logger and a "coffee machine" .

The glued piston rod and the piston could withstand the pressure and the high temperatures. It's amazing to see exactly what happens inside the chamber. I made the first measure in Celsius . A second one (in Fahrenheit) will follow soon. I will post the temp curves as well.

There are the temp curves.



only the pull:



It's amazing to see how nicely this tiny machine works. It was a single pull (no Fellini). It's great to study the temperatures during warming up the group as the water above the piston transfer the heat to the group (orange and grey). Or how one can recognise as the pull starts after preinfusion (dark red insert in the yellow line) the temp above the piston - orange - starts rising again.

It's nice to see the numbers. The 8 seconds it took to cool the water to 197 (91 C) is the key there - 91C is the proper brew temperature. The brass group acts as the heat sink. It would be interesting to see how much more it cools if you pre-infuse for another 10 seconds.

What is the boiler pressure used to get that boiler temp?

I've found by trial and error that the pre-infusion cooling time is the key with pressurized levers. I think the Cremina group sinks heat better than the Pavoni group, is that correct?

I expect that the best way to raise or lower brew temp is to change boiler temp. But it would be interesting to try some alternatives, including ones to change the shape of the curve (ie, brew temperature profile).

jonr wrote:I expect that the best way to raise or lower brew temp is to change boiler temp.

You can easily do that by switching off and blowing off a little steam, starting your shot at a lower boiler temp.* Of course at the end of the shot you flip it back on if you're planning to steam. I've used that method on LaPavoni, but am not convinced that it's any better than managing the group temp. Nowadays I generally leave the boiler pressure/temp up to the pStat and pump up the group temp more or less if I'm wanting to try a hotter or cooler shot. I agree that if you leave the machine on at idle group temp and simply "walk up and pull" it would be easiest to drop the boiler temp when you wanted to try a cooler shot.


*Dropping your pressure from 0.9 barg to 0.8 barg will lower your boiler temp by about 3F.

peacecup wrote:What is the boiler pressure used to get that boiler temp?

I've found by trial and error that the pre-infusion cooling time is the key with pressurized levers. I think the Cremina group sinks heat better than the Pavoni group, is that correct?

It idles between 0,9 and 1,1.

Pre-infusion time is very important for temp management, yes. It's logical. The longer it is the more heat will be transfered by the water to the group. And I think also that the temperature behavior of the Cremina is much more predictable is than that of the Pavoni.

@jonr

"I expect that the best way to raise or lower brew temp is to change boiler temp."

The temp behavior of a lever (or that of the Cremina) is much more complex (see the graphs). I think that playing with the group temperature has a bigger effect. I hope I can test it end of August.

I suggest that as soon as water hits the coffee, some of the extraction process has started. So with longer pre-infusion times, I'd expect taste differences beyond just the lower temperature effect.

Sure, but we agree that pre-infusion is just the start of the extraction. Pre-infusion has in this case a second (dual) role: further dropping the water temperature in the chamber.

Typical for that topic: the piston rod manometer-tuning will be completed just as the last time on the last day before my holiday.

Most probably I damaged a gauge as I attached it directly to the piston rod by the extreme heat of the brewing water (se post on that by Rich - OldNuc). Now I will install a cooling spirale between the piston rod and the gauge. That's why I needed to drill the hole of the new gauge a bit bigger.

As I'm preparing for the temp comparison of the three different Creminas (I bought a longer - 20cm - thermocouple for the boiler, tho previous one worked only with full boiler),



and I noticed the really nice looking pressostat of the 1974 Cremina. I could not resist and made a close up (and some "closer" up) video during heating up.

https://youtu.be/EkIq7wi7TvE

https://youtu.be/FYFwKuPp3-c

I decided to make a second round with the recent Cremina and the 4 channel temp logger. Three consecutive pulls in quick succession. I changed the group with the pressure gauge to the one with the sensors again.