another_jim wrote:Based on all this, I'm guessing that this may vary machine to machine, even within the "e61 box" tribe.
That's true. Although the HX Love
article suggests they behave similarly, it's a bit of a simplification. For example, the Expobar Lever's temperature rebounded like a rocket compared to just about any other E61-based machine. I'd expect the shape of the profile to be affected by your choice of rebound or flush-n-go technique too. But in all honesty, I was inferring there was a temperature rise for very slowly pulled ristrettos (I'll allow up to 40 seconds) versus the regular pace of a double (I'm getting itchy around 30 seconds) by taste, not direct measurement. I could be attributing the bitters of overextraction for those of over-temperature.
That said, I'm not sure what to make of this:
Red = regular, blue = preceded by 10 seconds of passive preinfusion (using thermofilter as a flow restrictor)
Since adding extra seconds of passive preinfusion, I've noticed the peak temperature reported by the TC adapter
was lower, but I never bothered recording it until tonight. In the chart above, the first 10 seconds of the blue line are the passive preinfusion. I expected the temperature to spike quickly like it does when the pump engages, but it barely rises (the first 10 seconds of the red line are idle temperatures I included for completeness).
I didn't check if the thermofilter picked up this difference too. My wild guess is that the pump's much higher flow rate is increasing the "reach" of the HX injector, essentially pushing the hotter water at the bottom of the HX further toward the group sooner than the more gentle line pressure would. If that's the case, the puck would get a hotter initial shock from the non-passive preinfusion case.
(Or maybe I need to take a break from all this thermofilter / TC adapter business... and switch full-time to a lever machine for a few months)
PS: For those reading along looking for a bit more detail, the diagram below shows the HX and boiler. The bottom portion of the HX (immersed in the super-heated water) will warm more quickly than the top portion. The HX injector (not shown) is a short tube that enters the HX from the pump. Manufacturer's "tune" the HX temperature mix by trimming the HX injector length.
The HX injector, if shown, would enter the HX from the bottom (dotted lines)