Preinfusion chamber warmup?

[AndyPanda]

I'm curious if the preinfusion chamber on the mini pulls the initial shot temp down due to all that extra mass hanging off the group. I was thinking it might be helpful to pull a couple of warming shots with a blind basket, in addition to the regular warming shots, so the preinfusion chamber gets filled with hot water. Has this been discussed? seems like everything under the sun has been discussed somewhere in this vast archive

[chas]

The preinfusion chamber connects to the side of the group head via a small diameter copper tube about 3" long. Therefore, there really isn't much mass hanging directly off the group.

The warming shots are due to the fact that the mass of the group head is just hanging out in the cold in front of the machine between shots. The so called "cold nose" group design.

[AndyPanda]

Has anyone tried wrapping the group head with insulation so it can hold the heat after the warming flush? Or you just get used to the flushing routine and go with it? With the Mini, all the flushes lead to frequent refills of the tank unless you are pulling several shots back to back. I generally have at least 5-10 minutes between shots so I have to do all the flushes again before each shot and then you run the risk of starting a shot and having the empty tank light come on in mid shot and stop the pump.

[AndyPanda]

I did some temp testing with and without the preinfusion chamber and it definitely changes the brew temp and warming flush routine required to get the brew head up to temp.

I connected a K-type thermocouple probe into a brass fitting so the probe is inside the water flow just above the dispersion block (thru the hole where the preinfusion chamber attaches). This is similar to the grouphead temp probe some of the e61 guys use. I found this to be very informative on learning when and how to do flushes to get the grouphead up to temp.

I found about the same offset that the e61 users report - when the hot water from the boiler is flowing quickly (before coming up to 9 bars pressure) you see 5-6 degrees F higher than the temp of the water hitting the coffee - but then when it comes up to pressure, the temp drops down (the hotter water from the boiler is not flowing quickly so it drops due to the mass of the grouphead which is cooler) and pretty closely matches what the coffee is seeing. I mean if you do a 2oz warming flush into a cup you will see 203-205F on the thermometer in the water flow above the grouphead . But into a blind basket (or into a coffee puck) you see the 203-205F water temp just until it comes up to pressure and starts flowing at the slow rate of the real extraction - and you see the grouphead temp stabilize at 198-200F (depending on your set temp and how well you warmed up the group). And I find that this temp reading at the brewhead when it's under pressure seems to match very closely the temp of the water hitting the coffee.

I should connect another thermometer to the outside metal of the grouphead and I expect I'd see the metal at around 188F (I think Endo did this test) when I'm seeing 199F in the water channel above the group (205F when it's flowing fast - 199F when it pressurizes and the flow slows) and 198-199 in the scace. But from tests I did on my Cremina, it is very dependent on the location of the thermocouple - hotter towards the back (closer to the boiler) and cooler towards the front. On my Cremina my group thermometer would read 188F when towards the back of the group and 184F on the side (middle) and 181 towards the front. I'm sure the S1 would behave similarly depending on exactly where the bead of the TC touches the group.

Anyway ... I'm very pleased with the consistent results I'm getting now, I'm able to warm the group to the same temp each time and get a predictable/repeatable brew temp for any given set temp.