Also of interest are two similar threads:
Temperature management of commercial dippers
Commercial Lever Temperature Management Techniques

buddman wrote:What is the size of the hole in your blind filter to get the fake shot to flow in about 15 seconds?

Does it significantly cut the time bring your group up to temperature?

Does your CMA lever connect directly to the boiler or does it have a reservoir between the boiler and group?

Also, is there a brass sleeve inserted in your group that disperses the boiler water coming into your group from several holes or does it enter from just one hole?

I used a flat rubber blind filter plug and drilled the smallest hole I could which I think is 1/32". I put the rubber plug into a regular filter basket so that the hole I drilled generally allows the water to flow through just one of the filter basket's holes.

It makes it better because it gives similar heat to what a shot does so that it doesn't overshoot or undershoot. It makes it consistent every time I walk up to the machine and pull shots. That's what I was going for.

My machine is a DIY dipper. There is a copper plate between the boiler and the group head through which the water flows. I control the temperature of the plate so that the group head is maintained at the idle temperature I want. It's kind of like how the Strega's group head is heated.

Yes, there is a brass sleeve and there are four holes in it for water flow. There is a flow restrictor that lets me control how fast the cylinder fills.

JohnB. wrote:2 fake shots is a lot of flushing to get the group up to shot temp?? Have you considered running the boiler a little hotter to raise the idle temp?

Yes, I tried that. I also tried regular flushes, too. I found that although the group head temperature read the same (at the base of the group head cylinder support) the first couple of shots were more sour than later shots. I tried a single blind filter shot and the second and third shots tasted the same but the first shot was slightly more sour. With two blind filter shots all three shots taste exactly the same.

It was surprising that it really took two blind filter shots but the taste tells the story so that's what I found tastes most consistent.

Curtis, do you mind sharing a picture where the probe location is?

From my measurement, the whole chunk of the group head measures differently at different location (front to back, top and bottom etc). The Aurora group head has no water sleeve so that may have been the reason. The most front portion of my group head measures about 70 deg Celsius(158F), and the neck at the back measures as high as >95C. This is so different from the CMA/Bosco style group. If I pump up the group head temp (measured at bottom front portion) to about 80C (176F), I definitely sense the bitter notes start creeping in. Under normal operation, the group head just seems want to creep back and idle at 70C - almost as if it's anchored to 70C.

How long is your usual warm up? Have you tried something more extreme like leaving it on for 2 hours from cold, and pull a shot?

samuellaw178 wrote:Curtis, do you mind sharing a picture where the probe location is?

How long is your usual warm up? Have you tried something more extreme like leaving it on for 2 hours from cold, and pull a shot?

I have my machine on a timer so that I can let my machine warm up at least 90 minutes before pulling shots.

The red circle highlights the probe location I have mounted permanently. The probe under the black zip-tie was a temporary location that I've used periodically.

After the two blind fake shots the two locations have a consistent temperature delta 3 minutes after a shot. They don't lose heat at the same rate but they both settle down similarly after enough time. Without the two warmup fake shots the delta between the two isn't consistent at the 3 minute mark when I want to pull the next shot.

samuellaw178 wrote:From my measurement, the whole chunk of the group head measures differently at different location (front to back, top and bottom etc). The Aurora group head has no water sleeve so that may have been the reason. The most front portion of my group head measures about 70 deg Celsius(158F), and the neck at the back measures as high as >95C. This is so different from the CMA/Bosco style group. If I pump up the group head temp (measured at bottom front portion) to about 80C (176F), I definitely sense the bitter notes start creeping in. Under normal operation, the group head just seems want to creep back and idle at 70C - almost as if it's anchored to 70C.

I have found that there is a lot of flexibility in where you can measure the group head temperature. I set the boiler temperature by taste (high enough to not be sour but not high enough to be bitter) then I remember what the group head temperature looks like 2-3-4 minutes after the shot. I picked a location that seemed to settle down after 3 minutes or so because that worked best for telling me when to start the next shot. Near the cylinder settled down much faster than the spot I now use.

Ahh, thanks for that! I don't have a dual-channel thermocouple reader so can't do that sort of measurement. I can see that is very helpful to understand the thermodynamics rather than relying on one-point measurement. The temp strip is not super accurate either (what I have on at the moment).

Another point worth mentioning - preinfusion was suggested to affect brew temperature as well. Has anyone been able to test that out? I tried testing that myself (3-15 sec), but I can't taste too much difference unfortunately. At least it doesn't seem to make enough difference to throw it out of the bitter-sour range?