Hi,

I got myself a k-type TC and digital meter. I attached the sensor either to the screw in the shower screen or inside the puck (through the spout and through a small hole in the basket). Here are my (by no means scientific!) results and conclusions:

in general
*PID setting 93 degrees Celsius.
*boiler pressure 1,2 bar.
*takes at least 30 minutes for the GH to warm up.
*GHT fluctuates between 84 and 88 degrees.
*single shots: 25 cc in 25 sec. with 8 gram
*double shots: 50 cc in 25 sec. with 15 gram

sensor at shower screen:
*single shot WITHOUT any flush: temp during entire shot about 93 degrees.
*double shot WITHOUT any flush: temp during 1e half about 93 degrees; during 2nd half rising to 97 degrees.
*double shot AFTER 10 sec. flush&go: temp during 1e half about 95 degrees; during 2nd half rising to 97 degrees.

sensor in puck:
*as above minus 3-4 degrees Celsius.

conclusions:
*machine warm-up time at least 30 minutes, better 1 hour.
*temperatures in puck about 3-4 degrees cooler than just above coffee (does coffee absorb so much heat?).
*cooling flush is actually a warming flush (GH acts as a heat sink and gets exhausted after about 40 cc?).
*single shots have a flat temperature profile.
*double shots have a rising temperature profile during the 2nd half of extraction.
*the BZ07/BZ10 (at least my machine) seem to behave better when used as a NO flush machine.

remaining questions:
*why do I get an 8 second flash boil (boiler pressure 1,2 bar) while others are talking of only a 2-3 sec. water dance (even at higher pressure)?
*why does Jim Schulman get a cooler shot after flushing 7 sec. while I'm getting a hotter shot after a 10 sec. flush? (as I remember he writes somewhere: "flash boil stops after 2 seconds and then flush 2 to 5 seconds more, 2 seconds for a high shot temperature, 5 for a low one")?
*does my theory makes sense: GH and brass diffuser disk act as a heat sink to cool down super heated HX water AND buffering capacity is exhausted after about 40 cc because of warming up of GH?

Kind regards,
Bas

I did the WBC series of measurements on the BZ07 and BZ02. They both show a slightly rising temperature profiles during the shots, and they do get hotter as shots where done more frequently, levelling out at around 96C to 98C during the set done at 1 minute intervals. This is similar to little Elektra, and presumably all other machines with bolt to the boiler groups (what Dan calls "Dragon" machines). These machines are very easy to get about right, impossible to get exactly right.

I used flushes to get to the "design profile" of the machine, the one that you get when pulling one shot per minute continuously, i.e. the design capacity of the HX and group. I find this approach intuitively appealing, but for these "Dragon" machines, it doesn't make much difference.

However, your machine's transient and design behavior could be quite different, especially with much lowered boiler settings run by a PID controller.

erics wrote:Jim - Could you define this one minute interval a little better, i.e. is it one minute between shot starts or one minute between the end of one shot and the start of another? This is far more rigorous than any test conducted on a machine (under HB "sponsorship") that I am aware of.

Most commercial espresso machines are rated at 120 shots per hour per group, i.e. a double per minute (not a double with a minute in between.)

My objection with home and WBC machine testing is that they do not use this as the benchmark. The machines we buy and test are built to make a double per minute per group, and they should be adjusted to do this. Once so adjusted, one should figure out a flushing routine to get them to this state from idle. This will get you to the intended performance of the machine, and therefore, unless the engineers screwed up, to the best performance.

so at least the Bezzera design is quite different from any E61 HX machine

@Márcio: the PID controls the boiler pressure only; GHT is regulated by a on-off thermostat.

@Márcio: I lowered my brewing pressure from 13 bar to 10 bar against a blind filter...can this affect HX flow?

@Jim: I read the HX volume in the BZ07 is only about 70 cc. If so I would expect brewing water to cool down after flushing for say 10 seconds, e.g. 80-100 cc water...

how to get a cool double shot on this machine, e.g. 91-92 degrees? I could lower the PID setting quite a bit and hence boiler pressure, but in that case I expect brewing temperature to be too cool in the beginning of the shot...or by means of longer flushing, e.g. more than 100 cc?

are there more BZ07/10 users getting a 8 second flash boil at a common boiler pressure, e.g. 1,1-1,2 bar? I only read and hear people of none at all or only a small 2-3 sec. water dance...

I'm going to measure how long it takes for the GH to come back to idle temperature (84-88 degrees Celsius) after a shot...

Something has changed. I got only a few seconds of flash boil at 1.4 bar. Maybe they've goosed the grouphead heater. The BZ02, where the group is directly connected to the boiler, ran hotter and seemed happier with longer flushes and lower boiler pressures.

Also, as I've said over and over about this style machines (although nobody seems to be listening): if you want accurate temperatures, sell it on Ebay and buy a different machine. If you want good taste, and are willing to get that with "about-right" temperatures that you can make a little hotter or colder; you're fine. This is simply not a machine for temperature geeks ...

... it does work well for dosing geeks though

@Jim: I'm more than happy with "about right temperatures" and I really like this machine

Still I'm wondering how I can get a cooler shot...I know how I can get a hotter shot (flushing for 5-10 seconds before extraction)...maybe for a cooler shot flushing 15 seconds...I'll try out!