Greetings Leo -

I chose 198 F because that happens to be the group temp that I use when making the great majority of espresso drinks. I have promised myself several times now to order some more beans from Espresso Vivace only to try out the very tight band of higher temps that these particular beans are noted for - again just for the fun of it. I did this pstat reduction just for the "heck of it" to see what the results would be - measurements wise and taste wise. There is very little, if any, measurable difference in group temp between what I did and what a PID'ed hx machine would deliver.

At a group temp of 198, I did ABSOLUTELY NO FLUSHING WHATSOEVER.

The difference in boiler WATER temperatures between 0.6 bar and 0.7 bar is ~3.3 F at sea level. The difference in group temperatures between 0.6 bar and 0.7 bar is ~ 3 F, maybe a touch less. So, if I tried my beans at your 0.7 bar (~ 201 F group temp), I BELIEVE I would be disappointed. What you are seeing in the graph is the reaction of the thermocouple in the thermofilter - when I start the pump, I'm asking it to crawl out of bed so it is inherently "slow". Don't forget that when hot water hits (er, nudges) a relatively cool puck, those first milliliters of hot water get cooled off and that cool puck gets warmed up - all pretty quickly.

I think temperature stability is important (certainly LM and NS and a host of other mfg's think so) BUT "consistency" and "predictability" would get my vote first.

edit: And to illustrate the point that grouphead temperature "rules" - here is a simulated shot with the same measuring gear done back in February. I think average temps are about 1 F higher but hey - boiler temps are about 18 F different (1.2 bar vice 0.6 bar). This shot involved about 8 oz of flushing and then starting the shot at a group temp of 198 F.

Ken Fox wrote:Stainless is a bitch to drill

That's what carbide bits are for

erics wrote:Greetings Leo -
There is very little, if any, measurable difference in group temp between what I did and what a PID'ed hx machine would deliver.

i assumed that, actually. well, difference, in theory, is that the PIDd machine can be adjusted easier.

At a group temp of 198, I did ABSOLUTELY NO FLUSHING WHATSOEVER.

now thats sweet.

but again, im not convinced that a water temp difference of 40-50degF from start to finish can be a good thing for where it counts - taste. i guess thats more of a general HX machine complaint.

Don't forget that when hot water hits (er, nudges) a relatively cool puck, those first milliliters of hot water get cooled off and that cool puck gets warmed up - all pretty quickly.

im not sure its happening that quickly. your water stabilization point on your graph shows a steady state at around 198/199F. the grouphead doesnt really ever stabilize. hot when idle, cools off as water passes through, and will continue to cool. if you pull a tight ristretto, in the 40 second range, im guessing grouphead temp would keep dropping. thats got to affect flavor.

it looks like your settings have gotten one as close as they can to a steady state for both, like i asked earlier. thats certainly good info, and impressive. BTW, whats your OPV set at?

I think temperature stability is important (certainly LM and NS and a host of other mfg's think so) BUT "consistency" and "predictability" would get my vote first.

i agree. no consistency on an HX. i think im just getting more disappointed with HX design as a whole the more i look into them. a $200 coffee pot can produce stable temps. (actually a $10 press pot produces completely stable temps!) a $100 thermoblock can produce fairly stable temps. HX looks fancy, but doesnt seem to match.ok. im just bashing now. obviously, ive had a string of bad luck lately and im not happy with my shots. lol

LeoZ wrote:
this sort of relates to my thread that youve been really helpful in. I havent had time to experiment further, but, at 0.7bar, some coffees are great, and some are terrible. HX inconsistency, well, rather, its tight deadband of temp/pressure, seems just too limited for my tastes. for now, ill try to work with it, but long term, like you said above, try a double boiler or so.



anywayyyyy..onto the meat of my post.

you chose your boiler pressure based on a group temp of 198. do you find that group temp ideal to pull shots without a flush, or, just a really short flush?

from what ive seen at 0.7bar, group temp is around 205(ish) and the water appears to start at a fairly low temp, around 155, then creep up to 198ish. im assuming it stabilizes around there, cant recall.

but, again, without a longish flush, youre still going to get temp instability. itll either drop at boiler pressures of 1.1 bar, or raise at 0.6 or 0.7 bar. your chart shows youre still flushing around 4-5oz in those 6 seconds or so until temp stability is maintained, or, are you actually pulling the shot from a cold start, and just letting the first amounts of coffee to be extracted cold?

that brings up another issue, if stability isnt maintained across the entire time of the shot, isnt final outcome affected?

so, start colder and increase, or start hotter and decrease. in the end, does it matter?

i think what im driving at, is that there must be an ideal pressure/temp crossover point where stability between grouphead temps and water temps are close enough that flushes are small and stability is maintained, and, of course, the results tastes good.
question is, what the hell is it!


lots of questions, huh?!

The answer to most of your questions is that the relationship between ideal boiler temp / pressure and brewing temp is machine specific. Different models of hx machines will behave differently in this regard. Some may not behave well with reduced boiler pressure in continuous duty, and some will. All except maybe the Simonelli Aurelia and Appia, and possibly the new Brasilia will compromise either intermittent duty or continuous duty. E-61 style machines with traditional thermosyphon action maintain the group temperature at close to the correct brewing temperature when the boiler temperature is quite hot. Reducing the boiler temperature can have unintended consequences in that the group temperature will be so cold that brewing temps end up stone cold with bizarre temperature profiles. Again, it depends on the specific machine.

The best way to determine what works for a specific machine is to use a thermofilter or Eric's group probe and make the measurements.

-Greg

gscace wrote:The answer to most of your questions is that the relationship between ideal boiler temp / pressure and brewing temp is machine specific. Different models of hx machines will behave differently in this regard. Some may not behave well with reduced boiler pressure in continuous duty, and some will. All except maybe the Simonelli Aurelia and Apea , and possibly the new Brasilia will compromise either intermittent duty or continuous duty. E-61 style machines with traditional thermosyphon action maintain the group temperature at close to the correct brewing temperature when the boiler temperature is quite hot. Reducing the boiler temperature can have unintended consequences in that the group temperature will be so cold that brewing temps end up stone cold with bizarre temperature profiles. Again, it depends on the specific machine.

The best way to determine what works for a specific machine is to use a thermofilter or Eric's group probe and make the measurements.

-Greg

interesting. i didnt think 250F water temp meeting a 200F grouphead temp would stabilize that quickly, or stay that way that long. i think im annoyed by flushing/timing/waiting/flushing...

thanks.

gscace wrote:The answer to most of your questions is that the relationship between ideal boiler temp / pressure and brewing temp is machine specific. Different models of hx machines will behave differently in this regard. Some may not behave well with reduced boiler pressure in continuous duty, and some will. All except maybe the Simonelli Aurelia and Appia, and possibly the new Brasilia will compromise either intermittent duty or continuous duty. E-61 style machines with traditional thermosyphon action maintain the group temperature at close to the correct brewing temperature when the boiler temperature is quite hot. Reducing the boiler temperature can have unintended consequences in that the group temperature will be so cold that brewing temps end up stone cold with bizarre temperature profiles. Again, it depends on the specific machine.

The best way to determine what works for a specific machine is to use a thermofilter or Eric's group probe and make the measurements.

-Greg

Excellent post, Greg. Having PID'd 2 Cimbali Jr. HX machines, I've learned that having 2 machines with very similar designs does not mean that they behave identically. Although I have both of their boiler temp setpoints at the low end of the range, the older vibe machine needs a higher boiler temp and a longer intershot recovery time in order to produce repeatable shot temps than does the newer rotary machine. I learned this only by doing a LOT of shot series with a Thermofilter and datalogger. Although the low boiler temp setup works well for my machines, an entirely different approach would probably be needed with other machine designs.

With some effort, most HX machines can probably be setup with a PID in a manner that will produce fairly repeatable shot temps both in shot series and with regards to "random walk up" shots. The key is experimenting with all the variables, an incomplete list of which would include boiler temperature, flush volume, PID parameters/tuning, and intershot time intervals.

ken