The temperature profile of a commercial lever group - Page 5

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the_trystero

#41: Post by the_trystero »

Chert wrote:
These tests confirmed one other impression I have had about the commercial lever group. If one keeps the group valve open more than 3-5 seconds, the water temperature above a tightly packed portafilter peaks and declines.
Can you expand on that last sentence? I've been pulling a lot of shots lately, haven't quantified anything, but have been greatly varying lever down pre-infusion, very slowly letting the lever up, and really long shots with very fine grinds.

For really light roasts I've been flushing a few milliliters of cold water from group before putting the portafilter in place, and I've been trying to pull the shots around 1 to 1.05 bar on the heating cycle.
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Chert (original poster)

#42: Post by Chert (original poster) »

The impression is based on the fact that a large mass of brass will act as a heat sink. Therefore the longer the dwell time of water above puck, the closer it will be to the ambient temperature of the brass group. If it is flowing from the boiler however, the water entering works to raise the temperature. I can't confirm this from the readings I took today as my measurements were not precise. Maybe the temperature changes more quickly than my digital thermometer can read.

But is the initial temperature crucial or somehow the curve of temperature during the extraction?
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the_trystero

#43: Post by the_trystero »

Yeah, got it now, thanks thanks.

I'd think the initial pre-infusion temp would be the most crucial?
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Chert (original poster)

#44: Post by Chert (original poster) »

I do too. That seems to be the case with the pourover and possibly other brew methods as well.
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drgary
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#45: Post by drgary »

allon wrote:One thing that the lever group has over a pump machine in this regard is that it allows a hot preinfusion followed by a cooler extraction, because the water for the extraction is pulled from the boiler and cools during preinfusion. Trying to do a hot preinfusion with an unflushed pump HX machine would do a hot preinfusion followed by a hot extraction. The temperature of a lever group isn't constant, that is clear - it would be interesting to log the temperature during a shot as well, and graphing the changes during the whole process.
I believe that allon is dead on with this idea. I was testing my Conti Prestina the other day to determine the deadband of the original Sopac PSTAT installed on the machine and determined that I do want to replace it with a Sirai PSTAT.* I built a basket with an inserted thermocouple (TC) to measure the temperature in the coffee cake. When taking my measurements I noticed something consistent and surprising. The temperature would start at my usual target and then decline 20 to 30 degrees F through the course of the shot. This seemed like a large decline but it was there on multiple shots. I'd pretested the TC for accuracy and have been using it along with an Amprobe data logger into my Mac computer running Artisan roasting software. Even though a pull is much briefer than a roast I found that Artisan has a zoom feature that allows one to highlight a small part of the curve and magnify it. This revealed very readable shot profiles. You'll see the shots run long, well over a minute, because I'm dialing in my machine and I was really testing for starting temperature. But if you look at the first 30 - 40 seconds of the shot you'll see this temperature decline. Here are a couple of those traces. The first of these is run at the low end of the PSTAT range, 0.45 bar as measured by an Orphan Espresso steam wand gauge. I began each pull with about 15 seconds of pre-infusion using 19 gm of coffee ground on a Rio Super Jolly and firmly tamped.



The second trace is pulled at 1.0 bar.



Here's my basket with probe inserted:



Okay, that's a geeky description. But here's what I think it reveals. Anyone who's tried a Conti Prestina raves about the shot quality.** I find the shots reveal many layers of flavor blending seamlessly one to the next. This is different than what I've been able to accomplish on my home lever machines, although my Elektra Microcasa a Leva (MCAL) comes close, but it doesn't stand apart in taste as much as the Prestina. I might measure the MCAL while retarding the boosted spring to see if there's a similar temperature drop on the pull. But back to commercial levers. Doug Garrott wrote this in my Owner Experience with Conti Prestina thread:
orphanespresso wrote:Gary....over on the restoration thread I actually did laugh out loud when you began to experience some espresso from your new commercial group for the first time...HA! I seem to recall a conversation with you before you bought it (for the sum of 300 bucks or so) [$200 FWIW but that's not what it cost to rebuild it, for sure -- GS] warning you that once you tried a commercial lever that it would ruin you for the smaller home machines....and now even your sweet wife is clearing counter space!!

So yeah I can now say I TOLD YOU SO!! :D

But to the point, you are going to be able to see some design quirks on the Prestina that are not shared on other commercial groups...but a lot of this may have to do with Conti-specific concepts....short(ish) lever plus strong spring using the linkages for force multiplication and piston centering...that odd choke down at the end of the piston effectively reducing the piston bore then expanding the diameter again in the filter basket....I am sure you will come up with a few more concepts unique to the Prestina...but to comment on your question..yes. I do think that by and large all commercial lever groups/machines produce a very similar shot as far as consistency and quality.

They all have some little or large design idea that sets them apart...some of these ideas are in the user preference area and some are obviously patent avoiders, but the espresso turns out to be very similar since the groups are by and large the same....Thermosiphons, direct bolt on dippers, HX setups etc....all produce by and large a very similar shot as far as the quality that you are now experiencing, though on each and every machine one has to learn what the machine likes to do and what it simply will not do (La San Marco is very dose specific, but comes with 6 different basket sizes to very dose).
So to expand on allon's idea, what if:

- Steady temperature and pressure decline reveal many more layers of flavor than a narrow temperature range?
- The declining pressure softens the effect of declining temperature so those flavor differences are subtly revealed?
- The large range of temperature decline reveals one after another layer without fixing on any one, again creating a subtle effect instead of spikes of flavor?
- Thermosyphons and other devices to warm commercial groups change the profile somewhat but don't change the overall principle of running the group temperature lower than the boiler temperature?



* The Sopac showed 0.55 bar deadband and the Sirai is said to start with 0.2 bar before that deadband begins to widen as the membrane stiffens. This is one reason that Sirai sells a rebuild kit for their PSTAT.

**For those pulls at very different starting temperature there was a strong taste difference. The low pressure pull of an underdeveloped roast was quite sour but not intensely so. The pull at 1.0 bar was slightly sour and also softened.
Gary
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peacecup

#46: Post by peacecup »

You should taste all the layers one gets with three temperature cycles, like I do with the Sama via three lever pulls (the so-called "triple Fellini with a half twist"). My layers' layers have layers. Cheers!

PC
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MaKoMo

#47: Post by MaKoMo »

Like your creative use of Artisan;)

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samuellaw178
Team HB

#48: Post by samuellaw178 »

Thank you Gary for sharing the data!

This is a very interesting observation. It does go against the holy grail of absolute intrashot temperature stability that are held belief by many - think GS3 or speedster, where so much effort was being put in to achieve that 0.001C stability. :P What about those single boiler Gaggias that are also known to have huge temperature drop intrashot? Somehow, they are not highly regarded because of the huge swing.

But man, all these are making me to crave for a commercial lever in my already limited kitchen. :oops:

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bostonbuzz

#49: Post by bostonbuzz »

Yes, I thought the only agreed upon fact was that "More than 10F = poor espresso". If I'm reading this table correctly, it looks like about a 40F drop in the first 30s!!!
The declining pressure softens the effect of declining temperature so those flavor differences are subtly revealed?
- The large range of temperature decline reveals one after another layer without fixing on any one, again creating a subtle effect instead of spikes of flavor?
^ I guess so? Theoretically, we should be able to pressure profile a machine and get the same results, but something tells me there aren't many pressure profiling machines that drop 40F during the shot.
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drgary
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#50: Post by drgary »

Pretty wild, isn't it? I'll do this again when I've got the Prestina reassembled with the new PSTAT and have shots dialed in. But I would love to see others' measurements of their commercial and prosumer levers. If you're already using TCs to track roasts, all it takes is a sacrificial basket to set this up.
Gary
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What I WOULD do for a good cup of coffee!