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Optimal pressure for good extraction?
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Discussions > Espresso > Machines > Optimal pressure...  
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kevinpeters
Senior Member


Joined: 20 Dec 2012
Posts: 6
Location: Peterborough, Ontario, Canada
Expertise: I love coffee

Espresso: Bezzera BZ09
Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 8:17am
Subject: Optimal pressure for good extraction?
 

Hi,
This is my first post, although I have read a number of them in the past.  I have a Bezzera BZ09 single boiler machine. I think the water comes out too fast for my machine because in order to get a single or double shot in 25ish seconds, the bar pressure reading on the machine hovers around 12. I keep reading that 9 bars of pressure is optimal for good extraction. I have tried a courser grind, and when the bar pressure reads around 9, the shot is complete in less than 15 seconds (i.e., the coffee comes out too fast and is on the sour side).  I appreciate that perhaps the pressure gauge on my machine might not be perfect, but I am curious if anyone on this site has had similar issues.  I am usually able to get a nice shot with crema, but there is no tiger-striping to the crema that I have seen before. I would be grateful for any tips.

Thanks!

Kevin
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cuznvin
Senior Member


Joined: 6 Oct 2011
Posts: 656
Location: NY
Expertise: I love coffee

Espresso: La Spaziale Mini Vivaldi II
Grinder: MACAP M4 Stepless /Baratza...
Drip: YouBrew
Posted Thu Dec 20, 2012, 9:12am
Subject: Re: Optimal pressure for good extraction?
 

kevinpeters Said:

Hi,
This is my first post, although I have read a number of them in the past.  I have a Bezzera BZ09 single boiler machine. I think the water comes out too fast for my machine because in order to get a single or double shot in 25ish seconds, the bar pressure reading on the machine hovers around 12. I keep reading that 9 bars of pressure is optimal for good extraction. I have tried a courser grind, and when the bar pressure reads around 9, the shot is complete in less than 15 seconds (i.e., the coffee comes out too fast and is on the sour side).  I appreciate that perhaps the pressure gauge on my machine might not be perfect, but I am curious if anyone on this site has had similar issues.  I am usually able to get a nice shot with crema, but there is no tiger-striping to the crema that I have seen before. I would be grateful for any tips.

Thanks!

Kevin

Posted December 20, 2012 link

I havent pulled a shot yet but from what I gather from endless reading is that if the "pull" is too quick, you need to grind finer, not coarser. Also, what kind of grinder are you using and are you using freshly roasted coffee?
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kevinpeters
Senior Member


Joined: 20 Dec 2012
Posts: 6
Location: Peterborough, Ontario, Canada
Expertise: I love coffee

Espresso: Bezzera BZ09
Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 10:12am
Subject: Re: Optimal pressure for good extraction?
 

Hi Cuznvin,
Thanks for your reply. I have a Compak K3 touch grinder. I think you are right in that normally I would need to use a finer grind if the pull is too quick. However, the burrs on my grinder are pretty much touching at my setting right now, and if I go any finer, the machine chokes. The only way that I can get the coffee pressure gauge down in the 9-10 range is to use a coarser grind, but then the coffee comes out even faster! Maybe that is just the way my machine is set up. It's not like I am suffering...the espresso is still good. I was just curious if I could make it better.

Kevin
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kevinpeters
Senior Member


Joined: 20 Dec 2012
Posts: 6
Location: Peterborough, Ontario, Canada
Expertise: I love coffee

Espresso: Bezzera BZ09
Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 10:13am
Subject: Re: Optimal pressure for good extraction?
 

Sorry, one more thing....I am using coffee that is fairly fresh, roasted within a week or so (get it from a local roaster).
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dyqik
Senior Member


Joined: 7 Oct 2011
Posts: 383
Location: Cambridge, MA
Expertise: I love coffee

Espresso: Bezzera BZ07 PM
Grinder: Baratza Virtuoso Preciso...
Vac Pot: Cona D
Drip: Bona-Vita, CCD, Aeropress.
Roaster: Gene Cafe, Modded Poppers
Posted Thu Dec 20, 2012, 10:26am
Subject: Re: Optimal pressure for good extraction?
 

The over-pressure valve in the machine should limit the pressure at the puck to about 9 bar when there is water flowing at the correct rate.  This usually means setting it to open at somewhere around 10 bar static (for a basic vibe pump).

Lowering the OPV setting to 10 bar static on my Gaggia Classic made a big difference to the amount of crema I was getting and made it easier to get a good extraction, with less channelling.  I've not measured the pressure in my BZ07, but I suspect it's about right.

If you install a blind basket and pull a shot, what pressure does your gauge show?  If it's up around 15 bar, then I suspect your OPV isn't opening.  If it's around 12 bar, then it probably just needs adjusting down a bit.

This discussion should help, and the OPV is the part marked TAV. 2 on page 11 of this document (and described on page 5).
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kevinpeters
Senior Member


Joined: 20 Dec 2012
Posts: 6
Location: Peterborough, Ontario, Canada
Expertise: I love coffee

Espresso: Bezzera BZ09
Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 10:40am
Subject: Re: Optimal pressure for good extraction?
 

Thank you very much dyqik.  When I use the blind basket, the gauge consistently reads 12 bars of pressure.  I will follow-up on the link you posted.

Thanks again,

Kevin
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calblacksmith
Moderator
calblacksmith
Joined: 25 Nov 2007
Posts: 8,034
Location: Riverside, Ca, U.S.A.
Expertise: I live coffee

Espresso: ECM Vene. A1, La Cimbali M32
Grinder: Azkoyen Capriccio, Major
Vac Pot: 40s era Silex
Drip: Msl. Com. brewers
Roaster: gave it a try, decided no
Posted Thu Dec 20, 2012, 1:20pm
Subject: Re: Optimal pressure for good extraction?
 

Something else to think about is that the pressure gauges can and do loos their calibration. You really don't know what your pressure is until you test the system with an external gauge that you know to be accurate.
Just adjust the grinder to get good shots and unless you have a reason to suspect that there is a major problem with the machine for other reasons, I would not worry about it until you can test with a known good gauge.

 
In real life, my name is
Wayne P.
Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!

Feed the newbs, starve the trolls and above all enjoy what you drink!
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kevinpeters
Senior Member


Joined: 20 Dec 2012
Posts: 6
Location: Peterborough, Ontario, Canada
Expertise: I love coffee

Espresso: Bezzera BZ09
Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 3:17pm
Subject: Re: Optimal pressure for good extraction?
 

Thanks calblacksmith - something to think about!  I would also want to verify that tinkering around inside the machine will not void the warranty before doing anything major.
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Frost
Senior Member
Frost
Joined: 26 Jul 2007
Posts: 2,116
Location: Sierra
Expertise: I love coffee

Espresso: Isomac Venus
Grinder: Lelit PL53
Roaster: Poppery I w/variac, MET, BT
Posted Thu Dec 20, 2012, 5:07pm
Subject: Re: Optimal pressure for good extraction?
 

Your pressure numbers are textbook for factory settings with a vibe pump. I would suggest you dial down to get around 9.5 bar during your typical shot(actual brew pressure is usually a bit lower depending on gauge placement). See how that works for your shot taste and timing. IMO, dialing in a shot at 11 bar pressure is a waste of time and coffee.
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kevinpeters
Senior Member


Joined: 20 Dec 2012
Posts: 6
Location: Peterborough, Ontario, Canada
Expertise: I love coffee

Espresso: Bezzera BZ09
Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 6:11pm
Subject: Re: Optimal pressure for good extraction?
 

Thanks for your advice Frost.
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