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Setting brew pressure - does it matter at all?
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Discussions > Espresso > Machines > Setting brew...  
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krumbak
Senior Member


Joined: 30 Mar 2005
Posts: 28
Location: Aalborg, Denmark
Expertise: I love coffee

Espresso: Andreja Premium
Grinder: Macap M4 (Doser)
Roaster: Gene Café, SC/HG, Poppers
Posted Sat May 28, 2005, 2:33pm
Subject: Setting brew pressure - does it matter at all?
 

Maybe someone can explain this to me, it seems im missing something here..?

We aim for a 9 bar brew pressure. If i adjust my brew pressure to 9 bar (according to the gauge on my Andreja Premium) using a blind filter, then i get a 9 bar brew pressure as maximum or the pull is stalled.

Then picture this... I grind a little coarser or tamp lighter and the flow is quicker and the brew pressure maybe hits 8 bar. No problem, the shot is not stalled, just brewed at a lower pressure. Then if i grind a little finer or tamp harder, the brew pressure hits 9 bar (but a pressure of e.g. 10 bar is needed, and the pull stalls or is too slow - not even risretto).

If a had set the brew pressure to e.g. 12 bar, then the shot would have been flowing ok and not stalled. Even if the shot needed 11 bar of pressure then it would have been flowing and not stalled - It probably wouldnt have been a good shot, but a stalled shot isnt good at all either, and just maybe the 11 bar shot would have been ok? Anyway this leeds me on to the following...

So im thinking the maximum brew pressure setting doesnt matter at all, as long as i tamp/grind just right to get that 25 second pull at 9 bar? Im sensing im completely wrong here, someone tell me whats going on ;)

The above scenario is purely hypothetically, its just something i have giving some thought, thinking about setting the right brew pressure.

So, what to set the brew pressure at using a blind filter then? Does it really matter as long as its over 9 bar? Or should i go for 10 bar so that i'll always know the pull didnt exceed that, and i dont have to keep looking at the brew pressure gauge, when pulling shots.

Best regards,
Thomas.
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nmayweather
Senior Member


Joined: 25 Jun 2004
Posts: 994
Location: nyc
Expertise: I live coffee

Espresso: expobar office, isomac venus
Grinder: mini mazzer
Vac Pot: bodum santos
Drip: mr coffee sp3
Roaster: toastmaster popper
Posted Sat May 28, 2005, 3:36pm
Subject: Re: Setting brew pressure - does it matter at all?
 

We aim for 9bar brew pressure - so we set the over-pressure / pressure-release valve to 9 bar

On most machines, pulling a normal shot will create about 9 bars.  So , we  do not need to 'trip' the pressure release valve to ensure 9bars

BUT some times, or every time if you pull a ristretto,  the puck will stand up to more pressure - lets say 11-13 bars (which my ristrettos tend to create)

11-13 bars on a ristretto tastes awful.  its bitter and oily.  

by tripping the opv at 9bars, we only expose the coffee to 9 bars of pressure

--

here's another way to look at it:

 A_ you adjust grind + tamp  until you get a puck that creates 9bars of resistance and prooduces 1.5oz in 25 seconds
 B_ you set the machine to only create 9 bars of resistance, then alter grind+tamp to produce 1.5 oz in 25 seconds

 to make a ristretto, you need to go with B, as a ristretto creates around 11-13 bars of resistance, but it tastes bad at that pressure

 to make a regular, you can go with A, but there's one less factor for you to account for in B, so its easier
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tom_b
Senior Member
tom_b
Joined: 19 Aug 2003
Posts: 537
Location: Maui, Hawaii

Espresso: Rancilio Silvia/PID
Grinder: Nuova Simonelli MCF
Roaster: USPS/Popper
Posted Sat May 28, 2005, 4:00pm
Subject: Re: Setting brew pressure - does it matter at all?
 

Brew pressure doesn't need to be watched each time. Set the OPV for 9.5 bar with no flow, and with flow it'll be around 9. Then you can turn your attention to all the other variables. [edit, mis-info deleted].. >>:)
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HB
Senior Member


Joined: 3 Apr 2003
Posts: 2,913
Location: Cary, NC
Posted Sat May 28, 2005, 4:44pm
Subject: Re: Setting brew pressure - does it matter at all?
 

krumbak Said:

So im thinking the maximum brew pressure setting doesnt matter at all, as long as i tamp/grind just right to get that 25 second pull at 9 bar? Im sensing im completely wrong here, someone tell me whats going on ;)

Posted May 28, 2005 link

The vibration pump's pressure is inversely related to the flow rate (see chart below). If you always pull a true double and not a ristretto, then the OPV acts only as a safety. That's probably why many are set to 12 bar from the factory, i.e., the manufacturer is concerned about protecting the plumbing from excessive pressure, not setting a ceiling on brew pressure.

Jim's "Adjusting vibe pump pressure on HX machines" explains this in further detail. The short answer is that the OPV keeps the brew pressure reasonable when pulling a ristretto or "accidental" ristretto. A rotary pump doesn't require an OPV for pressure regulation because it has a built-in relief valve and a flow rate capacity well beyond that needed for brewing espresso.

-- Dan

HB: ulka_E5.jpg
(Click for larger image)

 
www.home-barista.com
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Cajun_brew
Senior Member
Cajun_brew
Joined: 6 Feb 2004
Posts: 490
Location: Louisiana
Expertise: I love coffee

Espresso: Anita
Grinder: M4 doser----Rocky DL
Drip: Capresso MT500
Roaster: Gene
Posted Sat May 28, 2005, 6:36pm
Subject: Re: Setting brew pressure - does it matter at all?
 

Great chart Dan,

I'm trying to fully understand. Can I use this to get an approximate brew pressure on my stock Silvia? If so, which line do I need to be looking at?

 
I've been fairly untreated
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HB
Senior Member


Joined: 3 Apr 2003
Posts: 2,913
Location: Cary, NC
Posted Sat May 28, 2005, 6:52pm
Subject: Re: Setting brew pressure - does it matter at all?
 

Jím's "runoff" method can help you approximate the actual OPV / expansion valve setting and the Silvia Pressure Modification page shows how to tweak Silvia. The performance curve charts on the Ulka website list their models; most vibe pump espresso machines have an E5 variant. That said, the better choice is to have a pressure measuring portafilter. You can buy a pressure gauge kit for your existing portafilter (*), the whole unit, or build your own (below).

Specifically to your question, the center line is the specification and the dashed lines are the allowed variance. I've only tested a couple, but they fell well within the lines.

-- Dan

(*) Assuming it has a smooth edge. Note that "old style" Silvia portafilters with the ribbed handles had a cut groove, i.e., the portafilter must seal without the basket in place.

HB: pf_pressure_gauge.jpg
(Click for larger image)

 
www.home-barista.com
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Cajun_brew
Senior Member
Cajun_brew
Joined: 6 Feb 2004
Posts: 490
Location: Louisiana
Expertise: I love coffee

Espresso: Anita
Grinder: M4 doser----Rocky DL
Drip: Capresso MT500
Roaster: Gene
Posted Sun May 29, 2005, 1:41pm
Subject: Re: Setting brew pressure - does it matter at all?
 

Ok, I'm missin' something,
I tested my Silvia and got 630 ml(or cc) in one min. This doesn't seem to fit any of the charts from this link.

http://www.ulka.it/eng/E.htm



What pump is on a Silvia ? Anyone know an approximate brew pressure from this info?

 
I've been fairly untreated
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HB
Senior Member


Joined: 3 Apr 2003
Posts: 2,913
Location: Cary, NC
Posted Sun May 29, 2005, 3:05pm
Subject: Re: Setting brew pressure - does it matter at all?
 

I assume you measured with no resistance? If so, the E5 max flow rate is 650cc/min at zero bar, which is consistent with your measurement.

HB: ulka-max-flow-rate.jpg
(Click for larger image)

 
www.home-barista.com
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Cajun_brew
Senior Member
Cajun_brew
Joined: 6 Feb 2004
Posts: 490
Location: Louisiana
Expertise: I love coffee

Espresso: Anita
Grinder: M4 doser----Rocky DL
Drip: Capresso MT500
Roaster: Gene
Posted Sun May 29, 2005, 6:22pm
Subject: Re: Setting brew pressure - does it matter at all?
 

assume you measured with no resistance

Yes, no resistance.
Am I to assume my pressure is around 15 bar? (yipes) or is this the type of thing you MUST  have a pressure gauge for?

Assuming I have no channeling on a double or soon to receive triple basket and hit the golden rule, the high pressure shouldn't come in play...right or wrong?? Doesn't this  come into play only while pulling a restricted shot? I know about the pressure mod but don't know if I want to mess with it. I know I'm going to end up with a HX machine one day. Maybe I should stay away from the risto for now :]

 
I've been fairly untreated
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HB
Senior Member


Joined: 3 Apr 2003
Posts: 2,913
Location: Cary, NC
Posted Sun May 29, 2005, 7:19pm
Subject: Re: Setting brew pressure - does it matter at all?
 

You would have to measure the "runoff" from the OPV overflow tube to calculate the OPV setting (e.g., 200cc/min returned to the tank means the OPV opened at 10 bar). Unless you pull ristrettos, the OPV is irrelevant because the system pressure would be at or below generally accepted brew pressures at the "double espresso" flow rate. Below is a chart from Chris Nachtrieb and posted by Jim that further explains this point.

-- Dan

PS: The more important question in all this: How's the espresso taste?

HB: pressure-limiter.jpg
(Click for larger image)

 
www.home-barista.com
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