germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,041 Location: Philadelphia Expertise: I love coffee
Espresso: Duetto 3, A Dead Oscar Grinder: Vario-W, Preciso w/Esatto,... Drip: Brazen Roaster: Diedrich IR-1, HT B
Posted Tue Apr 10, 2012, 5:20am Subject: Re: Why do espresso machines come with chronically high OPV settings?
High pressure will certainly create a greater chance for channeling and exposing other flaws in the puck which then will certainly produce an off tasting shot. This does not mean a shot can not be built to deliver 9 or so bars even with a pump producing higher pressure.
The problem I see with vibe pump ( not familiar with rotary pumps yet) is that it is not constant with the pressure it produces. When measured pressure is measured against a blind insert the pump will show its maximum pressure or the point where the opv kicks in to limit the high, however this is not showing a true flow through a puck unless the puck is choking the machine. The pressure through a puck is ramping up and when the first few drops appear will be the highest pressure then it will drop as water flows through the puck. So if setting the opv to 10.5 bar against a blind you may very well be getting less then 9 bars with a shot pull. Next problem I have is how trusted an opv valve is, is it really giving you the pressure profile you desire throughout the shot? If an opv is diverting the water Is it being replaced by water that is cooler then the heated water one wants ( I am sure different machines do it different but I know with the Oscar I am pulling extra water from the reservoir and cooling the HX and group that much more during a pull).
Low pressure produces low crema yet a thicker syrupy shot like with lever machines, high pressure will give lots of crema and thiner liquid. So if the common person is using old beans (or pods) to get the results they expect a higher pressure machine is more likely to give these results.
Posted Tue Apr 10, 2012, 6:13am Subject: Re: Why do espresso machines come with chronically high OPV settings?
After I bought my alex2 back in december I had the same question. bar was set to 10.5 default so before ajusting to 9 bar I done some reading and made some calls. only common answer was the higher bar will make it harder to dial a shot in,but will produce a brighter shot with more acidic flavors.
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,041 Location: Philadelphia Expertise: I love coffee
Espresso: Duetto 3, A Dead Oscar Grinder: Vario-W, Preciso w/Esatto,... Drip: Brazen Roaster: Diedrich IR-1, HT B
Posted Tue Apr 10, 2012, 7:32am Subject: Re: Why do espresso machines come with chronically high OPV settings?
JDHarding Said:
I remember my Ascaso Steel Uno Pro was set at around 19 bar pressure, which is why I had a horrible time trying to get my Rocky to grind fine enough, and had to purchase a seperate grinder that would grind fine enough. Thankfully, I bought a pressure gauge and set the OPV down to 9 bar and now even the Rocky can grind fine enough. :)
The Ascaso machines tend to come with a POD basket, although I've never used it myself, but that's probably the main reason the OPV is set so high. 19 bars is a tad too high even for pods, so it really doesn't make any sense.
Wow, never read anything about a vibe pump being able to put out 19 bar, 15-16 seems to be the norm. So did you set your opv to 9 bar against a blind? If so your shots are seeing more like 7 bar max at the group. It comes to mind if your gauge was reading 19 bar which is about 3 bar more then the pump can deliver your gauge may be off and therefore your 9 bar setting is also off.
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,041 Location: Philadelphia Expertise: I love coffee
Espresso: Duetto 3, A Dead Oscar Grinder: Vario-W, Preciso w/Esatto,... Drip: Brazen Roaster: Diedrich IR-1, HT B
Posted Tue Apr 10, 2012, 7:40am Subject: Re: Why do espresso machines come with chronically high OPV settings?
kboom1 Said:
After I bought my alex2 back in december I had the same question. bar was set to 10.5 default so before ajusting to 9 bar I done some reading and made some calls. only common answer was the higher bar will make it harder to dial a shot in,but will produce a brighter shot with more acidic flavors.
Can only offer generalities. Taste wise, lower than 9bar I found the shots softer, maybe a little muddled. This was great for taming a coffee down or for a chocolate bomb spresso. Higher pressure I found more definition, but there's a point where a harshness can come out.
But when I've played around with pressure, more than taste I noticed forgiveness. Higher presser = less forgiving (YMMV).
Stuart Senior Member Joined: 9 Feb 2012 Posts: 113 Location: TX Expertise: I love coffee
Espresso: Breville Dual Boiler Grinder: Baratza Vario Roaster: Air Crazy popper
Posted Tue Apr 10, 2012, 9:36am Subject: Re: Why do espresso machines come with chronically high OPV settings?
I'd say I've had more consistent results since dialing down my OPV from 11.5 bar to 9.75 bar (into a blind; based on internal gauge reading), but I also have more experience with the machine. It's my impression that the lower blind pressure (and lower extraction pressure) means gentler flavors in the cup.
(I get 9.7-10 bar into a blind filter, nearly the same with a choker shot, and about 8.5-9 bar with a normale extraction -- all machine gauge readings.)
JDHarding Senior Member Joined: 31 Aug 2007 Posts: 1,099 Location: WA, USA Expertise: I love coffee
Espresso: Ascaso Steel Pro PID Grinder: Nuova Simonelli MDX,... Vac Pot: None Drip: Hario v60 Roaster: Behmor, Fresh Roast
Posted Tue Apr 10, 2012, 11:47am Subject: Re: Why do espresso machines come with chronically high OPV settings?
germantownrob Said:
Wow, never read anything about a vibe pump being able to put out 19 bar, 15-16 seems to be the norm. So did you set your opv to 9 bar against a blind? If so your shots are seeing more like 7 bar max at the group. It comes to mind if your gauge was reading 19 bar which is about 3 bar more then the pump can deliver your gauge may be off and therefore your 9 bar setting is also off.
From reading here and HB, this is why I built a gauge with a needle valve to adjust shot volume and a liquid filled gauge in parallel. That gives the ability to set the shot volume first (same as a shot in time specified), then read the corresponding pressure and adjust OPV from there. From what others have said on HB, that doesn't make a huge difference from just setting against blind basket, but I figured it was worth the exercise (made sense to me).
Posted Tue Apr 10, 2012, 12:43pm Subject: Re: Why do espresso machines come with chronically high OPV settings?
On machines with a 3-way solenoid valve there is very little difference (about 1/2 bar that I can tell on my machines but it depends on the specific pump and OPV valve etc. so I'm sure there are machines that have a larger difference) between just setting it with a blind basket or a PF gauge with no flow and setting it while using a needle valve to allowing a normal shot volume to flow. (and a difference between flowing a 1oz shot in 25 sec and a 2 oz shot in 25 sec too).
On a machine without a 3-way solenoid (also usually no OPV on these) - they typically have a spring loaded pressure resistance valve in the group instead - I find there is a huge difference between setting it when allowing a shot's worth of volume to flow and static without any flow. Static might read 15 bars and flowing a 2 oz double might read 8 bars - yes, that much difference and more depending on the particular spring tension and valve.
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,041 Location: Philadelphia Expertise: I love coffee
Espresso: Duetto 3, A Dead Oscar Grinder: Vario-W, Preciso w/Esatto,... Drip: Brazen Roaster: Diedrich IR-1, HT B
Posted Tue Apr 10, 2012, 1:35pm Subject: Re: Why do espresso machines come with chronically high OPV settings?
diggi Said:
From reading here and HB, this is why I built a gauge with a needle valve to adjust shot volume and a liquid filled gauge in parallel. That gives the ability to set the shot volume first (same as a shot in time specified), then read the corresponding pressure and adjust OPV from there. From what others have said on HB, that doesn't make a huge difference from just setting against blind basket, but I figured it was worth the exercise (made sense to me).
Then why is general consensus from trusted posters here and at HB to set a vibe pump at 11 bar against a blind basket?
For me it is what is in the cup that counts, not what 50 other people say because they saw it somewhere. I can build a shot and get 9 bars resistance even if the pump is putting out 16bar of pressure but any mistake in prep will result in a problem that will lead to over and under extraction issues. 9 bars is what is stated time and time again and I have no debate about that number, it is tried and true and spoken about to a nauseating degree.
I don't mean to debate the quality of gauges being used to adjust opv valves, or the quality of an opv valve and what it can do, or how a vibe or a rotary pump can actually deliver consistent pressure for the 20-45 sec it is running rather that a manufacture puts out a machine with the pressure set higher because it will give the most pleasing results to 92% of its customers. We are not talking commercial grade equipment here and if we where I would expect commercial grade tools for checking the calibration of the machine to be used not some sort of accurate stuff. If I cared about 1/100th of a gram in a shot I would use lab grade scales and calibration weights I never touched with my hands but for coffee if it is with in .5g I don't care and can't taste the difference.
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