Posted Sat Oct 30, 2004, 4:58pm Subject: Andreja Premium Brew Pressure Gauge
Having just purchased Chris' Coffee's gorgeous Andreja, I'm still learning the ropes of using a first class prosumer machine. I appreciate having the gauges, but am not certain what utility the brew pressure gauge has. I assume "brew pressure" means pump pressure. If so, what does this tell me about the machines' performance and how does this help me make a better espresso?
fateagk Senior Member Joined: 2 Jan 2004 Posts: 102 Location: Tampa, FL Expertise: I love coffee
Espresso: Andreja Premium, Pid'ed... Grinder: Mazzer Mini Roaster: iRoast
Posted Sat Oct 30, 2004, 5:16pm Subject: Re: Andreja Premium Brew Pressure Gauge
The brew pressure gauge will show you the pressure that is seen at the puck during a shot. If you put the blind basket in the PF and lift the lever up (as in a backflush), the brew pressure gauge will show the maximum pressure that your Over-Pressure Valve will allow you to see at the puck. This is the upper bound. I think my Andreja came set at around 11 bar. If you just run the pump with an empty double basket in the PF, the brew gauge will give you a lower bound. You can achieve the desirable ~9bar of pressure that everyone speaks of by adjusting your grind and tamp so that when you pull your shot, the brew pressure gauge reads ~9bar. Several people, myself included, have adjusted the OPV so that the brew pressure will max out at 9 bar. Dan Kehn wrote about this in his review of the La Valentina here (scroll down to ADJUSTING BREW PRESSURE in the Machine Performance section). You can also see my questions and responses about doing this on the Andreja here. I found this to help my overall shot quality with Andreja, but this is just my own opinion and YMMV.
You can use this guage to make better shots by seeing what pressure the coffee puck is experiencing during the shot and adjusting the grind and tamp variables as necessary to achieve the right pressure (~9bar).
Posted Sat Oct 30, 2004, 6:01pm Subject: Re: Andreja Premium Brew Pressure Gauge
Jim Schulman posted a wonderfully lucid explanation of the purpose and limitations of an expansion / over-pressure valve. It's so good, I believe it is worth repeating in its entirety, including the attached chart:
jim_schulman Said:
Chris asked me to post a short explanation of what limiting a Vibe pump will and won't do for you.
The illustration is the "pump curve" (black graph) of most Ulka espresso pump models, showing the pressure (vertical axis) for a 25 second shot with the volume shown on the horizontal axis.
As you see can see, if you're pulling a ristretto or single on an unregulated Ulka, you're going to get a pretty awful shot, since it's pumping out at around 15 bar. If you're pulling a regular sized double of 50 to 60 cc, you'll be fine, getting 8 to 9 bar pressure.
If you put in a pressure limiting relief valve, you improve SHORT SHOTS ONLY.
Chris sets the Isomacs up at 10.5 to 11 bar, so all shots below about 50cc will be at that level. According to him, this is the industry standard setting for commercial vibe pumps. Reset it at 9 bar, and all shots below about 55cc will be at 9 bar.
If you insist on 80 - 90cc lungo shots, you'll be getting strong coffee brewed at 3 to 4 bar, not espresso. The pressure limiter won't help, the Ulka pump simply cannot maintain 9 bar pressure at that flow rate.
If you pull ristrettos (or doubles that become "accidental ristrettos"), the expansion valve determines the brew pressure because of the flow rate / pressure relationship shown below. If you're pulling doubles and you want to see how close the puck resistance is to 9 bar, try setting the OPV a little higher, say 10 or 10.5 bar. The brew gauge will then confirm what measuring the pour time / volume would also indicate. As an experiment, try a ristretto with it set to 10, 11, and 12 bar, adjusting the grind to keep the same volume. I prefer it set to around 9.5 bar, but it doesn't get nasty harsh until around 12 bar.
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