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Effects of brew pressure on taste of espresso

Postby mitch236 on Thu May 12, 2011 1:20 pm

Not profiling but setting the overall brew pressure on a non-paddle. When I first got involved, I believed 9bar was the "correct" setting. But in the past few months I've been playing with pressures and find that the coffee tastes much better (to me) at 7.5bar.

So my questions

What am I affecting running a lower pressure?
For those of you that play with pressures, do you find certain pressures are better for certain coffees?
How low can I go before I'm no longer making espresso?!! (more of a joke!)

Thanks
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Postby another_jim on Thu May 12, 2011 1:49 pm

As a very rough guide, the sweet spot for rotary pumps is 7 to 9 bar. The slower ramp of vibe pumps puts their sweet spot at 9 to 11 bar. But these ranges are also affected by the details of the brew head, particularly the gicleur size and any other flow capacitances or resistances that affect the initial pressure ramp up.

According to Illy labs, the flow rate rate through a puck peaks at 9 bar, and drops at both lower and higher pressures. This means that the classic 25 second shot for proper extraction happen at 9 bar, and that higher or lower pressures would require slower shots for proper extraction. This, rather than taste, may be the reason 9 bar is used as the nominal pressure for espresso.
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Postby cannonfodder on Thu May 12, 2011 10:37 pm

At 7.5 bar you are probably getting very lever like espresso which tends to be lighter in body and crema but it brings out the floral and fruit in most blends. I run my elektra at 8.6 bars if I remember correctly. I would have to put the scace on it to measure again.
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Postby mitch236 on Fri May 13, 2011 1:14 pm

How much can I trust the built in pressure gauge? I recently replaced it so it is essentially new. I don't want to buy a Scace pressure device just to check!
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Postby HB on Fri May 13, 2011 1:28 pm

Rather than focus on a specific number, try increasing/decreasing the brew pressure at least 2.0 bar, then decide if you prefer the taste/texture of the resulting espresso. Halve the difference between the previous/current setting and repeat until satisfied.
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Postby cafeIKE on Fri May 13, 2011 1:30 pm

Scrounge an old PF, remove the spout, buy a gauge from eBay, valve and fittings from local ironmonger and voila :

Image

All in, less than $20 and within a pound of the High Price Spread.

NOTE : Liquid filled is not required. Liquid filling damps vibration and lubricates the mechanism
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Postby innermusic on Sat May 14, 2011 12:25 am

Should I be calculating brew pressure or backwash pressure? (About 1/2 bar difference on my machine.)
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Postby malachi on Sat May 14, 2011 12:30 am

trust your taste
"Taste is the only morality." -- John Ruskin
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Postby another_jim on Sat May 14, 2011 1:53 am

innermusic wrote:Should I be calculating brew pressure or backwash pressure? (About 1/2 bar difference on my machine.)


What's backwash pressure?
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Postby Compass Coffee on Sat May 14, 2011 3:05 am

another_jim wrote:What's backwash pressure?

Highly suspect meant with back flush blank.
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