# Re: portafilter pressure gauge (over simplification to pose question)

I'm still trying to get my mind around this issue.

As pointed out in another thread, I tested the pressure of new Gaggia
Classics & noted that all of them had OPV's set higher than 9 bar. At that
time I mentioned that my interpretation of an article by Illy was that the
pressure should be adjusted to 9 bar & the grind adjusted to the pressure.
more confused. So, what impact does pressure & coffee particle size have on
brewing espresso.

constant #1
a quality espresso pull is 25 milliliter in 25 seconds.

constant #2
tamp is same from shot to shot

variable #1
pump pressure = 12 bar
coffee ground = particle size x

variable #2
pump pressure = 9 bar
coffee ground = particle size y

variable #3
pump pressure varies by time & pressure build-up

Hypothesis #1
Particle size must be smaller as pump pressure goes up, so variable #1 would
result in over-extracted coffee.

Hypothesis #2
Particle size must be larger as pump pressure goes down, so variable #2
would result in under-extracted coffee.
--
Robert Harmon
--
http://www.tinyurl.com/mb4uj - My coffee pages.
http://www.tinyurl.com/2cr3e2 - I have things for sale here.
http://www.tinyurl.com/2j8jur - Gaggia User's Group
http://www.tinyurl.com/235dfr - BUG is Bunn User's Group (espresso)

.

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