Why 9 bar?

#1: Post by **endlesscycles** » August 21st, 2012, 9:16 am

Seriously, why 9bar?

#2: Post by HB » August 21st, 2012, 9:35 am

Try brewing at 6 bar and 12 bar. Then halve the difference (7.5 and 10.5 bar). Repeat until you detect no difference. Do you have a preference? Many end up around 9 bar, but there is no hard and fast rule.

#3: Post by **mitch236** » August 21st, 2012, 10:56 am

I've never done the experiment but I think I recall Jim stating that flow slows with both lower and higher pressures so 9 gives the best flow. However with pressure profiling, I generally pre-infuse then ramp up to 10 BAR then continually lower the pressure to keep the flow constant, generally ending up around 7-8 BAR.

#4: Post by **homeburrero** » August 21st, 2012, 11:34 am

I suspect the OP might be curious about historically who and how someone first came up with the 9 bar magic number. I am too. There a few online espresso histories that essentially say this:

some-random-espresso-history-on-the-internet wrote: Bezzera sold the patent on his machine to Desiderio Pavoni in 1905. It was Pavoni that realized that the bitterness of the coffee was due to the high temperature of the water and the steam pressure that Bezzera had been using. Pavoni experimented with different water temperatures until he discovered that 195 degrees Fahrenheit combined with 8-9 bar of pressure produced the best cup of coffee.

And I think they may all be repeating something untrue. I'd think the 9 bar number would have come from the people working on early piston machines (Arduino, Cremonesi, Gaggia.) It would be nice to see something from a trustworthy, referenced source.

August 21st, 2012, 1:29 pm

Coming out and just saying it: what about a unimodal, fines free dose? I suspect the most balanced extraction might come with much less pressure.

August 21st, 2012, 1:30 pm

Does any one have a sieve and pressure profiling capabilities?

#7: Post by **another_jim** » August 21st, 2012, 2:01 pm

endlesscycles wrote:Coming out and just saying it: what about a unimodal, fines free dose? I suspect the most balanced extraction might come with much less pressure.

Got close using a big Ditting. It isn't espresso: no fines, no crema.

#8: Post by **Peppersass** » August 21st, 2012, 5:51 pm

endlesscycles wrote:Seriously, why 9bar?

Because 9 is the magic number.

#9: Post by **Al deHyde** » August 21st, 2012, 7:41 pm

Peppersass wrote:Because 9 is the magic number.

Only for numbers of base 10. In octal, it's 7. Or in hex it's 5. An espresso machine operating in hex mode, appropriately yields a pentagram-ish magic number, would make devilish espresso.

#10: Post by **another_jim** » August 21st, 2012, 8:16 pm

It's not a dumb question to ask about pressure and grind characteristics

The Illy labs answer is that 9 bar creates the fastest flow through the puck, with more or less pressure creating a slower flow. But this may be dependent on both the overall grind fineness and the proportion of fines to coarse particles.

In any case, the fundamental design idea of espresso, the one that governs its development fron 1900 to now, is to brew a single portion of coffee as fast as possible. The brew speed is dependent on how fine the grind is. A Turkish grind will brew faster, but is too fine for percolation, and an immersion method adds decanting time. In practice, the finest usable percolation grind is at the espresso level, and the consequent brew speed is about 30 seconds, and the consequent pressure 9 bar.

I guess if one can change the proportion of fines and coarse particles, the 30 second brew time would require a different pressure. But when I tried using the fines free, big Ditting, I'd get a gush at the usual grind size, and a self defeating dwell time at finer grinds.

The tuning of espresso grinders and machines took place over 60 years. It was all trial and error, not science, but over this stretch of time, you can lay odds on it being pretty optimal.