Affects of brew pressure on espresso

Beginner and pro baristas share tips and tricks for making espresso.

#1: Post by dantyvogel »

So I've never pulled espresso at anything besides 9 bars. I've been looking at some of the roasters brew recipes for espresso and some recommend say 7 bars or 8 bars. I've been told you can lower pressure and fine your grind and lengthen the time of the shot and it's suppose to pull the flavors of say a lighter roast but in less volume, so more body.

I'm having a hard time wrapping my head around this. Any help dumbing this down for me. How does lowing brew pressure affect the espresso? Thanks ahead of time!


#2: Post by greenbean11 » ... re-rehash/

This is an interesting read on the subject. Hope it helps!


#3: Post by nuketopia »

I cannot make sense of that article. Wayyyyy tooo much caffeine by the author. All the F-this and F-that and I just can't find a point buried in all those words.

To be honest, I read his other articles and did experiment with reduced brew pressure. I didn't find some kind of pot of gold at the end of the rainbow in an espresso cup. In the end, I put the SCACE-II on the machine and dialed it back up to normal pressure. It just made it easier to exchange brewing parameters with others, since that's pretty much the reference pressure.

The brew pressure setting changes 2 things:

1. As most espresso machine have a small orifice between the brew head and the pump, it changes the water ramp up time at the coffee puck a little.
2. It changes the force at which water is pushed through the coffee bed, and thus pull-time for any fixed grind, or allows coarser grind for the same pull time.

There's nothing magical about 9-bars, nor is there about 8, 7, 6 bars. At 0 bars, well, you're brewing, not pulling shots anymore. Yes, the same coffee brewed tastes different when pulled as espresso, even if diluted to the same strength.

9 Bars is just a kind of reference - that evolved over time. It is just that, a reference. Most espresso beans are blended and roasted and ground to achieve desired results with a particular dose and pull time.

Higher pressure lets you grinder finer and generally, finer particles expose more surface area and lead to higher extraction yields. Higher pressure may also increase the probability of channeling. That's probably why we don't use 15-bar, or 100-bar of pressure.


#4: Post by jpender »

nuketopia wrote:There's nothing magical about 9-bars, nor is there about 8, 7, 6 bars. At 0 bars, well, you're brewing, not pulling shots anymore. Yes, the same coffee brewed tastes different when pulled as espresso, even if diluted to the same strength.
What about 3 bar?


#5: Post by nuketopia » replying to jpender »

That's simply practicing onanism. :?


#6: Post by jpender »

Well, maybe. I'll leave that to you to figure out.

I was just wondering...

How low a pressure would produce a beverage that most people would recognize as espresso?

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#7: Post by Jake_G »

dantyvogel wrote:How does lowing brew pressure affect the espresso?
To the OP.

I suggest reading the link in this post of my ramble. It's a link to a post regarding a tech paper by Synesso. Good stuff about pressure in various stages of the extraction and how it impacts taste.

It's not conclusive nor exhaustive, but it's interesting nonetheless.


- Jake
LMWDP #704

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#8: Post by another_jim »

Back in the early aughts, the University of Salamanca did a large scale survey on brew pressure, having people give preferences on 7, 9, and 11 bar shots of the same coffee, grind, dose and shot weight. The 11 bar shots came in last, while the 9 and 7 bar ones tied. The 7 bar shots were described as smoothest and gentlest, the 11 bar shots as harsh, and the 9 bar ones the creamiest.

They also did a survey on preinfusion, finding nothing at all (the shots were made by pros, so forgiveness was not an issue).

Obviously, they weren't doing any profiling studies with light roasts; but the results hold up pretty well.
Jim Schulman

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#9: Post by NoStream »

I've experimented quite a bit with this. First, with my old CC1 (just adjusting an OPV) and also with my current machine (a DE1+). My findings have been very consistent.

Pressures of 9+ bars at the puck create a maximum of traditional (or generic, depending on your perspective) espresso flavors - chocolate and butter and richness. Mouthfeel is also thickest.

Lower pressures create more fruited and distinct flavors. Lower pressures also cause reduced mouthfeel - less emulsion of oils and fines. At really low pressures (say, 3 bars), espresso pretty much tastes like strong drip coffee. At really low pressure, extraction yield also falls off. But EY is not extremely, obviously affected by pressures between 6 and 10 bars. (There's a more rigorous study online that shows maximum extraction yield at 7-8 bars - ... idamo-Guji ) Rao has said EY is maximimized at the pressure the maximizes flow, which is around 8 bars but can vary.

For me, the sweet spot is around 7-8 bars, where I get good mouthfeel and distinct flavors.