So 9-bar seems to be the accepted standard. And I'm assuming most would agree with that, +/- 0.5 bar.

I've read that higher pressures will intensify flavors. The shot will come out stronger. If this is true, why aren't people brewing (or at least experimenting) with 10 bar or something higher to get very intense shots. Can higher pressures amplify good flavors? Is this untapped territory?

h3yn0w wrote:So 9-bar seems to be the accepted standard. And I'm assuming most would agree with that, +/- 0.5 bar.

I've read that higher pressures will intensify flavors. The shot will come out stronger. If this is true, why aren't people brewing (or at least experimenting) with 10 bar or something higher to get very intense shots. Can higher pressures amplify good flavors? Is this untapped territory?

There is no obvious "untapped territory" in espressodom. This is not to say that everything obvious is understood, but if you take something so obvious as the pressure or temperature of espresso extraction, it has been looked at and is being looked at, ad nauseum.

10 bar is not "10 bar," always. If you are talking about the pressures produced by a vibratory pump, for example, the pressure is highly variable and although the peak pressure might be 14 bar, that is not the average or median pressure that the coffee is subjected to. Overpressure valves (OPV) attempt to smooth out this pressure somewhat, with somewhat uncertain results (in the cup).

Pressure "profiling" is currently a hot topic in espressodom; It is being "studied" as we type, however the likelihood that any great truths will evolve is very unclear.

One thing is however, very clear, at least to me. Something as simple as raising the extraction pressure to get "very intense" shots is unlikely to be very useful.

ken

I think it depends on the machine pump right? I was told to adjust my Silvia to 9bar and it was a horrible experience.. everything tasted horrific. I put it back up to stock pressure (which i think is 11 ) and I have been having some of the best coffee ever.

The standard is to adjust rotary pumps to 9 bar and vibratory pumps at 11 bar, measuring against a blind filter. The difference compensates for the generally looser OPVs on vibratory pumps (which means a greater pressure drop when the water flows) and their slower ramp to full pressure at the start of the shot. If you can measure pressure at the espresso flow rate, roughly 8 bar seems to be the most common recommendation.

Spring lever machines start out at 7 to 9 bar and finish at 4.5 to 6 bar as the spring uncoils. In addition, the operator holds the lever at the start of the shot for 5 to 8 seconds, allowing the puck to soak at 1 bar pressure.

The experimentation with precisely programmable pumps somewhat apes the spring lever profile, with an initial low pressure preinfusion, then maximum pressure at the start of the flow, and finally declining pressure towards the end of the shot. However, the numbers I see quoted are more extreme than the springs, 2 or 3 bar to preinfuse, 10 to 12 bar at the peak, and down to 4 or 5 to finish.

My personal experience is that the taste of the shot responds less to pressure changes than to grind, dose or temperature changes. So I think it will take time to assess the value of the pump profiling systems.

Ken Fox wrote:There is no obvious "untapped territory" in espressodom.

ken

Grind profiling? (Adjusting your grinder while you're grinding the shot)

another_jim wrote:The experimentation with precisely programmable pumps somewhat apes the spring lever profile, with an initial low pressure preinfusion, then maximum pressure at the start of the flow, and finally declining pressure towards the end of the shot. However, the numbers I see quoted are more extreme than the springs, 2 or 3 bar to preinfuse, 10 to 12 bar at the peak, and down to 4 or 5 to finish.

This is exactly the sort of thing I was wondering about. Based on your cited example it seems then, perhaps there might be an advantage to entering 10+ bar territory at some point during the brew to amplify certain flavors.

I'm trying to get my head around the same basic question - I got a used Andreja a couple weeks back; when I got it, the brew pressure gauge was reporting a peak of 13 bar during the shot, which seemed high. I adjusted the OPV back to 9.5/10 bar (puck vs blind), and have been having some trouble getting espresso that I enjoy. This may be related to playing with a triple basket and a bottomless, but I'm wondering now if my OPV is currently set too low.

Probably the best summary of where we are with pressure profiling right now:

http://www.jimseven.com/2010/11/14/wher...profiling/

ken

Interesting stuff. Thanks Ken.

That said, I am more interested in the change at peak pressure, more so than the "profile" or shape of the curve. So take any of the shot profiles in the LM chart, and adjust peak pressure higher to try for a more flavorful and intense shot.

While higher pressures may force out more solids, not all those solids are desirable. I think I get a lot of undesirable distillates in an uber high pressure profile. I just change baskets/grind/dose when I want to change what I get in the cup and let the machine run at 8.7 bar.