Real-Time Brew Pressure Adjustment for Profiling

Beginner and pro baristas share tips and tricks for making espresso.
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#1: Post by jrsd »

My Quickmill Carola has the pressure adjustment on top & can be simply adjusted by turning with a screw driver.

If I do this during an extraction does this equate to pressure profiling? ie; wait to pressure goes up to 9 bar & then slowly drop down to 8 or 7 bar.
I see some subtle improvement in taste or could I be dreaming?

The pressure profiling tool for E61 groupheads has an additional gauge, but I am wondering what's the difference with the gauge on the machine?

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#2: Post by Jeff »

Between usability and potentially longevity, I think you're dreaming. You would be making adjustments during a 5-15 second period. A screwdriver in an OPV (if that is what you've got) doesn't sound like a great way to do that.

What exactly does a brew pressure gauge measure?

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#3: Post by BruceWayne »

Your Carola has an E61 group head. Get a flow control kit if you want to play with brew pressure.

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#4: Post by Castillo2001 »

Yes you would be effecting the pressure reaching the basket, but I doubt that the OPV is designed for that kind of constant adjustment and I would think you are going to end up wearing something out a lot faster than is expected. If your machine is an E61 group head the easiest long term solution would be getting a flow control device for the group head. This this will control the amount of water flow with a nice adjustment knob, this will give you repeatable results while not over stressing any parts.

jrsd (original poster)
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#5: Post by jrsd (original poster) »

Thanks for your advice. You are absolutely right that I should invest in the flow control device.

To follow on from this, but still on the topic of pressure, I was actually also playing around with adjusting the pressure valve to achieve a desired pressure during an extraction.

If I am using my 18g basket. According to the pressure gauge on my machine I only reach 9 bars when the grind is fine enough, let's say for a 1:2 ratio that takes 30 seconds.

If I am to dose 14 or 16g or grind coarser & therefore shorten the extraction time, the pressure gauge will only reach 7.5 - 8 bars as far as I understand because the coffee is flowing faster through the coffee, ie less resistance.

Does this make sense? Should we always be striving for 9 bars?
I have also heard that lower pressure is better & gives a more gentle extraction with enhanced flavours.
Can anyone direct me to any research about this?

On the other side of the spectrum does higher pressure lead to over extracted flavour?
I have observed that my machine was shipped with the pressure set to up to 11 bars! So when grinding fine enough to have an extraction of 25-30 seconds the coffee was tasting bad/intense/bitter/over extracted & I was getting very good results at that pressure with extractions under 20 seconds.

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#6: Post by Jeff »

During extraction, flow and pressure are intertwined by the "resistance" of the puck to flow, restrictions and piping in the machine, and, especially with vibe pumps, what the pump can deliver.

My general recommendation is to grind and dose for flavor, and whatever comes out, comes out.

The next level is, over time and many, many shots, see if you get generally better results with a different pump pressure (or "style" on a manual lever). As an example, I found, for my machine, grinder, baskets, technique, coffees, and tastes, that I liked the shots better from my E61 with the blind-basket pressure around 8-8.5 bar than I did at 9 bar. This is one machine, one grinder, ... , so this is not "for everyone".

Now that I have a machine that is designed to be able to vary extraction pressure from shot to shot, my general experience with medium and lighter coffees has been (these are pressures "in the basket", so are probably about 1 bar below blind-basket pressures):
* Peak below 2 bars -- a different drink than espresso
* 2-4 bars -- generally boring, still more like "drip"
* 4-8 bars -- what I call "espresso" (most of my shots get pulled with a peak in the 6-8 bar range)
* Over 9 bar -- tastes somehow "flat" to me many times, not really over- or underextracted, just sort of boring