Under extraction with high pressure and normal extraction time

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summilux
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Joined: 2 months ago

#1: Post by summilux »

Hi there,

I noticed recently that high pressure (more than 10 bar on gauge) and normal brew time (approx 25 seconds from the start of preinfusion) generated very sour espresso. I use 20 g of coffee (in a 20 g portafilter) to get a double shot of approx 40 g at a brewing temperature of 92 degrees C (197 degrees F). The under-extraction became more obvious when I started drinking espresso directly, and more so when I recently got a refractometer and found out TDS was very low at around 8-9% (normal TDS should be 18-22% right?).

I'm running a WPM KD-310 espresso machine with an Eureka Silenzio grinder. I don't think there is anything wrong with the hardware, the espresso machine was recently cleaned, the grinder setting was not significantly changed, and the coffee I use was recently roasted to a medium-dark roast. The following practices were what I tried so far:
  • Same setting except for higher brew temperature at 95 degrees C, this did not seem to change the taste or the TDS at all.
  • Same setting except for coarser grind, this gave me lower pressure (9-10 bar on gauge) with very short extraction (around 16 seconds), and the sour taste is still there. (so it's not )
  • Decreased dose at 18 g, finer grind, lower brew temp at 92 degrees C, this gave me a choked machine with super high pressure and no liquid output.
Any thoughts?

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ei8htohms
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#2: Post by ei8htohms »

TDS is usually in the 8-12% range for espresso, with an EY% of approx. 18-22%.
LMWDP #751

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Jeff
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#3: Post by Jeff »

"Doctor, it hurts when I do this"

"Well, don't do that"

Several things are conspiring against you when extracting over somewhere around 8 bars where "secondary compression" starts to become significant. It's a non-intuitive thing that increasing pressure can result in less flow, not more.

Sour coffee, relative to what is possible from the coffee, is often a sign of under-extraction. In your case, it may be related to channeling.

Your reports on the ways you tried to resolve this seem from here to be like throwing darts at Reddit. My apologies if I have misinterpreted, but I'd suggest learning how to methodically dial in a shot at reasonable pressures (maybe 5-8 bars), if you haven't already. One good reference is Espresso 101: How to Adjust Dose and Grind Setting by Taste

summilux (original poster)
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Joined: 2 months ago

#4: Post by summilux (original poster) »

ei8htohms wrote:TDS is usually in the 8-12% range for espresso, with an EY% of approx. 18-22%.
Thanks John, clearly I got TDS and EY% mixed-up. I guess that's one relief that I'm at least not too far from a good pull as far as TDS is concerned.

summilux (original poster)
Posts: 4
Joined: 2 months ago

#5: Post by summilux (original poster) »

Jeff wrote:"Doctor, it hurts when I do this"

"Well, don't do that"

Several things are conspiring against you when extracting over somewhere around 8 bars where "secondary compression" starts to become significant. It's a non-intuitive thing that increasing pressure can result in less flow, not more.

Sour coffee, relative to what is possible from the coffee, is often a sign of under-extraction. In your case, it may be related to channeling.

Your reports on the ways you tried to resolve this seem from here to be like throwing darts at Reddit. My apologies if I have misinterpreted, but I'd suggest learning how to methodically dial in a shot at reasonable pressures (maybe 5-8 bars), if you haven't already. One good reference is Espresso 101: How to Adjust Dose and Grind Setting by Taste
That's some good advice, thanks Jeff.

Indeed I tried to adjust multiple parameters at once instead of in a methodical way as I don't want to "waste" too many beans (I'm the only coffee drinker in the family so I tend to purchase beans in small quantities). I'll definitely try to find some time this weeked and do a proper dial in. I think my previous attempt to "dian in" to around 9 bar was not quite complete as I'm not quite happy with what I got (the problem I found then was that the shot was pulled too quickly with very pale flavors).

Totally agree with the channeling after finding some samples and compare them to my pull. I guess that's just another problem brought in when I triedf to extract with too high pressure.

noob2024
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Joined: 2 months ago

#6: Post by noob2024 »

I would try 14G and keep the variables the same, but one. I would tinker with the grain size at a lower dose. usually Higher pressure will create a back pressure, and a slower flow. Too much beans can do the same. Once you get the right time and extraction, then try increasing the dose to lower the overall extraction time.

noob2024
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Joined: 2 months ago

#7: Post by noob2024 »

Do you have an open pf to observe the extraction? I found this, take a look. But if the lower dosage and fine tuning the grind size or the dosage doesn't help, try pre-soak. Are you making sure the groupheads is brought to correct temperature prior to brew? Lastly, have you tried a different size portafilter? How's the pressure, has this been checked? Is your opv working correctly? how many bars are you getting during the brew?

Bottomless Portafilter: Diagnosing Espresso Extraction Problems

noob2024
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Joined: 2 months ago

#8: Post by noob2024 »

If you can lower the pressure, you might get better results. My understanding on pressure, the higher the pressure, can slow the overall flow and extraction, at times causing a back pressure. Perhaps using a PF with larger openings, or less grind as suggested earlier.

summilux (original poster)
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#9: Post by summilux (original poster) »

Thanks, Pomer, It definitely helps when I'm lowering the dose (currently at 16 g and planning to try 14 g later) and it tastes more disirable with a much lower extraction pressure at slightly over 9 bar, it's not yet there but I think I'm on the right track. I'm now using the 18 g PF that came with the machine, and the grouphead is preheated before the brew. Currently I tend not to mess with the hardware settings as I'm 95% sure this is just caused by my bad technique but not the machine.

erik82
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#10: Post by erik82 »

The problem currently is your machine. The pump will be putting out 11 bar so grinding fine enough will give enough backpressure but way too high pressure. Grinding coarser and the puck can't take 11 bar as there's not enough resistance so lower pressure but way higher flow and thus short shots.

What you need to do is adjust the OPV (if your machine has one) and set the max pressure to 8-9 bar instead of 11 bar and all problems will probably be solved.