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#137

Espresso Brewing Pressure: Is 9 Bars really optimal?

Almost all semi-automatic espresso machines are calibrated and set by default to brew at roughly 9 bars of pressure. Lucky for us, we use the Slayer espresso machine, one of the few espresso machines out there that allows for easy tweaking of the brew pressure. This week, we will be setting out to test the impact of brewing pressure on the resulting espresso and it's extraction percentage.

Almost all semi-automatic espresso machines are calibrated and set by default to brew at roughly 9 bars of pressure. In many machines, adjusting the brew pressure is either not possible or a very difficult task that should only be performed by a technician familiar with the machine's inner workings. Lucky for us, we use the Slayer espresso machine, one of the few espresso machines out there that allows for easy tweaking of the brew pressure. This week, we will be setting out to test the impact of brewing pressure on the resulting espresso and it's extraction percentage.

Brew pressure is a relatively advanced topic, hence before we begin it's probably best to clear up some ideas with regards to brew pressure.

1. Many espresso machines have a gauge that shows the pressure of the machine. This is the pressure of the water pump in the machine, it is not an exact representation of the brew pressure that happens in the grouphead.

2. To measure the pressure at the grouphead, we need to use a tool called the Scace. It...

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12 Comments

    • Avatar
      Chas Kane
      Jul 5, 2018

      I love that you posted the stats. Your conclusion is fascinating, as every coffee shop I've been to uses 9 bars. Are you planning on expanding this work at all? Small sample size and diversity may mean that 7-8 bars is best for this coffee, or for this machine, grind size, etc.However, this could be big -- it's easy for people to simply copy what's already in place when changing is costly (few know how to change the pressure in their machines).

      • Avatar
        Kenneth Ong
        Jul 7, 2018

        Hey Chas,I'm glad you enjoyed the article :) There is loads more to research in this area of course. We've run a number of other experiments but haven't published just because it is extremely time-consuming to write about them.You are correct to say that there are other variables that contribute to the optimal brew pressure, the key variable among them being distribution of grinds in the portafilter. However, as the majority of us do not usually distribute 100% evenly, I would say this findings are applicable to many cases regardless of coffee, machine etc.. The reason why I say this is because we are not the only ones who have discovered that the optimal espresso brew pressure lies below 9 bars, where optimal is defined as ideal for even and higher extractions instead of speed.Other coffee professionals like Scott Rao, Matt Perger from St. Ali, Socratic Coffee and numerous others have had similar findings within their own research. My motto is always to try it for yourself and you can decide from your own tests.To greater coffee experiences, Kenneth

    • Avatar
      Cristian
      Nov 10, 2018

      Hi! Very interesting and nice work! I have a question and I am sorry if the answer is in the text. Did you adjust the grind setting when lowering the pressure? I.e., adjust the grinder such that the extraction takes 28 s as for 9 bars. Thanks!

      • Avatar
        Kenneth
        Nov 15, 2018

        Hi Cristian, No we did not change the grind setting throughout the experiment, only the brew pressure.Cheers, Kenneth

        • Avatar
          Michael Betz
          Dec 6, 2018

          Thanks for the excellent experimental work!Provided you did not adjust the grind, how did you manage to keep the extraction times constant?

          • Avatar
            Kenneth Ong
            Feb 22, 2019

            Hi Michael, I didn't publish the shot times in the post. But the extraction times were not constant as we lowered the brew pressure. That is a good point that I should have written in the conclusion. The higher extractions could have been a result of slower flow rates and longer contact times instead of a more even extraction.

    • Avatar
      Sherman
      Dec 6, 2018

      This is a flawed series of tests on so many levels and there is absolutely no value that anyone can extract from these results.

      • Avatar
        Kenneth Ong
        Feb 22, 2019

        Hi Sherman, I believe many experiments are flawed. The point of publishing is for peers to review and improve it to the point where it is sufficiently valuable for our audience to make use of the information within their work.

    • Avatar
      Ian
      Dec 8, 2018

      The authors clearly gave a disclaimer about the validity of the experiment, at the beginning of their report, and stated that they are prepared to receive criticism aimed at improving the methodology and validity of the results.That having been said, and without any comment on the methodology, I am not aware that there is a direct correlation between higher TDS and greater espresso quality. The most significant deficiency in the experiment is that there was no tasting component (which they admit is subjective, but that is the nature of all taste related experiences). I am not concerned about the TDS if the flavor at 9 bar is better than the flavor at 6 or 7 bar. A previous experiment about ‘DIstribution’, with a link on this page, mentions that, of all of the soluble components in ground coffee, only about 2/3 is desirable. If I understand this statement, which is unreferenced, higher TDS may, in fact, produce a less desirable coffee. Without being able to correlate TDS with flavor, the experiment has little value, regardless of the quality of the results. Why adjust your brew pressure to 6 bar, if it could result in an unpleasantly bitter, over-extracted brew? If, however, this page results in productive discussion, there may be value there.

      • Avatar
        Kenneth Ong
        Feb 22, 2019

        Hi Ian, thank you for your comment! There are many valid points raised. I think the takeaway from the experiment should be the higher consistency with lower brewing pressures. That alone should be a sufficient reason to reduce brewing pressures to 6 bars instead of the default 9 most machines come with.You are correct to say that higher TDS is pointless without a correlation to the taste component. The coffee was not over-extracted at the higher percentages but was instead more flavourful and sweeter. This would be another reason to lower your brewing pressure, but due to the subjectivity of the comment, It is not something we can put in the conclusion. For future experiments we might begin including it a part of a subjective discussion section.

    • Avatar
      William Sette
      Mar 25, 2019

      I brew in my espresso machine single estate coffee's from the best roasters in the US. It is shipped within 1 day of roasting and I get the coffee three or four days after roasting. I use the coffee only for three weeks and then discard it.I have found that 7 to 8 bars of pressure give me the best crema and the best flavor profiles from any and all coffees. It took me an entire year to come to this conclusion.

    • Avatar
      Pete
      Jul 1, 2019

      I'd be a little cautious on distinguishing the difference between pressure and flow as it relates to coffee extraction. Slayer already plays it a little fast and loose with that, using analogies that simply don't work.

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