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Coffee Data Science

Symptoms of O-Ring Failure in an Espresso Machine

Oh the joys of lever machines

I recently discovered the O-rings in my beloved Kim Express were going bad. The last symptom of failure is when water comes up through the spring and the top of the machine resulting in a pressure drop and a hot mess of coffee when I pull the lever down, but I would prefer not to get to that point.

This time, I realized I saw some other symptoms that had been going on for a few weeks at least. I take videos of all of my espresso shots for failure analysis, so I was able to go back in time to see these reoccurring symptoms.


  1. Dripping water from the shower screen which slowly increases over time.
  2. Some video evidence with difficult to see symptoms.
  3. Without the portafilter locked in, some steam or water was coming out of the shower screen.
  4. After cleaning shower screen, water dripped more and went up into the spring.

Visual Evidence

I present multiple examples showing an issue in the same spot, which helped me to identify the problem. Had I found it sooner, I could have replaced the O-rings sooner and not suffered from degrading shot quality.

For this shot, on the left size, there is early blonding. I thought this was due to shot preparation or the shower screen, but I suspect now that the O-ring was deficient on that side.

A similar problem of early blonding occurred in this shot as well.

This shows more blonding on the left side.

This shot was high extraction, but there were a few spot of blonding on both sides.

This shot flowed slower, and as a result, the left side blonded much more noticeably.

In Summary

Each of these images played into a better diagnose of a systematic problem.

Data has been very important for improving my espresso shots and to avoid a failure like this one below. I was able to salvage some of this shot with longer pre-infusion and light pressure pulsing, but that is not sustainable.

Hopefully, video evidence could help others diagnose not just bad shot preparation, but also machine maintenance issues.

If you like, follow me on Twitter, YouTube, and Instagram where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn. You can also follow me on Medium and Subscribe.

Further readings of mine:

My Future Book

Collection of Espresso Articles

A Collection of Work and School Stories

Personal Stories and Concerns

LEGO Story Splash Page




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Robert McKeon Aloe

Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.

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