Coffee Data Science
Shower Screen Deep Dive on a Decent Espresso Machine
Stripping down the shower screen
I found renewed interest in the shower screen in my espresso machine, the Decent Espresso machine. This piece of the espresso machine is not talked about much. The shower screen does control the water input to the puck, so it is probably as important as the filter basket. I look a deep look on how it worked to better understand why I was seeing some strange results in my experimental profile. I started with visual data where I saw one-sided behavior, so then I expanded data collection to better understand how the water flow was distributed along the puck. The visual data and flow data have an odd mis-match during analysis, but clearly the input water has a slight unevenness.
Let’s start with a top filter screen. I was using one for awhile, and the main benefit was keeping the shower screen cleaner. I didn’t pay much attention to deep cleaning it, but I would flip it between shots. I accidentally didn’t use it one day, and I saw a big improvement for my steam pre-infusion profile. So I cleaned the metal mesh, and I found less than 0.01g of stuff stuck in there from a simple cleaning. I tried not using the metal mesh for awhile too.
However, I noticed my new profile kept having the same channeling to the left side. Not just a few shots, but every shot exhibited this behavior.
So I pulled off the shower screen to look under the hood. I also removed the water dispersion screen. The water holes are only on the outer ring. I noticed water came out of one side slightly faster than the other. This could explain what I was seeing in the shots.
The Decent Espresso machine has water enter a dispersion screen then go to an IMS shower screen.
I wanted better information about the shot because maybe this was just happening at the beginning of the shot and not the root cause.
More Data Spatially
So I pulled out my mini ice-cube tray, and I measured.
I measured the water for the raw piece above the dispersion screen, then the dispersion screen or dispenser, and finally the shower screen. This could tell me where their water was coming in from. I was surprised to find the water did not come in as even as I would have thought.
Things got better with the dispersion screen, but there was still a donut caused by higher flow on the outside.
Things sort of improved for the shower screen, but it was the right side that had a higher water volume.
This makes me think there is far more work to understanding shower screens at each unit level, and there is a great opportunity to improve espresso shots. I am sure part of why some espresso profiles work better than others is because they compensate for the deficiencies in the shower screen design. So I believe a better design will also improve profile design.
There is one part that still lacks good explaination. Based on the data, the right side of the shower screen has higher flow, but in the shot examples above, the left side comes out faster. I’m not sure why this happens, and the machine is level. I have more data coming to show that the internal extraction tracks with higher flow on the left side. I have adjusted my profile and puck preparation to account for this odd flow, but I wish I had a better answer.
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