Coffee Data Science
Advanced Shower Screens for Espresso
Modifying shower screens to better improve water input
In the past few months, my focus in espresso has been water input. I have wondered how much of side channeling is simply coming from water input. So I started experimenting with aluminum foil, and I was quickly impressed. In this article, I will discuss the experiments I tried and what I settled on for changing the water input design given that it is a radical departure from all shower screen designs.
The first experiment I started with was simply to restrict the water flow to the center to see what would happen, and then I dove down the rabbit hole.
The first iteration ripped on one wide which caused a particular channel but not side channeling. So I tried again, and the result was better. I fit the tin foil on the basket and used the tamper to get it into shape.
Then I tried a few variants based on my experience with paper filters.
The star shape didn’t work well, but the circle did. Cutting aluminum foil is challenging. I used a sewing pin to poke holes and move around a circle.
I tried using shapes to give me a good outline.
However, tin foil is generally fragile so I need to get the heavy duty kind.
Decent Espresso Machine
So I thought I could put this design into the shower screen for the Decent Espresso machine given the previous issues I have found.
This worked, and I tried to put something to counteract any backflush issues.
However, I had trouble with this tinfoil.
I found through trial and error that the bottom of a medicine cup helped to cut the tin foil into shape.
I then started shifting this opening to counteract the water dispenser issue.
Before this change, I had made a divot in my pucks to lessen side channeling. This change allowed me to go to a flat distribution, and my extraction yield has greatly improved. I also do not have to use a paper star on top, so this change has eliminated two variables of my process routine.
Let’s look at some data.
Some of the baseline data was taken before the Pump & Dump profile. This profile has continued to be iterated on during these experiments, so there is some bias. I was not interested in investigating each separately as this new design allowed for the Pump & Dump profile to be more deterministic in testing.
Equipment/Technique
Espresso Machine: Decent Espresso Machine, Pump & Dump Profile
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
Pre-infusion: Long, ~25 seconds
Filter Basket: Unifilter, 20 Wafo Spirit
Other Equipment: Acaia Pyxis Scale, DiFluid R2 TDS Meter
Metrics of Performance
I used two sets of metrics for evaluating the differences between techniques: Final Score and Coffee Extraction.
Final score is the average of a scorecard of 7 metrics (Sharp, Rich, Syrup, Sweet, Sour, Bitter, and Aftertaste). These scores were subjective, of course, but they were calibrated to my tastes and helped me improve my shots. There is some variation in the scores. My aim was to be consistent for each metric, but some times the granularity was difficult.
Total Dissolved Solids (TDS) is measured using a refractometer, and this number combined with the output weight of the shot and the input weight of the coffee is used to determine the percentage of coffee extracted into the cup, called Extraction Yield (EY).
Intensity Radius (IR) is defined as the radius from the origin on a control chart for TDS vs EY, so IR = sqrt( TDS² + EY²). This metric helps normalize shot performance across output yield or brew ratio.
Data
Due to the work on the profiles, I haven’t taken paired data. So instead, I looked at a higher level: how are my shots are doing as a population? The “Al Shower Ring” (Al for Aluminum) proved to work as well as a paper star on top, but without the extra steps including puck preparation.
Taste has also improved. The lower numbers of taste on this chart are robustas, but as extraction goes up for robusta, I have ended up with scores in a similar range as arabica roasts.
Current Use
More work is necessary, and I’m trying to understand how long these aluminum pieces last. Currently, I use a double layer for the Decent because as water is backflushed during my Pump & Dump profile or at the end of the shot, it puts stress on the tinfoil to the right side which is closest to the exit hole.
I am now experimenting with a single layer of heavy duty aluminum foil on both my Decent and Kim Express machines.
I think shower screens are too wide. I think narrower shower screens will generalize to many more machines. So far, this improvement has worked on the Decent Espresso, la Pavoni, and the Kim Express. Using tin foil is only a prototyping step in hopes that someone like IMS comes out with a shower screen with this design in mind.
From a patent perspective, I could certainly patent this idea, and I did work through this development and invention. However, I would rather it be open to the world to use for all to improve their espresso shots. This improvement brings me closer to my ultimate goal of higher extraction in a smaller output ratio.
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