Coffee Data Science

Shredded Cloth Filters in Espresso

An experiment to understand cloth filters

Published in

Towards Data Science

4 min readJan 21, 2022

Previously, I found cloth filters speed up coffee flow by putting one at the bottom or the middle of the espresso puck. I decided to make a crazy experiment. What if I cut a cloth filter into small pieces and mix it into the puck?

Let’s find out!

I cut it up, wet the pieces, and dried them a little to insure they were damp but not soaked.

Then I mixed them into the coffee.

Equipment/Technique

Espresso Machine: Kim Express

Coffee Grinder: Niche Zero

Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)

Shot Preparation: Staccato Tamping

Pre-infusion: Long

Infusion: Pressure Pulsing

Filter Basket: 20g VST

Other Equipment: Atago TDS Meter, Acaia Pyxis Scale

Results

The shot certainly came out strange with some major channeling.

From the bottom of the puck, the pattern was definitely indicative of slow flow and channeling.

Left: Cloth in the middle of the puck. Right: Shredded cloth throughout the puck.

Looking from the side, the puck is a bit fragile.

Metrics of Performance

I use two 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).

Shot Performance

For comparison, I pulled a shot without a cloth, one with shredded cloth, and one with cloth in the middle. There wasn’t much difference in taste, but EY was higher for cloth in the middle as the flow was better. The roast was two weeks old, so I could have waited another week.

All three shots had similar shot times, which was tied to the age of the roast because I had to do a long pre-infusion time.

The initial thought behind this experiment was to improve the process of using cloth filters. Cloth filters are the best addition to improve espresso shots, but they are difficult to manage over time. The first two shots with a cloth filter aren’t the best, but the next few shots are better. But the filter starts to shrink, which causes more donuting from side-channeling. If you could add shredded bits of cloth, maybe you could still reap the advantages of cloth more consistently. Maybe there is also a better way to do this than how I did it.

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