Nov 29, 2022
Coffee Data Science
Moka Filter in an Espresso Basket
A weird experiment towards a theory
Lately, I have been looking at espresso baskets and the amount of hole openness. I started to think maybe small holes is not good. Precision baskets were designed based on flow rate at a standard pressure and temperature, but that’s not what many people use. In fact, lower pressures and flow rates are the new thing.
So I wanted to test this theory. Part of this theory came from cloth filters. They allowed incredibly fast flow, and I suspected that was due to the filter not impeding flow. However, cloth filters are hard to manage between shrinkage and leftover residue.
How could I test this easily? How about a Moka filter?
I pulled out one of my Moka pots, and I wanted to examine the filter more closely. I noticed it fit well into the basket like a bottom filter. This would have the benefit of larger holes without the potential problems.
I examined how open the Moka filter was, and even though it had fewer holes, it was more open than the CoffeeJack.
So I put it to the test:
The flow looks weird, but remember that the flow comes from one screen on top so it is hard to say if this flow is normal or expected.
The puck afterwards looked relatively normal. There were a few splotches, but overall, it looks like a good extraction.
Equipment/Technique
Espresso Machine: Decent Espresso Machine
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
Pre-infusion: Long, ~25 seconds
Infusion: Pressure Pulsing
Filter Basket: 20g VST
Other Equipment: Atago TDS Meter, Acaia Pyxis Scale
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.
Feasibility Data
This is a tiny amount of data, but if these shots were terrible, it could give direction. It turns out, the shots were about the same in taste and extraction.
I wasn’t sure what to think from this test, but it caused me to question precision baskets more. What comes next is the imprecision basket where I tested this idea out further on a regular basket.
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