Coffee Data Science
Modifying the Single Espresso Basket
Adding a spring and a metal screen
Espresso pucks expand during a shot, but at the same time, they lose coffee mass due to extraction. So they lose density throughout the shot that is replaced by water. I was curious if a spring could be used to hold a puck screen at a certain depth or maybe even compress the puck to maintain the same density.
So far, those experiments haven’t performed well because they cause a higher tamp pressure at the beginning. New hardware would be needed to reduce headspace as the shot progressed via a mechanical mechanism rather than water. I first saw this possibility with the Flair even though it was not by design.
However, I saw an opportunity in single baskets for a spring. One of the issues I have had with the single basket (7g) is that there is too much headspace. Typically, the coffee will come out of the depressed area of the basket. The only way to compensate is to fill the basket to almost 14g.
Theory: if you better contain the grounds in a single basket using a spring, the shot would perform better.
Spring Setup
I used a shower screen to sit on top, and I put a spring on top to keep the grounds contained. The spring is from the Happy Tamper as it was the right size and tension.
After the shot, the coffee stayed inside regular basket area.
However, the taste and extraction metrics showed little impact.
Equipment/Technique
Espresso Machine: Decent Espresso Machine
Coffee Grinder: Niche Zero
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
Pre-infusion: Long, ~25 seconds
Infusion: Pressure Pulsing
Filter Basket: 7g VST
Other Equipment: Atago TDS Meter, Acaia Pyxis Scale
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).
Using a spring makes for a cleaner shot, but it doesn’t help with the fundamental issues. This short experiment has me rethinking headspace considering this experiment showed headspace didn’t impact the shot like I thought it should have.
I also realize that I’m not into drinking single shots like I used to be.
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