Coffee Data Science
Wafo Soe Spirit vs VST for Espresso
2023 is the year of the espresso basket. So many new baskets have become widely available, and I have been waiting to test some new baskets especially the Wafo Soe Spirit. The Spirit’s design is a striking departure in both the number and shape of holes. So I did a paired test against my VST basket to understand the differences.
Each pair was done with controlled shot parameters in terms of input weight, grind setting, and profile. On average, the output weights were within 0.75g. I randomized the order of the baskets across a few roasts.
I used a new profile on the Decent Espresso machine called the Pump & Dump profile. This profile aims for really high extraction espresso, and it is more complicated than most. My goal for this study is to find the best filter basket, and I encourage anyone with more than one filter to collect their own data on their own profiles and machines.
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
Pre-infusion: Long, ~25 seconds, Pump & Dump Profile
Filter Basket: 20g VST, 20 Wafo Spirit
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.
I originally aimed for 30 pairs of shots, but I ended the study after 11 shots because the difference between the two baskets was far larger than I had thought it would be. In both taste and EY, the Wafo was superior for this data set.
This is also true for IR, and there are a few shots on or below the line, the differences for some shots was very dramatic.
Wafo shots tended to run a little bit longer because they took a little bit longer for the filter to cover (Time to Cover Filter (TCF).
In looking at average taste metrics, the Wafo improved across the board.
I added the general statistics with two tailed paired t-tests, and all the values aside from the time metrics were below 0.05 meaning they were statistically significant.
I found the Wafo Spirit outperformed the VST, and this is the first time I have found a performance difference in espresso baskets. My previous tests didn’t show much difference when comparing to Pesado or IMS Superfine.
As a result, I have switched to the Wafo Spirit as my default espresso basket.
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