Coffee Data Science
Unifilter vs Wafo Spirit for Espresso
Exploring advanced filter baskets
I originally was not going to get the Unifilter. When it came out, I knew the Wafo was also coming soon, and I didn’t want to continuously buy the latest and greatest. So I did a comparison of the Wafo Spirit compared to the Unifilter in the same way that I did a comparison to the VST.
This comparison used the same profile, and the aim was to control shot ratio and all other variables. The one challenge is that the Unifilter needed 1 gram more of coffee because the basket is just a little bigger. So to get to the optimal extraction for the Unifilter, the dose was higher for all but the first 3 shots.
Just to note, I warmed up the Unifilter with a rinse before each shot, but I typically don’t warm up the Wafo basket. I was worried the direct contact of the large body of metal would have an impact on the basket. I haven’t studied it with an thermal camera, but that would be an interesting exploration.
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, Pump & Dump Profile
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
With respect to taste, the Unifilter could only achieve the same taste.
I broke this down by roast, but I didn’t see a particular pattern.
For TDS/EY, the Unifilter under-performed WAFO.
I expanded this to include Intensity Radius (IR), and the results were the same.
I broke down the individual taste scores and averages:
According to the statistical analysis of this data, the difference in performance is statistically significant, but the sample size is small (N = 11). I didn’t run a larger sample size because the difference was large enough for the time being.
After correcting the basket weight for the Unifilter to make optimal performance, I thought the performance would be closer. The Unifilter felt heavy, and it was well made.
Another challenge: cleaning the basket. The Unifilter is much more difficult to clean in part because of the straight walls. I was able to improve this experience a little by running a rinse through the puck before knocking it out. I had a lot of struggle with cleaning.
I am also aware that the Unifilter was designed with a paper filter on the bottom of filter, and I didn’t use paper filters.
Other Data: I’m excited to see how both of these filter baskets work on other profiles and machines. I’m fully aware that my profile is optimized for my machine and workflow, and it quite possible that the Unifilter is better than the Wafo Spirit under certain conditions and not others.
If you like, follow me on Twitter, YouTube, and Instagram where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn. You can also follow me on Medium and Subscribe.
