Coffee Data Science
Ultrasonic Mixing for Espresso: Reducing Bitterness and Acidity
Post-shot coffee treatment
A little over a month ago, I saw a video talking about a routine at WBC using vibration waves to improve the coffee. Jack Simpson competed for Austria using this post-shot technique with claims of improving flavor. I dug into this a bit; there was more talk about using ultrasonics to improve cold brew, which has been done using the Osma system a few years ago.
Could there be a simple post-shot espresso improvement using ultrasonics?
Answer: Yes, shockingly so.
Ultrasonic mixing post-shot is not new. 10 years ago, these tests were done with a more powerful ultrasonic tool. So I explored using a cheaper tool to do something similar.
Ultrasonic Tool
The Waved Tech out of Singapore used by Jack Simpson has not been released yet, so I don’t know how it works just yet. However, I can buy a cheap ultrasonic tool to test. I bought this beer foamer for $20 on Amazon Here is the link, but the one pictured here doesn’t seem to be available anymore (not an affiliate link). I suspect any type of ultrasonic drink mixer will work.
I had difficulty determing if the tool was working unless I put just a few drops of water on it. I found I needed to use it in the cup for about 20 seconds to gain taste benefits. So I collected a bunch of data.
Tasting Equipment/Technique
Espresso Machine: Decent Espresso Machine, Thermal Pre-infusion
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Pre-infusion: Long, ~25 seconds, 30 second ramp bloom, 0.5 ml/s flow during infusion
Filter Basket: 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).
Shots
I pulled 37 paired shots. I wanted to extend testing across a few variants. In almost all cases, taste improved. In particular, sourness and bitterness were greatly reduced. The mouthfeel also became more like velvet.
TDS and EY were about equal for all the shots so there was not a bias from the strength of the shot.
Looking at Taste vs EY, there wasn’t a clear trend either.
I separated taste by bean origin. I would have liked to do more, but I didn’t have enough variety. I had beans from two farms for Guatemala and two from Ethiopa. I tried on some dark roasts, and I was surprised that ultrasonic mixing made darker roasts almost drinkable.
I’m tempted to try ultrasonic mixing on Starbucks coffee.
Ultrasonic mixing affected all the individual taste metrics by a large margin compared to many improvements I have tested.
From a statistical standpoint, all the taste metrics had a statistically significant difference using a two-tailed paired t-test.
This study was so enlightening. Aside from extract cooling, I didn’t think a post-shot method could improve taste so much. I’m excited to see how the Waved technology also changes flavor. I’m particularly interesting in roasting coffee a bit darker and using ultrasonics to bring up the taste scores.
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.
Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
