Coffee Data Science
Brew Water for Espresso: Introduction to Exploration
You can thank my wife!
When I was asking people for topics, my wife suggested brew water. I said, “No, there is plenty of that out there.” I had already tested Third Wave Water, and I felt like exploring water would be difficult. Water is challenging because how do you determine a good starting point?
Let me help you by sharing what helped me start. I’m far from finished, and there are plenty of things to experiment with. I didn’t want to do another paired comparison; I wanted to build a new recipe. To even explore the space and finding interesting local maximums involves a lot of time and effort.
Water Basics
Plenty of people have written about brew water. Typically, you use distilled water or Reverse Osmosis (RO) water, and you add minerals. In this case, I used the droppers from Lotus to experiment which allowed me to look at four key minerals:
- Sodium
- Potassium
- Calcium
- Magnesium
Brews
Let’s look at some brew recipes of other people in a few ways.
First, we can look at the raw values of parts per million (ppm); then we can look at the percent of the total recipe. Sodium plays a large roles, and most recipes call for Sodium and Potassium to be close to half of the total mineral content.
Droppers
To test, I needed to use the droppers. This requires data because I want to know how common it is for a drop to have a consistent weight.
I used each dropper and I found a distribution of drop weights. After the initial data collection, Nick at Lotus suggested holding the dropper at a 45 degree angle to improve consistency, and this helped, but there was still a distribution.
I know drops are easier to count, and I am aware a few drops into water is difficult to measure without an accurate scale. I suppose these recipes could be modified for weight instead of drops because the drop assumes a certain weight or average weight.
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
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).
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.
Initial Data
My first tests were to use 1 drop of each in a shot of espresso. The espresso was at close to the same strength for each shot, and I would not recommend ingesting so many minerals in such a short time period. However, this test helped me taste very clearly what each mineral was doing. I found out that I love potassium.
Then I looked a total taste scores over these individual drops and a mix. I made the mix with some rough assumptions from the first test. The mix was then diluted a few times until I felt it was at peak taste.
Here is the ppm of the mix. I was surprised at how little was being added to the shot and how much effect it had on taste.
I used this 1/8 mix as my added minerals and pulled 10 paired shots using a few roasts.
The TDS/EY/IR were all similar, but taste was not. Adding minerals seemed to improve taste. I measured TDS before adding minerals.
This addition improved taste overall as well.
The taste improvements overall were not statistically meaningful except for Sour and the average score. More data is needed.
My investigation into brew water is just beginning. I have gotten side tracked a few times, but at least I can say the lesson is to experiment and see what tastes best for you.
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