Coffee Data Science
Third Wave Water vs Filtered Water for Espresso
Do I prefer the water I’m accustomed to or is it better water?
The first time I used Third Wave Water (TWW), I used a general recipe, not the one specific to espresso. I decided to try the espresso blend, and Taylor from TWW sent over a sample. I looked at a set of paired shots across multiple roasts, and I found a decrease in taste but no significant effect on extraction.
The idea behind TWW is that you take distilled water and add in their mineral packet. This allows you to have consistent water good for coffee or espresso regardless of the quality of your local water.
I live in Santa Clara County in California, and I used filtered water from my refrigerator. The caveat of this experiment is that I have been this filtered water for espresso since I’ve been in California eight years ago. So it is quite possible that I am biased, and I encourage people who are interested to do their own study to better understand their tastes.
Another caveat is that I prefer a higher level of salt than most people in my food. When something tasted appropriately salted for me, it seems over salted for others. So everyone’s taste buds are different.
Equipment/Technique
Espresso Machine: Decent Espresso Machine
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped and Staccato
Pre-infusion: Long, ~25 seconds
Infusion: Pressure Pulsing
Filter Basket: 20g VST
Other Equipment: Atago TDS Meter, Acaia Pyxis Scale
Metrics of Performance
I use 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
I had two sets of data using the full packet (TWW 100%) and 89% of the packet (TWW 89%). I had 89% of the packet as leftover water of a previous taste experiment where I cupped one coffee with four concentrations of water.
In total, I had 19 shot pairs over 12 coffee roasts.
In both of these concentrations, TWW was not better than my filtered water. At best, it was close. I also didn’t see a trend going from 89% to 100% that suggested I should consider increasing the concentration of the TWW minerals.
When looking at TDS, EY, and IR, I didn’t see any trend. All the shots were very similar to each other.
So I broke them down by the individual taste metrics, and most had gaps aside from Sour and Bitter.
I aggregated the data from the two sets of data to see the gap, but it didn’t change any conclusion.
I rounded this data out with some statistics. The difference in taste was statistically significant except for the Sour and Bitter notes. There was no statistical significant difference in TDS, EY, and IR, which leads me to suspect that whatever affects the water had on taste were from the water, not what it was able to extract from the coffee.
The difference in taste wasn’t statistically significant for the TWW 89%, so I could try a lower concentration, but I wasn’t interested in pursuing the study further.
In this study, I collected paired data using Third Wave Water compared to filtered tap water. I found that the filtered tap water tasted better, but there wasn’t a difference in the ability to extract coffee. For now, I’m sticking with the filtered water unless the data could say otherwise.
Water seems to be a tricky variable to dial in when our taste buds are so different.
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