Coffee Data Science
Total Dissolved Solids Meter Compared to Groundtruth in Coffee
Discovering the breadth of unknowns
I have been measuring Total Dissolved Solids (TDS) in espresso for a few years using a refractometer. I was always curious how accurate the TDS measurement was to the groundtruth. There isn’t much publicly available information, so I decided to collect some.
I used espresso powder as a groundtruth. Espresso powder is made by dehydrating espresso until you are left with just the dissolved solids. The espresso powder I had clumped together a little bit so I had to break it up.
Here is the protocol I followed:
- Break up some espresso powder and measure with a scale
- Add hot water and weigh with the scale (aim for a certain TDS)
- Measure the TDS with three samples
- Use the median sample
The samples themselves were very stable. Typically, when measuring TDS from coffee, the TDS can have some noise. None of these samples were filtered. However, the variance was very low as if they had been filtered.
I purposely collected samples with an aim for a specific TDS. When collecting a few samples at the same TDS, the results were similar. A best fit line shows a slight error in measurement, but the R² value is high. If we use the TDS measurement, then the groundtruth measurement is slightly higher with a very strong linear correlation.
These results were very interesting to me because the error grows in absolute size. A sample measured at 15% TDS could actually be closer to 17%. This would seem to suggest my extraction yields are even higher than I previously thought. The difference could also be attributed to not all of the espresso powder dissolving in solution. This is one experiment amongst many to understand a took that I think is still wonderful and important to coffee.
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:
Collection of Espresso Articles
