To measure solubility, the best is a digital refractometer. They are expensive. There are cheaper refractometers, but they require more effort to take the measurement. I also experimented with using a calibrated cup. I took a video of a glass cup being filled with water slowly. Then when I pulled a shot, I would compare where the shot was to that video. The difference in weight at that water mark was the amount of coffee dissolved. This method was the least precise.

I settled on a cheaper refractometer which measures Brix. Then use some equations to get interesting data:

TDS = 0.85 * Brix / 100 CoffeeExtracted = TDS * OutputEspressoWeight % Coffee Extracted = CoffeeExtracted / InputCoffeeWeight

From the common knowledge of espresso, a good shot will have extracted 18% to 22% of the coffee. About 30% of a coffee bean is soluble, and you don’t want all the things that can dissolve. The same bean brewed differently will taste different for better or worse. This is why many people brewing espresso take extreme care to control grind size, temperature, pressure, extraction times, and extraction volume.

However, the information out there uses only a single point of data, which is the TDS measured at the end of the shot. Typically, the shot is a 3:1 shot. As a data scientist, I wanted to go beyond this. I wanted to understand what was going on within the shot.

I decided on two initial experiments:

Measure TDS at multiple points during extraction to see how it develops. Measure TDS for a 1:1 and 3:1 shot on a regular basis for every shot I pull. What I call the first part (1:1) and measuring the second part which if combined with the first part will give a 3:1 shot.

Experiment #1: Solubles throughout the shot

How does one collect solubility over time? An ice cube tray or a lot of cups. My first few attempts were with an ice cube tray. The difficulty was measuring the weight of the liquid for each cube.