Coffee Data Science

The Many Ways to Add Water to Coffee Beans

More espresso explorations

Robert McKeon Aloe


Previously, I found moisture to be key for roasted coffee, especially for speeding up degassing. When I started, I used humidity bags, and for the past year, I have added water by weight. Typically, I aim to add 4% moisture to the beans. I explored a few ways to add water to search for potential taste improvements.

I added water four ways:

  1. Baseline: adding 4% moisture
  2. Using a Sous-vide with water below and the beans in a dish on top to slowly absorb water from a nearly 100% humidity environment.
  3. Steaming green beans using an instant pot
  4. Steaming roasted beans using an instant pot.

The last variant proved to be very challenging, and it was easy to add 10% moisture by waiting just 1 minute too long. This is far too much to be able to grind well.


I used Scott Rao’s roast profile that uses bean temperature as turning points for inlet temperature on the Roest.

I used a Colombia coffee and a Burundi coffee.

Tasting Equipment/Technique

Espresso Machine: Decent Espresso Machine, Thermal Pre-infusion

Coffee Grinder: Zerno

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).

Shot Data

I had only a few shots per variant, so these results are by no means conclusive.

For the Colombia coffee, the steamed beans had a taste improvement, but the other two tasted similar.

The results were similar for Burundi.

I had a few other variants, but only steamed green beans saw something interesting.

For extraction yield, I didn’t see particular issues.

There was some variances, but not so much I would connect it to differences in taste.

The same was true for the other roasts.

This dataset was interesting because it suggests there is not a more optimal way to add moisture to coffee aside from simply adding in the desired amount of water and mixing. The extra benefit is that RDT is not necessary because the beans have enough moisture.

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

My Links

Collection of Espresso Articles

A Collection of Work and School Stories



Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.