Coffee Data Science
Humidified Roasted Robusta Coffee
Applying arabica techniques to robusta
Previously, I have explored using humidity to degas coffee faster which has allowed for drinking coffee sooner and retaining more flavor. The key concept was that coffee loses flavor over time, but good espresso extraction is inhibited by CO2. As the coffee degasses, you can extract espresso more efficiently, but you lose some flavor.
My previous study was on arabica beans only. As part of my continued efforts to collect some data on robusta, I explored the effects on robusta. Robusta has a lot of potential for improvement by applying modern techniques from arabica. However, there is even less data on robusta than arabica.
For this small study, I used a single roast, split into two jars. One jar had a humidity bag in it for five days. This process added 3.8% water to the coffee beans. I started using the humidifixed beans before the control. I wanted the best comparison, so I waited to use the control beans for an extra week.
Equipment/Technique
Espresso Machine: Decent Espresso Machine
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
Pre-infusion: Long, ~25 seconds
Infusion: Pressure Pulsing
Filter Basket: 20g VST
Other Equipment: Atago TDS Meter, Acaia Pyxis Scale
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.
Data
I compared the average taste score, and humidity improved everything but sweetness. Robusta doesn’t have too much sweetness compared to arabica.
I plot the scores for the shots over time:
In terms of average TDS/EY/IR, humidifying coffee makes a huge difference.
There was some odd points that could potential be outliers when looking at the points compared to coffee age.
A scatter plot for TDS/EY/IR shows a general trend, but there isn’t enough data.
So far, the humidified robusta data shows a similar improvement as humidifying arabica beans had. I don’t want to assume robusta performs similarly in every aspect as arabica, and the only way to test that theory is to collect some data across a range of variables.
This test is a short experiment to suggest evidence for a broader theory, not to be the definitive statement on humidifying robusta.
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