Coffee Data Science
Experimental Coffee Roasts on the Roest
Nano batch experiments
I borrowed a Roest from Sweet Maria’s for a month, and I ran quite a few experiments. My friend Hiver at Chromatic Coffee gave me some green coffee to test, and I was off to the races. The key factor in these tests is that the Roest can do very repeatable tests, so I can modify variables with some confidence.
I wanted to explore:
- Profile development time (First crack + 1 minute or 2)
- Slow or fast rate of heat input
- Steaming beans for 1 minute before roasting
- Roasting by using bean temperature instead of air temperature.
The Roest gives a lot of data:
It also detects the first crack which is helpful in counting the number of cracks.
I did 100g roasts for all of these experiments.
Steamed Beans?
Previously, people have found that there is an optimal moisture content for green beans to have (usually aimed for 16%). For fun, I tried steaming the green beans in an instant pot for 1 minute, and then roasting those beans. I was curious if you could add moisture faster to coffee before roasting.
Post-roast processing
After each roast, I would add 4% water to simulate humidified coffee. Then I would let the coffee rest for one day before being put into a vacuum chamber for another 6 days. This allowed me to degas the coffee beans very quickly.
Equipment/Technique
Espresso Machine: Decent Espresso Machine, Pump & Dump Profile
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
Pre-infusion: Thermal Pre-infusion, Blooming Ramp
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).
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.
Experiments
I pulled a single shot for each roast. I didn’t have time to pull more shots, and I wanted to see what a single shot told me.
This is the overall data, but there’s too much, so I will break it down.
Again, there is too much data on extraction, so let’s eat the elephant in bite sizes.
Roast Development
I clearly don’t prefer roasting more than 1 minute past the first crack (FC).
I wonder if part of the reason has to do with lower extraction yield.
Roast Speed
This was the speed at which the coffee hit the target temperature. I thought slow would have been much better or that I would have seen a bigger gap, but I didn’t.
In terms of extraction, they all pulled similarly.
Odds and Ends
I looked at doing a much slower roast at double the time as previous (FC+1 Slow Special), but it didn’t taste as good. It might have been baked.
The steamed coffee was surprisingly good.
Not much could be said about extraction numbers though.
We can pull some other numbers to look at steamed data. The steamed roast went to FC+2 because it didn’t look right at FC+1. This is typical for high moisture coffee and robustas in my roasting experience.
In this case, the extraction rate was higher.
These experiments were the tip of the iceberg. I plan to explore more in the realm of roasting, which requires some fun designs of experiment. None of these results should be taken with anything but a grain of coffee. They are definitely feasibility experiments, and the main experiment I would try again is steaming coffee.
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