Coffee Data Science
Experimental Coffee Cherry Processing
Collecting some data across fermentations
A few months ago, Hiver at Chromatic Coffee gave me some experimental coffees. These coffees were the same coffee cherries but processed in different ways. So I pulled shots over a month, and I compared coffees using espresso. I didn’t know what I was going to find, and I wanted to have some fun.
The Farm
These experiments started at the farm.
The cherries are beautiful.
The processing required tracking temperature and pH as the fermentation progressed.
Hiver sent me these as well, and they are nice photos of the processing involved.
Then there is the finished product.
Coffee Taste Descriptors
Hiver and friends cupped the coffees and added taste descriptors. I pulled them together to see what is common. So on the left is a table of all the descriptors per coffee, and on the right is the sum of common descriptors between rows and columns.
Barolo and Oro have a lot in common. The control has a few things in common, but not much. Then there are the Bourgogne and Champagne that are very different.
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
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
Looking across the taste scores, Lactic acid won out in sourness and bitterness, but Cotez du Rhône was better above all others.
The processing had a slight elevation for Cotez du Rhône and Lactic Acid which may have played into taste.
I looked at how these coffees aged, and Oro had a nice improvement while Intenso seemed a little flatten out.
I sorted the scores to compare the best against the best, and from this view, Cotez du Rhône aged better.
EY over time didn’t seem to increase so much.
These experiments were so much fun. Often, we buy coffee that is washed, natural, or some other processing, but it isn’t easy to tell if the processing impacted the experience. I’m hopeful more farms will do these experiments so we can get a better insight on processing in a more controlled way.
The other thing I would be curious about is the same experiment using a little more development in the roast. These types of fermentations allow for a darker roast without the usual downsides.
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