Coffee Data Science
Frig vs Freeze for Espresso Beans
Another experiment but sometimes it doesn’t work out
I have found adding moisture to coffee after roasting speeds up degassing and improves flavor. Furthermore, I looked at putting these moisturized beans into a vacuum chamber, which improved flavor and extraction as well. So I went on a tangent to looking at freezer vs frig with a simple theory: freezing coffee after absorbing 4% adding moisture improves extraction and taste because it fractures the bean pores.
However, the data did not support this conclusion. I present this experiment because I think failed experiments still tell us something. It does make me wonder how much moisture would be required to then freeze and crack the cell structures.
For this experiment, I compared storing these jars in the frig, and for the freezer, I put the beans into the freezer after water absorption (~12 hours). Once they were frozen, I took them out and put them into the freezer. Each day, I put both jars into the vacuum chamber to suck out all the gases.
Equipment/Technique
Espresso Machine: Decent Espresso Machine, Thermal Pre-infusion
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
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).
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.
Performance
Taste didn’t have much variation.
This was true even at the individual taste components.
This conclusion is supported by TDS/EY/IR because there wasn’t a clear change on extraction.
Focusing on TDS and EY, there is no trend either positive or negative.
This data suggests freezing coffee even with more moisture doesn’t affect taste or extraction in the short term. This may also be the same for a longer term experiment, but that is more difficult to assess. Current literature suggests freezing coffee does not affect its cell structure, of course without the added moisture.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
