Coffee Data Science
Flat, Curved, Smooth, and Rippled Tampers for Espresso
Another look at data of another
Espresso tampers come in a variety of shapes and sizes, but there is not a lot of good data on them. There is some data on tamp pressure for flat tampers, but some of the new tampers have changed style significantly. The two biggest differences are curved bottoms and rippled surfaces.
Lance Hedrick collected some data on these tampers and shared the data publicly, and as I love data, I pulled the data to put it in some scatter plots.
Definitions
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). Typically, one aims for 18% to 22% extraction or some times higher, but it is difficult to get more than 30% EY.
Data
Lance compared 5 tampers, and more specifically, he used 1 tamper with 4 interchangeable bottoms to help control the variable.
I took this data, and I sorted the samples by EY performance to compare the best to the best of all 5 samples. The samples were not collected in a way where pairing them in such a manner adds any variation to them.
The flat tamper or flat rippled seemed to perform similar to the Decent Tamper as a baseline.
Let’s compare curved tampers and flat tampers directly using this data. There is a clear performance gap, which was suggested to be caused by side channeling. I would have expected such performance, but I am curious how thermal pre-infusion would play into this variable.
The overall difference in the 10 pairs (smooth and rippled combined) is statistically different (P-value 0.00000003).
Looking at rippled compared to smooth surfaces, the story changes. The two surfaces don’t seem to affect performance suggesting surface structure doesn’t matter.
The ten pairs had a difference that was not statistically significant (p-value of 0.31).
These tests showed the surface structure does not impact the performance for these shots, but the curvature of the tamper does. This is a small dataset, so it is quite possible under other conditions, coffees, or shot profiles, the results could be different.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
