Coffee Data Science

Double Tamp vs Single Tamp for Espresso

Another data set on tamping

Robert McKeon Aloe


Recently, Lance Hedrick explored single vs double tamping in a video. I pulled the data to take a look. Many people tamp more than once, and so do I. I don’t have a good reason to tamp more than once other than feeling confidence in my tamp. This data doesn’t support double tamping being better or worse than single tamping.


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.


40 shot pairs were collected, so I plotted them first as they were collected. They used two different grind settings, so that data is part of the plot.

From a statistical standpoint, a two tailed t-test with even samples gave a -value of 0.27, so from this view, the differences are not statistically significant.

We could also sort all the samples and compare the highest EY for double tamping to the highest EY for single tamping.

The results of a two-tailed paired t-test shows a p-value of 0.31 for all of the data, 0.11 for Setting 2.1 and 0.73 for Setting 2.2, so none of these show a statistically meaningful difference (p-value < 0.05).

One more view is a control chart of TDS vs EY:

These tests were helpful to show double tamping doesn’t hurt performance, and it does not have an improvement on performance either.

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Further readings of mine:

My Second Book: Advanced Espresso

My First Book: Engineering Better Espresso

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Collection of Espresso Articles

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Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.