Coffee Data Science

Ending Pre-infusion based on TCF for Espresso

Explorations in blooming

Robert McKeon Aloe
2 min readMay 26


I have used visual cues to understand when to end pre-infusion for espresso. Visual cues give a lot of information on how espresso extracts. The key cue is Time to Cover the Filter (TCF) which is when the coffee covers the filter.

A typical bloom profile on the Decent Espresso machine goes to the next step based on 4 bars. I decided to try going to the next step (manually) at TCF. I also used a ramp bloom instead of a bloom because I previously found a ramp bloom already extracts more than a bloom.

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When stopping at TCF, the profile looked normal.

Waiting for the 4 Bar Move-on, the shot ended because I had already hit the desired output.

So in some ways, this comparison is not fair, and in some ways, this test speaks more of stopping and doing a bloom than only doing a ramp.

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).

To compare, I did a salami shot to examine how extraction changes over time.

This test showed the importance of a bloom phase, but it didn’t quite test the usefulness of moving on at TCF. It is quite possible the Blooming Ramp would have had higher extraction if it got to the bloom phase. This is part of a bigger story to understand how to optimize each part of the profile.

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Further readings of mine:

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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.