Coffee Data Science

Do Fines Clog the Filter in Espresso?

Gas Contributions to Espresso Shots

Robert McKeon Aloe
2 min readMay 30


When discussing coffee extraction and any particle migration that may occur, there is often this question of coffee grounds clogging the filter screen. I wanted to better answer that question using spent coffee, a sifter, and some baking soda.

I sifted some spent coffee, and I made a staccato shot with and without baking soda. Baking soda should simulate gas released during coffee extraction, and the spent coffee removes solubles from the list of variables. Then we can focus on flow rate.

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Adding baking soda did slow the flow. Adding baking soda on top didn’t change flow.

We can look at different doses with baking soda, and the flow was slowed for 22g, but that is conflated with headspace.

I tried pulling a spent staccato shot and then adding baking soda on top of the puck afterwards. I pulled it again, but the flow went straight through.

So I pulled a fresh spent staccato shot, and I added 1g of baking soda. This greatly slowed the flow.

If fines clog the filter, then they should slow down the shot to a stop, but the only way I could slow down the shot was adding far more baking soda (1 gram) than would produce the amount of CO2 released from coffee (< 0.1 grams of baking soda). This is particularly true when pushing more water through a spent puck.

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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.