Coffee Data Science

The Elusive Donut in Espresso Shot

Chasing a dream

Robert McKeon Aloe
2 min readMay 23, 2023


I recently added baking soda to understand how CO2 impacted coffee extraction, and then I kept adding more because why not? I thought the videos were interesting though because they gave evidence to where some unevenness lies in my espresso extraction.

The bubbles came out of the puck before the water, so the pattern was a bit clearer especially during the bloom phase of the profile. This allowed the water to sit for a few seconds, and water slowly came out.

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Here are a few images from this shot that used baking soda, around 1 gram. It led to beautiful striping, but I could also see the donut.

However, in the past, the donut didn’t have any coffee coming out in the center. This confirms my suspicion after my shower screen modifications. I still thought I saw some evidence that water flowed faster on the sides and in the middle than that ring in between the center and side is clear.

I made a visualization of how I thought water was flowing based on watching dozens of shots. I think a restricted shower screen can help the coffee start coming out of the center, but there is still places half way between the center and the side that are slower.

This experiment makes me want to try modeling flow again based on density to experiment with restricted shower screens.

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Further readings of mine:

My Future Book

My Links

Collection of Espresso Articles

A Collection of Work and School Stories



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.