Coffee Data Science

Espresso Experiments with Added Farts

CO2 from baking soda to better understand gas interactions in coffee extraction

Robert McKeon Aloe
3 min readMay 16, 2023

Espresso extraction is inhibited by two factors: gas and solubles. To better understand espresso, I have been testing some coffee that is 3 to 6 months old, and it doesn’t have much CO2 remaining from roasting. This allows me to test the impacts of gas by adding my own in the form of baking soda, which will let off CO2 when in contact with water.

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Baking soda breaks up into three components in solution. This allows for me to control the amount of CO2 released during extraction. From here, I wonder if CO2 can slowdown extraction throughout the shot.

I did this testing using salami shots on the Decent Espresso machine. A salami shot can be used to measure extraction as well as better understand when different taste components are extracted into the cup.

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).


The amount of CO2 released during the shot is roughly the same as 0.1g of baking soda added. I added a few variants, and the extraction yield went up.

However, baking soda adds sodium (Na) to the water, and this causes a change in the refractive index. I did a short to test to see how much that would be.

Then I added 1.04g of salt which is the equivalent for 6g of baking soda. A slight mistake, but it causes a bump up. This shows adding baking soda does have an impact of extraction yield that isn’t simply from modifying liquid sample to read higher on the refractometer.

There was a big impact on time because more baking soda slowed down the shot which most likely impact extraction. This could be done similarly with slower flow.

Here are some of the videos just for the visual:

These experiments were interesting, and they helped motivate me to slow my shots down even more. Adding 1g of baking soda is impractical from a taste standpoint, but adding 0.1g is much more reasonable and only added 0.018g of salt. One pinch of salt is typically 0.30g for reference.

More testing is needed!

If you like, follow me on Twitter, YouTube, and Instagram where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn. You can also follow me on Medium and Subscribe.

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.