Coffee Data Science

Coffee Grounds Expand with Water

Using grind distributions to understand how water impacts coffee

Robert McKeon Aloe
Towards Data Science

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Previously, I looked at the idea that coffee grounds expand with the addition of water. I used the puck’s shrinking volume to come to this conclusion. However, I had an opportunity to take a closer look by using coffee grounds and grind distribution. I had also looked grind distribution before and after a shot, which the grounds shrink as a result of extraction.

AIl images by author

I first noticed in some data the effects of drying. I had measured the distribution of two samples from a pile of grounds. More specifically, I took a sample from the top and bottom of a dried, spent coffee puck. I then took another sample a day later, and I noticed a shift in both distributions.

This was compelling evidence that coffee grounds had absorbed water, but I wanted more control because I measured two separate samples.

So I took a single sample, and I measured the distribution. Then I let it dry for 12 hours (overnight); my house is pretty dry. The new measurement was of the same sample, and there was a definite shift in distribution.

I measured the distribution for this sample a few times from the start, and there is a definite trend of the particles shrinking.

This shift in distribution is good evidence that coffee absorbs water during extraction causing it to expand as this water dried out from the coffee grounds showing them shrink.

This data also would suggest that potential gaps between coffee grinds would shrink once a shot started, so the primary time for any particles inside the puck to move would be at the very beginning of the shot.

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