Coffee Data Science

Coffee Roast Development Across Two Drum RPM’s

More data across test coffee

Robert McKeon Aloe
3 min readMay 3, 2024


Drum speed can impact how the coffee beans heat. I was particularly curious on how this could impact coffee across roast development. So I looked at a three roast levels across two drum RPM speeds.

Roast Profile

I used Scott Rao’s roast profile on the Roest that uses bean temperature as turning points for inlet temperature. This is my baseline profile.

Data During the Roast

For 20 RPM at First Crack (FC), I had made a mistake, so I am not reporting data on it.

I then did FC, FC+1 minute, and FC+2 minutes. Going at slower RPM extends development time.

The Rate of Rise (RoR) are pretty similar for both.

Post-Roast Data Across Development

The main difference seems to be at FC+2 where there is higher weight loss at 65 RPM.

Roast color also showed a darker roast for 65 RPM than for 20 RPM at the FC+2 mark.

Moisture seemed different though because the moisture for 20 RPM was lower at FC+1. Does a slower roast drop bean moisture faster?

Coffee density was a lot lower for the 65 RPM at FC+2, which isn’t too surprising considering it was darker than the rest.

These tests were part of my series using test coffee to get some initial intuition on how different variables impact the roast. I am using these initial tests to drive larger tests with drinkable coffees. As always, I wish I had more data.

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Further readings of mine:

My Second Book: Advanced Espresso

My First Book: Engineering Better Espresso

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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.