Coffee Data Science

Acidity Throughout the Coffee Roast

Academic explorations

Robert McKeon Aloe
3 min readAug 13, 2024

A recent academic paper explored acidity throughout the coffee roast. That means they pulled samples every minute, and then they measured the acidity in each sample. This was quite a bit of data collection. I thought I would re-plot their data.

You can find their article here with their own plots and a bit more data. I wanted to simplify their graphs to see what I could more easily see.

They looked at a few coffees:

  1. Sippi Falls: African washed coffee from Uganda Sipi Falls
  2. Honey: a Central American honey processed coffee from El Salvador Ataco
  3. Sumatra: an Indonesian washed coffee from Sumatra

For each of these, they had three test runs, and I took the average. There was not so much sample variation, and I’m trying to get some intuition.

Fast, Slow, Extended Maillard

They used a few styles of roasts, and we can compare them. For the Fast Start, the acidity pattern didn’t change amongst the three coffees.

The same was true with the Slow Start, but the Sippi Falls matched the Honey a bit more than the Fast Start. What is interesting is that the Slow Start delays the development of acidity.

Sumatra had a higher acidity peak from the Extended Maillard.

So let’s look at each coffee across the three roast variations:

The Extended Maillard seems to widen the window of acidity increase while the Fast Start drops the acidity more steeply than the other two.

Sumatra follows a similar trend.

Sippi Falls also followed this trend.

The extra bonus for Sippi Falls were a few other variations like Production, Medium, Exaggerated Flick, and Negative Rate of Rise. The last one really dropped acidity.

We can then compare Fast Start because that seems to overlap a bit between Exaggerated Flick at the beginning and then Negative Rate of Rise at the end.

This data set took a long time to produce, and my main take away is that acidity can be dialed in by the roast development both in the roast profile curve and the development time. However, the challenge with measuring acidity is that this acidity was titratable acidity. This is a bit more difficult to measure than a simple pH test strip. Maybe one day, more tools for molecular analysis will become available for coffee roasters.

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Further readings of mine:

My Second Book: Advanced Espresso

My First Book: Engineering Better Espresso

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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.