Water Activity in Specialty Green Coffee

A Long Term Observational Study by Ian Fretheim

Since 2012, Cafe Imports’ sensory analysis team has been collecting water activity (Aw) data on every coffee sample that crosses their cupping table, logging the results in a massive database that has now topped 25,000 samples. After noticing that water activity is one of the most-discussed but least-understood variables in specialty coffee at the moment, sensory analysis director Ian Fretheim decided to put the numbers collected through rigorous evaluation, to see if he and U.S. sensory lab manager Megan Person could arrive at any definitive conclusions about the role of water activity in specialty green coffee. This paper is the result of that long-term study.

There are two relevant measures discussed and compared throughout the paper presented here, and it is helpful to briefly understand them both before diving in: moisture content (MC) and water activity (Aw). Moisture content is measured in percentage (%), and is the amount of water in a system. Water activity (Aw) is a reading that states the energy status of the water in a system. Think of a pot of fresh water and a pot of saltwater side-by-side on a stove: The amount of water in the pots is the moisture content, and the energy it takes for each to boil relates to its water activity.

Other reports in specialty coffee have drawn direct correlation between Aw and coffee shelf-life stability, which is one of the theories Ian and Megan set out to test against their data. In the meantime, they were able to analyze the numbers for a host of possible contextual frameworks for Aw, and they sought answers as well as standards that could be shared industry-wide. Additionally, thanks to the large collection of readings they already had, Ian and Megan were also able to apply other’s theories to see if they seemed to ring true statistically.

Over the course of a year, Ian worked on the tabulations, evaluation, and composition that comprise this paper. It has been submitted for peer review and vigorously edited, though it remains open for discussion, criticism, contribution, and open-source use. Ian says that one of his hopes is that someone will read this and say, “Oh, you have 25,000 readings? Well, I have 50,000!” The more data available to analyze, the better the analysis can be. (We now have more than 30,000 readings, and continue to collect data to create a robust sample.)

We hope that you find this report insightful and that you appreciate the additional questions it raises about the relevance and usage of water activity as a measure in specialty green coffee.


Ian Fretheim and Cafe Imports would like to thank:

Paul Songer of Songer and Associates in Colorado for his immeasurable help in making the scientific underpinning of water activity more understandable.

Michael Beermann at Sci-Fi Food in Norway for reviewing an early draft and making such insightful suggestions for areas that needed clarification and improvement.

Shawn Steiman, PhD at Daylight Mind and Coffea Consulting in Hawaii for encouraging Ian to take a scientific attitude during the writing process, making the time to review the paper, and offering valuable questions and suggestions.

Ever MeisterCafe Imports’ resident copyediting nerd, for painstakingly dotting I’s and crossing T’s and for making sure Ian’s leaps of thought were as tied down to the ground as they possibly could be.

Ian Fretheim, Cafe Imports’ Director of Sensory Analysis