Water Activity in Specialty Green Coffee: A Long Term Observational Study by Ian Fretheim

Posted on February 11th, 2019

We know that water is wet, but that fact alone isn’t enough to capture water’s immense power. That power is evident in coffee, not simply in the cup but also in the seeds themselves: Water activity (Aw) is the relative equilibrium that exists (or doesn’t exist) between the vapor pressure inside a food or a coffee seed as compared with the surrounding humidity or environment. In perishable foods, it is a significant measure for the sake of safety and the prevention of food-borne illness, but in coffee, it’s a significant measure…why, exactly?

Starting in 2012, the Cafe Imports sensory analysis department, led by director Ian Fretheim, set out to start collecting and monitoring water activity in green coffee in the hope that “it would provide a more insightful measurement than moisture content, specifically with regard to predicting the shelf life of coffees. We hoped to answer (or at least partially answer) the question of why some coffees arrive as purchased and some do not.”

Ian, along with U.S. sensory lab manager Megan Person, have collected more than 25,000 water activity readings to date, comparing their results against a host of variables and changeable characteristics to attempt to really understand what Aw might indicate or predict, if anything. Over the past 12 months, Ian has been organizing and synthesizing that data into a 42-page report on his findings—though the conclusions are a bit surprising.

(When asked whether the study proved what he expected or whether he was surprised by the results, Ian answered somewhat enigmatically, “Yes.”)

Over the past several years, more and more conversations about water activity have come to the fore in specialty coffee, many relying on small or limited data sets.

“One of the things about this study is that we have a really, really big sample set,” Ian says, which has allowed him and Megan to not only draw their own conclusions, but to also test others’ hypotheses against the information we have in house. “If someone releases something about water activity, we could essentially test it against our data: Does this theory hold up against what we’ve seen? There are examples out there where—it’s understandable—you get a meter, you’re excited about it, you read some stuff and with a sample size of very few [coffees] you say, ‘We’ve seen this.’”

Another aspiration, however, is that the release of this document will tease out more information from others who are doing this type of analysis. “Somewhere in there is also my hope that someone will come along and say, ‘Oh, 25,000 huh? Here’s 50,000!,” Ian laughs. “Now this is the new game. This is the new paradigm.”

Beyond the conclusions this study draws itself or allows its readers to draw, Ian says, “One of my hopes is that it gives a framework for water activity in green coffee, and that a person could read this and decide not to buy a water activity meter based on feeling comfortable that they don’t need it. Another hope is that someone might read it and say, ‘Maybe I should buy a water activity meter, because based on this information I feel comfortable that I need it.’”

While the information is dense and undoubtedly statistical, Ian says, “I don’t think that people need to understand the scientific ins and outs of water activity” in order to read, comprehend, and even apply the information contained within—or to accept the fact that water activity simply isn’t a practical or useful measure for some coffee businesses. “If the baseline is that you don’t really need to be using [water activity monitoring], then you don’t need to have a huge grasp of it.”

To read the report and decide for yourself whether it holds water, click on the downloadable .pdf link below, or visit cafeimports.com/water-activity-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 Meister, Cafe 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.