At each stage of the coffee supply chain, the moisture content of a green bean must diminish – or the bean might become moldy, defective, and less valuable than before. Ensuring a bean dries correctly is essential in order to optimize its quality potential and minimize the chance of problems.
Roasters, near the end of the supply chain, have two tasks when it comes to managing moisture content. On the one hand, they must maintain the lots they store onsite within a narrow moisture range that is acceptable to their quality standards. They need to hold their coffee in this range for a period that will, hopefully, not be longer than a year.
On the other hand, and in the span of a few minutes, the roaster is responsible for driving the last remaining bits of moisture out of the bean via the application of intense heat and pressure. In these minutes, the coffee is exposed to the most energy it will experience at any point in the coffee supply chain and the roast is set up for either success or failure.
It’s easy to see why roasters should care about the moisture content of their coffee. But how useful is a number supplied by an importer, and how can roasters integrate moisture content readings into their craft? I spoke with Fred Seeber of Shore Measuring Systems, a supplier of moisture content meters, about measuring and making sense of moisture content in green coffee.
What Is The “Ideal” Moisture Content?
There is no official standard for ideal moisture content in green coffee, although the ICO recommends 11% as a good target. However, it’s commonly accepted that 10-12% is a reasonable range. Anything less than 10% is likely to result in loss of cup quality, while humidity at higher levels begins to create a risk of mold growth.
Yet a coffee’s humidity is not static. While the pre-export drying process drastically increases a bean’s stability, changes in moisture content are still possible. Environmental factors, such as being in a particularly humid or hot location, are a common cause of this.
Measuring Moisture Content: Is It Really Necessary?
Before getting into the technical details of measuring moisture content, it’s worth digging a little deeper into why it’s worth measuring moisture content. Knowing this will help you establish protocols suited to your specific needs.
For roasters of a certain scale, it’s simple: you pay for coffee by weight; the more water in that coffee, the more you’ve paid for water which you’re going to burn off anyway.
Fred describes a common situation roasters find themselves in: “So, [an importer] sends you a sample, and… it’s showing 11.5% moisture in that sample. Then when your container shows up, that’s 40,000 pounds, and all of the sudden you discover it could be 13% moisture. Well, you just got blanked for two percentage points of water of a commodity that’s four bucks a pound… that’s [a lot] of money.”
For the smaller, quality-focused roaster, those kinds of calculations may or may not be relevant. But moisture content still plays an indirect role in a roaster’s costs, regardless of whether or not they’re buying a few containers or a few bags.
There is no direct link between a coffee’s quality and its moisture content. A 10% humidity coffee is not necessarily better or worse than a 12% coffee. However, over time, green coffee will gradually lose vibrance. This will eventually result in the dreaded “past crop” flavor, and this process is associated with the drying out of the coffee.
Therefore, even for a small roaster, it’s important to keep track of moisture content. If you paid for an 85-point coffee at 12% moisture, by the time it reaches 10% moisture it may be more like an 83-point coffee. Yet, you still paid 85-point prices for it originally.
By comparing moisture content loss with quality degradation over time, you can make smart buying and consumption decisions with your green lots. And, when combined with water activity measurements, you can even predict the shelf life of your green coffee. Again, precision here is key: you want to track your coffee through a narrow range of percentage points over a long time frame.
Lastly, you may think to yourself that you don’t need to measure moisture content yourself, since your importer supplies those numbers already. Fred cautions against this thinking. He points out that coffee is shipped on water and that ports can often be warm and humid, which will affect moisture readings.
So, if you’re a roaster in a dry part of the United States but your importer is located in New Orleans or Houston, and is taking moisture readings from lots right as they arrive, those numbers might not be applicable to you by the time your coffee arrives at your facility.
