All of these measurements are important in how a coffee will roast.
● Moisture content shows the total percent of water in bean. Too high and the coffee will fade quickly or develop mold and other cup defects. Too low and the coffee will taste faded. 10-12% is the ideal range with decafs being slightly less and Indonesia, slightly more.
● Water activity is a measurement that is relatively new to coffee. It measures free water in coffee, not the total moisture. Free water is important to measure as it is the water that is available to allow for chemical changes or allow yeast, bacterial and mold development.
● Density and roasting is a little more complex. You can measure the density of your green comparatively by always using the same container, doesn’t matter the size. Fill the container to the top, weigh it and log it. Over time you will notice that some coffees will weigh more, some less for the same volume. The denser coffees are higher grown and will need greater heat input to develop. Conversely, less dense coffees require a more gentle approach.