An overly bitter and sometimes even burned taste can occur when coffee is over-extracted. The most common reason this happens is that the coffee grind is too fine. Under-extracted coffee is often the cause of a weak and flavorless brew. Under-extraction can occur if your coffee is ground too coarsely and/or unevenly.
For the Moccamaster, we recommend a medium-coarse grind, which should look like coarse sand or sea salt. If having your coffee ground, use these descriptors to ensure you get optimal coarseness. Note that most pre-ground, bagged coffee tends to be too finely ground for ideal operation.
Make sure you are also using the correct amount of coffee grounds to water. To brew to the SCA Golden Cup standard, use 2 tablespoons of ground coffee for every 6 oz of cold water. See our formula chart for specific water volumes here.