Cooks should use a coarsely ground coffee in percolators. It takes a coarser coffee because it takes longer to brew coffee in a percolator than many other methods.
Finer ground coffee should be used for quicker methods, as it makes it easier to extract flavor. For instance, espresso requires a finely ground coffee. Some experts say that percolators should not be used for coffee, as it draws out too much from the coffee, making it bitter. Also, many experts agree that coffee should be ground just prior to brewing; doing so means more of the oils stay intact for brewing.