Controlling extraction is all about surface area. Fine Grind Increases surface area. Water extracts flavor quickly. Essential for Espresso where water is in contact for only 30 seconds. If used for French Press, it over-extracts (bitter). Coarse Grind Decreases surface area. Slows down extraction. Perfect for French Press or Cold Brew where water and coffee hang out for minutes or hours. The Golden Rule If your coffee is sour, grind finer (extract more). If your coffee is bitter, grind coarser (extract less).