Have you ever had a cup of coffee that tasted weak and sour? How about overly strong and sharp? Those unappealing flavors are a result of either under-extracting or over-extracting coffee grounds during the brewing process.
When you brew coffee, you are extracting the soluble solids from the coffee grounds. According to the Specialty Coffee Association of America’s Gold Cup Standards, to get a good cup of coffee you should extract about 20% of the soluble solids.
There are a number of different variables that can cause your coffee to under or over-extract. The most common variable is an improper grind setting. When you grind coffee beans, you’re exposing surface area from which to extract soluble solids. If your grind is too coarse, there isn’t enough surface area exposed, so your coffee will come out weak. If your grind is too fine, too much area is exposed, so your coffee will come out sharp and bitter.