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.
Water temperature plays a huge role in extraction, too. The ideal temperature for brewing coffee is around 200 degrees. If your water is too cool, your coffee will be weak. If the water is too hot, your coffee will be over-extracted and potentially scorched.
The amount of time the water is in contact with the grounds affects the end flavor. If your brew time it too fast, the water isn’t in contact with the grounds for long enough to properly extract. A brew time that lasts too long will bring out ugly flavors in your coffee.
The ratio of coffee to water will alter a cup’s flavor drastically. Contrary to popular belief, using too much coffee for your brewing method will make your coffee under-extracted, while using too little will make it over-extracted. That’s why we always recommend that you change your grind settings rather than using more or less coffee to get a better cup.
Strangely enough, it is possible to have coffee that is under, and over-extracted at the same time. If you use a blade grinder rather than a burr grinder, you can end up with particles that vary in size dramatically and extract at different rates. When making espresso, an uneven tamp can cause uneven extraction, and cracks in the espresso puck can lead to water channeling.
Understanding a little more about the extraction process and what can potentially go wrong will help you consistently brew better coffee.