What is under-extraction?

Under-extraction is the opposite of over-extraction and is a common issue for those just starting their coffee journey. It happens when the brewing process is cut short or is inefficient, meaning the water doesn't have enough time or the right conditions to pull out the full spectrum of flavors from the coffee. Coffee extraction is a sequential process: acids and salts come out first, followed by sugars, and finally, the heavier, bitter compounds. If you stop too early, you are left with only the first stage.

There are three main variables that cause under-extraction: grind size, water temperature, and contact time. If your grind is too coarse, the water flows through the coffee too quickly, not spending enough time in contact with the grounds to extract the sugars. If your water temperature is too low, it lacks the energy to dissolve the necessary compounds. Finally, if your brew time is simply too short, the process is incomplete.

How do you know if your coffee is under-extracted? The most obvious sign is a sharp, sour, or salty taste. The coffee will often feel thin or 'watery' on the palate, lacking the rich mouthfeel and lingering sweetness of a well-balanced cup. It can be quite jarring, especially if you are using a high-quality, light-roasted coffee that already has a naturally high acidity. The goal is to find the balance where that acidity is pleasant and vibrant, not sour and aggressive.

In practice, fixing under-extraction is a matter of increasing the efficiency of your brew. Try grinding your coffee finer to increase the surface area, using slightly hotter water, or extending your brew time. As with all coffee troubleshooting, change only one variable at a time. By systematically adjusting your process, you can unlock the hidden sweetness and complexity in your beans, turning a sour, disappointing cup into a balanced and delicious one.