What is a common reason for coffee to taste sour?

A common reason for coffee to taste sour is under-extraction, which occurs when the brewing process does not extract enough of the coffee's soluble compounds. This can happen when the brewing time is too short, preventing the water from fully interacting with the coffee grounds. As a result, the flavors that contribute to the coffee's body and balance, including the sweetness and bitterness, are not adequately extracted, leaving behind a predominance of the more acidic flavors, which can manifest as a sour taste.

The ideal extraction process relies on the right balance of time, temperature, and grind size, and under-extraction can disrupt this balance, leading to a dissatisfied tasting experience. Understanding this can help you adjust your brewing parameters to achieve a well-rounded cup that minimizes sourness.