Why does my espresso taste sour?

When you encounter a sour espresso, you are experiencing the result of under-extraction. During the brewing process, water extracts compounds from coffee in a specific order: first, it pulls out acids and salts, followed by sugars and sweetness, and finally, the heavier, bitter compounds. If your shot is sour, the water has successfully extracted the initial acidic notes but failed to reach the later, balancing sugars.

In practice, this almost always points to the water moving through the coffee puck too rapidly. The most common culprit is a grind size that is too coarse, which creates large gaps between particles, allowing water to bypass the coffee rather than saturating it. If your shot pulls in under 20–25 seconds, your grind is likely the primary variable to adjust. Moving your grinder to a finer setting increases the surface area of the grounds, creating more resistance and forcing the water to spend more time interacting with the coffee.

Beyond grind size, water temperature plays a critical role in extraction efficiency. If your machine is not properly preheated or the water temperature is set below the standard 195–205°F (90–96°C) range, the water lacks the thermal energy required to dissolve the coffee solids effectively. Even with a perfect grind, cool water will consistently produce a thin, sharp, and sour cup.

Finally, consider the role of puck preparation. If your distribution is uneven or your tamping is inconsistent, you may experience channeling. This occurs when water finds a path of least resistance through the puck, over-extracting a small portion of the coffee while leaving the rest under-extracted. This can result in a cup that tastes simultaneously sour and watery. By focusing on a consistent, level tamp and a finer grind, you can bring your extraction back into balance, moving from sharp acidity to a sweet, syrupy finish.