Why does my coffee taste bitter?

When you experience a harsh, dry, or aspirin-like bitterness in your coffee, you are likely dealing with over-extraction. Brewing is a sequential process: water dissolves bright, acidic compounds first, followed by sugars and sweetness, and finally, the heavier, more astringent bitter compounds. If your brewing process continues too long, you push past the point of balance and into the territory of over-extraction.

Technically, this happens because the water has had too much contact with the coffee grounds. The most common culprit is a grind size that is too fine, which increases the surface area and slows down water flow, forcing the water to linger and extract those undesirable phenolics. Similarly, using water that is too hot can accelerate the breakdown of chlorogenic acids, which are responsible for a significant portion of coffee's inherent bitterness.

To troubleshoot, start by adjusting one variable at a time. If your coffee is consistently bitter, try a slightly coarser grind. If that doesn't resolve the issue, consider lowering your water temperature or reducing your total brew time. It is also worth noting that the coffee-to-water ratio plays a role; using too much coffee relative to water can lead to an overly concentrated, harsh brew that feels astringent on the palate.

Beyond technique, the quality and roast level of your beans matter. Darker roasts naturally contain more carbonized compounds that can lean toward bitterness, and stale coffee—where oils have degraded—can also taste flat and bitter. If your equipment is clean and your technique is dialed in, but the bitterness persists, you might simply be brewing a bean that was roasted darker than your personal preference.

In practice, think of your brewing variables as dials. If the cup is bitter, you need to 'dial back' the extraction. By making your grind coarser or shortening your brew time, you stop the water from pulling those final, harsh compounds, leaving you with a cup that highlights the sweetness and acidity you actually want to taste.