Why does my espresso taste bitter?

Bitter espresso is typically over-extracted. Common causes: grind too fine (restricts flow, over-extracts), water temperature too high, extraction time too long (over 35 seconds), or stale beans. Fix: grind coarser, reduce extraction time, lower temperature slightly. Note: some bitterness is normal and desirable in espresso — it should be a background note, not the dominant flavor. If shots are fast but still bitter, the beans themselves may be stale or low-quality.