What is an ideal espresso extraction time?

The traditional target is 25–30 seconds from when the pump starts to when the shot ends, producing 25–35ml of liquid from 18–20 grams of ground coffee (a double shot). Faster shots (under 20 seconds) are often under-extracted and taste sour or weak. Slower shots (over 40 seconds) are often over-extracted and taste bitter and astringent. Dialing in grind size is the primary way to control extraction time.