Next to a bitter taste, the volume of espresso in a cup is the best indicator of whether it is over-extracted or not. A properly made single shot espresso is only about 1¼ ounces.
However, most places in America - and San Francisco is no exception - serve espresso that caters to this American preference for quantity over quality. The result is two or three ounces of bitter liquid with almost no crema. In the land that gave birth to the 46-oz. Big Gulp® and the phrase "super size it!," consumers apparently complain about the amount of espresso far more than its flavor.
If it takes more than three sips to finish, you're not drinking espresso.
The guidelines we used for sizing each espresso are as follows: