Ristretto (Italian pronunciation: [risˈtretto]) is a "short shot" (30 ml from a double basket) of a more highly concentrated espresso coffee. It is made with the same amount of ground coffee, but extracted with a finer grind (also in from 20 to 30 seconds) using half as much water. A normal short shot might look like a ristretto, but in reality, would only be a weaker, more diluted, shot. The opposite of a ristretto (which means in Italian, "shortened, narrow") is a lungo ("long"), which is a double shot. The French call a ristretto a café serré.
Regardless of whether one uses a hand pressed machine or an automatic, a regular double shot is generally considered to be around 14–18 grams of ground coffee extracted into 60 ml (2 fl oz or two shot glasses). Thus, a "double ristretto" consumes the same amount of coffee beans but fills only a single shot glass.
Coffee contains over a thousand aromatic compounds. A ristretto's chemical composition and taste differ from those of a full-length extraction for three reasons:
Straight ristrettos—shots that are traditionally drunk from a demitasse and not diluted into a larger cup containing milk or water—could be described as bolder, fuller, with more body and less bitterness. These characteristics are usually attributed to espresso in general but are more pronounced in a ristretto. Diluted into a cup of water (e.g. Americano or long black) or milk (e.g. latte or cappuccino), ristrettos are less bitter and exhibit a more intense “espresso” character.
The flavor is more intense, sweeter, less bitter since bitter components are introduced at the end of the shot....Overall, you end up with a much more pleasant and flavorful beverage.