Ristretto

Ristretto is traditionally a short shot of espresso coffee made with the normal amount of ground coffee but extracted with about half the amount of water. Since ristrettos are essentially the first half of a full length extraction, the faster-to-extract compounds predominate in a ristretto. The opposite of a ristretto is a lungo, which is typically double the shot volume. Ristretto means “limited” or “restricted” in Italian whereas lungo means “long.” The French equivalent of ristretto is 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 aroma 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.

A manual espresso machine

A semi-automatic (electrically pumped) espresso machine

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Wikipedia