Ristretto

Ristretto 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.[1] 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.

A double ristretto with the first half of the shot in the glass at the bottom of the image, and the second half in the glass on the right.

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).[2] 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.[3] A ristretto's chemical composition and taste differ from those of a full length extraction for three reasons:

1. More concentrated: The first part of any extraction is the most concentrated, its color typically lying between dark chocolate and umber, whereas the tail end of shots are much lighter, varying from the color of dark pumpkin pie to varying shades of tan (see photo, above right). This is an important factor when drinking straight espresso shots.
2. Different balance: Different chemical compounds in ground coffee dissolve into hot water at different rates. A ristretto contains a greater relative proportion of faster extracting compounds, proportionally fewer of the compounds characteristic of over-extraction, and thus, a different balance.
3. Fewer total extracts: Relative proportions aside, fewer total coffee compounds—caffeine being just one—are extracted into ristrettos versus full length shots. This is an important factor when diluting shots into water or milk.

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.[4]

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  A manual espresso machine
• 
  A semi-automatic (electrically pumped) espresso machine