Caffè espresso, espresso, or expresso is a concentrated coffee beverage brewed by forcing hot water under pressure through finely ground coffee.

Espresso was developed in Milan, Italy, in the early 20th century, but up until the mid-1940s it was a beverage produced solely with steam pressure. The invention of the spring piston lever machine and its subsequent commercial success changed espresso into the beverage as it is known today.

The defining characteristics of espresso include a thicker consistency than drip coffee, a higher amount of dissolved solids than drip coffee per relative volume, and a serving size that is usually measured in shots, which have traditionally been between 25 and 30 mL (around 1 fluid ounce) in size. Many of espresso's chemical components quickly degrade by oxidation. A distinguishing characteristic of espresso is "crema," a reddish-brown foam that floats on the surface and is composed of vegetable oils, proteins and sugars.

As a result of the high-pressure brewing process, all of the flavors and chemicals in a typical cup of coffee are concentrated. For this reason, espresso lends itself to becoming the base for other drinks, such as lattes, cappuccino, macchiato and mochas.

While there can be significant variation, on a per-volume basis, espresso contains approximately three times the caffeine content of regular brewed coffee (1.700 g/l (50 mg per fluid ounce) of espresso versus 0.50–0.75 g/l (14–22 mg per ounce) for brewed coffee). Compared on the basis of usual serving sizes, a 30 mL (1 fluid ounce) shot of espresso has about half the caffeine of a standard 180 mL (6 fluid ounce) cup of American-style coffee, which varies from 80 to 130 mg.

Brewing process

This process produces a rich, almost syrupy beverage by extracting and emulsifying the oils in the ground coffee. Some prefer espresso shots directly into a pre-heated demitasse or shot glass, to maintain the a higher temperature of the espresso and preserve all of its crema.

Espresso can also be made with a stovetop espresso machine.

Espresso roast and blends

Espresso is not a specific bean or roast level. Any bean, combination of beans from different origins (referred to as a blend), or roasting level can be used to produce authentic espresso. While some major North American chains claim dark roasts as their espresso roastsFact: date=August 2008, some of the winning blends used in the World Barista Championship have been what is classified as a medium, "City,” or "Full City" roast, with little or no visible surface oil on the beans.