Espresso is a concentrated beverage brewed by forcing a small amount of nearly boiling water under pressure through finely ground coffee beans. Espresso often has a thicker consistency than coffee brewed by other methods, a higher concentration of suspended and dissolved solids, and crema (meaning cream, but being a reference to the foam with a creamy texture that forms as a result of the pressure). As a result of the pressurized brewing process the flavors and chemicals in a typical cup of espresso are very concentrated. Espresso is the base for other drinks, such as a latte, cappuccino, macchiato, mocha, or americano. Espresso has more caffeine per unit volume than most beverages, but the usual serving size is smaller—a typical 60 mL (2 US fluid ounces) of espresso has 80 to 150 mg of caffeine, a little less than the 95 to 200 mg of a standard 240 mL (8 US fluid ounces) cup of drip-brewed coffee.
An Italian espresso is a polyphasic beverage prepared from roasted and ground coffee and water alone, constituted by a foam layer with a partiucular "tiger tail" pattern, on top of an emulsion of microscopic oil droplets in an aqueous solution of sugars, acids, protein-like materials, and caffeine, with dispersed gas-bubbles and solids ... The distinguishing sensory characteristics of italian espresso include a rich body, a full fine aroma, and equilibrated bitter-sweet taste with an acidic note, and a pleasant lingering after-taste, exempt from unpleasant flavor defects.