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 flavours and chemicals in a typical cup of coffee 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 ounce) of espresso has 80 to 150 mg of caffeine, less than the 95 to 200 mg of a standard 240 mL (8 US fluid ounces) cup of drip-brewed coffee.
Espresso is made by forcing very hot water under high pressure through finely ground, compacted coffee. Tamping down the coffee promotes the water's even penetration of the grounds. This process produces an almost syrupy beverage by extracting both solid and dissolved components. It also produces the definitive crema, by emulsifying the oils in the ground coffee into a colloid, which does not occur in other brewing methods. There is no universal standard defining the process of extracting espresso, but there are several published definitions which attempt to place constraints on the amount and type of ground coffee used, the temperature and pressure of the water, and the rate of extraction. Generally, one uses an espresso machine to make espresso. The act of producing a shot of espresso is often termed "pulling" a shot, originating from lever espresso machines, which require pulling down a handle attached to a spring-loaded piston, forcing hot water through the coffee at high pressure. Today, however, it is more common for the pressure to be generated by an electric pump.
