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 through the grounds.
This process produces an almost syrupy beverage by extracting both solid and dissolved components.
The crema is produced 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 several published definitions attempt to constrain 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 called "pulling" a shot, originating from lever espresso machines, with which a barista pulls down a handle attached to a spring-loaded piston, which forces hot water through the coffee at high pressure.
Today, however, it is more common for an electric pump to generate the pressure.

The technical parameters outlined by the Italian Espresso National Institute for making 
a "certified Italian espresso" are:
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 through the grounds. This process produces an almost syrupy beverage by extracting both solid and dissolved components. The crema is produced 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 several published definitions attempt to constrain 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 called "pulling" a shot, originating from lever espresso machines, with which a barista pulls down a handle attached to a spring-loaded piston, which forces hot water through the coffee at high pressure. Today, however, it is more common for an electric pump to generate the pressure.
The technical parameters outlined by the Italian Espresso National Institute for making 
a "certified Italian espresso" are:
Espresso