Espresso is both a coffee beverage and a brewing method. It is not a specific bean, bean blend, or roast level. Any bean or roasting level can be used to produce authentic espresso. For example, in southern Italy, a darker roast is generally preferred. Farther north, the trend moves toward slightly lighter roasts, while outside Italy, a wide range is popular.
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.
Espresso shots begin with whole beans. It is imperative that you begin with whole beans because the volatile oils (which give coffee its incredible range and depth of flavor) begin to dissipate off of the coffee as soon as it is ground. In fact, the effect of lost oils is so pronounced on espresso’s flavor that it’s important to pull as shot as soon as possible after you have ground the beans and it is almost always recommended that you grind for each and every individual shot you pull.