An espresso machine is used to produce the traditionally Italian coffee beverage called espresso. A professional operator of such a machine is called a barista. The knowledge required in making the finest espresso is considered to be a craft, similar to artisan baking.
The act of producing a shot of espresso is colloquially termed pulling a shot, because old lever-style espresso machines required pulling a long handle to produce a shot. To pull a shot of espresso, a metal filter-basket is filled with either 7-10 grams or 12-18 grams of ground coffee for a single shot or double shot, respectively. The espresso is then tamped, or compressed into a densely packed puck of espresso. The portafilter (or group handle) holds the filter-basket and is locked under the grouphead’s diffusion block. When the brew process begins, pressurized water is forced into the grouphead and through the ground coffee in the portafilter. Water cooler than the ideal zone causes sourness; hotter than the ideal zone causes bitterness. High-quality espresso machines control the temperature of the brew water within a few degrees of the ideal.
This process produces a rich, almost syrupy beverage by extracting and emulsifying the oils in the ground coffee. An ideal double shot of espresso should take 25-30 seconds to arrive, timed from when the machine’s pump is first turned on. Varying the fineness of the grind, the amount of pressure used to tamp the grinds, or the pump pressure itself can be used to bring the extraction time into this ideal zone. Most prefer to pull espresso shots directly right into a pre-heated demitasse or shot glass, to maintain the ideal temperature of the espresso.
An espresso machine also has a steam wand which is used to steam and froth milk for milk based espresso beverages such as the cappuccino and latte.