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. However, it is more common for an electric pump to generate the pressure. Tamping down the coffee promotes the water's even penetration through the grounds. This process produces a thicker beverage by extracting both solid and dissolved components. The "crema" is a layer of dense foam that forms on top of the drink. It consists of emulsified oils in the ground coffee turned into a colloid, which does not occur in other brewing methods. Crema is produced when water, placed under very high pressure, dissolves more carbon dioxide, a gas present inside the coffee that is produced during the roasting process. The technical parameters outlined by the Italian Espresso National Institute for making a "certified Italian espresso" are: Espresso roast 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. History Angelo Moriondo, from Turin, is often erroneously credited for inventing the beverage, since he patented a steam-driven coffee beverage making device in 1884 (No. 33/256), probably the first Italian coffee machine similar to other French and English 1800s steam-driven coffee machines. The device is "almost certainly the first Italian bar machine that controlled the supply of steam and water separately through the coffee" and Moriondo is "certainly one of the earliest discoverers of the expresso machine, if not the earliest". Seventeen years later, in 1901, Luigi Bezzera, from Milan, devised and patented several improved versions of the espresso machine, the first of which was applied for on 19 December 1901. Titled "Innovations in the machinery to prepare and immediately serve coffee beverage"; Patent No. 153/94, 61707, was granted on 5 June 1902, and was the first espresso machine. In 1903, the patent was bought by Desiderio