ESPRESSO
Espresso is a coffee-brewing method of Italian origin, in which a small amount of nearly boiling water (about 90 °C or 190 °F) is forced under 9–10 bars (900–1,000 kPa; 130–150 psi) of pressure through finely-ground coffee beans. Espresso coffee can be made with a wide variety of coffee beans and roast degrees. Espresso is the most common way of making coffee in southern Europe, especially in Italy, France, Spain and Portugal. It is also popular in Switzerland, Croatia, Bulgaria, Greece, and in Australia.
Espresso is generally thicker than coffee brewed by other methods, with a viscosity similar to that of warm honey. This is due to the higher concentration of suspended and dissolved solids, and the crema on top (a foam with a creamy consistency). As a result of the pressurized brewing process, the flavors and chemicals in a typical cup of espresso are very concentrated. The three dispersed phases in espresso are what make this beverage unique. The first dispersed phase is an emulsion of oil droplets. The second phase is suspended solids, while the third is the layer of gas bubbles or foam. The dispersion of very small oil droplets is perceived in the mouth as creamy. This characteristic of espresso contributes to what is known as the body of the beverage. These oil droplets preserve some of the aromatic compounds that are lost to the air in other coffee forms. This preserves the strong coffee flavor present in the espresso.
Espresso is also the base for various coffee drinks—including caffè latte, cappuccino, caffè macchiato, caffè mocha, flat white, and caffè Americano.
Espresso has more caffeine per unit volume than most coffee beverages, but because the usual serving size is much smaller, the total caffeine content is less than a mug of standard brewed coffee.
The actual caffeine content of any coffee drink varies by size, bean origin, roast method and other factors, but a typical 28 grams (1 ounce) serving of espresso usually contains 64.50 milligrams of caffeine, whereas a typical serving of drip coffee usually contains 150 to 200 mg.
Espresso brewing
Finely-ground coffee for espresso
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. For most coffee drinkers, one of the key features of espresso is the layer of dense foam that forms on top of the drink. Crema is the natural head of foam that forms on top of the coffee. Crema is produced when water, placed under very high pressure, dissolves more carbon dioxide, the gas present in coffee that is produced during the roasting process.