Pressure

Espresso is made by forcing hot water at 91Ц95 ∞C (195Ц204 ∞F) under a pressure of between eight and fifteen bars (800Ц1500 kPa, 116Ц220 psi), through a lightly packed matrix, called a "puck," of finely ground coffee. The 30Ц60 cc (1Ц2 oz.) beverage is served in demitasse cups; sugar is often added. It is consumed during the day at cafes and from street vendors, or after an evening meal. It is the basis for many coffee drinks. It is one of the most concentrated forms of coffee regularly consumed, with a distinctive flavor provided by crema, a layer of flavorful emulsified oils in the form of a colloidal foam floating on the surface, which is produced by the high pressure. Espresso is more viscous than other forms of brewed coffee. The moka pot, also known as the "Italian coffeepot" or the "caffettiera," is a three-chamber design which boils water in the lower section. The generated steam pressure, about one bar (100 kPa, 14.5 psi), forces the boiling water up through coffee grounds held in the middle section, separated by a filter mesh from the top section. The resultant coffee (almost espresso strength, but without the crema) is collected in the top section. Moka pots usually sit directly on a stovetop heater or burner. Some models have a transparent glass or plastic top. Single-serving coffee machines force hot water under low pressure through a coffee pod composed of finely ground coffee sealed between two layers of filter paper or through a proprietary capsule containing ground coffee. Examples include the pod-based Senseo and Home Cafe systems and the proprietary Tassimo and Keurig K-Cup systems. The AeroPress is another recent invention, which is a non-mechanical/non-electronic device where pressure is simply exerted by the user manually pressing down with their hand, forcing medium-temperature water through coffee grounds in about 30 seconds (into a single cup.) This method produces a smoother beverage than espresso, falling somewhere between the flavor of a moka pot and a Fre

ch Press. Espresso is a concentrated beverage brewed by forcing a small amount of nearly boiling water under pressure through finely ground coffee beans. Espresso often has a thicker consistency than coffee brewed by other methods, a higher concentration of suspended and dissolved solids, and crema (meaning cream, but being a reference to the foam with a creamy texture that forms as a result of the pressure). As a result of the pressurized brewing process the flavours and chemicals in a typical cup of coffee are very concentrated. Espresso is the base for other drinks, such as a latte, cappuccino, macchiato, mocha, or americano. Espresso has more caffeine per unit volume than most beverages, but the usual serving size is smallerЧa typical 60 mL (2 US fluid ounce) of espresso has 80 to 150 mg of caffeine, less than the 95 to 200 mg of a standard 240 mL (8 US fluid ounces) cup of drip-brewed coffee. Espresso is made by forcing very hot water under high pressure through finely ground, compacted coffee.[2] Tamping down the coffee promotes the water's even penetration of the grounds.[3] This process produces an almost syrupy beverage by extracting both solid and dissolved components. It also produces the definitive crema,[4] 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,[5] 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.[6][7] 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.