Espresso

Espresso or caffè espresso is a concentrated coffee beverage brewed by forcing very hot, but not boiling, water under high pressure through coffee that has been ground to a consistency between extremely fine and powder. Invented by Edward Loysel de Santais in 1843, Santais's machine impressed visitors to the Paris Exposition of 1855 by producing "two thousand cups of coffee an hour". Santais's machine brewed coffee a pot at a time, however, and used steam pressure, though not to force the brewing water directly through the coffee. Instead, it raised the water to a considerable height above the coffee. From there it descended through an elaborate system of tubes to the coffee bed. The weight of the hot water, not the trapped steam, applied the brewing pressure.

Espresso was developed in Milan, Italy in the early 20th century, but up until the mid-1940s it was a beverage produced solely with steam pressure. The invention of the spring piston lever machine and its subsequent commercial success changed espresso into the beverage we know today. Espresso is now produced with between 9 and 10 atmospheres or bars of pressure.

The defining characteristics of espresso include a thicker consistency than drip coffee, a higher amount of dissolved solids than drip coffee per relative volume, and a serving size that is usually measured in shots, which is about 30ml (1 ounce) in size. Espresso is chemically complex and volatile, with many of its chemical components quickly degrading from oxidation or loss of temperature. Properly brewed espresso has three major parts: the heart, body, and the most distinguishing factor, the presence of crema, a reddish-brown foam that floats on the surface of the espresso. It is composed of vegetable oils, proteins and sugars. Crema has elements of both emulsion and foam colloid.

As a result of the high-pressure brewing process, all of the flavors and chemicals in a typical cup of coffee are concentrated. Because of its intense and high concentration of ingredients (including caffeine), espresso lends itself to mixing into other coffee based drinks, such as lattes, cappuccini, macchiati and mochas, without being diluted in the resulting drink. Espresso contains approximately twice the caffeine content per volume as regular brewed coffee, at approximately 40 milligrams per fluid ounce, but only about 1/3 the content per serving.