Caffè espresso, or just espresso is a concentrated coffee beverage brewed by forcing hot water under pressure through finely ground coffee.
Compared to other coffee brewing methods, espresso often has a thicker consistency, a higher concentration of dissolved solids, and crema (foam). As a result of the pressurized brewing process, all of the flavours and chemicals in a typical cup of coffee are very concentrated. For this reason, espresso is the base for other drinks, such as lattes, cappuccino, macchiato, mochas, and americanos.
Espresso is not a specific bean or roast level, it is a method of making coffee. Any bean or roasting level can be used to produce authentic espresso. Acidity diminishes and a rich bitter-sweetness emerges.
A darker or lighter roast will translate into a bitter or acid flavor respectively. Mixtures where there are several roast levels are common.
In Italy, roast levels can vary quite a bit. In Southern Italy, a darker roast is often preferred, but the farther north one goes in the country, the trend moves toward lighter roasts.