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.
The first espresso machines were introduced at the beginning of the 20th Century, with the first patent being filed by Luigi Bezzera of Milan, Italy, in 1901. Up until the mid-1940s, when the piston lever espresso machine was introduced, it was produced solely with steam pressure.
While espresso has more caffeine per unit volume than most beverages, compared on the basis of usual serving sizes, a 30 mL (1 US fluid ounce) shot of espresso has about half the caffeine of a standard 180 mL (6 US fluid ounces) cup of drip brewed coffee, which varies from 80 to 130 mg, and hence a 60 mL (2 US fl oz) double shot of espresso has about the same caffeine as a 180 ml (6 US fl oz) cup of drip brewed coffee. In coffee brewing terms, espresso and brewed coffee should have the same extraction (about 20% of the coffee grounds are extracted into the coffee liquid), but espresso has a higher brew strength (concentration, in terms of dissolved coffee solids per unit volume), due to having less water.