CaffÃ¨ espresso, espresso,  is a concentrated coffee beverage brewed by forcing hot water under pressure through finely ground coffee. 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. Characteristics of properly made espresso, which distinguish it from drip and other brewing processes, include a thicker consistency than drip coffee, a higher amount of dissolved solids than drip coffee per relative volume, and crema, a reddish-brown foam that floats on the surface and is composed of vegetable oils, proteins and sugars. As a result of the pressurized brewing process, all of the flavors 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 and mochas. While there can be significant variation, on a per-volume basis, espresso contains approximately two to three times the caffeine content of regular drip brewed coffee. Compared on the basis of usual serving sizes, a 30 mL (1 fluid ounce) shot of espresso has about half the caffeine of a standard 180 mL (6 fluid ounce) cup of drip brewed coffee, which varies from 80 to 130 mg.