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 (foam). 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 smaller—a 30 mL (1 US fluid ounce) shot of espresso has 40 to 75 mg of caffeine, which is less than half the caffeine of a standard 240 mL (8 US fluid ounces) cup of drip-brewed coffee. A professional operator of an espresso machine is a barista, the Italian word for bartender.