A cappuccino machine, more correctly called an espresso machine, forces hot water at a steady pressure through a small reservoir of finely ground coffee beans. The combination of the pressure and the fine grind leaves a crema, or bubbly foam, atop the coffee. For a cappuccino, steamed milk is added.
There are two main types of espresso machines: steam and pump. Steam machines create their own internal pressure to push water through the coffee, but higher heat may scald the coffee and affect the crema. Pump machines allow more control over the water temperature and pressure and produce better-quality espresso shots. Steam machines are easier for beginners to use, while more experienced cappuccino lovers tend to opt for pump machines.
In addition to the main brewing apparatus, many espresso machines also include a milk-frothing wand for making cappuccinos and other drinks. The wand is immersed in a pitcher of cold milk and the steam valve opened, heating and aerating the milk. As the wand moves through the pitcher, it creates a froth of bubbles on the top that are one of the signatures of a properly prepared cappuccino. Once the desired level of froth is reached, the steam valve is shut off and the heated milk added to the espresso to create the completed drink.