The extraction of espresso from ground coffee is a markedly different process from brewing drip coffee. Espresso is created when hot water is forced through finely ground coffee at very high pressure. What follows is an explanation of the different types of machines available, and how they achieve this.
Manual: Manual espresso machines are the most basic when it comes to espresso extraction. Water is heated inside of the machine's boiler, while the pressure needed to extract the espresso is generated by manual levers that are pulled by operator, which is how the term "pulling a shot" originated. Manual style machines make use of portafilters and require the coffee to be ground and tamped prior to brewing.
Semi-Automatic: Semi-automatic espresso machines are a bit more sophisticated than manual machines. In addition to possessing a boiler to heat water for espresso extraction, semi-automatic machines generate the 9 bars of pressure via the use of an electric pump. Semi-Automatic machines can feature levers, rocker switches, or push buttons to operate the pump. Like manual espresso machines, semi-automatic machines also make use of portafilters and require the coffee to be ground and tamped prior to brewing.
Super-Automatic: Super-automatic espresso machines incorporate more technology in their design than manual or semi-automatic machines and are designed to simplify the user experience. In addition to utilizing boilers and pumps to produce heat and pressure, super-automatic machines also possess internal grinders and tamp coffee through the use of a mechanism known as the brew group, where the grounds are compacted into a puck similar to that in a portafilter.