These machines utilize a single boiler for both brewing espresso and steaming milk. A thermosiphon, a smaller pipe running inside the larger boiler, carries brewing water to the group head. This water is heated indirectly by the surrounding boiler water, which is kept at a higher temperature suitable for steaming. This design provides a compact and often more affordable solution for both brewing and steaming functionalities within one machine.
The ability to brew and steam almost simultaneously offers significant advantages in terms of workflow efficiency, particularly in busy caf environments. This design became prominent as a way to offer both functionalities in a relatively compact footprint, offering a practical solution for smaller spaces. While precise temperature control can be more challenging compared to dual boiler systems, advancements in thermosiphon technology and PID controllers have greatly improved temperature stability in these machines.
