The primary purpose of the control panel found on the front of most espresso machines is to automatically control the volume of water dispensed by the machine. When Faema built the E61, the existing lever machines had one major advantage over machines with an electric pump: The fixed volume of the piston chamber meant that the espresso machine always dispensed a fixed amount of water. For machines with an electric pump, the barista had to stop the shot manually, which resulted in much less consistency and forced the barista to remain at the machine until the shot was finished.
The first attempt to solve this problem was to use clockwork timers to shut the machine off after a set amount of time. Controlling a shot by time rather than volume made for inconsistent espressos, however. The first commercially successful machine that had the ability to control the shot volume was Faema’s E66 machine — a follow-up to the E61.
Ernesto Valente’s patent (1966) describes a piston in the middle of a chamber, which is filled with pressurised water while the shot is running. As the brewing water passes through the chamber, the piston moves with it. The movement of the piston controls the volume of liquid dispensed, and the movement of a pin attached to the piston physically turns off the group. The volume of water dispensed can be changed by altering the size of the pin.
Detail from Valente’s 1966 patent. The piston (50) moves through the chamber as brewing water passes to the group. As the piston moves upwards, the attached pin (7) pushes upwards on the lever (51). This action unlatches the brew lever (33), stopping the shot.
The control panel on the E66 is thus a mechanical control rather than an electronic one. By turning the wheel above each group, the barista selects among different-sized pins and thus different volumes of water.