E-61 is a class of espresso machine, defining a standard size and fitting for the portafilter which holds the ground coffee. E-61 is a common standard for commercial espresso machines. The name E-61 comes from the Faema E-61 espresso machine, which was named for the solar eclipse in its year of introduction, 1961.
The Faema E-61 revolutionized the espresso industry in several ways. Prior to the invention of the E-61, espresso machines used the piston-lever design of the 1950s. This was groundbreaking for several reasons:
The E-61 was the first machine to deliver pressurized water through a mechanical pump at 9 bar pressure, which is the industry standard today.
With the E-61, Faema also upgraded the espresso making process by running cold water through the pump and flash heating it using a heat-exchanger as opposed to running hot water through the pump in the first place. This led to a much more even coffee extraction.
Finally, the E-61 boasted a new group-head design which is the main group-head design used today. This group-head is kept warm by cycling water from the boiler through the group-head using a thermosyphon unit. This keeps the group-head at brew temperature. Thus, when extraction starts, the coffee bed is soaked immediately with brew temperature water which doesn’t need to heat up. This also allows for a smoother extraction and a more delicious cup of espresso coffee.