How Do Espresso Machines Work? - Clive Coffee

The Group Head

The group head is the final stop for water as it moves through an espresso machine. All group heads involve four basic parts: a portafilter, a place for the portafilter to lock in, a way to activate the pump, and a pathway for the water to move from the boiler to the portafilter.

There are three primary styles of group heads: an E61 Group head, used in the Profitec Pro 700; a Saturated Group head, used in the La Marzocco GS3; and a Semi-saturated Group head, like the one used in the La Spaziale LUCCA A53.

The Group Head – E61

Originally patented in 1961 by La Faema, the E61 Group head is a classic component of espresso machine design. You’ll see this kind of group head on a wide variety of machines at many different price points.

The E61 has a few distinct features. The whole group head is machined out of brass and weighs a hefty nine pounds. While it will take about 15 minutes for the whole group to come to temperature, it will easily hold that temperature once it’s ready. Also, for the mechanically inclined, it is relatively easy to get into an E61 to do regular maintenance and repairs. It is important to note that these group heads require more active participation from the user. You won’t be able to start a shot, walk away, and have the machine stop it for you; instead, you’ll have full control of the length and volume of the shot.

At its most basic, an E61 is a large, mechanically operated three-way valve: one valve to let the water into the group head from the boiler, one valve to move water from the group to the portafilter, and a third valve to relieve back pressure from the portafilter.

Heres how it works: water enters the group head from the boiler through a large opening on the back of the group head: the water inlet. The water fills the outer chamber at the top of the group head and moves up to the very top chamber, called the filter chamber. From here, the water passes through a gicleur, or water intake nozzle, into the brewing channel. When the brew lever is down, the brew valve seals the top chamber, and no water runs to the rest of the group.

When the brew lever is up midway, the water inlet cam begins to lift the brewer valve and water moves from the brew channel into the area around the water inlet cam. From here, the water goes two places. It travels up through the infusion channels and out through the dispersion screen onto the ground coffee. It also flows down, past the still open pre-infusion valve into the pre-infusion chamber. At this stage, the pump isn’t activated. Instead, water moves through the system from the gentle pressure generated by heating.

This gentle pressure stage is often referred to as pre-infusion. With pre-infusion, the bed of coffee in the portafilter basket is given extra time to stabilize with the hot water before adding the intense pressure of brewing. This can help reduce the risk of channeling and also compensate for any variations in dosing, distributing, and tamping. As the E61 is operated by a mechanical lever, a user can completely control the length of pre-infusion.

It should be noted that pre-infusion is not necessary to produce great espresso; it only helps make great espresso easier to achieve.

When the brew lever is all the way up, the pump is activated and pressurized water begins to move through the machine. At this stage, the water inlet cam will complete raising the brew valve while simultaneously sealing the pre-infusion valve. With the pre-infusion valve sealed, the intensely pressurized, hot water is only allowed to travel out through the dispersion block and onto the ground coffee.

At the end of the brewing cycle, the lever is returned to the down position and the pump is deactivated. At this point, the water inlet cam seals the brewer valve, ending the flow of water to the rest of the group. At the same time, the water inlet cam reopens the pre-infusion valve and the drain valve; this releases any back pressure in the portafilter basket and dries the spent puck.

E61 Group Head Pros: Sturdy build with high heat retention, relatively easy to repair, manual control over pre-infusion and brewing Cons: Longer heating times, only manual controls Machines: ECM Synchronika, ECM Classika