Coffee Group-heads

 The group head, also known as the brew head, is the part of an espresso machine where water from the boiler is dispensed into the coffee filter basket. 

Espresso machines utilize different types of group heads, which are essential components responsible for delivering pressurized water to the coffee grounds in the portafilter for extraction. The design of the group head can affect factors such as temperature stability, water distribution, and espresso flavor.

It serves as a meeting point, connecting the machine to the group handle and the hot water to the coffee grounds.

The group head essentially consists of two main components: the portafilter and the water distribution system.

Most commonly, group heads come in 8-hole (single), 12-hole (double), and 20-hole (triple) configurations. 

There are many types of group heads. Technology is constantly evolving

and its difficult to keep up with new improvements.

 it is not that straightforward to classify them into simple categories. Some may share the same name but with a slightly different mechanism, while some have different designs but works the same.

The main types of group heads that you will come across are :

Conventional.

Saturated.

semi-saturated

E61.

Lever.

Pre-infusion

Electrically heated

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Conventional.

These are not heated.

Also known as traditional or commercial group heads, these are the most common type found in espresso machines. Standard group heads typically have a large, circular design with a central dispersion screen or shower screen. While it may not be the best group head for thermal stability, 

it is a proven tech with simple construction, and is cheaper to produce than other group heads.

Examples are  Rocket Boxer, Nuova Simonelli Musica, and Rancilio Silvia V6.

Saturated

These are connected to the boiler itself.

The water circulates continuously around the group head from the boiler.

The entire group head is thus heated, ensuring that the brewing water remains at a consistent temperature throughout the extraction process. 

This results in improved temperature stability because the group is saturated with the same body of water whose temperature is being controlled in the boiler. 

Synesso and La Marzocco both use saturated groups. Obviously, a saturated group can only work with machines that have separate steam and brew boilers.

Saturated group heads are often found in higher-end espresso machines and are favored by specialty coffee enthusiasts.

examples:  La Marzocco GS machine in 1970.  GB5, Linea Classic, and GS3 

or Slayer, Synesso, and Kees van der Westen.

Semi-saturated

The group head is separated from the boiler by a heat exchange mechanism that directs water flow around the group head.

 A semi-saturated group head features a separate water path from the boiler to the group head, which allows for precise temperature control and consistency. .....maybe the temps are a little less stable than a saturated head.

Lever

There are two sub-categories within this type: spring piston and manual piston. With a manual piston group head, the user has direct control over the water flow through the coffee grounds to brew the espresso. On the other hand, a spring piston group head uses a lever to compress a spring, creating pressure to force water through the coffee grounds. Both of these types offer varying degrees of control to the barista and may impact the espresso quality.

Examples; Pro 800 by Profitec and Leva by La Marzocco ,  Robot Barista by Cafelat 

E61

Named after the Faema E61 espresso machine.

The Faema got its name from a solar eclipse that occurred in 1961.

It's a design that is very tried and true and is one that is used on many prosumer grade espresso machines and even some commercial machines like the Faema Legend and the Faema Jubile.

This design uses a thermosyphon heating system

 where heated water circulates between the boiler and the group head to maintain a stable temperature.

These are easy to spot as the portafilter sits outside the machine and is connected to a brew lever that operates it.

 This design helps to prevent temperature fluctuations during brewing and ensures consistent extraction. Thermosyphon group heads are commonly found in high-quality commercial espresso machines.

The E61 became a group head template for manufacturers, each making slight variations on the design to suit their own requirements leading to the introduction of multiple boilers to their machines.

it takes about 15 minutes or longer to heat up an E61.

The Rocket Appartamento is an iconic E61 machine, followed by ECM Classika, Profitec Pro 400, and Lelit Bianca.

Pre-Infusion Group Head: 

Pre-infusion group heads incorporate a pre-infusion stage into the brewing process, where a small amount of water is initially delivered to the coffee grounds at low pressure to saturate them evenly before full pressure is applied for extraction. This helps to enhance flavor extraction and consistency, resulting in a smoother, more balanced espresso shot. Pre-infusion group heads are found in some specialty espresso machines designed for enthusiasts who prioritize precise control over extraction parameters.

Electrically heated.

the group head is electrically heated with heating elements and is usually controlled by a thermostat, or PID. The heating elements are embedded in the group head and helps maintain thermal stability.

You often see these in entry level machines.

They are cheap and very fast at reaching brewing temperatures