A consumer espresso machine has only one grouphead, while professional machines, used in commercial coffee shops, can contain up to seven groupheads.
Located on the front of the machine, the group head is a metal, permanent attachment that brings water out of the machine and into the filter basket.
The group head is often simply known as the group. Hot water is forced through the group head under pressure. The group head contains many tiny holes, known as the shower. The shower then attempts to distribute pressurized water evenly over the ground coffee bed. If coffee is ground unevenly, this won’t be possible and the result will be an uneven extraction.
It is important that group heads are maintained, to avoid regularly having to fix or replace them. Good practices include back-flushing the espresso machine, which consists of running water through the machine to wash coffee grinds away, as well as making sure the seals for the group head are in good condition.