"Time to extract the caffeine - So your machine has done quite a bit of work to get to this next stage, now lets get that water through to your grinds."

On very early espresso machines, extracting the espresso was was achieved using a hand operated lever that employed a series of pistons and springs

Thankfully, the baristas work has been made a lot easier with the use of an electrically operated pump, electrical valves and cleverly designed group heads.

Whilst they are several designs on group heads, by far the most popular is the E61 type shown below and quite a few machine manufactures now use this format.

Depending on your machine, the layout of the group head may look different at first glance, but once you study the design, you will see that the format is the same as laid out here.

You will also notice that the modern group head does contain quite a lot of moving parts and tiny channels that could easily become blocked, either by dirt or the build of coffee oils from the brewing process.

For the above reasons, you can understand why we stress the use of a quality water filtration system and the need for a good cleaning regime.

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Group Head Workings

Group Head Operation

Once your machine is up to the correct operating temperature, water circulates around the group head and the heat exchanger using thermal dynamics which maintains the temperature, see the animation on slide 3.

Upon pressing the dose select button the following sequence occurs:

• Machine pump starts and takes the water pressure up to 9 bar.
• Group head solenoid opens allowing water into the group handle.
• Machine stays in this state until either you stop the group, or the flow meter informs the control circuit that the correct level has been reached in the cup.
• Machine pump stops.
• Group head solenoid is switched off which allows the pressure to be relieved through the 3 way valve.

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Group Head Faults & Possible Cures

Low Temperature Coffee

If you have noticed that over time the temperature of your coffee is getting less, then this is most likely down to a slow build up of scale within the system. The machine really needs descaling and the correct water filtration added to the incoming water supply.

No Water Flow From Group Head

When you operate the group and no flow is seen coming from the group head, there is a multitude of reasons that can cause this problem.

• Is the water supply turned on - it seems obvious, but it happens so check first.
• Are all other control functions working on the machine.
• Does the Group Head Solenoid work, you should hear a click when you press to operate.
• Was the machine back washed last night and not rinsed correctly causing the solenoid to jam.

Water Leaking Around Handle

When you operate the group and leakage is spotted coming around the sides of the group handle, this is most likely a badly worn group gasket, and a very easy problem to sort out. Check out the video below and you can shop for spare parts for the most popular Group Head gaskets using the shopping link: