Understanding the features and workings of your espresso
machine.
An espresso machine is, quite simply, a hot water boiler
and steam generator with one or more integral, pressurised,
coffee brewing points. With the emphasis on maintaining an
optimum brewing temperature the machines is designed to
produce 1-1.5 fluid ounces of concentrated coffee liquor,
by forcing hot water at a temperature of between 92-96
degrees Celsius at a pressure of 9 bar (130psi) for a
duration of between 20-25 seconds.
Inside the machine
Boiler - A typical semi or automatic espresso machine
comprises of a boiler (or boilers) to generate hot water at
approximately 96 degrees Celsius and steam at about 120
degrees. This is achieved by an electrical heating element
and heat exchangers which transfer the heat from the main
boiler to fresh mains water as it is required at the point
of brewing.
Pump - This takes water from the mains supply (or integral
tank) and passes it through the heat exchangers to the
point of brewing operating at a pressure of 9 bar.
Electronics - Various electronic pressure and temperature
values and switches to ensure a safe operation.
Due to the high operating pressure of the pump and boiler,
there are no user adjustable parts inside the machine and
access is restricted to qualified engineers.
Outside the machine
Steam Wands - One or more steam wands draw steam from the
boiler at approximately 120 degrees and terminate with a
nozzle with 3 or more holes where jets of hot steam issue
from to foam milk.
Hot Water Tap - This is used for drawing off hot water at
96 degrees Celsius for topping up espressos into longer
drinks.
Group head assemblies - These comprise of a dispersal plate
to break up the flow of water and a rubber sealing gasket.
The gasket seals the filter handle into the head and
prevents the water/coffee from seeping out.
Filter handles - Solid metal alloy filter handles that fit
into the group head and contain the initial dry espresso
coffee grinds. The handles have single or double spouts, to
brew one or two drinks at a time respectively.
Dials and gauges - Indicating pump pressure, boiler
pressure, water temperature and sometimes water levels.
Brewing buttons - These are either preset (automatic model)
or on - off toggle buttons for controlling the duration of
the brew cycle and consequently the amount of beverage in
the cup.
Drip Tray - A tray used to collect spillages with a waste
outlet leading to a small reservoir or drain pipe.
Heated top tray - An area used for cup storage. It is
warmed naturally from conduction from the boiler. It is
recommended that cups are stored bottom down (not upside
down) so that the bottom of the cup is warmed, not the lip.
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For more information about coffee and coffee making
equipment visit http://www.cafebar.co.uk and view our
Coffee School Section
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