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.

There is not usually any user access to the inside of an espresso machine. This is due to the high pressures involved and access is solely 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 - Metal alloy filter handles contain the espresso ground coffee and fit snugly into the group head. 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. The cup warming tray is simply heated by natural conduction from the boiler and does not have an independent heating source. It is recommended that cups are stored bottom down (not upside down) so that the bottom of the cup is warmed, not the lip.