Scalpel sister...

People buy espresso machines like never before. Both home machines and professional machines find their way to owners around the world. But how many of these buyers actually know how their machine looks inside? Well to clarify this issue we need to do some surgery. Lets open the hood :)

For a coffee maker to be considered an espresso machine it needs some basic features:

• A pump which can produce pressure at around 9 Bar
• A thermostat controlled boiler
• A steam outlet for making cappuccino
• And of course a group head accompanied with a porta filter

There sometimes seems to be a competition among home espresso machine producers to have a pump which can produce the most of pressure calculated in bars. How much is a "bar" anyway? Well, 1 bar is 1 kilogram per square centimeter. Consider number of bars that is applied when making your espresso, the porta filter is often approx. 58 mm in diameter. This meens that when the machine makes an espresso it applies 9 kilograms x 26 cm² water pressure. 237 kilos, thats a lot!

It is important to remember though that most machines, if not all, are dependant upon the resistance of the coffee. If you have to coarse grind or to little coffee in the porta filter the pressure never really builds up and the actual pressure will be way lower than 9 bars.

Under the hood of a small machine...

Take a look at the simple diagram of a typical home espresso machine. This shows all the important parts in the machine as well as the flow of water from water main to porta filter.

This generally happens when you turn on your machine

1. The machine starts its heating element in the boiler.
2. A good machine starts the pump if the boiler is empty.
3. The machine signals when the water in the boiler has reached its optimal temperature.

This happens when you flick the coffee switch

1. The processor signals to the pump to start building pressure by pumping in new cold water in the boiler.
2. Hot water is forced into the group head.
3. The water is dispersed evenly thanks to a dispersion screen in the group head.
4. If the coffee is of the right grind and dosage the resistance will build up the right pressure and the coffee will be extracted in 20 - 30 seconds.
5. As long as the pump is running the water temperature will drop and soon the processor will light the "warming up" light.

This happens when you flick the steam switch

1. The processor signals to the thermostat to raise the temperature in the boiler to 130 C degrees.
2. The level of steam builds up and raises the steam pressure to around 1.2 bars.

This diagram shows the inner parts of a machine with an exchange heater. More expensive european machines like BFC Junior, Isomac, ECM etc use such heaters. Many pro machines also use this kind of heater. The exchange heater uses a large boiler to heat up smaller containers where the coffee water is held. The large boiler is responsible for the steam.
The great thing about this kind of heater is that even though you use steam the coffee water temperature is unaffected. This is absolutly preffered by every serious espresso and latte lover.

So what of the features in an espresso machine should be considered most important? Well quality has improved in the last years but a good rule is that you pretty much get what you pay for.

Dont forget that the machine has to be able to cope with very high pressure. This often meens that cheap boiler starts leaking or simply breaks.
All seals are very important, rubber seals are cheap and results in leakage sooner than the much better silicone seals.
The boiler and pipes should be made from high quality materials such as brass. This meens that the machine heats up the water more quicky and makes the machine easier to descale.

Ok, now you dont have to disassemble your machine. And for you who are interested in buying a machine or upgrading your machine, best of luck :)