If you have ever been to a coffee shop or Seattle you are probably familiar with the term "espresso". When someone orders an espresso, however, they are not ordering a type of coffee bean but a process.
The basic espresso machine is very simple. Is all it is doing is using pressure to push water through ground coffee beans and into your cup.
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The water is heated up in the bottom of the machine and as the pressure builds the water is forced into the filter where the coffee is located and then as the pressure continues to increase it is forced through the spout. A good shot of espresso should take approximately 25 seconds to get through the coffee. Because the pressure depends on the temperature of the water, the pressure may not be sufficient at the recommended brewing temperature to move the water through the filter and spout. Because of this, there are electric machines with pumps that pump cold water into a heating chamber at high pressure.
Interesting but useless: The word espresso comes from the italian verb esprimere which means "to press out".