How Espresso Machines Work | HowStuffWorks - Home And Garden

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Coffee beans (left) and ground espresso coffee (right)

If you go to a cafe or espresso bar and ask for an espresso, what you will get is a shot-sized glass holding a small amount of very strong coffee. There are many different types of espresso drinks (see iVillage: Coffee Glossary for a good list), including cappuccino, cafe latte and cafe mocha. All are made with one or more shots of espresso.

A shot of espresso is made by forcing about 1.5 ounces of hot water through tightly packed, finely ground espresso coffee. If everything goes well, what comes out is a dark brown, slightly thick liquid with a small amount of crema (a foam, sort of like the head on a beer) on top.

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There are many variables in the process of making a shot of espresso. The temperature of the water, the pressure of the water, the fineness of the ground coffee and how tightly the coffee is packed are just a few. The skilled espresso maker, or barista, controls all of these variables to produce a quality shot of espresso. Let's start with one of the most crucial variables: the coffee.

The Coffee

Espresso coffee is a blend of several different types of coffee beans from different countries. The beans are roasted until they are dark and oily-looking.

The beans are ground very finely -- much finer than for drip coffee makers. The consistency is almost like powdered sugar. The more finely the coffee is ground, the slower the espresso comes out. Generally, for the best shot of espresso, it should take about 25 seconds for the water to pass through the coffee. Sometimes the grind is adjusted to control the brewing time.

Let's take a look at what happens to the coffee in an espresso machine.

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