Espresso consumption in the United States has grown tremendously in the last decade or two. In Seattle, Washington, you can't walk more than a couple of blocks without seeing a cafe or espresso cart -- they're in bookstores, grocery stores, laundromats, gas stations and movie theaters. There are drive-through espresso shops in parking lots. Sometimes an espresso cart will just park on the sidewalk, like the hot-dog vendors in New York City.
People have been buying espresso machines for their homes, too. These machines are smaller than the commercial machines found in cafes, but they work on the same principles. In this edition of HowStuffWorks, we'll learn how these household espresso machines work. But first, let's see what espresso is.