If you were to visit a bar or coffeeshop in Italy, you might very well encounter a uniformed bartender called a barista. In Italy, a barista is a trained mixologist familiar with both alcohol and coffee-based drinks. He or she might even wear an elaborate jacket similar to that of a bandmaster or military officer. A barista is usually treated as a respected specialist, in the same vein as a wine steward or sommelier.
When the gourmet coffee industry exploded onto the scene during the 1980s and 1990s, however, the term barista took on a slightly different meaning. A barista in the coffeehouse sense is an expert in producing espresso and espresso-based drinks. Expresso is an intensely-flavored form of coffee generally served in a small cup called a demitasse. In order to brew a perfect cup of espresso, a barista must place a measured amount of ground coffee into a wire basket and tamp it down firmly. The wire basket is then locked under the spout of an espresso machine.
A trained barista should know precisely how much hot water should be forced through the mesh and for how long. If the time is too short, the espresso will be weak and watery. If the barista spends too much time, the espresso will be too strong to drink. It is this intimate knowledge of an espresso machine's capabilities that make a good barista indispensable to a coffeeshop. A barista may also have to create a good froth from steamed milk or allow the espresso to form a natural dark layer on top called a crema.
The skills of a barista go beyond being a good coffee maker. In some coffeeshops, a barista is also expected to have a working knowledge of all of the different blends of gourmet coffees offered. Customers may also ask a barista about roasting times or which grinder settings work best. A good barista also learns different garnishing techniques, such as creating signature designs with stir sticks and cream. There are national and international barista competitions which put all of these skills to the ultimate test.
From WiseGeek.com