Coffee is a brewed beverage prepared from the roasted or baked seeds of several species of an evergreen shrub of the genus Coffea. The two most common sources of coffee beans are the highly regarded Coffea arabica, and the "robusta" form of the hardier Coffea canephora. Once ripe, coffee "berries" are picked, Coffee is slightly acidic (pH 5.0–5.1[1]) and can have a stimulating effect on humans because of its caffeine content. It is one of the most popular drinks in the world.[2] It can be prepared and presented in a variety of ways.