Coffee is a brewed beverage with a bitter flavor prepared from the roasted seeds of the coffee plant. The beans are found in coffee cherries, which grow on trees cultivated in over 70 countries, primarily in equatorial Latin America, Southeast Asia, South Asia and Africa. Green (unroasted) coffee is one of the most traded agricultural commodities in the world. Coffee can have a stimulating effect on humans due to its caffeine content. It is one of the most-consumed beverages in the world. Wild coffee's energizing effect was likely first discovered in the northeast region of Ethiopia. Coffee cultivation first took place in southern Arabia; the earliest credible evidence of coffee drinking appears in the middle of the 15th century in the Sufi shrines of Yemen. From the Muslim world, coffee consumption and cultivation spread to India, to Italy, and on to the rest of Europe, Indonesia and the Americas. Coffee berries, which contain the coffee seeds or 'beans', are produced by several species of small evergreen bush of the genus Coffea. The two most commonly grown are the highly regarded Coffea arabica, and the 'robusta' form of the hardier Coffea canephora. Once ripe, coffee berries are picked, processed, and dried. The seeds are then roasted to varying degrees, depending on the desired flavor. They are then ground and brewed to create coffee.