There are hundreds of different coffee species but the two most commercially viable are coffea robusta and coffea arabica. The sturdy, disease-resistant coffea robusta, which thrives at lower altitudes, produces beans with a harsher, more single-dimensional flavor than the more sensitive coffea arabica, which grows at high altitudes (3,000 to 6,500 feet) and produces beans with elegant, complex flavors. The coffee plant is actually a small tree that bears a fruit called the "coffee cherry." Growing and tending these coffee trees is a labor-intensive process because blossoms, unripe (green) and ripe red cherries can occupy a tree simultaneously, necessitating hand-picking the fruit. The coffee cherry's skin and pulp surround two beans enclosed in a parchmentlike covering. Once these layers are discarded, the beans are cleaned, dried, graded and hand-inspected for color and quality.