Imagine a grape drying into a raisin. The once smooth and shiny outer skin, over time, turns into a rippled and tight fruit leather. The process and ending result is not all that different in the coffee harvesting and processing world of natural coffees. When coffee fruit on the tree is determined to be ripe, the cherries are picked and laid to dry out in the sunshine. Often this process will take anywhere from 20-30 days, on raised beds or patios. Keeping in mind that coffee grows best between the tropic of Capricorn and Cancer (+20 degrees north -20 degrees south), these locations have ample daily heat and hopefully not an excess amount of humidity that will effect the bean negatively in taste.
Inside this cherry are multiple layers of skin including a parchment, mucilage, and outer layer (which takes on pigmentation and indicates when to harvest). Click here for an illustrated cross-section diagram.
Because the mucilage has naturally occurring sugars and alcohol, a natural fermentation will occur in the small environment. What this yields for taste is often a dense heavy body, less acidity, with fruit "bomb" wildness and rustic flavors.