1. The coffee is mechanically de-pulped, removing the cherry.
2. Next, it is fermented in a tank for an average of 18-24 hours. This process helps detach the mucilage (the fleshy interior of the coffee fruit) from the bean, which is then washed thoroughly with water.
3. Small producers usually dry the beans in the sun — a slower and more careful approach to processing, which helps preserve quality. Beans can also be dried mechanically in silos.
Popularized by Colombian producers in the early 20th century, washed processing remains the most common methodology used among producers of high-quality coffees. The fermentation process, when done in a controlled manner, can greatly improve cup quality. During this process, natural yeasts and bacteria from the surrounding environment break down the mucilage, separating it from the grain and leaving behind several different by-products, including fatty acids like terpenes and esters. These fatty acids, which dilute in the water during coffee extraction, add great complexity to the final cup.
Tip: If done with care, combining beans harvested across multiple days, fermentation can go on for 5 days without damaging the coffee. Longer periods of fermentation can lead to very complex cups with high levels of sweetness. This process, however, has its risks.
A similar process is used by many larger farms, which, instead of fermenting the cherries, remove the mucilage mechanically, saving time and water. Leaving out the fermentation process, however, affects the sensory qualities of the end product.