Wet Milling

Wet milling, often referred to as the washing station, factory, or beneficio, is the primary processing center where freshly harvested coffee cherries are brought for initial transformation. The primary objective of the wet mill is to remove the outer skin and the sticky mucilage layer surrounding the coffee seed. This process is fundamental to the 'washed' or 'wet-processed' style of coffee, which is prized for its clarity, acidity, and clean cup profile.

Upon arrival at the wet mill, cherries are typically sorted by density in water channels or flotation tanks to remove under-ripe or damaged fruit. The cherries are then passed through a depulper, a machine that mechanically strips the outer skin. Following depulping, the beans—still covered in a layer of mucilage—undergo a fermentation stage. During this time, natural enzymes and microbes break down the mucilage, a process that can be carefully controlled to influence the final flavor profile of the coffee.

After fermentation, the coffee is thoroughly washed with clean water to remove any remaining mucilage residue. The resulting product is known as parchment coffee, which must then be dried to a specific moisture content before it can be stored or sent to a dry mill. Modern wet mills are increasingly focused on water conservation and wastewater management, utilizing eco-pulpers that require significantly less water than traditional systems.

For the producer, the wet mill is the heart of the farm's infrastructure. It is where the most critical decisions regarding fermentation time, temperature, and water usage are made. These choices directly impact the quality and consistency of the final cup. For the consumer, the wet mill is responsible for the 'clean' character often associated with high-quality washed coffees, as it effectively separates the seed from the fruit in a controlled, hygienic environment.

In practice, the wet mill is the bridge between the coffee tree and the dry mill. It requires precise management of equipment and timing to ensure that the delicate sugars and acids within the bean are preserved. A well-run wet mill is essential for producing specialty-grade coffee, as even the best-grown cherries can be ruined by poor processing at this stage.