Coffee beans are processed by removing the fruit layers surrounding the seed inside each coffee cherry, then drying the beans to a moisture content between 9% and 12%. There are three primary methods for doing this: the washed (wet) process, the natural (dry) process, and the honey process. Each method strips away different amounts of fruit at different stages, which directly shapes the flavor of the final cup.
What’s Inside a Coffee Cherry
A coffee cherry has several layers wrapped around the seed you eventually grind and brew. The outermost layer is the skin, followed by a sticky, sugary layer called mucilage (sometimes called the pulp). Beneath that sits a papery shell called parchment, and under the parchment is a very thin membrane called silver skin. Processing is the work of removing all of these layers while drying the bean to a stable moisture level for storage and shipping.
The Washed (Wet) Process
Washed processing removes all the fruit from the bean before drying begins. Right after harvesting, the cherries go through a machine called a depulper, which strips away the outer skin and most of the fruit. The beans, still coated in a thin layer of mucilage, then sit in water tanks where fermentation breaks down that remaining sticky layer. This fermentation stage typically runs 24 to 48 hours, though specialty producers sometimes extend it to 72 or 96 hours to develop specific flavor characteristics. Yeast and lactic acid bacteria naturally present on the fruit drive the fermentation, consuming sugars and producing organic acids that influence the bean’s final taste profile.
After fermentation, the beans are rinsed clean and spread out to dry on raised beds or concrete patios. Traditional wet processing uses a significant amount of water. One study of Ethiopian processing mills found that producing a single kilogram of green coffee beans required about 63 liters of processing water. Because of this, some producers have adopted eco-pulping machines or recirculating water systems to cut consumption.
Washed coffees tend to have a cleaner, brighter flavor. Because the fruit is removed early, the taste reflects the bean itself and the conditions where it was grown, rather than sugars absorbed from the cherry during drying.
The Natural (Dry) Process
The natural process is the oldest and simplest method. After picking and sorting, whole coffee cherries are spread out to dry with the fruit still intact around the seed. The cherries sit on patios or raised drying beds, typically in thin layers, and are turned regularly to prevent mold and ensure even drying. Open sun drying takes roughly 33 to 47 hours depending on the thickness of the layer, though in practice many producers spread drying over two to four weeks since cherries are only exposed to sun during daylight hours and must be covered or sheltered overnight and during rain.
The target is a moisture content between 9% and 12%. Beans dried above 12% are prone to mold during storage. Beans dried below 9% lose flavor and aromatic compounds. Once the cherries are sufficiently dry, the dried fruit is mechanically removed, leaving the green coffee bean ready for storage.
Because the bean sits inside the fruit for the entire drying period, natural-process coffees tend to be sweeter and more fruit-forward, with heavier body. This method uses very little water, making it common in regions where water is scarce.
The Honey Process
Honey processing sits between washed and natural. The skin of the cherry is removed with a depulper, but a specific amount of mucilage is intentionally left on the bean before drying. The name comes from the sticky, honey-like texture of that mucilage layer, not from any honey flavor.
Producers control how much mucilage stays on the bean, and this creates distinct subcategories:
- Yellow honey retains about 25% of the mucilage and dries in direct sunlight, producing a lighter, cleaner cup.
- Red honey keeps about 50% of the mucilage and dries under partial shade, slowing the process and developing richer sweetness.
- Black honey retains nearly all the mucilage and dries in fully shaded conditions with no direct sunlight, resulting in a heavy, fruit-sweet profile close to a natural-process coffee.
The more mucilage left on, the longer drying takes and the more labor-intensive the turning and monitoring becomes. Honey-process coffees generally land between washed and natural in flavor: more body and sweetness than washed, more clarity than natural.
Hulling and Polishing
Regardless of which method was used, dried coffee beans still have the parchment layer (and sometimes the silver skin) attached. These are removed in a step called milling, which has two stages. First, a peeling machine strips away the parchment hull. Then a polishing step removes the silver skin, a thin membrane that clings to the bean even after the parchment is gone. Some mills use a combination machine that handles both steps in a single pass. After milling, the beans are sorted by size and density, and any defective beans are removed.
What Goes Wrong During Processing
Processing errors create defects that ruin the taste of the final cup. The most common issue is over-fermentation. If beans sit too long in fermentation tanks or dry too slowly with fruit still attached, unwanted microbial activity produces harsh, vinegary compounds. These “full sour beans” are considered a Category 1 defect, the most severe classification in coffee grading. They’re usually discolored, ranging from brownish to reddish, and introduce a sharp, acrid taste that can spoil an entire batch.
Under-drying is another frequent problem. Beans stored above 12% moisture are vulnerable to mold growth, which can produce off-flavors and, in serious cases, mycotoxins. Over-drying below 9% causes the opposite issue: beans become brittle and lose the volatile compounds responsible for aroma and complexity. Careful, consistent drying with regular turning and moisture checks is the single most important quality control step in any processing method.
Storing Green Coffee Beans
Once processing and milling are complete, green (unroasted) coffee beans need to be stored properly until they reach a roaster. The International Coffee Organization recommends a bean moisture level of 11% to 12.5% for storage, though some specialty roasters prefer beans dried slightly further, to around 10% to 10.5%.
Warehouse temperature should stay at roughly room temperature, between 20°C and 25°C (68°F to 77°F). Consistent conditions matter more than hitting an exact number. Fluctuations in temperature and humidity cause the beans to absorb and release moisture, which degrades flavor over time. Hermetic (airtight) packaging offers extra protection, keeping beans stable across a much wider range of warehouse conditions. Under good storage, green coffee holds its quality for several months to a year, depending on the variety and how it was processed.