How is Coffee Processed?

After coffee is grown and harvested, it needs to be processed. The main goals of processing are to:

  1. Sort the suitable crops from the unsuitable
  2. Separate the coffee cherries’ outer layers from the beans
  3. Allow the beans to reach a state of optimal moisture and flavor.

Winnowing

The first step in processing is to remove any debris such as twigs, dirt, and leaves from the beans. Next, the cherries are submerged in water to separate the over-ripe cherries for discarding. The undesirable over-ripe cherries float, while the ripe and unripe ones sink.

Combined, these two steps combined are called winnowing. They’re often done manually, with a sieve, but they can also be mechanized.

Coffee beans on bush

After winnowing, there are three ways to process coffee: dry processing, semi-dry processing, or wet processing.

These methods differ based on when and how different layers of the coffee cherry are removed from the bean. Keep in mind that a coffee cherry has five main parts – the beans, the silver skin (a thin membrane that coats the beans), the parchment (a thicker papery covering), the mucilage (a sugary substance that becomes slimy and gelatinous when the fruit is ripe), and the pulp (outer skin). 

Dry Processing

In dry processing, the sorted cherries are laid on large patios or raised drying beds to dry in the sun and air. As they dry, workers periodically rake and turn them to make sure all cherries are exposed and mold doesn’t accumulate in the moisture. Throughout the dry processing, the coffee ferments in its natural flavors.

It’s important that the coffee cherries don’t over-dry and become too brittle to be hulled without breaking. Dry processing is continued until the coffee reaches optimal moisture content, usually between two and four weeks. At the end of dry processing, the coffee cherries must have all outer layers (pulp, mucilage, parchment, and silver skin) removed from the beans through hulling and polishing.

Coffee beans drying

Dry processing is the oldest processing method. Because it’s done manually, it’s accessible to low-income processors who can’t afford the machinery required for wet processing. Most practical in sunny regions where rain and humidity don’t interfere with the drying process, dry processing is widely used in Brazil, Ethiopia, and Indonesia. Check out our Mocha Java coffee for an example of dry processed beans.

Semi-Dry Processing

In semi-dry processing, pulps are removed from the ripe cherries using a hand- or motor-operated pulper. The pulper uses water pressure to push the cherries against a slotted surface. Only the softer, ripe cherries make it through the slots, leaving their pulps behind. At the end of semi-dry processing, the coffee cherries still have their mucilage, parchment, and silver skin attached. The mucilage-coated beans are dried for hulling and polishing. Semi-dry processing goes by many other names, including “pulped-natural,” “wet-hulled,” and “semi-washed” processing.

Wet Processing

In wet processing, the coffee cherries are de-pulped using a different type of pulper than for semi-dry processing. This mechanism uses water pressure to push the cherries against a rough metal disk or drum. The textured surface scrapes most of the pulp, but not the mucilage, from the beans. To remove the mucilage, the coffee is either wet- or dry-fermented in tanks. In fermentation, yeasts and bacteria break down the sugars in the mucilage until it’s completely gone. Wet fermentation means the cherries ferment in added water, while dry fermentation means they soak only in their own juices. A byproduct of the fermentation are acids that lend the coffee flavor, but the coffee must be closely monitored to ensure it doesn’t over-ferment and become sour. It usually takes eight to 36 hours to do away with the mucilage.

Coffee plant

An alternative to fermentation is a mucilage remover, which detaches the mucilage via mechanical scrubbing. At the end of wet processing, the coffee beans still have their parchment and silver skin attached. They are dried in the sun, on drying racks, or in heated rotating drums.

Try our Honduran coffee for a great example of wet processed beans.

Hulling and Polishing

Finally, the dried coffee cherries are hulled to remove the parchment skin from the bean. Various types of machines are used for hulling, ranging from rotating cylinders with “cleats” (rough edges) that tear off the fruit skin via friction to cross-beater wire drums with blades that cut it away. At the end of the hulling step, all that’s left are the green coffee beans.

Polishing is the final step in processing. Designed to remove any silver skin that escaped the hulling process and improve the beans’ appearance, polishing is optional and skipped by some processors.

Different types of processing have different effects on flavor. Dry-processed beans absorb the fruity flavors from its intact outer layers, while wet-processed beans have more pronounced acidity. Semi-dry processing, being a hybrid of the two, has a more moderate flavor than either.

Coffee beans in bag

Luckily, Cadena sources beans that have been processed in a variety of ways! Explore all our different roasts here.