Washed processing – also known as wet processing – is a way of processing wherein which the pulp is removed from the coffee fruit, and the coffee is dried with only the parchment skin left on. This is a resource-intensive process, which is often makes it too expensive for some farmers or cooperatives to consider. Washed processing typically translates to clean and refined flavours with crisp, sparkling acidity.
First, beans are separated by weight as they pass through a series of water channels. Lighter, undesirable beans along with sticks and leaves will float, whereas the heavier ripe beans sink to the bottom. The beans then pass through a series of rotating drums that separate the coffee by size. After sorting, cherries are put through a pulping machine to separate the skin and some fruit mass from the seeds.
After pulping, batches are placed into a water-filled fermentation tank for anywhere from 12 to 48 hours. This is an absolutely necessary step, as it is where the slick layer of mucilage can be dissolved away from the parchment layer. The fermentation step depends on a number of factors, ranging from the condition and varietal of the beans, all the way to the altitude of the washing station, or cloud cover. In Kenya, it is common to see a double fermentation washed process – here, the beans are soaked for a second period which demands more water usage, but produces an incredibly clean cup.
When fermentation is complete the mucilage will be fully removed, and the beans will feel rough to the touch rather than slimy. This means they are ready for another quick rinse, then the drying stage.
Drying is usually done on large concrete patios in the sun or under canopies, but it may also be done on raised beds, inside greenhouses, or mechanically with a large hot air tumbler.
Once dried to about 10-15% moisture content, the coffee still needs to be separated from its protective parchment (a stiff outer coating) with a de-hulling machine. The parchment is cracked, allowing the green coffee inside to be released. This green coffee is then packaged up for grading and export.
Washed beans in Los Pirineos, El Salvador