This weeks Journal post is the second of a three part series on coffee processing.
Processing using the washed method is sometimes referred to as wet processed, fully washed and semi washed to name a few.
Once ripe coffee cherries have been picked, the fruit is removed as soon as possible. This is referred to as 'pulping' or 'milling'. The cherries are fed, by gravity and water flow, through a channel that contains a spinning disc that rubs the coffee fruit off the seed. Some mills have a few of these discs in line to gradually remove more and more fruit without damaging the beans. The water channels separate dense beans from light beans and send them to different fermentation tanks.
The pulping discs cannot remove the sticky layer that covers the coffee seeds, the mucilage. To remove this layer, the coffee is either left in a tank with or without water. Dry fermentation is a faster process than wet fermentation, as the temperature of the coffee is higher and it is exposed to the air. In wet fermentation, where the coffee is soaked in water, the fermentation times can be double that of the dry method. The aim of them both is to allow the mucilage to break down without adding any fermented flavour to the coffee.
Once the mucilage has been removed and the beans have been rinsed, they need to be dried. This step can also be done in many ways. Weather is a major deciding factor for the way a mill will dry their coffee. If conditions are favourable, the coffee can be dried outdoors either on a cement floor/patio or on raised drying beds. The raised beds are great as they allow air flow to the top and bottom of the beans as they dry. If weather conditions are unfavourable, there are two options; mechanical drying machines or traditional outdoor methods, done undercover.
When the coffee has reached it's desired dryness, usually 10-12% moisture content, the final layer can be removed. This parchment is a husk that is removed by a 'huller' or 'dry mill'. This is a spinning cylinder that sits in a housing with an adjustable gap between the cylinder and the housing walls. The parchment coffee is fed through the housing and the spinning cylinder separates the parchment from the bean.
The coffee beans are then cleaned and sorted to be sold to different coffee buyers around the world. The grading systems differ for each producing country, just to add another layer of confusion. You might of heard of a 'Grade 1' coffee, 'AA' or 'Fancy'. These are all examples of different size and quality grading systems.
Each seemingly insignificant one of these steps can ruin coffee. If under or over-ripe cherries are picked, the rest is pointless. If the coffee is not pulped immediately after picking, the coffee will taste fermented. If the mucilage removal period goes for too long, the coffee will taste fermented. If the coffee is left in a big pile to dry it will go mouldy, so the coffee must be dried in a thin layer to ensure even drying. If the coffee is not dried properly before it is hulled, the beans will be soft and can get damaged in the hulling machine. The more we understand about the coffee process, the more we appreciate good quality coffee when we get it.