What processing methods for coffee beans ?
After harvest, the fruits of the coffee tree go through different processes to obtain the beans that we know. According to the varieties and the techniques of the producers, there are several methods of coffee processing. What are they ? How do they differentiate themselves?
Dry process for natural coffee
Once harvested, the coffee cherries are left to dry directly in the sun on large flat concrete areas or on an “African bed”. This is a mat weave suspended on four legs, allowing the grain to dry from above and below. This so-called “African bed” technique is certainly the most suitable for drying fine coffee.
The pulp dries out, little by little, shrinks and eventually solidifies. For about three weeks, the cherries are turned regularly so that all the coffee beans can dry harmoniously.
Once dry, the coffee beans are shelled to remove the rest of the pulp. There is still the very fine parchment envelope coating the beans, resulting in the straw yellow color and slightly disparate of the so-called plain coffee.
A plain coffee is distinguished by its fruity profile and its wilder taste.
Wet process for washed coffee
In this process, the coffee cherries are pulped within a maximum of 12 hours after harvest, in order to separate the pulp from the beans. These beans still have their mucilage, a little sweet skin enveloping the coffee bean. They are then fermented in washing tanks, and stirred between 12 and 36 hours.
After this fermentation period, the cherries are dried using three methods: drying in a large hot air oven, drying on a concrete floor or drying on an “African bed”.
On the taste side, you will have a fine, subtle and aromatic coffee in a cup, most often with good acidity.
The Honey Process is a mixture of two methods: Washed / Natural. The coffee cherry is first pulped as for a washed transformation, then is dried in the sun as for the natural transformation. So, just after pulping, the material that surrounds the grain (the mucilage) is still present. During drying, it then integrates the coffee bean.
This method makes it possible to obtain more sugar than with a washed transformation (where the mucilage disappears during fermentation with water) and to gain in aromatic clarity compared to a natural transformation.
Different kinds of Honey Process exist (mainly black, red, yellow, white) depending on the amount of pulp left during the dehulling.
In a cup, honey coffees have a very marked body and sweetness. Indeed, it is the drying of the parchments with the mucilage that will have a direct impact on the sweetness of the coffee.
Wet Hulled process
Or Giling Basah, is a type of coffee processing that is unique to Indonesia and most often used in Sulawesi and Sumatra.
The mature coffee fruit is harvested and farmers remove the outer skin mechanically using locally built pulping machines. The coffee beans, coated with mucilage, are stored for up to a day during which a natural fermentation breaks down the sticky residue. Afterwards the coffee beans, protected by a parchment hull are washed off before being let out to dry.
Contrary to other traditional drying methods, where the parchment coffee is dried until it reaches about 12% moisture content, the beans in the Giling Basah process are hulled when they reach between 30 and 40% moisture content (still semi-wet).
The green coffee beans are then further dried to reach the exportable 12% moisture content. This operation gives the beans a unique bluish-green appearance and sometimes the hulling machine partially crushes a soft bean, giving the bean a shape resembling a goat’s foot.
Anaerobic fermentation is a new method allowing the development of new aromas and the search for new flavors.
The coffee (whole cherry) is processed in a fully sealed, air-free fermentation bag. Oxygen is removed when coffee is added at the start of the process, and valves on the tanks prevent oxygen from seeping in during the process while allowing the release of CO2 that builds up during fermentation.
After about 18-24 hours, the process causes the mucilage to break down and a huge build-up of CO2 pressure in the reservoir. This pressure forces the flavors of the juicy mucilage into the coffee parchment. Yeast and bacteria convert the sugars and acids in the coffee mucilage (the honeyed substance that surrounds the coffee beans).
An oxygen-depleted environment slows down the fermentation process. Which offers totally different aromatic notes.
Once this step is completed, the coffee will be able to finish its fermentation in flully washed, natural process or honey process. The result of this process is a coffee with a much more fruity taste with a creamier texture on the palate. It is a coffee that will also have very little bitterness.