Now that we know more about growing conditions and how Kona coffee cherries are harvested, we can move on to the next stage: coffee processing. There is a lot to do before the beans are roasted and your cup of coffee is ready!
There are two common methods for processing coffee – the dry process and the wet process. Although the dry process is the oldest known method of processing coffee, and is useful for producing some special sun dried varieties such as our Kona Naturals – it is not always the most practical method to use in wetter growing regions where humidity can be an issue. The Royal Kona Coffee Mill and many Kona coffee farms use the wet process.
How the Wet Process Works
An advantage of the wet process is that while water is integral to preparing the coffee, it helps to physically move it through the stages of the process itself. The hilly Kona terrain also helps us take advantage of gravity to keep things flowing.
After the sacks of coffee are received and inspected, the coffee cherry is loaded into large hoppers and fed through a system for washing and filtering – the unsuitable beans are separated and the remainder are sent on to machines called pulpers. The pulpers are motorized metal cylinders with spinning parts that squeeze and strip the flesh from the fruit – leaving beans that are covered in a sticky, sugary layer known as mucilage.
Since we process such a large volume of Kona coffee beans, we separate some of the mucilage mechanically… but not all of it. The right balance is required to achieve a suitable rate of fermentation and avoid the beans fermenting too fast (or too much) and taking on undesirable flavors. The beans remain in the fermentation tanks and are monitored carefully. Once the natural enzymes have broken down the remaining mucilage layer (anywhere from 12 to 48 hours later) fermentation is complete, and the beans are left with their parchment skin intact. Now the beans are rinsed and sent on to the drying stage.
You might think that the drying stage is simple, but like all the stages leading up to it, there is more than meets the eye! It’s important that the beans are dried gradually and consistently until they contain a stable moisture content. We use mechanical dryers to obtain a consistent and controllable rate of drying, and to ensure the beans are dried evenly. These dryers look like large perforated metal drums… slow rotating for 28-36 hours depending on the outside ambient moisture levels. Once dry the beans are left covered in a thin, papery membrane known as parchment, and are transferred to the dry mill area for the next stage of processing.
The hulling process uses a machine that utilizes the friction of the dried beans rubbing against themselves to remove the parchment, which is then extracted via air into storage. The green beans are now ready for grading.
Sorting and Grading
The green beans are now fed onto a system of tilted oscillating screens that shake them into storage bins, separated by size as they move downwards. Now that the beans are sorted by size, they are passed through a gravity table, where they screened by weight. These steps are important to maintain the quality and integrity of the Kona coffee grading system, where factors such as size, shape, moisture content and number of defects determine the final grade of the coffee, ranging from the primary grades of Kona extra fancy (highest quality) through to Kona prime. We may also pass our coffee through an electronic optical sorting machine for an additional layer of quality control.
Now that the green coffee has been processed, it is packed for storage and sent to our roasting facility.