Coffee processing
There are two types of coffee processing – The Dry, and The Wet. From plant to cup, the process is not a simple one. Bringing coffee to you is an art in itself. Here's how...
The Dry Method
The dry method is the oldest and most widely used method for processing coffee cherries. Nearly all robusta and around 50% of arabica coffees are processed using this method. Done properly there needs to sufficient space to lay out the cherries. If they are piled too thick the quality can suffer. They need to be regularly turned for a period of 10 to 30 days. There is the potential for foreign or undesirable elements to infiltrate the crop at this stage. Also the distinct earthy taste of most robustas are as a direct result of this drying process. The best unwashed arabicas are given far more meticulous processing than most unwashed robustas.
During the drying process the humidity within the cherry falls from 70% to 15 – 30%, ultimately to a maximum of 12% at the very end. With the dry method the sugars migrate to the bean itself from the pulp (in the wet process a percentage of the beans mineral content is lost). For this reason they show greater body and sweetness and retain their aromatic qualities for longer.
Coffee beans go through three stages during the drying process. The first stage is drying the whole bean. The second is hulling the cherry. Finally, they are cleaned sorted and graded in dry mills ready for export. The Wet Method (Washed) Where there is high humidity or rainfall the dry method can become very protracted. In the mid-eighteenth century the earliest form of wet processing was developed.
Washed arabicas comprise nearly all the output of Latin America, with the partial exception of Ecuador and in particular Brazil. They also account for a large part of arabica production in Africa apart from Ethiopia, and Asia, except for Indian coffees. An ample supply of pure water is vitally important to this process.
To avoid unwanted fermentation, the cherries must be processed as soon as possible after harvesting. The cherries are places into tanks of water which sink leaving impurities and rotten cherries at the surface. From here they go to depulping machines removing their outer skin and pulp. Again the pulp must be removed as quickly as possible to avoid fermentation. The next step involves removing the sticky mucilage that still covers the coffee bean. They are immersed in fermentation tanks where the mucilage decomposes through bacteria.
During fermentation the temperature of the coffee reaches about 40C and needs to be continually moved about to ensure even fermentation. The whole process can take on average 12 to 36 hours. If not actioned properly the coffee can have a decidedly rancid taste. Once completed the beans need to be washed immediately through a series of sluices. This process will remove any remaining defective beans which will rise to the surface. During fermentation and washing around 1.5 to 2% of minerals and solids are lost. As a result , while unwashed coffees show greater body and sweetness, washed arabicas display a more decided acidity and are more aromatic in the cup.
Finally, coffee beans are laid out on cement or terracotta patios and dusted with powdered lime to guard against the spread of fermentation. Drying can last between three and twenty days. Coffee beans go through five stages during the wet process. Firstly, seperating the cherries in tanks. Then onto pulping through the depulping machines. From there they are placed into fermentation tanks, before being washed. Finally, they are laid out to dry.
