Education: Coffee Processing
The coffee bean we all know and love comes from a coffee cherry. Like most fruit, the ideal time to pick the coffee cherry is when it is ripe on the tree. Mature coffee cherries can manifest themselves in red, yellow and even orange pigmentation, i.e. orange bourbon. The cherries are then processed to remove the coffee bean, a time consuming process, and then prepared for shipment. Coffee beans are then roasted at their destination for somewhat immediate consumption.
Cross-section of a coffee cherry
Structure of a coffee cherry:
1: center
2: bean
3: silver skin
4: parchment
5: pectin layer
6: pulp
7: outer skin
STEP ONE: PICKING THE COFFEE CHERRY
There are two types of picking: strip picking and selectively picking. Selectively handpicking only ripe cherries, an obviously more expensive route, requires multiple passes over the same tree over a period of time as all of the cherries become ripe. Strip picking is the understandably cheaper route, but if about 15% of unripe cherries are used, the resulting coffee will taste sour or bitter. The specialty coffee industry typically only sources coffee through growers that pick selectively due to the emphasis on quality. Through Direct Trade relationships, this quality is encouraged and employees of these producers are often paid higher wages.
STEP TWO: DEPULPING THE COFFEE CHERRY (THREE WAYS)
1. Natural (or Dry) process:
Natural or Dry processing of coffee is the historically used method. The coffee cherries with the beans still inside are dried in the sun. In some coffee regions, such as southern Ethiopia, coffee cherries are dried on patios or raised drying beds. The coffee cherry undergoes a sort of natural fermentation which develops the final flavor profile of the coffee. The result is often strong berry flavors that natural process coffees are known for. Naturally processed coffees typically have lower acidity levels.
2. Honey (AKA Pulped Natural or Semi-washed) process:
Honey processed coffee cherries are stripped of their outermost layer by a machine in a process called depulping. The stripped coffee beans are left in the sun to dry with their mucilage, but without their skin. They are constantly racked to make sure they dry evenly to avoid fermentation or rotting. Semi-washed coffees are often sweet and have moderate acidity.
Indonesian processing is a bit unique and is referred to as ‘wet hulling’. It is somewhat of a mix between washed and semi-washed in that the cherries are de-pulped, but instead of avoiding fermentation like a honey processed coffee, some fermentation takes place. They are then washed, lightly dried, then stripped of their parchment and dried completely. Sumatran coffee is known for its low acidity and unique flavor profile which develops from this process.
3. Washed:
Washed coffees are stripped of the complete cherry, including the mucilage. This can be done mechanically or by fermentation. The fermentation process can take ½ a week’s time. Mechanical demucilagers are also used to remove the mucilage. They are then dried in the sun and stored within their parchment layer. Washed coffees are known for having bright acidity. Kenyan coffee is known for fantastic flavor profiles and their ’72 hour’ washed process, a very complicated method of processing washed coffee, is a major factor.
STAGE TWO: DRYING
After the coffee cherry is removed from the coffee bean in one of these three ways, the bean is then dried. This process can be a very tricky step to avoid mold and drying the bean out too quickly. There are four typical methods of drying coffee: concrete or clay patios; raised drying beds; covered, raised beds (‘parabolic’ drying beds); and mechanical dryers. Patios are very common in Central America. They allow producers to dry large amounts of coffee on an easily rakeable surface. The disadvantage is that only one side is dried at a time. Raised drying beds and parabolic beds are waist high drying wracks fitted with screens to allow airflow around the whole bean (Parabolic beds are covered in plastic). Raised beds are often used for natural processed coffees in Africa while parabolic beds are used in Colombia. Mechanical dryers dry the coffee below 104 degrees F oven after they’ve undergone another drying process.
STAGE THREE: RESTING
After undergoing drying, the coffee bean is left to rest for about 3 months, depending upon where it will be shipped, in its final layer of parchment.
STAGE FOUR: DRY MILLING
Dry milling is the process of removing this parchment. Usually sent to a dry mill, the coffee is inspected and sorted either by hand or by an electronic device. At this stage peaberries, a genetic mutation of the coffee bean that produces one rounded bean instead of two flat beans, are separated.
The coffee that is then shipped to its destination is called green coffee because it’s still unroasted. The roasting takes place at its destination for almost immediate consumption.