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Coffee Processing
- Coffee beans are the seeds of the red fruits, known as
coffee “cherries”. The cherries are ready for
picking when they have turned a
ripe red, and they are still immature when green.
- Inside each cherry, there are two beans, lying flat sides pressed together. (On rare occasions, there is only one bean. In such instances, it is usually larger and rounder in shape than normal beans. These are referred to as peaberry beans). The beans are surrounded by a parchment. If the fruit is ripe, a thin, gooey layer surrounds the parchment, called the mucilage. Both the pulp and the parchment need to be removed before the coffee can be roasted. There are two methods of doing this: dry processing and wet processing.
Dry processing:
This is the oldest, simplest method, and requires little machinery.
Essentially, the goal of the method is to dry the whole cherry, achieved in three steps: cleaning, drying and hulling.
First, the harvested cherries are sorted to remove anything that should not belong (everything from damaged cherries to the occasional twig). This is usually done by hand, with the help of a sieve, a process known as winnowing. They also commonly use flotation in washing channels to remove ripe cherries, as these will float to the top.
The next, most important step, is the actual drying. The
cherries are spread out in the sun, on either huge concrete patios or raised
matted trestles. They are periodically
turned over by hand to ensure an even drying process. This can take up to 4 weeks, though some larger plantations use
machine drying to speed up the process, after the coffee has been pre-dried for
a few days. The goal is to get the coffee
to its optimum 12.5% moisture level.
They need to get the drying just right, as overly dry beans will break
apart in the hulling process, and overly moist beans are prone to mould.
Next, the coffee is stored in silos until they are sent to a mill, where they will hull, sort, grade and bag the coffee for shipment. The hulling machine removes all the outer layers of the cherry in one fell swoop.
Wet method:
The wet method uses more equipment than the dry method, and
usually results in a product that is more homogeneous, containing fewer
defects. The first step, similarly to dry processing, is preliminary sorting in
order to remove all items that should not be there, such as twigs, rocks and
unripe/overripe cherries. This is done
with screens, and separation through floating in water. The next step is the
removal of the
pulp from the cherry.
This is the primary element that distinguished dry from wet processing:
in the dry method, the pulp is removed after drying, whereas the pulp is
removed beforehand in the wet method. A pulping machine is used, leaving the
beans with their mucilaginous parchment covering.
Vibrating screens are then used to separate out the beans from any leftover pulp, or poorly depulped beans.
The next important step is the removal of the mucilage, the gooey stuff covering the parchment. This is achieved through fermentation of the bean for 24 to 36 hours, during which time the mucilage is broken down by enzymes, and can thus be washed away. Farmers can tell fermentation is complete by feel. Quite simply, once they can no longer feel the slimy texture of the mucilage, it is ready to be washed.
Afterwards, the coffee is either laid out to dry on huge patios or using mechanical driers, in order to get the coffee down to its optimal 12.5% moisture level. Sun drying can take 8 to 10 days.
The final step is called curing, which is done just before
the coffee is sold for export. The parchment is removed from the coffee beans,
and then passed through a series of cleaning, screening, sorting and grading
processes. Some use red eye sorting to remove defective beans.
- Finally, we are left with the green bean. This is how your coffee gets exported, and
what we at Cooperative Coffees import.
However, most people would not recognize a green bean as coffee. The
next step, roasting, is what gets coffee
beans into its near final form: the roasted coffee bean.
- Roasting is how we achieve the rich flavour and aroma that we commonly associated with coffee.
Roasting is the practice of heating coffee beans from 180oC to 240oC for 8-15 minutes, inside a large piece of machinery called a roaster. Popping sounds alert the individual roasting the coffee that the process inside is underway. A chemical process is initiated inside the bean, where among other changes, starches are converted into sugars. The most important development that occurs is the extraction of “caffeol”. Caffeol is the essential oil of coffee. It is its essence, in other words, what makes coffee taste and smell like coffee. The heating process precipitates the caffeol from the bean, so that it can be later infused with water to make a cup of coffee.
Depending on
the qualities inherent in the green bean, the beans will be roasted for
different lengths of time and at different temperatures, resulting in what we
call light, medium or dark roasts.
Quite simply, a light roast has been roasted for a shorter amount of
time, and a dark roaster for longer. Choosing how long and at what temperature coffee should be roasted
is considered somewhat of an art form. To get the best quality out of every
bean, an experienced coffee roaster will know how to coax it
out.
References
http://www.ico.org/field_processing.asp
