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Harvesting
Each year coffee is harvested during the dry season when the coffee cherries are
bright red, glossy, and firm. Ripe cherries are either picked by hand, stripped
from the tree with both unripe and overripe beans, or all the beans are collected
using a harvesting machine. These processes are called selective picking, stripping,
and mechanical harvesting, respectively.
To maximize the amount of ripe coffee harvested it is necessary to selectively pick
the beans from the ripe tree by hand and leave behind unripe, green beans to be
harvested at a later time.
About 12-20 kg of export ready coffee will be produced from every 100 kg of coffee
cherries harvested.
Drying
Before shipment coffee must be dried from approximately 60% moisture content to
11-12% moisture content. Coffee is typically dried on large patios made of asphalt
or cement and then transferred to mechanical dryers. The coffee on the drying patios
is shifted every 30-40 minutes and is shaped into long rows of no more than 5 cm
in height. Next to each row is open ground, which is warmed and dried by the sun.
The coffee is then shifted onto the dry portion of the patio, and the section where
it was previously is now allowed to dry in the sun. This helps accelerate the drying
process and prevents fermentation and moldy beans from developing. To dry coffee
solely by patio drying it takes 6-7 days for washed coffees, 8-9 days for pulped
naturals (semi-washed), and 12-14 days for natural (dry-processed) coffees. This
is why coffees are typically dried on a patio until they reach a moisture content
of 15% and are then transferred to mechanical dryers. Once the coffee reaches 25%
moisture or less it can be piled at night and covered with cotton cloths to allow
the coffee to breath. If it rains these piles can also be covered with plastic.
Coffee should not be covered with burlap sacks since this will impart a distinct
burlap flavor and aroma to the coffee.
There are several dryer systems available. Many older dryers are converted grain
dryers that are not as efficient as the new horizontal barrel dryers. The new dryers
are designed to mix the coffee evenly to ensure uniform drying. Drying by using
mechanical dryers accelerates the slowest part of the drying process (15-11%) and
helps prevent fermentation. In some environments that have a high humidity the entire
drying process must take place in mechanical dryers. Mechanical dryers should never
be set higher than 40-45°C and this question should be asked before buying any coffees
that have been mechanically dried. At higher temperatures the germ is killed and
the flavor potential of the coffee is ruined. At extreme temperature the bean crystallizes
and when smashed with a hammer will break like glass.
The best, but least utilized method of drying coffee is by using drying tables.
In this method the pulped and fermented coffee is spread thinly on raised beds,
which allows the air to pass on all sides of the coffee. The coffee is mixed by
hand and the drying that takes place is more uniform and fermentation is less likely.
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