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Processing
Processing of coffee is the method of converting the raw fruit of the
coffee plant (cherry) into the commodity green coffee. Coffee beans are
the seeds of fruits, which resemble cherries, with a red skin when ripe.
Beneath the pulp, each surrounded by a parchment-like covering, lie two
beans, flat sides together. Underneath the parchment the beans are covered
in another thinner layer, the silver skin. Coffee beans must be removed
from the fruit and dried before they can be roasted; this can be done
in two ways, known as the dry and the wet methods. When the process is
complete the unroasted coffee beans are known as green coffee.
Wet
Most specialty coffees are processed by the "wet" or washed
method. After being picked at the peak of ripeness, the coffee beans are
"squeezed" out of the cherry-like skin by a pulper and separated
with the aid of water. The beans are then allowed to ferment for 36 to
72 hours and washed with clean water. This process removes the mucilage
or fruity layer before the coffee beans are put out to dry for about 2-3
weeks. The beans are turned several times a day to ensure that all the
beans dry evenly. After an additional "conditioning" period
of about 6-8 weeks, the coffees are then milled (to remove the parchment
or pergamino layer) before being sorted to remove imperfections and graded
for size, weight, and most importantly - liquor or cup quality. In the
dry or natural method, after being picked, the whole cherries are placed
directly on drying patios and left to dry in the sun. The dried cherries
are later milled, sorted, and graded for export.
Even after careful harvesting, a certain number of partially dried and
unripe cherries, as well as some stones and dirt, will be present among
the ripe cherries. As in the dry method, preliminary sorting and cleaning
of the cherries is usually necessary and should be done as soon as possible
after harvesting. This operation can be done by washing the cherries in
tanks filled with flowing water. Screens may also be used to improve the
separation between the ripe and unripe, large and small, cherries.
As with most agricultural products, not all lots are the same. Therefore,
it is up to the coffee roaster to buy, blend, and roast each coffee in
such a manner that you, the consumer, can expect the same product each
time you buy a pound of your favorite coffee from your retailer.
Dry
The dry method (also called the natural method) is the oldest, simplest
and requires little machinery.
This method involves drying the whole cherry. There are variations on
how the process may be carried out, depending on the size of the plantation,
the facilities available and the final quality desired. The three basic
steps, cleaning, drying and hulling, are described below.
First, the harvested cherries are usually sorted and cleaned, to separate
unwanted fruit, leaves, soil, and twigs. This can be done by winnowing,
which is commonly done by hand, using a large sieve. Any unwanted cherries
or other material not winnowed away can be picked out from the top of
the sieve. The ripe cherries can also be separated by flotation in washing
channels close to the drying areas.
The coffee cherries are spread out in the sun, either on large concrete
or brick patios or on matting raised to waist height on trestles. As the
cherries dry, they are raked or turned by hand to ensure even drying.
It may take up to 4 weeks before the cherries are dried to the optimum
12.5% moisture content, depending on the weather conditions. On larger
plantations, machine-drying is sometimes used to speed up the process
after the coffee has been pre-dried in the sun for a few days.
The drying operation is the most important stage of the process, since
it affects the final quality of the green coffee. A coffee that has been
over dried will become brittle and produce too many broken beans during
hulling (broken beans are considered defective beans). Coffee that has
not been dried sufficiently will be too moist and prone to rapid deterioration
caused by the attack of fungi and bacteria.
The dried cherries are stored in bulk in special silos until they are
sent to the mill where hulling, sorting, grading and bagging take place.
All the outer layers of the dried cherry are removed in one step by the
hulling machine.
The dry method is used for about 95% of the Arabica coffee produced in
Brazil, most of the coffees produced in Ethiopia, Haiti and Paraguay,
as well as for some Arabicas produced in India and Ecuador. Almost all
Robustas are processed by this method. It is not practical in very rainy
regions, where the humidity of the atmosphere is too high or where it
rains frequently during harvesting.
Decaffeinated
Processing
European Process
Most decaf coffees are made using a chemical process first used in Europe.
This process involves soaking the beans in water and then "washing"
them in methylene chloride to absorb the caffeine from the bean. After
this, the beans are rinsed clean of the chemicals, dried and shipped
to the coffee roasters. The advantage of this method is that it provides
decaf coffee with more flavor than the Swiss water processing. Although
there is virtually no trace of any chemicals left in the bean after
roasting, some people are uncomfortable knowing that the coffee they
are drinking was chemically processed.
Swiss Water Process
The second method is known as "Swiss water processing". This
process uses no chemicals, but rather hot water and steam to remove
the caffeine from the coffee. The "life" of the bean is taken
into the water, and then the water solution put through activated charcoal
filters to remove the caffeine. Once the caffeine is removed, these
same beans are then put back into the decaffeinated solution to re-absorb
everything except the caffeine. The beans are then dried and shipped
to the roasters. The disadvantage is that the water processing removes
more than just the caffeine. Some of the oils from the coffee bean are
removed as well, making it less flavorful.
The best thing to do for those who really want this kind of decaf is
to start out with a high quality, Arabica bean. Even though some of
the flavor will be lost, there will still be a lot left to enjoy.
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