of the harvesting method, green coffee beans and overripe
coffee cherries inevitably end up mixed with the perfectly
ripe cherries and must be separated during coffee processing.
Overripe coffee cherries, undeveloped coffee cherries,
sticks and leaves float in water.
Ripe coffee beans and green coffee cherries are dense
and sink. Therefore,
the first step in coffee production consists of separating the
"floaters" from the "sinkers."
The coffee floaters are usually sent directly to the patio
to be dried and are often slated for internal consumption.
The ripe and green cherries can be sent to the patios
to be dried using the natural process of preparing coffee or can be sent
to the coffee pulping machines.
Coffee Processing Equipment
The first stage of coffee pulping
is used to remove the green coffee cherries from the ripe cherries.
In the coffee pulping machinery, the internal pressure is monitored
to push the coffee against a screen with holes only large
enough for a coffee bean (not cherry) to pass through.
Since the ripe cherries are soft, they break and the coffee
seed is released through the screen.
For more information about coffee processing equipment, view this video
showing coffee pulping machines: medium (5.6 Mb) or small (1.5
The green cherries are
hard and cannot be pulped.
Instead of passing through the screen, the green
coffee beans pass to the end of the barrel system and are separated
from the ripe coffee beans.
The pressure inside the barrel controls how many
cherries will be pulped. A very high pressure will cause all of the cherries including
the green beans to be pulped.
It is necessary to continuously monitor the pressure
so that about 3% of ripe cherries are not pulped and are
removed with the green cherries.
This margin of error ensures that no green cherries
are mistakenly pulped.
The pulp and coffee beans are then separated by centrifugal
force and a barrel screen system.
For more information about coffee pulping, view this video showing the
inside of the pulp separator: medium (1.24 Mb). Video showing another pulp separator in
action: medium (4.2 Mb) or small (985 Kb).
The coffee beans covered in the
slippery mucilage can be sent to the patios to dry as pulped
natural coffees or can be sent to coffee fermentation tanks.
The coffee fermentation tanks are used to remove the mucilage
before drying. The
pulped coffee beans are put into cement tanks with water and are
allowed to ferment for 16-36 hours. On
the way to the fermentation tanks, another density separation
can occur. The highest quality coffees are the densest and should be separated and fermented in a different
For more information about molecular density sorting, view this video showing a newly designed density sorting
tank: medium (6.5 Mb) or small (1.4 Mb).
coffee fermentation time depends on a number of factors including
the amount of coffee fermenting, water temperature, and
humidity. The mucilage
is made up of pectin materials including protopectin (33%),
reducing sugars including glucose and fructose (30%), non-reducing
sugars such as sucrose (20%), and cellulose and ash (17%)
455). Protopectin is not water soluble and will
hydrolyze to pectinic acid in the fermentation tanks (Wrigley,
455). Hydrolysis of the protopectin and degradation
of the pectin by enzymes is the process that occurs to remove
the mucilage during fermentation (Wrigley, 455). Currently,
the best way of determining the end of coffee fermentation is to
feel the coffee beans to determine if they are still encased
in mucilage. If
the coffee beans are fermented for 36-72 hours, stinker beans develop.
Lactic, acetic, and propionic acids are produced in this
process and are believed to prevent the traditional fermentation
taste by inhibiting mold growth that regularly occurs during
drying on a patio in humid conditions (Wrigley).
For more information about coffee fermentation, view this video
showing the coffee in the coffee fermentation tanks: medium (1.1 Mb).
the coffee fermentation tanks, the beans are moved to drying patios
and dried to 11-12% moisture content. See coffee drying
section for more details.
A small portion of the lot is hulled and milled by a
hundred grams of coffee is classified for defects (100 grams
is often used), and the percentage of each screen size is determined.
Then, 200-300 grams of coffee is roasted in a sample
roaster and cupped to determine coffee quality.
Ideally no lots will be mixed until the coffee has been
classified and cupped.
The coffee remains in pergamino until shipment time to
help protect the flavor and aroma of the coffee.
For a complete look at coffee production, view this video
showing the steps of coffee processing (shown individually above): Medium
(14.6 Mb) and Small
For more information about coffee processing, visit the National Coffee Association or Wikipedia.
Flavor Characteristics Due to Processing
Density Sorting Coffee
Color Sorting Coffee