2009_Book_FoodChemistry

21.1 Coffee and Coffee Substitutes 939
kg) of fresh coffee cherries which yields 1 kg of
marketable coffee beans is for C. arabica 6.38,
C. canephora 4.35, and C. liberica 11.5. The
most important countries providing the world’s
coffee harvest in 1996 are listed in Table 21.1.
21.1.2 Green Coffee
21.1.2.1 Harvesting and Processing
The coffee harvest occurs from about December
until February from the Equator north to the
Tropic of Cancer, while south of the Equator to
the Tropic of Capricorn harvest occurs from May
until August. Harvesting is done by hand-picking
of each ripe berry or by strip-picking all of the
berries from three branches after most of the
berries (often present as clusters) have matured.
Harvesting may also be done by sweeping under
the tree, i. e. collecting the ripe berries from the
ground. Processing commences with removal of
the fleshy pulp by using one of the two following
processes:
The dry or natural process used in Brazil involves
rapid transport of the harvested berries to a central
processing plant, where the whole fruit is
spread out on sun-drying terraces and dried until
the beans separate by shrinking from the surrounding
parchment layer.
Dehulling machines – conical screws with a helical
pitch increasing toward the discharge end –
remove the dried husks and parchment from the
dried berries and, as much as possible, the silverskin.
The dehulled and cleaned coffee beans
are then classified according to size and packed
in 60 kg bags. Often, the fresh cherries, instead
of being spread on the drying terrace, are piled
up, left for 3–4 days under their own heat to ferment
the fruity pulp, and are then processed as
outlined below. In both cases unwashed beans are
obtained.
The wet (washing) process is more sophisticated
than the dry process, and by general consent leads
to better quality coffee. The method is generally
used for Arabica coffee (except in Brazil) in Central
America, Colombia and Africa. The freshly
harvested berries are brought to a pulper in which
the soft fruit is squeezed between a rotating cylinder
or disc and a slotted plate, the gap of which
is adjustable. The passage of the fruit produces
a rubbing action which detaches the skin and the
pulp from the beans without damaging the seed.
The removed pulp is used as fertilizer.
The pulped beans still have the silver-skin, the
parchment and a very adhesive mucilaginous
layer (mucilage). Hence, such coffee is carried
into water stream fermentation tanks made of
concrete, the water is drained off and the beans
are left to ferment for 12–48 h. During this
time, the mucilaginous layer, which consists of
84.2% water, 8.9% protein, 4.1% sugar, 0.91%
pectic subtances and 0.7% ash, is hydrolyzed by
enzymes of the coffee and by similar enzymes
produced by microorganisms found on the fruit
skins. The mucilage is degraded to an extent
which can be readily dispersed by washing with
water. The beans are then collected, sun-dried on
concrete floors or dried in mechanical dryers in
a stream of hot air (65–85 ◦ C). Beans dried in this
way are still covered with the parchment shell
(“pergament” coffee or “cafe pergmino”) and are
further processed by dehulling machines as in the
dry process. This yields the green coffee beans.
Premium-priced coffee beans are often polished
to a smooth, glossy surface and the silverskin,
except that retained in the centrecut of the beans,
is removed.
21.1.2.2 Green Coffee Varieties
About 80 varieties of the three coffee bean species
mentioned above are known. The most important
of the species Coffea arabica are typica, bourbon,
maragogips and mocca; and of Coffea canephora
are robusta (the most common), typica, uganda
and quillon. All varieties of Coffea canephora are
marketed under the common name “robusta”.
The names of green coffees may be characteristic
of the place of origin; i. e. the country and the
port of export. Important washed Arabica coffees
are, for example, Kenyan, Tanzanian, Colombian,
Salvadorian, Guatemalon or Mexican.
Unwashed Arabica beans are the mild Santos and
the hard Rio and Bahia beans. All three are from
Brazil. Robusta coffees, mostly unwashed, are,
for example, those from Angola, Uganda, the
Ivory Coast and Madagascar.
Arabica coffees, particularly those from Kenya,
Colombia and Central America, have a soft, rich,