Food Chemistry

21.1 Coffee and Coffee Substitutes 939

kg) of fresh coffee cherries which yields 1 kg of
marketable coffee beans is forC. arabica 6 .38,
C. canephora 4 .35, andC. 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 cen-
tral processing plant, where the whole fruit is
spread out on sun-drying terraces and dried un-
til the beans separate by shrinking from the sur-
rounding parchment layer.
Dehulling machines – conical screws with a he-
lical pitch increasing toward the discharge end –
remove the dried husks and parchment from the
dried berries and, as much as possible, the sil-
verskin. 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 fer-
ment 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 Cen-
tral America, Colombia and Africa. The freshly
harvested berries are brought to a pulper in which
the soft fruit is squeezed between a rotating cylin-
der 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 speciesCoffea arabicaaretypica, bourbon,

maragogipsandmocca; and ofCoffea canephora

arerobusta(the most common),typica, uganda

andquillon. All varieties ofCoffea canephoraare

marketed under the common name“robusta”.

The names of green coffees may be characteris-

tic 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,