Traditional cereal processing in Nigeria and Ghana

mill. A dish or raffia mat is placed in front of the
baseplate to receive the ground material. The
roller is originally round in cross-section but
becomes flattened after some use.
The pestle-and-mortar mill is carved from wood.
The mortar is about 60-70 cm high with a diameter
of about 30 cm. The pestle weighs about
3 kg, is about 1·20 m long, 6 cm in diameter and
has bulbous ends, one rather more pointed than
the other.
The grain is pounded by one, two or three
women, each working at about 60 strokes per
minute. There are three types of stroke: (1) up
and down; (2) down, across and up; and (3) down,
"rotary scrape" and up. Both the stroke across
in 2 and the rotary scraping motion in 3 serve to
knock the side of the mortar to prevent bridging
of the cereal. During grinding the women vary
these three patterns and, since each produces a
different sound, the effect is similar to that produced
on a drum.
Usually the stone mill is used for harder
materials, the pestle and mortar for softer ones.
On one occasion the writer saw dry maize being
ground in a mortar with a 5-6 cm diameter iron
rod as a pestle. The wear on the mortar in this
case would be severe.
Normally, maize is soaked for 24 h before
grinding. As an example of the milling process,
the reduction of sorghum to flour may be described
as observed near Kano. 2-3 kg of grain was
placed into the mortar with about 250 ml of water
and gently pounded with the more pointed end
of the pestle (Fig. 2) and so dehusked. (If the tip
is too pointed the seeds tend to jump out of the
mortar during the process.) The husk was then
separated from the grain by winnowing on a plate
or mat (Fig. 4). The husk was discarded and the
grain returned to the mortar where it was pounded
vigorously with the flattened end of the pestle.
The material was then sieved (Fig. 5). The overtails
were ground on a stone mill (Fig. 1) and the
resulting flour combined with the throughs of the
sifting operation. The flow diagram of the traditional
milling process is given in Fig. 6 and the
sieving analysis in Table 2.
P~stl~ & mortar
sh~1I ing
I
Winnowing
I
P~st I~ & mortar
grinding
I
Siev i ng
I
Stone milling
Bran
Flour
,
TABLE 2
Sieving Analysis of Stock from Traditional Sorghum Milling (%)
Mesh:
5 18 36 40 60 80 100