Page 26 - Vol.38-No.2

CROP PROTECTION

WET AND DRY

PROCESSING OF RICE

where it accounts for a sizable slice of
production in the West African region.
This traditional but highly specialised
method of rice production has to cope
and deal with a variety of problems re-
lated to soil salinity and acidity, which
DR. TERRY MABBETT are not faced by mainstream irrigated
rice farming, and because mangrove
Striking feature about rice is the
forests are invaded by salt water.
range of environmental conditions and
agronomic techniques under which the West Africa is the undisputed hub of
crop can be cultivated and produced rice production across the continent of Water is the key to success of paddy
and alongside the disparate post-har- $IULFD DOWKRXJK D VLJQLÞFDQW DPRXQW rice well into the later stages of the
vest, crop processing methods used. In of rice production comes from upland rice crop
both production and processing the ex- farming where the rice crop relies
act methods and techniques employed solely on rainfall for its growth and
all hinge on one single factor which development. Upland rice farming is of grains to give good quality shelled
is water. carried out on well-drained soils above rice. Rice bran is rich in oil so hulling
the flood line and where natural rainfall also extends the shelf life of grain by
eliminating this source of rancidity.
and capacity of soils to retain water
are the sole factors which determine Hulling followed by polishing has
and underpin rice growth and devel- been carried out for thousands of years
opment. Upland rice was traditional- using traditional village methods and
ly produced using varieties of native during the last 200 years by the use
African red rice (Oryzae glaberrima) of small manufactured metal rice hull-
although this has gradually been re- ers. International organisations advise
placed with O. sativa. against rice polishing as it removes too
much of the Vitamin B complex leading
The dry rice process WR DQ LQFUHDVH LQ GHÞFLHQF\ GLVHDVHV
VXFK DV o%HULEHULp
Importance of water for rice growing is Harvested rice grains are enclosed
already evident in the earliest stages in glumes, which are in close contact However, the expanding rice har-
of the crop (Picture courtesy Omex) with the grain. Prior to consumption as vest is increasingly processed within
grain, or further processing into flour, DQ LQWHJUDWHG oULFH PLOOLQJp RSHUDWLRQ
Differences in rice cultivation es- snack foods and beverages, the glumes This may be small (e.g. 75-100 tons/
sentially hinge on the amount of wa- are removed by hulling. day) or massive (1000+ tons/day), in-
ter available at particular times in the First secret of successful rice pro- stalled as a turnkey operation with full
crop cycle as rainfall and/or irrigation, cessing and storage is drying grain computerised control. Summary of the
while the way in which harvested rice is to an optimum moisture level of 12-14% operations involved includes cleaning,
processed depends on whether or not weight/weight (w/w). Moisture con- hulling, bran separation from shelled
water is used in either wet processing WHQWV ZLWKLQ WKLV UDQJH DUH VXIÞFLHQWO\ ULFH SHDUOLQJ SROLVKLQJ FODVVLÞFDWLRQ
or dry processing of rice. low to inhibit enzyme action and there- (whole/broken grains etc) and bag-
ging.
Rice is generally regarded as a low- fore microbial activity in rice storage. In
ODQG FURS JURZQ LQ IORRGHG ÞHOGV FDOOHG addition it facilitates the easy removal Irrespective of the scale of rice pro-
paddies, and which covers a range of of the outer covering (bran or husk) cessing, paddy rice must be harvested
cultivations where soil is covered with by hulling with minimum breakage at full maturity and timed carefully so
water to a variable depth and for a var- here is no hiatus. Delays during har-
iable period of time. This can be the vest leading to alternating periods of
whole crop growth and development wet and dry conditions cause stresses
cycle. The amount of water supplied to develop in the kernel, resulting in
may range from several metres (deep high levels of grain shattering during
water rice or floating rice cultivation) milling further down the line. Grain
to just several inches. shattering during milling can also be-
come a real problem if the grains are
Mangrove rice cultivation is a highly
overheated during post-harvest drying
VSHFLÞF W\SH RI ORZODQG SURGXFWLRQ LQ
by, for instance, being left for too long
which the rice crop is grown in man-
in the hot sun.
grove forests in river estuaries or along
the coastline. This method of cultivation Threshed grain needs to be sorted
has developed across West Africa in- Direct-seedling of the rice paddy has to remove stones and insects and win-
cluding in Guinea-Bissau, Sierra Leone, produced a good and even stand of nowed to eliminate light material such
The Gambia, Nigeria and Senegal and rice plants (Picture courtesy Omex) as stalks, leaves and dust particles.
24 Vol. 38 No. 2