World Grain - November 2017 - 68

GRAIN OPERATIONS

Maintaining grain quality
in tropical climates
Chilled aeration is often the better option
in the warmer areas of the world
by Dirk Maier

As the temperate crop growing regions of the Northern Hemisphere are wrapping up the fall harvest and are approaching the
colder winter climate, decreasing temperatures allow for cooling stored cereals, oilseeds and pulses to safe conditions using
ambient aeration. Handlers of bulk and bagged commodities in
the subtropics and tropics have to contend with warm ambient
temperatures year-round except in select highland locations of
East Africa, Australia, Central and South America.
Approaching winter weather allows for cooling of grain in
most of the United States, Central Europe and China, and pretty
much all of Canada and Northern Europe to well below 5°C
(41°F). In the tropics and subtropics, grain temperatures typically remain between 25-35°C (77-95°F), which are ideal growing conditions for stored grain insect pests. Grain needs to be at
VX൶FLHQWO\ORZPRLVWXUHFRQWHQWWREHVDIHIURPPROGVSRLODJH
which requires drying after harvest but remains a challenge during storage due to high relative humidity of ambient air.
So this is as good a time as any to review a stored grain
preservation technology that allows for cooling of grain yearround independent of high ambient temperature and relative
humidity conditions.

stored grain with air that is chilled by large capacity air conditioning systems. So called grain chillers are typically mobile
and may be moved between storage structures to cool grain
below about 15°C (60°F) soon after harvest independent of
local weather conditions.
Grain chillers function similarly as air conditioners but are
high capacity and portable (see Figure 1, page 70). They may
be connected to storage structures such as silos and warehouses via existing aeration fans and operate on three-phase power. Once cooling of a silo or warehouse is complete, a grain
chiller can be moved to the next structure, or depending on
size and chiller capacity, one grain chiller may be connected
to more than one silo or warehouse section at a time.
Grains such as wheat and rice are excellent insulators, so
once cooled a grain mass would typically not need to be rechilled. For example, wheat harvested in the Great Plains of
the United States could be chilled in July to 15-17°C (5963°F) before ambient aeration in the late fall can be used to
lower grain temperatures further for storage through the winter and beyond. Paddy rice in Malaysia could be chilled to
20-22°C (68-72°F) soon after harvest and remain cool for four
to six months before mill capacity catches up.
AMBIENT VERSUS CHILLED AERATION
Chilled aeration is not a new technology but commercial
Aeration of grain with ambient air after harvest is an impor- equipment has not been widely available in North America
tant tool to maintain quality and minimize post-harvest losses XQWLO UHFHQWO\ 7KH WHFKQRORJ\ ZDV ¿UVW LQWURGXFHG LQ WKH
due to biological deterioration caused by insect pests and mold United States in the early 1960s and then again in the late
VSRLODJH +RZHYHU WR EH H൵HFWLYH DPELHQW WHPSHUDWXUHV RI VZLWKWKH¿UVWFRPPHUFLDOXQLWVROGIRUWKHFRROLQJRI
less than 20°C (68°F) and relative humidity of less than 70% milled rice in California in 1993. Most units sold in the United
are required. Such conditions are usually not available during States are used for the conditioning of bulk seed and the coolthe summer harvest season of wheat and other small grains in ing of pesticide-free rice, wheat, food maize as well as organic
temperate climates and during most of the year in subtropi- grains, oilseeds and pulses, which has been documented to be
cal and tropical climates when rice, maize, wheat and other economically feasible.
staples are harvested. This increases the dependence of stored
Grain chilling was commercially developed in Germany
JUDLQPDQDJHUVRQFKHPLFDOVVSHFL¿FDOO\IXPLJDQWVDQGLQ- during the 1960s and gained popularity in Europe where it
secticides, to suppress and prevent insect pests.
initially was used to hold harvest-wet small grains ahead of
An alternative, non-chemical technology is the aeration of dryers, which at the time were undersized. Today, several Eu68

November 2017 / World Grain / www.World-Grain.com
http://www.World-Grain.com
World Grain - November 2017

Table of Contents for the Digital Edition of World Grain - November 2017
