World Grain - June 2020 - 70

GRAIN OPERATIONS

Relative Humidity (%)
Temperature (°C)

50

55

60

65

70

75

80

15

11.6

12.2

12.9

13.5

14.3

15.1

16.1

20

11.2

11.8

12.4

13.1

13.9

14.7

15.7

25

10.8

11.4

12.1

12.8

13.5

14.4

15.4

30

10.4

11.0

11.7

12.4

13.2

14.0

15.0

35

10.1

10.7

11.4

12.1

12.9

13.7

14.7

Table 1. Moisture content (%) of corn as a function of temperature and relative humidity of air surrounding kernels in the stored grain mass of a silo or warehouse.

Foreign material removal rates

Percent of FM before screening

Percent of FM after screening

20%

0%
1%

15%

2%
3%

10%
5%

4%
Index point

5%
6%

0%

7%

Figure 2. Approximate removal rates of foreign material (FM) in the form of fines for gravity screeners. The solid line estimates corn containing 7.5% FM before screening would contain approximately
2.75% FM after screening.

ability of the imported corn. An additional
EHQH¿WRINHHSLQJVWRUHGJUDLQDVFRRODV
possible is prevention of insect development, which is slowed substantially below 20°C. Exported US corn is generally
free of live insects for two reasons:
(1) The US grain grading system limits
the number of live insects that can
be present without the special designation "infested" recorded on the
R൶
FLDOJUDGHFHUWL¿FDWH
(2) Most purchase contracts require
fumigation aboard ship as a precautionary phytosanitary measure.
Thus, insect infestation likely occurs when grain is discharged from
70

the ship and passes through the handling and storage system of the import terminal and from there to local
grain facilities and feed mills.
MOLD INHIBITORS
Mold inhibitors originally were developed for application to high-moisture
corn (greater than 18%) immediately after
harvest as a less expensive alternative to
DUWL¿FLDOO\ GU\LQJ FRUQ RU WR H[WHQG WKH
holding time before corn could be dried.
Mold inhibitors never gained acceptance among US grain producers, handlers, and exporters, so they are not applied to exported US corn. They are based

on propionic acid and are considered safe
for human and animal consumption.
The inhibitory action is primarily by
keeping fungal spores from growing
rather than destroying them. In many
countries they are used to extend the shelf
life of animal feeds. They should not be
needed for imported US corn, especially
ZKHQ PRLVWXUH DQG ¿QHV DUH PDQDJHG
with best practices to prevent the on-set of
grain spoilage and self-heating.
FINES AND DUST MANAGEMENT
Fines in exported US corn consist
mostly of starch from broken corn enGRVSHUP 7RJHWKHU ¿QHV DQG GXVW DUH
good feed ingredients, but their presence can cause problems in storage and
must be properly managed. When corn
drops into a silo or warehouse from an
overhead spout or cross conveyor, a pile
shaped like a cone forms. Corn kernels,
larger pieces of broken corn, and light
pieces of foreign material (e.g., cob and
VWDON SLHFHV ÀRZ GRZQ WKH VXUIDFH RI
the pile increasing its diameter while
¿QHV WHQG WR DFFXPXODWH LQ WKH FRUH RI
the pile below the peak. In silos only
one so-called spoutline forms while in
warehouses spoutlines form below each
conveyor drop point.
The accumulation of small pieces of
broken kernels and associated exposure
of starch in spoutlines is highly susceptible to the onset of spoilage, especially
when the equilibrium relative humidity
of the air trapped in the core is greater
than 65% to 70%. Sporulating fungi respire heat, water vapor and CO2. The
GHQVHO\ SDFNHG VSRXWOLQH WUDSV WKH ¿UVW
two, which accelerates mold growth and
deterioration - neither is easily detected. Fortunately, CO2 is a gas that is not
trapped and can be detected in the headspace of a silo or warehouse.
CORING AND UN-PEAKING
Spoutlines in silos can be managed by
partially unloading the silo until a suf¿FLHQWDPRXQWRIJUDLQLVUHPRYHGIURP
the core, and the peak is inverted into the
surface of the grain mass to about onethird to one-half of the diameter. This is
June 2020 / World Grain / www.World-Grain.com

Source: Dirk Maier, AGCO.

Temperature and relative humidity impact


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World Grain - June 2020

Table of Contents for the Digital Edition of World Grain - June 2020

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