107 / 116
105
October 2017
Quality overview of maize
South African grading results
The maize crop was of good quality, with 72% of white and 78%
yellow maize, graded as maize grade one, compared to 83% and
76% of the 2014/2015 season. The percentage total defective ker-
nels above and below the 6,35 mm sieve, 6,2% for white and 5,7%
for yellow maize, was respectively 0,9% higher and 0,2% lower than
the previous season.
The percentage defective kernels for both white and yellow maize
above the sieve, increased slightly (0,3%) compared to 2014/2015,
the percentage defective kernels below the sieve stayed the
same (2,5%).
Defective kernels include amongst others, mouldy, discoloured, in-
sect damaged and small kernels that can pass through the 6,35 mm
round hole sieve. The percentages Diplodia as well as Fusarium in-
fected kernels were 0,1% lower and 0,3% higher than the previous
season’s 0,7% and 0,9% respectively.
Foreign matter (0,2%) and other colour maize (0,3%) did not pose
significant problems on the samples received, with only two white
and yellow maize samples each, downgraded to class other due to
foreign matter exceeding 0,75%. Foreign matter means all matter
above the 6,25 mm sieve other than maize, glass, stones, coal, dung
or metal.
No samples were downgraded as a result of the presence of other
colour maize. The average percentage combined deviations of white
maize were 6,7% compared to the 5,8% of the 2014/2015 season,
that of yellow maize was slightly lower – 6% compared to 6,2%.
USA grading results
Of the 920 maize samples graded according to USA grading regu-
lations, 58% were graded US1, 22% US2, 10% US3, 5% US4, 2%
US5, while sample and mixed grades represented 2% and 1% re-
spectively. The percentage samples graded as US1 varies substan-
tially over seasons, namely 58%, 64%, 42% and 79% over the last
four seasons. The percentage samples graded as US2 was similar to
the 23% of the previous season.
The main reason for downgrading the samples was the percent-
age total damaged kernels exceeding the maximum limit per grade,
followed by broken corn and foreign material. Per definition, dam-
aged kernels are kernels and pieces of maize kernels that are badly
ground-damaged, badly weather-damaged, diseased, frost-dam-
aged, germ-damaged, heat-damaged, insect-bored, mould-dam-
aged, sprout-damaged or otherwise materially damaged.
Physical quality characteristics
Bushel weight/test weight is applied as a grading factor in the
USA grading regulations, but is also routinely done at most intake
points locally.
White maize had an average test weight of 78,1 kg/hl compared to
the 76,7 kg/hl of yellow maize. The test weight in total varied from
59,8 kg/hl to 83,9 kg/hl and averaged 77,3 kg/hl, equal to the previous
season and the ten-year average.
Only 23 samples reported values below the minimum requirement
(56 lbs or 72,1 kg/hl) for USA grade 1 maize, eight of these samples
were from North West Province, seven from Mpumalanga, six from
the Free State and one each from Gauteng and KwaZulu-Natal.
The 100 kernel mass averaged 32,1 g which is 2,3 g higher than
the previous season and equal to the ten-year average. As in pre-
vious seasons, white maize (32,4 g) averaged higher than yellow
maize (31,8 g). The kernel size of white maize was similar to the
previous season while yellow maize kernels were larger than the
previous season.
Kernel size is determined by sieving a 100 g whole maize sample
through both 10 mm and 8 mm round-hole grading sieves. The per-
centage yellow maize kernels above the 10 mm sieve were on aver-
age 3,4% lower than white kernels and the percentage kernels below
the 8 mm sieve 3,4% higher than that of white maize.
The kernel sizes observed this season, especially that of yellow
maize, were slightly larger than the previous season, but still some
of the smallest the past ten seasons.
Both white and yellow maize were less susceptible to breakage than
during the previous season. The percentage stress cracks observed
varied from 0% to 31%, averaged 5% and was a percent lower than
in the previous season. White and yellow maize both averaged 5%.
Milling index values varied from 21,7 to 120,1 and averaged 95,5,
2,1 lower than the previous season. The average milling index for
white maize is higher (99) than that of yellow maize (92,6). Milling
index is an indication of the milling abilities and milling quality of
maize kernels, where a higher milling index means a higher extrac-
tion of the high-grade and most profitable products like samp, maize
rice and maize grits (de-germed products).
Roff milling and whiteness index
The average percentage extraction of total meal in white maize ob-
tained with the 150 series roff mill, averaged 78,4% (0,3% lower than
the previous season) and varied from 71,8% to 86,4%.
The whiteness index averaged 26,1 for unsifted and 17,5 for sifted
maize meal. Sieving the sample through a 300 μm sieve and combin-
ing the fractions above and below the sieve in a 87:13 ratio, eliminate
variations in the readings resulting from particle size differences.
The whiteness index of the previous season averaged 22,9 for un-
sifted maize meal. Sifted maize meal averaged 14,9.
The higher the whiteness index value obtained, the whiter the meal
sample. The main contributing factors causing differences in white-
ness index values are the presence of other colour maize like yellow
maize, the presence of defective kernels, the type of cultivar as well
as the soil composition.
The three samples with the lowest sifted whiteness index of values
of -14,61, -9,30 and -7,41 this season, also had the highest percent-
ages other colour maize ranging between 8% and 7,7%. The sample
with the fourth lowest sifted whiteness index value had the highest
percentage total defective kernels.
Nutritional component values
The fat, protein and starch nutritional component contents are meas-
ured with an Infratec 1241 – Generation 3 standard version whole
grain analyser and reported as percentage (g/100 g) on a dry base.
Foss updated the calibration on the Infratec 1241 Grain Analyser (NIT)
during 2016, using NIT spectra and international primary chemical
method results of maize crop quality samples from the 2012/2013
to 2014/2015 seasons, provided by SAGL.
The results obtained by the Infratec 1241 Grain Analyser on the
2015/2016 season’s samples, were checked by analysing every tenth
sample by means of the primary methods.
RELEVANT