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Augustus 2015
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A look at the maize crop quality of
the 2013/2014 production season
D
uring the 2014 harvesting season (April to August), a
representative sample of each delivery of maize at the
various silos was taken according to the prescribed grad-
ing regulations and forwarded to the Southern African
Grain Laboratory (SAGL).
A total of 930 composite samples, representing white (451) and
yellow (479) maize of each production region, were received and
analysed for quality. The major maize producing provinces were
the Free State, North West Province and Mpumalanga, contributing
84% of the total maize production in South Africa.
Yellow maize contributed 67% of the total maize production in
Mpumalanga while the majority of maize produced in the Free State
and especially the North West Province is white.
Maize crop quality 2013/2014 – summary
of results
South African grading
The maize crop was of good quality, with 70% white and 77%
yellow maize, graded as maize grade one. The percentage total of
defective kernels above and below the 6,35 mm sieve (6,2% for
white and 6,1% for yellow) compared well, but was higher than the
previous two seasons.
The percentage defective kernels above the sieve increased, com-
pared to the two previous seasons, but the percentage defective
kernels below the sieve decreased. Both the percentage of Diplo-
dia and Fusarium infected kernels were 0,4% higher than the pre-
vious season’s 0,6% and 1,1% respectively. Foreign matter and
differently coloured maize did not pose significant problems.
The average percentage combined or total deviations of white
maize were 6,8% compared to the 4,9% of the 2012/2013 season;
that of yellow maize was also higher – 6,4% compared to 4,8%. The
average percentage of total deviations on South African maize this
season was 1,7% higher than the previous season.
USA grading
Of the 930 maize samples graded according to USA grading
regulations, 42% were graded US1, 31% US2, 11% US3, 7% US4,
6% US5 while mixed and sample grade represented 1% and 2%
respectively.
The percentage samples graded as US1 was significantly lower
than the 79% of the previous season. The percentage samples
graded as US2 was significantly higher than the 13% of the previous
season. The main reason for downgrading the samples was
the percentage total damaged kernels exceeding the maximum limit
per grade.
Physical quality factors
Hectolitre mass or bushel weight or test weight is applied as a grad-
ing factor in the USA grading regulations, but also done routinely at
most intake points locally.
White maize had an average hectolitre mass of 77,6 kg/hl compared
to the 76 kg/hl of yellow maize. The hectolitre mass in total varied
from 56,6 kg/hl to 81,9 kg/hl and averaged 76,8 kg/hl, slightly lower
than the ten year average. Only 28 samples reported values below
the minimum requirement (56 lbs or 72,1 kg/hl) for USA grade one
maize – 15 of these samples were from Mpumalanga and eight
from the Free State.
The 100 kernel mass averaged 32,9 g which is 3,9 g higher than the
previous season and also 0,6 g higher than the ten year average.
White maize averaged 34 g and yellow maize 31,8 g.
The kernel size of both white and yellow maize was larger than
the previous two seasons. The percentage of yellow maize kernels
above the 10 mm sieve were on average 9,8% lower than white
kernels and the percentage of kernels below the 8 mm sieve were
7,4% higher than that of white maize.
The breakage susceptibility of both white and yellow maize
compared well with the 2012/2013 season, although slightly higher.
The percentage stress cracks varied from 0% to 53%, averaged
7% and was also slightly higher than in previous seasons.
The milling index varied from 46,5 to 120,4 and averaged 90,9 – 4,2
lower than the previous season. The average milling index for white
maize is higher (93) than that of yellow maize (89).
Roff milling and whiteness index (WI)
The average percentage extraction of total meal in white maize
obtained with the Roff mill averaged 79% (0,2% higher than the
previous season) and varied from 73,5% to 84,8%.
The whiteness index averaged 25,3 for unsifted and 15,6 for sifted
maize meal. Sieving the sample eliminates differences in the
readings as a result of particle size. The whiteness index of the
previous season averaged 25,1 for unsifted maize meal. Sifted maize
meal averaged 15,9.
The higher the WI value obtained, the whiter the meal sample. The
main contributing factors causing differences in WI 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 sample with the lowest sifted whiteness index
of -18 this season also had the highest percentage of other maize
namely 9,2%.
Nutritional values
The fat, starch and protein nutritional components are reported
as percentage (g/100 g) on a dry base. In general, white maize
tends to have a higher fat content than yellow maize, but a lower
starch content. No clear trend can be observed with regards to the
protein content.
The average fat content of the 2013/2014 crop samples was
3,9%, equal to the weighted ten year average and 0,1% lower than
the 2012/2013 samples. The average protein content (8,6%) was
equal to the weighted ten year average and 0,6% lower than the
9,2% of the previous season. The starch content this season
increased on average with 1,4% compared to the 71,6% of the
previous season and is also 0,6% higher than the ten year weighted
average of 72,4%.
RELEVANT
JOLANDA NORTJÉ,
laboratory manager: The Southern African Grain Laboratory NPC