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I received
my results. What do the numbers mean?
Food corn buyers
want hard endosperm corn and often pay a premium
for it. Why is it important?
Is the canned,
frozen, or fresh corn I buy in the supermarket
“food-grade” corn? What about popcorn?
What is the corn
dry milling process?
What is the corn
wet milling process?
What is the alkaline
cooking process?
What is the
dry-grind ethanol process?
What is “NIR”
testing?
What does the
“db” or “as is” next to my
results mean? Why is the notation of moisture
basis necessary?
I
received my results. What do the numbers mean?
A wide range of information
concerning the importance of tests, methods employed,and
interpretation of results is available by clicking
on the test name in the appropriate “Test
List” sections of the IPG Lab web site.
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Food
corn buyers want hard endosperm corn and often
pay a premium for it. Why is it important?
The primary characteristic desired
by essentially all food-grade corn users is a
large fraction of hard endosperm. Hardness is
important for several reasons. It has been found
that kernels with high levels of hard (also referred
to as vitreous, horneous, or horny) endosperm
are more resistant to breakage during handling.
This has two positive consequences for a food
corn processor. First, when the corn is cleaned
over screens as it enters the processing facility
or elevator, a smaller amount of the corn (for
which a premium has most likely been paid) will
pass through the screens to become low-value animal
feed. More importantly is the effect of breakage
on the process.
For a dry miller, profits depend
highly on the amount of large “flaking”
grits that are produced. Flaking grits are the
highest value endosperm product, followed by smaller
grits, meals, and then flour. If the kernels are
soft or broken significantly, there is less opportunity
to produce the large grits. It is always possible
to mill large pieces further to make smaller pieces
as required; the reverse is impossible.
In the case of an alkaline cooker,
(tortilla, tortilla chip maker, etc.) broken kernels
lead to inconsistent cooking. The result of this
is overcooked kernels which can lead to sticky
dough (masa) that may slow the process or even
cause expensive downtime. If the cooking time
is reduced to prevent this, the opposite may occur
– undercooked particles which give the dough
and resulting product a gritty texture. Product
composition and color, as well as process stability,
can also be affected by hardness and breakage.
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Is
the canned, frozen, or fresh corn I buy in the
supermarket “food-grade” corn? What
about popcorn?
The corn available in most stores
still on the cob or as kernels cut from the cob
is sweet corn. Most people are familiar with popcorn
and its small, hard kernels. The corn comprising
the vast majority of the U.S. corn acreage is
“dent” type corn. The three types are
completely different.
Dent type corn is an efficient
starch producer with starch contents typically
higher than 70%. The dry kernels are plump, rounded
and solid, usually having a dimple (dent) on the
end of the kernel away from the cob attachment.
This dent occurs as the kernel dries if there
is not sufficient hard endosperm to maintain the
structural integrity of the kernel.
Popcorn is much like dent corn
in that it contains considerable starch, but it
has a very hard texture and therefore, no dent.
Popcorn also has a very tough pericarp (outer
seed covering) that can withstand great internal
pressures. When heated rapidly, moisture in the
kernels becomes superheated (still in “liquid”
phase) at temperatures approaching 175°C or
350°F (normal vaporization occurs at 100°C
or 212°F) because of the tremendous pressure
buildup inside the kernel. The higher the pressure,
the higher the vaporization temperature will be.
When the internal pressure reaches a certain point,
the pericarp will rupture from the stress, instantly
dropping the internal pressure to normal atmospheric
pressure. The moisture “flashes” (instantly
changes to steam). Because the water requires
a larger space as steam than as liquid, it expands
the intracellular spaces within the endosperm.
This gives the popcorn its fluffy texture.
Sweet corn, especially as the
young ears are just beginning to mature, contains
low quantities of starch and high sugar levels.
This is why fresher sweet corn is the sweetest
and most tender it can be. As sweet corn matures
further, the kernels become tougher, and some
of the sugars are converted to starch. This reduces
the sweetness level of the corn, but will allow
the corn to be handled with less damage. Dry mature
sweet corn, without substantial starch to fill
the kernel, has a shrunken, wrinkled appearance.
Food-grade corn refers to hard
endosperm dent corn that will be dry-milled or
alkaline-cooked to make food products. Common
food uses for corn are cereals, snack chips, and
corn tortillas. Related uses include corn meal
and corn flour used in batters, breadings, and
in the brewing industry. These food uses account
for approximately 2% of the total corn production
in the U.S. The remainder of the corn crop is
exported, fed as animal feed or used in the corn
wet milling process or for ethanol production.
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What
is the corn dry milling process?
Corn dry millers physically
separate corn to make grits, flour, and meal.
Incoming corn is “tempered”
for 10-45 minutes by adding water (liquid or steam)
to raise the moisture content of the grain. The
moisture will primarily enter through the “tip
cap” (cob attachment point) of the kernel
and be absorbed by the germ and the cells between
the pericarp (outer seed covering) and the endosperm.
This moisture differential between various kernel
components promotes efficient separation of the
endosperm from the pericarp and germ.
The tempered corn enters a degerminating
mill. The goal at this stage is to rub or peel
the pericarp from the kernel and then to remove
the germ from the endosperm. It is strongly desired
to have the endosperm remain as intact as possible
while getting clean separation of the germ and
pericarp. A series of screening, grinding, rolling,
and aspiration steps are performed to separate
the corn into the desired finished products.
High flaking grit yield has
traditionally been the goal of the dry miller.
Flaking grits are large pieces of endosperm (approximately
two grits per kernel) that are used to make corn
flakes. One grit makes one flake; bigger grits
make bigger flakes. Big grits can be made smaller.
You can not make big grits from smaller ones.
The grits are cooked, rolled, and toasted to make
the flakes. Other endosperm material is separated
into smaller grits, meals, and flour based on
particle size requirements. The germ is processed
to remove the oil. The spent germ, pericarp, and
tip cap fractions are sold as a low-value animal
feed.
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What
is the corn wet milling process?
The corn wet milling process
separates corn by physical and chemical methods
to produce starch, high protein animal feed, and
corn oil. The starch is often processed further
to make corn syrup, corn sugar, ethanol, or other
products. Wet milling should not be confused with
the alkaline cooking process or the dry-grind
ethanol process.
Cleaned (fine materials removed)
corn is steeped in a weak sulfurous acid solution
for 24 to 48 hours at temperature close to 50°C
(122°F). The kernels absorb moisture, and
the sulfurous acid breaks chemical bonds in the
protein matrix which encapsulates the starch granules.
After steeping, the corn is loosely ground to
rupture the pericarp (outer seed covering) and
release the germ (ideally intact). The germ is
removed by utilizing its difference in density
from the rest of the components (i.e. it floats).
The remainder of the material is ground more finely
and separated by screening methods (to remove
fiber) and differences in density (starch from
protein).
The primary goal of the wet
miller is high starch yield. Genetics and environment
can affect starch yields. A corn sample may contain
73 grams of starch for every 100 grams of dry
corn material. Typically around only 66 (around
90%) of those 73 grams of starch are recovered
after processing as “starch”. The other
seven grams end up in the low-value feed products.
In the U.S. the feed and oil are valuable co-products
that produce significant revenue for the miller.
In other markets, such as Japan, there is little
value placed on the co-products. High starch yield
is a requirement there.
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What
is the alkaline cooking process?
The alkaline cooking process
is used to make corn chips, corn tortillas, and
corn tortilla chips. While many tortillas in the
United States are made from wheat flour, corn
tortillas the traditional favorite throughout
Latin America.
In the alkaline cooking process,
corn is cooked in a 0.5-2% lime (calcium hydroxide)
solution at 98-100°C for 5-60 or more minutes.
The traditional name for the cooked corn is nixtamal;
the cooking process is nixtamalization. During
nixtamalization, the pericarp (outer seed covering)
is dissolved. The dissolved pericarp is rinsed
away and the nixtamal is ground to make “masa”
(tortilla dough). The masa can be flattened by
several methods and baked to a finished tortilla.
To make corn tortilla chips,
masa is formed into a thin sheet and cut to the
desired chip shape. The raw chips are toasted
to remove some of the water (imparting the characteristic
black “toast points” observable on one
side of a chip) then fried in hot oil. Additional
seasonings or flavorings may be added. Corn chips
do not undergo the toasting process. The raw dough
is formed into chips and fried immediately.
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What
is the dry-grind ethanol process?
The dry-grind ethanol producer
converts corn into fuel ethanol. This is the fastest
growing area of corn processing.
Dry corn is ground, mixed with
water, and cooked with enzymes to break the starch
in the corn down to sugars. The sugars are then
fermented into ethanol. The residual solids (Distillers
Dried Grains with Solubles – DDGS) are used
for animal feed. Much research is being done to
improve the economics of the dry-grind process
by various means, particularly by capturing more
value from the materials traditionally sold as
DDGS.
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What
is “NIR” testing?
Near-Infrared (NIR) spectroscopy
utilizes the reflective or transmissive properties
of specific wavelengths of light (the near-infrared
band) in a sample. The term for these properties
across a range of wavelengths is “spectra”.
The instrument for measuring these characteristics
is called a spectrophotometer.
It is possible to predict chemical
or physical characteristics of a sample based
on comparison of its spectra to the spectra of
samples of known characteristics as determined
by traditional laboratory reference methods. The
NIR method is approved for analysis of many agricultural
products and is much faster and less expensive
than wet chemistry when many samples are to be
evaluated.
However, the startup costs for
NIR are relatively high due to the technical nature
of the equipment and the need for a calibration.
The calibration, or model, merges the spectral
and laboratory data of calibration samples in
order to predict information about unknown samples.
If the sample spectra are not similar enough to
the calibration spectra, the calibration will
not be able to accurately analyze the sample.
The greater the diversity and scope of the calibration
samples, the more accurate and capable the calibration
will be. Some companies develop calibrations for
licensing to other parties, eliminating the need
for duplication of extensive laboratory testing
effort among NIR users.
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What
does the “db” or “as is” next
to my results mean? Why is the notation of moisture
basis necessary?
Chemical and physical components
are typically reported on an “as is”
(wet) basis or dry (0% moisture) basis.
A wet basis result is the percentage
of the component of interest out of the entire
sample including moisture. A dry basis result
is the percentage of the component out of the
entire sample neglecting moisture. For example:
A soybean sample is analyzed to
contain 38% protein, 10% moisture, and 52% other
components as it sits in a sample container. The
protein content is 38% on a wet basis. Since 10%
of the sample is water, 90% is “dry material”.
Thus 38 parts protein divided by 90 parts of dry
material gives a protein content of 42.2% dry
basis.
The IPG Lab reports moisture contents on an “as
is” basis. All other results are generally
reported on dry basis (if applicable) so comparisons
are not skewed by differing moisture bases. Soybeans
may be reported an a 13% basis, but this will
be noted accordingly.
Conversion for a value at one moisture content
(represented by V1, & M1) to the corresponding
value at a different moisture content (V2 &
M2) can be performed according to the equation:
V2 = [(100-M2) / (100-M1)] x V1
To
use the previous example: Protein (0% moisture)
= [(100-0) / (100-10)] x 38%
Protein (0% moisture) = [(100) / (90)] x 38% =
1.11 x 38% = 42.2%
This equation will work for conversion between any
two moisture contents.
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