DRY AND WET MILLING OF
CCS HAU, HISAR
STRUCTURE AND COMPOSITION
The mature corn is composed of four major parts:
C o m p o n e n t s o f Yellow Dent Corn
CORN DRY MILLING
Dry milling process consists of the following steps:
When corn is received at the mill, it is cleaned by both dry
and wet process. Cleaning steps are sieving, separating
particles by shape and density and removing ferromagnetic
metals by permanent magnets.
The cleaned corn is conditioned, which basically means that
water is added and the moisture allowed to equilibrate
within the kernels.
A moisture content of 21% is considered optimal.
The purpose of degerming is to remove hull, tip cap and
germ and leave the endosprum into large grits.
The degermer product are to be dried to 15-18% moisture
content for proper grinding and sifting. Drying is performed
by conventional rotary steam tube dryers.
Counter-flow or cross flow rotary cooler can be used for
cooling the dried products.
Recovery of various primary products is the next step. The
through-stock is sifted or classified by particle size and enters
into a conventional long reduction system having the function
of removing bran and germ while releasing a maximum
amount of clean large grits.
The milling operation consists of the steps of
grinding, sifting, classifying, purifying, aspirating and in some
case, final drying.
The normal flow is through break rolls and then to sifters. The
break rolls are followed by reduction roll which grind the
endosperm to the desired particle size.
Clean the shelled corn to ensure that they are free from dust
and foreign bodies.
The corn is soaked in water, called steepwater, at 50˚C for
between 20 and 30 hours, during which time it doubles in
Sulphur dioxide is added to the water to prevent excessive
bacterial growth. As the corn swells and softens, the mildly
acidic steepwater starts to loosen the gluten bonds with the
corn, and to release the starch. The corn goes on to be
MILLING AND SEPARATION
The corn is coarsely milled in the cracking mills to separate
the germ from the rest of the components (including
starch, fibre and gluten).
The corn flows to the germ separators to separate out the
The corn germ, which contains about 85% of the corn’s
oil, is removed from the slurry and washed. It is then dried
and sold for further processing to recover the oil.
FINE GRINDING AND SCREENING
After the fine grinding, which releases the starch and gluten
from the fibre, the slurry flows over fixed concave screens
which catch the fibre but allow the starch and gluten to pass
through. The starch-gluten suspension is sent to the starch
The collected fibre is dried for use in animal feed.
SEPARATING THE STARCH AND GLUTEN
The starch-gluten suspension passes through a centrifuge
where the gluten, which is less dense than starch, is easily
The gluten is dried and used in animal feed.
The starch, which still has a small percentage of protein
remaining, is washed to remove the last traces of protein
and leave a 99.5% pure starch.
The starch can either be dried and sold as corn starch, or it
can be modified to turn into other products, such as corn
sweeteners, corn syrups, dextrose and fructose.