STARCH MANUFACTURE PROCESS DESCRIPTION
Maize kernels are screened and air cleaned in steeped in SO2 water
for 60 to 70 hours at a temperature 50-55 ͦC to prevent bacteria growth. The softened
grains are passed through coarse grinder No.1. Coarse grinding is done to
separate the germ without breaking or disturbing it because otherwise if fine
grinding was done germ would liberate oil and cause further process problem, in
a degerminator cone is maintained at about 40 ͦC be at which all germs tend to
float and rest of heavy media passes as the under flow to next operation,
second coarse milling is done just to ensure the breaking of any uncrushed grain.
All the overflow of the degerminators are collected in the germ
tank, and further germ is fed for germ washing, germ dewatering, germ drying,
germ expelling and maize oil is collected.
The underflow from
degerminator 3 comes to pin mill feed tank and then to pin mill and then to
concave screens that are 50μ and its outlet goes to primary separator (Alfa
Calval) and underflow to pin mill again and collected from there to houdi tank
and is fed to 75μ screens and screen underflow again goes to primary separator
and overflow to stone grinder and then fed to 1 DSM of 120 mesh and remove
oversize as byproduct i.e. bran obtained from three stage washing and
screw pressing for dewatering.
The underflow of DSM goes to raw material tank and then to series
of 3 DSM screens and any overflow left is send to filter press to recover grit
or fine bran and underflow of DSM goes to stone grinder again. The
underflow is collected in alpha feed tank and are then to primary separator
machine which works on density difference and separates light pure yellow gluten
as overflow and heavy white slurry which is mixture of both starch and
traces of protein (not more than 2%) as underflow.
The overflow is settled in series of large settling tanks. The
sediment obtained is thereby pumped to filter press, which gives cake which is
flash, dried and converted into dry gluten.
The impure underflow starch slurry is washed in series of
hydro-cyclones called as Dorr cyclones. This is counter current washing and
thickening station. Total 9 stages are employed in which impure starch and
water flows in opposite directions. Water as a overflow collect all the light
impurities and impure water collected at the end of the first stage while
starch as a underflow becomes pure and thick is collected at the 9th stage at
come of 20 oBe. This starch milk is centrifuged to get wet cake, which is
further flash dried to get dry starch powder and is finally packed in
silos bags.
