Cereals processing technology

Wheat, corn and coarse grains milling 31
Fig. 3.2 Block diagram of milling process.
significant amount of material is released into the purification and reduction
blocks by the subsequent sieving operation. A small amount of flour is also
produced at this stage and is removed before further processing occurs. The
material that remains in the break system after first contact is presented to a
second set of rollers for further grinding. Again, material is released into the
purification and reduction blocks and some flour is released. This procedure is
repeated four or five times. When the desired amount of material is released
from the wheat berry, the remaining material is discharged to the wheat feed
stream, the co-product of flour milling.
The purification block contains three machine types: purifiers, roller mills
and sifters. Purifiers are machines that separate particles on the basis of
differences in size, air resistance, and particle specific gravity, simultaneously.
The streams feeding the purification system come from the break system
discussed above. The streams are classed on a size basis before entry to the
purification system and contain a mixture of pure endosperm and intermediate
purity particles. Particles that are pure enough are separated immediately, exit
the purification system and are passed to the reduction system for further
processing. The remaining particles are processed on roller mills whose surfaces
have a fine saw tooth profile. Further bran and endosperm separation is possible
as a result of this grind. Ultimately most of the material that enters the