Cereals processing technology

Wheat, corn and coarse grains milling 35
This development reduces sifting and conveying requirements within the
process significantly. Considerable capital savings can be made in terms of
equipment purchase requirements and the size of building required to contain the
process.
The most radical of recent developments has been the advent of debranning
as a unit operation in flour milling (Posner and Hibbs 1997). This is the process
of removing the outer bran layers from the wheat berry before the milling
process proper. A rationalised process flow is possible with debranning installed.
The conventional break system is rendered obsolete with only one or two fluted
rolls 8 being required. Because of the purity of the semolina 9 produced in such a
grinding system, the requirement for a purification system is significantly
reduced. Both these features of debranning enable a streamlined process with
corresponding savings in building size and running costs.
Pin mills 10 have also been adapted for use throughout the process. They have
been among the key factors in reducing the amount of grinding equipment
required in flour mills. The pin mills used are standard machines but the
innovation is in the process locations where they have been applied. Pin mills
are favoured where starch damage of the bulk flour will not be adversely
affected or where flour production rates are relatively low. Pin mills are widely
used in plants where starch damage production is not an issue or where it is
undesirable.
There are two features that these newer developments have in common.
These are that they typically do not enhance product quality and cannot be
applied universally. However, significant capital and operational savings are
possible through even limited application and so they are always worth applying
as extensively as possible. The application of double grinding at 1st/2nd break
and A/B 11 reduction rolls is one example of this approach. The application of
debranning in durum or bobtail mills 12 is another.
3.4.4 Conclusion
The stimulus for development in the flour milling process is the flour miller’s
requirement to produce the highest quality products at minimum cost. This has
been achieved in the past through investment in new technologies, which are
8 Fluted rolls refer to the rolls employed in the break system that are finished with a saw tooth profile.
9 Semolina is the term used to describe the coarse endosperm material produced at all stages during
the milling process. It is too coarse to be considered as flour and must be further reduced in size.
10 Pin mills are a type of comminution device which consist of a revolving rotor with a series of pins
attached. The material to be comminuted enters the mill at the centre of the rotor and is thrown
towards the periphery by centrifugal forces. The particles impact the pins along this route and are
comminuted as a consequence of these impacts.
11 These are the terms used to describe the sequential stages in the milling process. The British
convention is to use 1st, 2nd, etc., for the rolls in the break system, and A, B, etc., for rolls in the
reduction system.
12 A bobtail mill is the term used for a flour milling unit that utilises surplus machine capacity from
an adjacent processing plant in order to minimise equipment requirements.