Cereals processing technology

30 Cereals processing technology
3.3 The flour milling process
There are a number of aspects of the overall process of flour milling that are
particular to it and are not to be found in other industries. Thus a group of terms
are used which would be unfamiliar to individuals not acquainted with the
process. This section aims to provide a brief introduction to the process and the
terms employed to describe aspects of it. Posner and Hibbs (1997) describe the
process in greater depth and the reader is urged to consult this book for further
insight into the process.
Flour milling is the continuous process that is used to transform the raw
wheat berry into a form which is of use to the baking and other industries and the
domestic consumer. A small portion of production is geared towards the
production of whole-wheat flours, employing a simplified process flow sheet,
but most demand and effort is directed towards the production of white flour.
White flour is the ultimate product of flour milling. The aim of white flour
milling is to extract a maximum amount of endosperm from the wheat berry in
as pure a form as possible. The outer bran layers become the co-product of the
process called wheat feed. Many operations also separate the embryonic part of
the berry, known as the germ. This is a high value co-product when a market
exists. Where a market for germ does not exist, it is sold for animal feed with the
wheat feed produced. These co-products contribute significantly to the financial
viability of milling operations.
One of the keys to the success of a flour milling operation is the efficient,
economical separation of starchy endosperm from the rest of the berry. The
process has developed along very specific lines towards achieving this goal.
There is just one accepted manner in which flour is produced globally. This is
known as the gradual reduction system.
The gradual reduction system of flour milling is the process of taking the
whole wheat berry and, via a series of grinding and sieving stages, producing
white flour of the desired quality and yield. The gradual reduction system has
enabled the production of flours of low ash content and high yield. Specialist,
high quality flours, are produced by extracting high purity sub-products from
within the process.
The flour milling process can be represented by a simple block diagram (Fig.
3.2). There are three principal divisions within the process. These are known as
the breaking system, the purification system and the reduction system. The
purification system is not favoured by many millers and may be absent from
processes. It is often replaced by what is known as the Sizing system. However,
the other two blocks are present in all gradual reduction flour mills in operation
today.
The breaking block or break system is the area of the process where most
endosperm separation is achieved. This work is performed principally on roller
mills whose surfaces have a saw tooth profile. The rollers run at different speeds
towards each other. The combination of these two attributes in operation mean
that, in the first contact with the wheat berry, the grain is split open and a