WHEAT MILLING
Wheat is a farinaceous grass, known botanically as triticum spp., is one of the most consumed
cereal grains worldwide and makes up a substantial part of the human diet. It provides more
nourishment (calories & proteins) for humans than any other single food crops. According to
Statista 2013/2014, the global production volume of wheat amounted approximately
710
million metric tons, which has shown a 7.7% increment from the previous year. It is the
second most important food crop in the developing world after rice. In sub-Saharan Africa,
14
countries produce wheat; Ethiopia and South Africa are the two major producers. Along with
Teff, wheat and maize represent the three most important cereal crops in Ethiopia. Wheat is
one of the various cereal crops largely grown in highlands of Ethiopia. It is produced largely
in the southeast, central and northwest parts of Ethiopia (Karin & Leo, 2013).
Wheat grains are generally oval shaped, although different types of wheat have grains that
range from almost spherical to long, narrow and flattened shapes. The grain is usually
between
5 and 9 mm in length, weighs between 35 and 50mg and has a crease down one side where it
was originally connected to the wheat flower. The wheat grain contains 2-3% germ, 13-17%
bran and 80-85% mealy endosperm (all constituents converted to a dry matter basis)
(Sramkova et al. 2009).
As populations expanded and the demand for more and better flour and bread grew, so a new
milling process was devised. Originating in Hungary in the late 1870s, this new process
involved passing the grain between sets of spinning metal rollers. These mills operate by
passing the grain between a series of paired counter-rotating rollers with fluted surfaces. The
resulting crushed grain is sieved between each roller pair in order to separate the bran (coarse
and brown in colour - see image below) from the starchy endosperm (fine and white in colour
- see image below). The end product is a super-fine white flour. To produce wholemeal flour
from this type of milling it is necessary to collect the bran that have been sieved off during
the early stages of milling and add them back to the final product. To obtain a brown flour a
proportion only of the extracted material is added back.
An important property of a milled wheat is the activity of an enzyme called alpha-amylase, an
enzyme that breaks down starch resulting in poor quality flour. Both breeders and millers use
the Hagberg Falling Number (HFN) to indirectly determine alpha amylase. The HFN test
measures the number of seconds a plunger takes to fall through a mixture of wheat flour in
water. The plunger will fall slowly if the mixture is thick with starch indicating low alpha
amylase activity. conversely, it falls more rapidly if some starch has been converted to sugar
through the action of the enzyme. Flour with a low HFN value will produce bread that is
sticky and so clogs slicing machines. Such flour will be rejected by millers.
However, depending on the wheat variety and the blending processes used by millers,
different types of flour, each with a different purpose, are obtained. For example, there are
flours intended for cake/biscuit making, for bread making, for household use, and for pasta
production. The intended use of the various types of flour on sale is usually listed on the
packet. Wholemeal flour, as its name suggests, is flour made from the whole grain of the
wheat, from which nothing is extracted and to which nothing is added; it contains all parts of
the wheat grain including the outer layers of bran and the germ. There is no difference
between wholewheat and wholemeal flour, unless the packaging on wholemeal flour states
that barley and/or rye have been added to the wheat. White flour, on the other hand, contains
only the inner portion of the grain called the endosperm (see image). Unless the packaging
explicitly states that the it is unbleached, the flour will have gone through a bleaching
process; such bleached flour may be called refined flour. Flour that is referred to as 'Brown' is
usually roller-milled, bleached flour to which caramel and sometimes some bran has been
added. The primary rule for producing a really good wheat loaf is to use strong bread flour,
which is made from semi-hard wheat with a medium to high protein content. When water is
mixed into the flour, two of the flour proteins combine to form gluten. The gluten forms a
network that is able to stretch as the dough ferments and carbon dioxide gas is released. On
baking this stretched gluten network sets to give the structure and texture of the bread.
Although gluten is a present in all wheat in varying amounts, strong flour is needed to ensure
that sufficient gluten is formed to produce bread of good volume and appearance. What
differentiates a bread flour from flour more suited to making cakes and biscuits, is the gluten
content. The ideal flour for making most cakes and biscuits has a lower protein content than
bread making flour and is milled from soft wheat varieties. The protein needed to form the
structure of cakes and biscuits is not from the flour used but from other ingredients such as
egg. Use of cake flour gives a tender soft product as the gluten in the flour does not
contribute significantly to the cake structure. If flour that is too strong is used the resultant
cakes will be tough and dry and biscuits will not spread out when baked. Self-raisng flour
was invented by Henry Jones and patented in 1845. It is made by combining soft, biscuit
flours with chemical aerating agents such as baking powder. The flour and raising agents are
sifted together many times to ensure even distribution and consistent product quality. The
aerating agents in the flour produce lighter and softer baked products as a result of creating
small gas bubbles and cause batters to rise when heated. Sef-raising flour is used in the
baking of cakes, scones and suet pastry.
REFERENCES
1. Cornell H. In: Cauvain SP (ed) Bread Making: Improving Quality. Woodhead
Publishing, Cambridge, 2003.
2. Doty NC. Value-Added Opportunities and Alternative Uses for Wheat and
Barley. Agricultural Utilization Research Institute, 2012.
3. Karin de Punder, Leo P. The dietary intake of wheat and other cereal grains and
their role in inflammation. University of Girona, Plaça Sant Domènec, Spain
and
Uni for Life, University of Graz, Austria, 2013.
UNIVERSITY OF GHANA
SCHOOL OF ENGINEERING
FOOD PROCESS ENGINEERING
COURSE
ENGINEERING AND DESIGN III
PLANT PRODUCTS
COUSE INSTRUCTORS
PROF. F.K SAALIA
MISS KONTOH GLADYS
STUDENT NAME AND ID
PROSPER KOLOGO JAMBEDU
10728015
ASSIGNMENT 1
TOPIC
WHEAT MILLING
DATE
29TH MARCH, 2022.
