WHEAT INTO FLOUR: THE MILLING PROCESS
Farmers grow wheat plants and the grain from those plants is used to make
flour. Flour is used to make lots of different food
products, such as bread, breakfast cereals, biscuits and cakes. These
products are delivered to shops and supermarkets so that we can buy them.
All these steps link together to make the grain chain. You
can find out more about the first step in the chain – farming the wheat –
here.
The milling process is a key step in the grain chain,
because it is the process by which the wheat grains are made into flour. Find
out about the structure of the wheat grain
here. Different parts of the wheat grain are used to make different types of
flour.
White flour is made from the endosperm only. Wholemeal
flour uses all parts of the grain: the endosperm, the wheatgerm and the
bran layer.
Brown flour contains about 85% of the original grain, but some
bran and germ have been removed. The miller must use his skill to buy, blend and
mill the wheat to produce the right kinds of flour.
Watch a video about the milling
process here, then read more about it below.
The milling process
Have a look at this diagram, then read the explanations below.
Delivery and storage
Each load of wheat from the farmer must meet specifications for:
- Variety: different varieties produce different flour
qualities.
- Moisture content: this determines the length of time
that a grain can be stored.
- Specific weight: a high specific weight is considered
to be better.
- Enzyme activity: high enzyme levels can result in a
sticky loaf of bread, making slicing difficult.
- Protein quality and quantity: these are important for
baking purposes.
Cleaning and conditioning
Powerful magnets, metal detectors and other machines are used to extract
metal objects, stones and other grains such as barley, oats and small seeds from
the wheat grain. Throughout the cleaning process, air currents are used to lift
off dust and chaff.
Conditioning with water softens the outer pericarp (bran) layer of the wheat
and makes it easier to remove the floury endosperm during milling.
Gristing
The cleaned and conditioned wheat is blended with other types of wheat in a
process called
gristing. This means using different types of wheat and mixing
them in different proportions to make different kinds of flour. Occasionally,
wheat gluten is added to increase the protein content of milled flours.
Milling
The miller’s art lies in finely tuning a sequence of breaking, sifting and
rolling operations to achieve the desired colour and consistency of flour.
- Stage 1: The grist is passed through a series of fluted
'break' rolls rotating at different speeds. These rolls are set so that they
do not crush the wheat but shear it open, separating the white, inner
portion from the outer skins.
- Stage 2: The various fragments of wheat grain are
separated by being passed through a complex arrangement of sieves. White
endosperm particles are channelled to a series of smooth 'reduction' rolls
for final milling into white flour.
Coarser fractions of bran with endosperm still attached will go to a second
break roll, with stages 1 and 2 being repeated until the flour, bran and
wheatgerm are completely separated. The result is a number of flour streams: a
white flour stream, a bran stream and a wheatgerm stream.
The whitest flours are produced from the early reduction rolls, with the
flour getting less white on later rolls as the proportion of bran particles
increases. Brown flour is a mixture of white flour and a portion of the other
streams. To produce wholemeal flour, all the streams must be blended back
together.
Packing
The different flours are packaged and sent to the bakeries. The flour is used
for many types of bread as well as biscuits, pies, cakes and confectionery.
Wheatgerm and bran may be used for certain breads and cereals or sold as health
foods. The remainder is blended into wheat feed which is used for animal food.
