WHEAT INTO FLOUR: THE MILLING PROCESS

Farmers grow wheat plants and the grain from those plants is milled to make flour. Flour is used to make lots of different food products, such as bread, pasta, 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 turns wheat into flour and is a key step in the grain chain. Find out about the structure of the wheat grain here. Different parts of the wheat grain are used to make different types of flour. 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

Look at this diagram, and read about how flour is made below.

Delivery and storage

Wheat 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 weight is considered to be better.
• Enzyme activity: high enzyme levels can result in sticky bread, making slicing difficult.
• Protein quality and quantity: important for baking purposes.

Cleaning and conditioning

Powerful magnets, metal detectors and other machines extract metal objects, stones and other grains such as barley, oats and small seeds from the wheat grain. Throughout the cleaning process, air currents 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 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 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 fragments of wheat grain are separated by a complex arrangement of sieves. White endosperm particles are channelled to a series of smooth 'reduction' rolls for final milling into white flour.

Coarser pieces of bran with endosperm still attached go to a second break roll, and stages 1 and 2 are repeated until the flour, bran and wheatgerm are completely separated. The result is a number of flour streams containing white flour, bran and wheatgerm.

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 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 for animal food. As all components of the wheat grain are used, waste is kept to an absolute minimum.

Topics for 11-14 year olds

• Curriculum relevance for 11-14 year olds