Historical Development | Flour Milling in Australia | Flour Milling Processes
Wheat Cleaning | Wheat Conditioning | Flour Milling
Historical Development
The milling of flour from grain has its origins in the early history of all major civilisations. It is generally regarded as the oldest known industry. The basic milling technique was to grind the grain between two stone surfaces. This enabled the tough fibrous bran skin to be separated from the endosperm, which then was ground into a fine powder. This method, utilising saddle stones or pestles and mortars, appears to have developed independently in a number of areas around the world.
The progression from these simple implements to rotary stone mills occurred in Europe, the Middle East, Central Asia and the Far East. The size of the mill stones increased in the Middle Ages as animal, water and wind power was harnessed.
White flour as we know it today was first produced in Hungary and Germany in the 18th Century. It became so popular that the exported product sold in Europe for up to ten times the value of unrefined wholemeal. White flour was manufactured by arranging a number of stone mills to form a series of grinding passages. The grinding severity of each passage was adjusted so that the grain was broken down progressively, and in this way the separation of bran skin from endosperm was enhanced. Primitive purifiers were introduced in 1810 to remove bran from intermediate stocks, and the remaining material, which had a high endosperm content, was ground into white flour on additional stone mills. The process was referred to as the 'Gradual Reduction System of Milling'.
In modern flour mills, millstones have been replaced by steel rollers. Old style reel sifters have been replaced by modern plansifters. The design of purifiers has been radically improved, and many new ancillary machines have been incorporated into the milling system. The same basic principles of the Gradual Reduction System of Milling, however, are still universally employed. Even the world's most advanced flour mills are still utilising processing technology that was fully developed as long ago as 1930. The flow diagrams of flour mills in all countries have been made progressively less complex over the last fifty years, with the exception of the Japanese flour milling industry, which produces exceptionally white flour of very low ash (or mineral) content. The development of the flour milling industry has been associated with advances of equipment design, which has improved operating capacity and efficiency, but no major technological breakthrough has occurred.
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Flour Milling in Australia
The Australian flour milling industry has changed considerably since the 1870s, when more than 500 flour mills were operating, powered by steam, water or wind.
Mill ownership has evolved from small family concerns to large diversified companies. Those remaining in the industry have extended their operations into fields such as stockfeed milling, bakeries, household flour, packaged cake mixes, pasta and biscuit production, starch, gluten and glucose manufacture, and livestock production. Australian owned companies produce the majority of the flour milled in Australia.
The decline in the number of flour mills operating in Australia has been largely due to the application of new technology and the search for economies of scale. It is no longer feasible for each town to have its own mill to supply the local population. Another important factor was the steady loss of export flour markets in the Asia/Pacific region when countries in these areas set up their own mills following World War II.
The total domestic market for flour products has experienced steady growth under the influence of rising population.
Currently, around 1.75 million tonnes of flour is milled for domestic human consumption each year. Use of flour for industrial purposes, such as starch, gluten and their derivatives, has increased significantly in recent years and now amounts to about 460,000 tonnes a year.
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Flour Milling Processes
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Wheat Cleaning
Before milling starts, the wheat is tested for protein content and other characteristics and graded into various categories. It is then cleaned to remove foreign material such as stones, dust and weed seeds. A number of grades are usually then blended together to produce the desired type of flour. Soft, low protein wheats are most suitable for biscuit flours, while flours for bread making are usually made from harder, higher protein wheats.
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Wheat Conditioning
Water is added to the wheat blend in a process called conditioning or tempering. The amount added is usually between 4–6%, depending on the initial moisture content of the grain and the type of wheat being milled. The wheat is then allowed to lie in the conditioning bins for between 10 and 20 hours. The bran layers are toughened by the addition of water, minimising shattering during milling and the endosperm is made more friable (crumbly), requiring less power to be ground into flour.
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Flour Milling
The separation of the endosperm material from the bran layers of the kernel and the gradual reduction in size of the endosperm particles is achieved by a complex combination of grinding rolls (break and reduction rolls), sifters, purifiers, and other equipment.
The tempered wheat is fed into roller mills which house two steel cylindrical rolls with longitudinal grooves (flutes) cut into their surface. As wheat passes between the rolls which rotate towards each other at different speeds, the bran is gripped by the flutes on the slower rolls. The friable endosperm is torn away into granular chunks (semolina) or fine powder (flour) by the overtaking flutes on the faster roll.
Rotating plan sifters, which incorporate a number of superimposed sieves of varying sizes, grade the ground stock into bran fragments, coarse semolina, fine semolina and flour according to particle size. The larger bran fragments are processed by a further three or four break roll-sifter passages, until all of the endosperm is removed.
The purpose of the 'break' system is to break open the wheat grains to release semolina particles and leave bran in the largest particle size possible, thus minimising bran contamination in the semolina. The granular stocks produced are predominantly semolina interspersed with bran particles. Although undesirable, some flour is produced at this time. The main production of fine flour comes from the later reduction stage.
To purify the mixed granular stocks of semolina and bran coming from the break system, they are passed through the purification system. A purifier is essentially a long rectangular machine with oscillating sieves through which a current of air is drawn. Semolina stock is conveyed along the length of sieves and the shaking motion, together with the upward current of air, causes the stock to stratify. The lighter bran fragments are floated above a layer of pure semolina which gradually passes through the sieves. The bran fragments pass over to the end of the sieves.
The particles of purified semolina are then crushed to fine flour by the 'reduction' system. This is comprised of roller mills fitted with smooth rolls operating at slightly different speeds. Flour is removed by sifting the ground stock over fine mesh nylon screens. Coarse mesh sieves separate the bran flakes. The size of any intermediate product is gradually reduced by subjecting it to repeated roll and sifting treatments. Up to eight to twelve passages may be employed, depending on the design of the plant.
Stock failing to pass through the flour sieves at the completion of the reduction system becomes offal (pollard), as does the course material (bran) rejected at the termination of the break system.
All the mill products, including flour, wheatgerm and bran are either bagged or stored in bulk bins. Flour is normally stored for at least three days before being delivered to bakeries and food processing factories. The ageing process has a beneficial effect on the flour for most purposes.
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