How the Roller Mills Changed the Milling Industry

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How the Roller Mills Changed the Milling Industry

How the Roller Mills Changed the Milling Industry
by
Theodore R. Hazen

Milling was founded on sound information and tradition passed on from one generation to another. This is the way it was both in England and when it came to this country. The millstone was the miller's symbol of his art and his industry, and they were reluctant to accept roller mills in place of the millstone. One of the practices that was involved in milling was that metal should never come into contact with ground meal. Grinding grain with something other than stone, was un-heard-of. The millstones were a familiar and trusted device. When roller mills first appeared, the traditional millers never believed that the roller mills could ever replace the millstone as the prime flour milling device.

A natural conflict resulted between the millstone and the roller mill, there was also a conflict between the water wheel and the turbine. Many millers held a belief that the water wheel was superior to the turbine. There were arguments as to which system would work better together, the millstone or roller mill.

When millstone grinding began to be threatened by the roller mills, the miller tried to improve the dressing of the millstone. They tried to increase the number of quarters on the millstone. This they discovered could not make a noticeable improvement over the old style of dressing. They tried to increase the number of furrows but it did not improve the product output. Even with improvements, the millstone still was slower grinding than roller mills.

The roller mill became a good alternative to the progressive millers who wanted a better milling process. They wanted to improve the quality and quantity of their flour product. This led to the primary attraction of the use of roller mills. In replacing the millstone with roller mills, the miller gave up the time consuming process of dressing millstones.

The early roller mills could not do as well of a job in flouring middlings as millstones. It was not until roller mills were improved that their use grew. The first use of roller mills was to break up the grain. Then a pair of millstones would be used to regrind the particles into flour. Eventually this practice became obsolete with the addition of other rollers replacing the millstones. The miller had to learn new skills. He learned that by increasing the number of breaks he could extract almost all the bran and produce superfine white flour.

In the larger milling operations they started to bleach the white flour. It was soon determined that any remaining particles of bran and germ were made more noticeable.

A large-scale milling operation was built as an automatic mill. In these automatic mills there were improvements in the mill's bolters. At this time came the introduction of the purifier and wheat cleaning was greatly improved. Almost every impurity was removed from the grain before it was ground. The germ which effects the shelf life of flour could be scraped off after the first break. The roller mill would break the grain to produce floury middlings. The floury middlings could be bolted and purified to remove some of the bran. Then the middlings would be reground using a slower grinding speed and there would be a more extensive bolting to extract as much flour as possible.

The roller mills increased the amount of flour as well as speed up the milling process. Roller mills could produce more marketable flour than millstone ground operation.

The first (gear driven) roller mills used in Washburn "A" Mill, Minneapolis, Minnesota.

Roller mills used more belt pulley drives with metal shafting and less large gears. The newer roller mills had better roller mountings, using belt drive. These rollers could run faster than the earlier gear operated roller mills. The first noticeable difference was that the belt drive roller mills made considerably less noise. The roller mills had corrugated cast-iron rollers with better bearings and feed control. The differentials, on each roller pair, control the rotation. The non-touching rollers, each ran at a different speed. If both rollers ran at the same speed the grain would travel though with little or no treatment done to it. The slower roller tends to hold the grain while the faster roller shears open the kernel of the grain. This process produces break flour mixed with bran. Increasing the number of breaks and bolts, the total extraction of flour would remain the same as from millstones., The use of gradual reduction with rollers, the percentage of best-grade flours could be increased, while the poor-grade flour would remain the same or be reduced.

The main argument against rollers was the expense of the roller mills themselves. The roller mills became more useful with other gradual reduction equipment being added to the expense such as increasing the number of bolting reels, purifiers and aspirators. Roller milling became more adapted to the larger milling enterprises, the roller mills caused a great demand of capital, which the larger mills could provide to purchase new equipment.

The roller mills are used primarily in the large merchant mill. They were never really identified with the term roller mill. Many of the more successful milling operations converted from millstones to rollers. As the millers installed roller mills, their mills were no longer referred to as grist mills, but they were to be known as roller mills for generations to come. The Leeper Roller Mill, Germania Roller Mills, Juniata Roller Mills are such examples.

Roller mills became identified with the less nutritious whiter flour, while other mills still continued to use millstones to make their stone-ground flour. The nutritional value of the white flour was evident in that so much of the nutritional value was removed from the flour that insects, that infested stone ground flour, could not sustain themselves in the new varieties of the white flour. The insect infestation, which plagued the milling operations was reduced, but it produced a less nutritional flour.

Roller mills in a large merchant flour mill

It was not until the 's that the American milling operations started to enrich flour. Flour became enriched with thiamine, niacin, riboflavin and iron. Whole wheat flour does not need to be enriched. Enrichment may have been a great step forward but why was it needed in the first place?

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How Can Biomass Briquette Machine Technology Transform Singapore's Sustainability Efforts?

Note: A version of this article by T. R. Hazen appeared in OLD MILL NEWS, January , Vol. VIII, No. 1, Whole Number 30, page 6.

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Origin

The milling of grains is an ancient art and craft. The first evidence of grinding grain dates back 8,000 years. As people use to say, &#;The first miller was the first person to put a wheat kernel into the mouth and bite.&#; There is evidence of sieves or nets to separate flour from unwanted parts of the wheat grain as early as B.C. The first mechanical mill, known as quern, employed two horizontally mounted stone disks. Grains such as wheat and corn were fed between them, while the disks were manually rotated.2

How does roller milling work?

The seven main steps in roller milling are:3

1. Tempering or conditioning. Cereals such as wheat need tempering so the bran layers can be softened enough to become flexible and removed as larger pieces. Tempering also softens the endosperm to facilitate its reduction during milling, reducing the occurrence of damaged starch.
2. Break system. Thanks to a combination of shear, friction/abrasion and impact forces, the grain or kernel is broken/fractionated into wide particle-sized pieces during distribution. This step separates the endosperm from the bran and germ components. Fluted or corrugated roller mills are used for this step.
3. Sizing or classification system. This step separates the small bran pieces attached to the ground large pieces of endosperm, according to particle size and specific gravity (density). Sifters and purifiers are involved in this step.
4. Reduction system. This step reduces the endosperm pieces (known as middlings) to flour. This step uses smooth roller mills.
5. Tailings system. This step separates the fiber or bran from the endosperm recovered from the other three systems.
6. Blending. Based on the final use or application, the miller adjusts or blends the different flours (streams) that are produced during the milling process. Parameters such as ash and protein content can be controlled at this point.
7. Final treatment. In certain wheat flours, treatments may include enrichment, bleaching, and enzymes or malt supplementation.

These steps require a series of repetitions in order to obtain the different fractions of granular materials such as straight grade flour, germ and bran (mill feed). Quality aspects related to dry milling often include:4

• Amount of damaged starch
• Variations in color due to ash content (bran contamination)
• Particle size distribution
• Protein and moisture content
• Water absorption
• Enzymatic activity
• Baking strength or quality
• Pasta making strength or quality

The American Association of Cereal Chemists (AACC) has established and published several standardized methods for quality analysis usually performed during milling. The following are a few examples:

Contact us to discuss your requirements of flour mill introduction. Our experienced sales team can help you identify the options that best suit your needs.

References

1. Aleksandar Z. Fišteš and Đuro M. Vukmirović. &#;Reduction of Wheat Middlings Using a Conventional and Eight-roller Milling Systems.&#; Institute for Food Technology, APTEFF, 40, 1-220 (), pp. 25&#;34.
2. Finnie, S., and W.A. Atwell. &#;Milling.&#; Wheat Flour, 2nd ed., AACC International, Inc., , pp. 17&#;30.
3. Posner, E.S. &#;The Grinding Process.&#; Wheat Flour Milling, 2nd printing, AACC International, Inc., , pp. 185&#;200.
4. M.A. Loza-Garay, and R.A Flores. &#;Moisture, Ash and Protein Flow Rate Study in a Wheat Flour Pilot Mill Using Simulation Models.&#; Institution of Chemical Engineers (IChemE), Volume 81, Part C, , pp. 180&#;188.