Apparatus that grinds grain into flour

If you are looking for more details, kindly visit China Portable Grinding Mill.

Allied Mills flour mill on the banks of the Manchester Ship Canal in North West England

A gristmill (also: grist mill, corn mill, flour mill, feed mill or feedmill) grinds cereal grain into flour and middlings. The term can refer to either the grinding mechanism or the building that holds it. Grist is grain that has been separated from its chaff in preparation for grinding.

History

[

edit

]

Early history

[

edit

]

Senenu Grinding Grain, c. 1352–1336 BC. The royal scribe Senenu appears here bent over a large grinding stone. This unusual sculpture seems to be an elaborate version of a shabti, a funerary figurine placed in the tomb to work in place of the deceased. Brooklyn Museum. The basic anatomy of a millstone; this diagram depicts a runner stone. Grinding mechanism in an old Sweden-based flour mill The old water mill at Decew Falls in St. Catharines in Southern Ontario

The Greek geographer Strabo reports in his Geography a water-powered grain-mill to have existed near the palace of king Mithradates VI Eupator at Cabira, Asia Minor, before 71 BC.[1]

The early mills had horizontal paddle wheels, an arrangement which later became known as the "Norse wheel", as many were found in Scandinavia.[2] The paddle wheel was attached to a shaft which was, in turn, attached to the centre of the millstone called the "runner stone". The turning force produced by the water on the paddles was transferred directly to the runner stone, causing it to grind against a stationary "bed", a stone of a similar size and shape.[2] This simple arrangement required no gears, but had the disadvantage that the speed of rotation of the stone was dependent on the volume and flow of water available and was, therefore, only suitable for use in mountainous regions with fast-flowing streams.[2] This dependence on the volume and speed of flow of the water also meant that the speed of rotation of the stone was highly variable and the optimum grinding speed could not always be maintained.[2]

Vertical wheels were in use in the Roman Empire by the end of the first century BC, and these were described by Vitruvius.[3] The rotating mill is considered "one of the greatest discoveries of the human race". It was a very physically demanding job for workers, where the slave workers were considered little different from animals, the miseries of which were depicted in iconography and Apuleius' The Golden Ass.[4][5][6] The peak of Roman technology is probably the Barbegal aqueduct and mill where water with a 19-metre fall drove sixteen water wheels, giving a grinding capacity estimated at 28 tons per day.[7] Water mills seem to have remained in use during the post-Roman period.

Manually operated mills utilizing a crank-and-connecting rod were used in the Western Han dynasty.[8]

There was an expansion of grist-milling in the Byzantine Empire and Sassanid Persia from the 3rd century AD onwards, and then the widespread expansion of large-scale factory milling installations across the Islamic world from the 8th century onwards.[9] Geared gristmills were built in the medieval Near East and North Africa, which were used for grinding grain and other seeds to produce meals.[10] Gristmills in the Islamic world were powered by both water and wind. The first wind-powered gristmills were built in the 9th and 10th centuries in what are now Afghanistan, Pakistan and Iran.[11] The Egyptian town of Bilbays had a grain-processing factory that produced an estimated 300 tons of flour and grain per day.[12]

From the late 10th century onwards, there was an expansion of grist-milling in Northern Europe.[9] In England, the Domesday survey of 1086 gives a precise count of England's water-powered flour mills: there were 5,624, or about one for every 300 inhabitants, and this was probably typical throughout western and southern Europe. From this time onward, water wheels began to be used for purposes other than grist milling. In England, the number of mills in operation followed population growth, and peaked at around 17,000 by 1300.[13]

Limited extant examples of gristmills can be found in Europe from the High Middle Ages. An extant well-preserved waterwheel and gristmill on the Ebro River in Spain is associated with the Real Monasterio de Nuestra Senora de Rueda, built by the Cistercian monks in 1202. The Cistercians were known for their use of this technology in Western Europe in the period 1100 to 1350.

Classical British and American mills

[

edit

]

Wayside Inn Grist Mill in Massachusetts Stretton Watermill, a 17th-century operational mill in Cheshire, England

Although the terms "gristmill" or "corn mill" can refer to any mill that grinds grain, the terms were used historically for a local mill where farmers brought their own grain and received ground meal or flour, minus a percentage called the "miller's toll."[14] Early mills were almost always built and supported by farming communities and the miller received the "miller's toll" in lieu of wages. Most towns and villages had their own mill so that local farmers could easily transport their grain there to be milled. These communities were dependent on their local mill as bread was a staple part of the diet.

Classical mill designs are usually water-powered, though some are powered by the wind or by livestock. In a watermill a sluice gate is opened to allow water to flow onto, or under, a water wheel to make it turn. In most watermills the water wheel was mounted vertically, i.e., edge-on, in the water, but in some cases horizontally (the tub wheel and so-called Norse wheel). Later designs incorporated horizontal steel or cast iron turbines and these were sometimes refitted into the old wheel mills.

In most wheel-driven mills, a large gear-wheel called the pit wheel is mounted on the same axle as the water wheel and this drives a smaller gear-wheel, the wallower, on a main driveshaft running vertically from the bottom to the top of the building. This system of gearing ensures that the main shaft turns faster than the water wheel, which typically rotates at around 10 rpm.

The millstones themselves turn at around 120 rpm[dubious – discuss]. They are laid one on top of the other. The bottom stone, called the bed, is fixed to the floor, while the top stone, the runner, is mounted on a separate spindle, driven by the main shaft. A wheel called the stone nut connects the runner's spindle to the main shaft, and this can be moved out of the way to disconnect the stone and stop it turning, leaving the main shaft turning to drive other machinery. This might include driving a mechanical sieve to refine the flour, or turning a wooden drum to wind up a chain used to hoist sacks of grain to the top of the mill house. The distance between the stones can be varied to produce the grade of flour required; moving the stones closer together produces finer flour.

The grain is lifted in sacks onto the sack floor at the top of the mill on the hoist. The sacks are then emptied into bins, where the grain falls down through a hopper to the millstones on the stone floor below. The flow of grain is regulated by shaking it in a gently sloping trough (the slipper) from which it falls into a hole in the center of the runner stone. The milled grain (flour) is collected as it emerges through the grooves in the runner stone from the outer rim of the stones and is fed down a chute to be collected in sacks on the ground or meal floor. A similar process is used for grains such as wheat to make flour, and for maize to make corn meal.

In order to prevent vibrations from the millstones shaking the building apart, they were usually placed on a separate timber foundation, not attached to the mill walls, known as a husk. This foundation isolated the building from vibrations coming from the stones and main gearing and also allowed for the easy re-leveling of the foundation to keep the millstones perfectly horizontal. The lower bedstone was placed in an inset in the husk with the upper runner stone above the level of the husk.

The automatic mill

[

edit

]

A grist mill, c. 1880

American inventor Oliver Evans revolutionized the labor-intensive process of early mills at the end of the eighteenth century when he automated the process of making flour. His inventions included the Elevator, wood or tin buckets on a vertical endless leather belt, used to move grain and flour vertically upward; the Conveyor, a wooden auger to move material horizontally; the Hopper Boy, a device for stirring and cooling the newly ground flour; the Drill, a horizontal elevator with flaps instead of buckets (similar to the use of a conveyor but easier to build); and the Descender, an endless strap (leather or flannel) in a trough that is angled downward, the strap helps to move the ground flour in the trough. Most importantly, he integrated these into a single continuous process, the overall design later becoming known as the Automatic (or Automated) mill. In 1790 he received the third Federal patent for his process. In 1795 he published "The Young Mill-Wright and Miller’s Guide" which fully described the process.[15]

Evans himself did not use the term gristmill to describe his automatic flour mill, which was purpose designed as a merchant mill (he used the more general term "water-mill"). In his book his only reference to "grist" (or "grists") is to the small batches of grain a farmer would bring in to have ground for himself (what would be generally called barter or custom milling). In his book, Evans describes a system that allows the sequential milling of these grists, noting that "a mill, thus constructed, might grind grists in the day time, and do merchant-work at night."[16] Over time, any small, older style flour mill became generally known as a gristmill (as a distinction from large factory flour mills).

Modern mills

[

edit

]

Interior in Tartu Mill, the largest grain milling company in the Baltic states

Modern mills typically use electricity or fossil fuels to spin heavy steel, or cast iron, serrated and flat rollers to separate the bran and germ from the endosperm. The endosperm is ground to create white flour, which may be recombined with the bran and germ to create whole grain or graham flour. The different milling techniques produce visibly different results, but can be made to produce nutritionally and functionally equivalent output. Stone-ground flour is preferred by many bakers and natural food advocates because of its texture, nutty flavour, and the belief that it is nutritionally superior and has a better baking quality than steel-roller-milled flour.[17] It is claimed that, as the stones grind relatively slowly, the wheat germ is not exposed to the sort of excessive temperatures that could cause the fat from the germ portion to oxidize and become rancid, which would destroy some of the vitamin content.[17] Stone-milled flour has been found to be relatively high in thiamin, compared to roller-milled flour, especially when milled from hard wheat.[17]

For more information, please visit Valve Core Grinding Tools.

Gristmills only grind "clean" grains from which stalks and chaff have previously been removed, but historically some mills also housed equipment for threshing, sorting, and cleaning prior to grinding.

Modern mills are usually "merchant mills" that are either privately owned and accept money or trade for milling grains or are owned by corporations that buy unmilled grain and then own the flour produced.

Pests

[

edit

]

One common pest found in flour mills is the Mediterranean flour moth. Moth larvae produce a web-like material that clogs machinery, sometimes causing grain mills to shut down.[18]

Gallery

[

edit

]

See also

[

edit

]

References

[

edit

]

• Wikander, Örjan (1985). "Archaeological Evidence for Early Water-Mills. An Interim Report". History of Technology. Vol. 10. pp. 151–79.

• Wikander, Örjan (2000). "The Water-Mill". In Wikander, Örjan (ed.). Handbook of Ancient Water Technology. Technology and Change in History. Vol. 2. Leiden: Brill. pp. 371–400. ISBN 90-04-11123-9.

Further reading

[

edit

]

• Richard Bennett & John Elton. History of corn milling (London, Simpkin, Marshall and company, 1898).

The History and Importance of Stone Milling

Since the third century B.C., the process of milling grains into flour consisted of passing whole grains through two large moving millstones. Traditionally, one of the stones turned (the runner stone) via water, animal or human power source, while the other (the bed stone) remained stationary. This method crushes the grains but keeps all the parts of the grain (the germ, bran and endosperm) intact. Millstones grind at a slow rate, so the friction only produces a low heat, which keeps the germ fat from oxidizing and becoming rancid, which can destroy some of the nutrients inherent in the grain.

Stone milling was the norm throughout history until around the 19th century. As times and cooking practices changed, it was found that stone milling didn’t produce flour that was fine enough for making pastries. Stone milling also produces a nutty flavor and texture that consumers were finding less than ideal for some of their recipes. Millstones also wear down after use, and have to be “dressed” or sharpened about every 90 days or so, creating concern that corundum dust from the grinding stones became part of the flour being produced. These concerns, plus the growing demand for flour vs. the slow production time of stone mills, led to the development of a faster alternative to stone milling, called roller milling.

The roller milling, or “high grinding” method slowly replaced most existing traditional stone mills. With roller milling, steel rollers quickly explode the grain over a series of passes through the mill. The reground flour is thoroughly sifted to remove the bran and germ, thereby also removing some of the nutrients. The friction of the roller milling process also produces higher temperature flour, which is reported to affect the nutrients as well. According to a publication by the Ecological Agriculture Projects, “heat causes the fat from the germ portion to oxidize and become rancid and much of the vitamins to be destroyed” (Aubert, 1989, http://eap.mcgill.ca/publications/EAP35.htm). Similarly, the Flour Milling, Baking and Confectionery Technology Department at the Central Food Technological Research Institute found that some loss of essential fatty acid and amino acids occurs at milling temperatures above 170°F.

The roller milling process produces flour that is whiter than traditional dark-colored, nutrient-rich, stone ground flour. Upon its introduction, the lighter color appealed to consumers, particularly the wealthy, and so white flour became desirable to all, even though it was less nutritious. With its ability to be produced faster in order to meet growing consumer demand, white flour eventually dominated the market.

Certainly, millers knew that nutrients were being lost in the process, which led to the development of enriched flour, where synthetic vitamins and minerals are added to the flour after milling. Of course, synthetic is never the same as the real thing. Which raised the question, what effect would this flour have on people’s health over time? The responses to that question called for change.

In the 1920s, the Food and Drug Administration’s Dr. Harvey Wiley attempted to ban refined, bleached white flour due to how it was made and the resulting loss of nutrition. In that same decade, engineer and nutritionist Dr. Royal Lee was beginning to take his own action against the process of commercial milling by developing a household mill that made the full nutrition of whole grains possible again.

By 1950, Dr. Lee’s mill was available to consumers. Using an air current to propel grains against a stationary corundum stone, Dr. Lee’s mill was able to produce a flour fine enough for pastry, while retaining all the nutritional value of whole grains. According to Lee and other nutritionists, milling by stone, in the amount needed for immediate use, is the only way to retain the complete grain and it’s nutrients, which include dietary fiber, phosphorus, thiamin, niacin, and B6. According to an essay published by Ecological Agriculture Projects, “The nutritional importance of using fresh stone-ground grains for bread-making was revealed in the results of feeding studies in Germany (Bernasek, 1970).”

Prices for household stone mills start at around $600 and can range to over $1000. The stone, technology, accompanying parts and country of manufacturing are all factors in the cost. Mills priced below that range use metal burrs instead of stone. These burrs shred or cut the grain, produce higher temperature flour due to friction, and don’t offer the nutritional and other benefits of stone referred to in this article.

The history of stone milling is an interesting look at the economy’s effect on nutrition. Fortunately, there is now a growing movement to go back to the stone milling methods that provide people the nutrition they need.

Are you interested in learning more about Valve Test Bench Supplier? Contact us today to secure an expert consultation!