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A gristmill (also: grist mill, corn mill, flour mill, feed mill or feedmill) grinds cereal grain into flour and Wheat 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.
The early mills had horizontal paddle wheels, an arrangement which later became known as the "Norse wheel", as many were found in Scandinavia. 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. This simple arrangement required no , 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. 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.
Undershot wheel were in use in the Roman Empire by the end of the first century BC, and these were described by Vitruvius. 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. The peak of Roman technology is probably the Barbegal aqueduct and mill where water with a 19-metre fall drove sixteen , giving a grinding capacity estimated at 28 tons per day. 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.Hong-Sen Yan, Marco Ceccarelli (2025). 9781402094842, Springer Science and Business Media. . ISBN 9781402094842
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. Geared gristmills were built in the medieval Near East and North Africa, which were used for grinding grain and other seeds to produce Flour. (1996). 9780415124102, Routledge. ISBN 9780415124102 Gristmills in the Islamic world were powered by both water and wind. The first Windmill gristmills were built in the 9th and 10th centuries in what are now Afghanistan, Pakistan and Iran.Adam Lucas (2006), Wind, Water, Work: Ancient and Medieval Milling Technology, p. 65, Brill Publishers, The Egyptian town of Bilbays had a grain-processing factory that produced an estimated 300 tons of flour and grain per day.
From the late 10th century onwards, there was an expansion of grist-milling in Northern Europe. In England, the Domesday Book 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.Gimpel, J., The Medieval Machine, Gollanz, 1976, Chapter 1.
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 in 1202. The Cistercians were known for their use of this technology in Western Europe in the period 1100 to 1350.
Classical mill designs are usually water mill, though some are powered by the wind or by livestock. In a watermill a sluice gate is opened to allow water to flow over 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 it was aligned horizontally (the tub wheel and so-called Norse wheel). Later designs incorporated horizontal steel or cast iron turbines, which 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. 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 stone, 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. This process, which may be automatic or controlled by the miller, is called tentering. (1971). 9780715353653, David and Charles. ISBN 9780715353653
The grain is lifted in sacks to the "sack floor" at the top of the mill by a hoist. The sacks are then emptied into bins, from which the grain falls 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 flour sack 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, the stones were usually placed on a separate timber foundation, known as a husk, which was not attached to the mill walls. That isolated the building from vibrations coming from the stones and the main gearing, and also allowed for 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.
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."Evans, Oliver, The Young Mill-Wright and Miller’s Guide, Oliver Evans, Philadelphia, 1795, Chapter II, pp.88-90 Over time, any small, older style flour mill became generally known as a gristmill (as a distinction from large factory flour mills).
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.
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