Flour Milling

I recently finished Six Thousand Years of Bread: Its Holy and Unholy History by H. E. Jacob. It a comprehensive collection of the history of bread, beginning with the discovery of yeast and plowing over 6,000 years ago up until the Second World War. Jacob keeps the history lively and entertaining, clearly forwarding his own ideas on every topic and imbuing the characters with very human and tangible qualities. I would highly recommend this book to any baker. While hefty in its length, it is quite readable. Read it with and open mind and take some of Jacob’s long-winded sagas with a grain of salt.

While I do not want to review the book here, I do want to discuss one topic that I found particularly interesting: the history and process of milling. As a baker, I believe that I should be well informed about the origin of my ingredients, how they were grown or made and what defines their quality. Understanding milling is essential, in this respect, to ultimately understanding flour.

“Flour” is a term applied to triturated (finely ground or pulverized) constituents of some type of grain berry. The first methods of producing flour involved using a rounded stone approximately the size of an adult fist to pound and crush grains into a coarse meal against another stone. Usually the stone were made of a rough, but durable sandstone. St. Bridget’s Stone, a flat, table-like stone on the shore of Lough Macnean in Ireland with many indents on the surface is thought to have been an early, primitive mill. Most likely, several women stood around the stone and pounded meal. There are many similar stones found throughout the rest of Ireland, the Orkneys, and the Shetland Islands. In the Americas, Indians would boil maize or acorns and then mash it into a paste using stones. Often they would use a round stone or a “muller” and a concave hollow in a rock. Crushing stones varied in size and shape from the round, ball-like “muller” to an elongated pestle.

The next step in milling evolution involved the saddle-stone, consisting of a stone with a concave face onto which grain was placed and then ground into meal. These have been discovered in ancient caves and dwellings of Italy, Switzerland, France, and the British Isles. The ancient Romans appeared to have used the saddle-stone, referring to it as the mola trusatilis, or the “thrusting mill,” which would describe the forwards and backward motion need to grind flour using the saddle-stone. Variations on the saddle stone are still used today. For example, the metata is used in Mexico for pulverizing maize for tortilla.

Later the Romans also had the mola versatilis, which refers to the revolving millstone or “quern.” The querns consisted of an upper, funnel-like stone through which grain passed. As the grain flowed downward it eventually encountered the space between the revolving and a lower, stationary bed stone.The meal was then discharged around the edges of the two stones. The upper stone, also known as the “runner,” had a wooden handle attached used to rotate the stone. Classical examples of these can be found at the ruins of Pompeii. The Romans also invented the use of water wheels to turn the millstones, but slaves typically did the manual labor involved with grinding flour. The first documentation of water wheel was by Strabo, who described the horizontal waterwheel at Cabira in 63 B.C. Later the Barbegal aqueduct boasted a 19-meter waterfall that powered sixteen water wheels that combined had a milling capacity of 2.4 to 3.2 tons per hour.

Jacob emphasizes that watermills were only slowly accepted by various cultures after the fall of the Roman Empire. This was due, he claims, to the ‘barbarians’ belief that it was irreligious to control the spirits of free rives and brooks. Indeed, “they let the mills rust and decay. Where mills continued to be used, where the wheels rattled on, the people tried to appease the elemental power by sacrifices, by throwing flour or breads into the river.” Mills and millers were associated with devilish, secretive works. Accused of stealing or adulterating the flour with foreign substances, millers were disliked and mistrusted by much of the community. Furthermore, mills were considered places full of lascivious doings. According to Jacob, referencing Goethe’s Annette, “The rumbling of the mill, which vibrated in all other rooms of the building; the flow of the flour; the warm atmosphere of mingled spray and dust—these things made the mills places of untrammeled sexuality.” Jacob further provides the example of Ethelbert’s law book in the sixth century which stated, “If anyone molest a maidservant of the king he shall pay fifty shillings amends. Or if she be a maid who grinds at the mill, he shall pay only twenty-five shillings.”

But, practical use eventually won out over superstition and hearsay. Watermills became popular elsewhere and were used for centuries. According to the Domesday survey in 1086, England had around 500 mills in Norfolk and Suffolk Counties alone and 5,624 throughout the entire nation. An invention acquired from the Middle East, wind power was eventually introduced after the Crusades and quickly became popular in the Netherlands. Boulton and Watt installed the first steam engine at the Albion Flour Mills in London in the late 1700’s. Other advances in the mid-1800’s that occurred in the milling process included a cooling mechanism for the stones and the exchange of woolen bolting cloth for silk gauze.

A wheel-driven mill consists of a large gear or pit wheel that is installed on the same axle connected to the water wheel. The pit wheel powers a wallower, or smaller gear, through a driveshaft that extends from the top to the bottom of the building. This design allows the main shaft to rotate faster than the water wheel. The millstones generally turn at around 120 rpm. The top stone or runner is attached to a spindle driven by the main shaft, while the bottom stone or bed is fixed to the mill floor. The runner is detachable through a wheel called the stone nut that links the runner’s spindle to the main shaft. This allows for mill stone maintenance and for the main shaft to do power other mill work such as the mechanical sieve for refining flour or to hoist sacks of grain.

The milling process begins when a sack of whole grain berries is lifted to the sack floor at the top of the mill. The sack is then emptied into bins, where the grain descends through a hopper to a stone floor below. The flow of grain to the millstones is then controlled by shaking it along the slipper (or sloping trough) from which it drops into a hole in the center of the runner stone. Next the milled product or flour is collected as it exits from the peripheries of the outer rim of the stone.

The wheat berry consists of a starch-rich endosperm and a fat-rich germ surrounded by a husk or bran. The degree to which these three ingredients are left in the flours determines the properties and qualities of a flour. Millstones were often set close together resulting in “low” milling, which extracted as much flour as possible from one round of grinding. This technique pulverized the endosperm, germ, and bran all together, damaging the flour’s durability due to the germ’s high fat content and tendency to go rancid. In the 1870’s Minnesota millers were experimenting with a European method of “high” milling and gradual reduction, which involved several millstones placed progressively closer to each other. The first grind separated the. bran covering that was then separated from the flour by bolting between grinding. This method produced a finer flour, but it still left much of the bran and germ in the final product.

In the 1830’s Sulzberger, a Swiss engineer, designed the first ancestor of the modern roller mills, or machines with either horizontal, vertical, or obliques chilled iron corrugated rollers. Roller mills twist the grain, rather than pulverizing it, and allow for more exact spacing between the milling surfaces. The result is a finer product at each stage in the milling process. This design was used in the Pester Walz-Miihle, a Hungarian mill founded in 1839 by Count Szechenyi. Hungarian wheat is particularly hard and durable and thus greatly benefited from the roller milling technique. Later, a Swiss miller by the name of Friedrich Wegman invented porcelain rolls in the 1870’s, which yielded a finer grind. Due to their superiority in producing a finer flour, roller mills have now almost entirely replaced millstones as the primary machine for grinding flour.

Roller mills differ from the stone mills because they are capable of efficiently separating the bran and the germ from the endosperm. Three important milling terms with roller milling include ‘semolina,’ ‘middlings,’ and ‘dunst.’ They each describe a product of roller mills. They are very similar in composition, but represent different phases in the process of grinding the endosperm of the wheat berry to flour. In order of increasing fineness of broken up endosperm the terms are; ‘semolina,’ ‘middlings,’ and finally ‘dunst.’ The term ‘pure’ placed in front of any of these indicates a total lack of bran or wheat husk in the flour. In the milling process the germ is straightforwardly separated from the remainder of the berry because it is flattened instead of pulverized by the rollers and thus can easily be sifted from the rest of the flour. In addition, the bran is removed to leave a white to off-white flour consisting of almost wholly endosperm. In white flours only the endosperm is included in the final product. Whole-wheat flour is the result of recombining both the bran and the germ with the endosperm at the end of the milling process.

The newest advance in milling technology since the advent of the roller mill is the turbogrinder. In 1959 Pillsbury Mills designed this grinder that utilizes high-velocity air vortices the reduced flour particle grain size through the abrasive erosion of particle collision. Air classifiers then divide the particles into protein and starch. This technology is useful in that it allows millers to process flours with extremely high protein contents that would otherwise be unfit for flour.

Most mills today are “merchant mills.” This means that they are privately owned entities that either accept money or trade for milling grain or that they buy unmilled grain and then become the owners of any flour they produced. Early mills were community owned and supported by payment in the form of a certain percentage of a farmer’s grain or a “miller’s toll.”

There is a wealth of information about milling. I could not possibly put it all into this entry. If you are interested in learning more I highly recommend reading the resources listed at the bottom of the page. And if you are interested in a thorough and engaging history of bread, do pick up a copy of Six Thousand Years of Bread if you have a chance. Also, if you know of a local mill that you can visit, I highly encourage it. Ask about the process of grinding, who owns the mill, how they choose their flour, etc… Find out where your flour is coming from!



Also: Check out this recent article in the New York Times: Rebuilding a Dutch Tradition, One Windmill at a Time

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