by Jerseyman ©2010
A gristmill exists to grind a variety of grains into flour, meal, or feedstock. While some mills derived their power from the wind, the water-powered mill ground the largest quantity of grain in the eighteenth and nineteenth centuries. Wind could not generate the horsepower available to water-powered operations. An economy of scale existed with watermills located on never-failing streams, which remained profitable for generations, while windmills could only grind during ideal wind conditions and often suffered great damage at the mercy of the elements.
Three types of waterwheels could be used at water-powered mills, depending on the topography and location. These included:
1. Undershot wheel—water would strike the waterwheel at the bottom, forcing it to rotate clockwise; this method generated the least amount of horsepower and offered approximately 30% efficiency;
2. Breast wheels—water arrived at the wheel through a penstock, striking the wheel just above the center-point between the top and bottom, turning the wheel clockwise; this generated more horsepower and offered an efficiency of circa 65%;
3. Overshot wheels—again, water arrived to the wheel via a penstock and then dropped just beyond the top of the wheel, turning it counter-clockwise; this type of wheel generated the most horsepower available at a water-powered mill, offering an efficiency of 75%.
By damming a stream and forming a millpond, the water was directed to the waterwheel through a headrace and/or a penstock-a wooden trough or iron pipe that channeled the flowing water to strike the wheel. The water would then enter the wheel “buckets” or chambers and the weight of the water would force the wheel to turn. The greater the water velocity, the faster the wheel would turn, although water traveling at a high rate of speed, such as during a freshet, would be counterproductive and could wreak major damage to the wheel and the mill. This principle applied to any and all of the three types of waterwheels outlined above.
With the wheel brake released and the clutch engaged, the wheel began turning, generating horizontal power. That is, the wheel and its axle rotated on a horizontal plane. However, gristmills required power on a vertical plane to operate the grindstones. This perpendicular change in power was achieved through gearing. In early mills, these gears comprised all wood components.
When grain first arrived at the mill, the miller weighed it and either stored it for future grinding or dumped it into a rolling screen that removed chaff and other impurities prior to grinding. Some mills would also run the grain through a set of stones specifically arranged to remove sand and other foreign matter before the actual grinding process occurred.
The grindstones used to transform grain into flour, meal, or feedstock, were dressed with long furrows running from the inner hole to the outer edge at a set angle. These furrows would allow friction-generated heat to escape during the grinding process. They also provided a channel in which to move the finished product to the edge of the stone, into the surrounding casing or vat and out of the grinding area. Two dressed grindstones, when assembled, were known as a run of stone. The top stone, called the runner, would turn while the bottom one, called the nether or bed-stone, remained stationary. The miller would pour the grain in a hopper suspended above the run of stones. When the miller set the runner stone in motion, the grain would feed out of the hopper, onto a “shoe” and into the center of the stone assembly. The actual grinding process took place on the flat sections (called “land”) of the stone between the cut furrows. A set gap between the two stones allowed just enough room for the grain to run between them and be ground. The ground grain would drop below the grinding floor level and enter moving elevators or conveyors for transport to other processing. After the flour has moved through the grinding process, it remained warm and moist. It was necessary to cool and dry the product by spreading and raking it.
The horizontal power generated by the waterwheel also powered a series of shafts and belts to operation other equipment. Once the flour or other product had been ground, it required sifting and would be placed into a bolting chest. In this machine, three or more grades or fineness of bolting fabric wrapped around a cylindrical frame sifted the ground grain into finished flour. The bolting chest was mounted at an angle to permit gravity feed of the product. The flour entered the bolting chest and passed through the fabric, trapping any oversized clumps or other impurities in the surrounding “chest.” The flour that passed through the finest cloth the miller considered finished and it could be marketed. The flour passing through the medium grade of cloth—called “middlings”—was normally reground to make it finer. The product passing through the coarsest cloth usually included the bran and other impurities and the miller either threw it away or mixed it with animal feed. After completion of this sifting or bolting process, the miller stored the finished flour in hoppers for future distribution. It could also be bagged or placed in barrels and weighed immediately preparatory to ship the finished product to market.
Many improvements occurred in the milling industry over the centuries. In the United States, inventor Oliver Evans made a major contribution to mill design and construction. In 1795, Evans published his first edition of The Young Mill-Wright & Miller’s Guide. The Evans Mill became a standard of mill construction for many years. For those of you who do not have this work in their library, you can view a digital copy here:
The book is reproduced complete with all of the engraved illustrative plates, which will aid you in gaining a better understanding of what I have written here. In the 1850s, water turbines began being applied to the milling business. Supplanting the waterwheel, turbines had the capacity of generating higher horsepower ratings through greater efficiency and gearing.
The nineteenth century also produced other improvements, most notably the introduction of roller mills to grind the grains into flour. Manufacturers fabricated roller mills from cast iron and the equipment consisted of corrugated rollers that ground the grain into middlings, or coarse flour. The same type of rollers without corrugation then produced the finished flour. The first roller mill in the United States began operations in 1878 and, by 1890, roller mill use grew in an ever increasing proportion. The roller mill caused many small, rural mills to close, leaving flour production to large industrial establishments.
Mills used other equipment, too. Mechanical corn shellers could pull dried kernels off the husks very quickly. The miller then ground the corn either coarsely into millet, used as fowl feed, or finely ground into meal for human consumption. Over the years, millers made a concerted effort to decrease dust generated during the manufacturing process. This need resulted in the invention of numerous “dustless” machines. Dustless separators and scourers, used to further refine the ground flour, dustless sifters, dustless baggers—manufacturers produced all of this equipment to decrease the health and explosion hazards associated with any type of fine dust. As machinery became more sophisticated, it also became larger and much more expensive, providing yet another reason to create large industrial milling establishments, which displaced the smaller, rural water-powered gristmill.
1795 The Young Mill-Wright & Miller’s Guide. Printed for and sold by the author, Philadelphia, Pennsylvania.
Weiss, Harry and Robert J. Sim
1957 The Early Grist and Flouring Mills of New Jersey. New Jersey Agricultural Society, Trenton, New Jersey.
Zimiles, Martha and Murray Zimiles
1973 Early American Mills. C.N. Potter, New York City, New York.