Grist Mills and Gravity

By Deane Rykerson
TMI President

Tide mills had all the functions that stream mills did, from cutting lumber to milling flour. But did you ever wonder why gristmills are so much more vertical than sawmills? There is often a roof monitor or cupola in a gristmill. Well, form follows function and gravity is an important part of the function of grinding grain. If we follow a kernel of wheat from harvesting to being ready for bread, we can see how important height can be to aid the milling process. What goes up must come down.

At the top of the mill there is storage for the grain, fed by a hopper. The grain then descends to a screening process that shakes and sifts to remove gravel and sticks from the food product. At the next lower level the clean kernels are fed between the grinding stones, gradually working outward on the grooves of the bedstone. A rotating screened tube, called a bolter, can then be used to separate the coarser meal from the finer flour.

But how did the cereal get from a wagon or boat to the top of the mill to begin its descent? The most labor-intensive method was hauling bags of grain up by hand. The use of ropes and pulleys for a basic elevator made this easier, but the biggest innovation came from the American inventor Oliver Evans. Evans (who also perfected the steam engine which resulted in the demise of water-powered mills) devised a belt with buckets that could use water power instead of human power to get the grain to the very top of a mill. He also patented other mill innovations, and one of the first mill owners to use his system was George Washington in his Mount Vernon gristmill.

So gravity was the natural force that was harnessed in two ways for gristmills. The gravity of falling water drove the mill and the gravity of falling grain allowed its transformation to meal and flour.