- Students will create a model that demonstrates how stones grind.
- Students will compare millstone patterns to identify how the grain is turned into flour as it runs from the central hopper to the perimeter.
How Millstones Grind
Robert P. Rich and Steven A. Walton
In order for a millstone to cut the grain into flour - for that is exactly how grain is ground - the millstone faces need to have grooves cut into them. The pattern of these grooves varied from stone to stone and from region to region, and stone dressers developed both elaborate and subtle variations for different grains, different grinds (much like the range of grinds of coffee available today), and different grain conditions. The patterns on the stones working together act like a pair of scissors to cut the grain as the stones rotate.
When we speak of a grindstone, we can either mean each of the pair or the two together, for you must have a pair to do any useful grinding. The bottom stone is called the bedstone and it remains stationary - in fact, it is set into a bed of concrete or mortar to make it literally rock stable. The top, rotating stone is called the runner stone, and it has a hole in the middle through which the grain is fed. Both stones have a pattern of grooves cut into their working faces (top face for the bedstone and bottom face for the runner stone) that act as feed channels for the flow of the grain to the outside edge. As the two stones rotate against one another - never touching! - the grain is repeatedly scissored between the grooves, whose gap varies from well less than 1/8" near the center down to thousandths of an inch at the perimeter. Individual grains are cut again and again on their journey from the center out to the edge. A stone dresser would come to the mill once a year and re-face the stones to keep the grooves crisp and the stones milling smoothly through the year.
For more information on the patterns in millstones, see Jon A. Sass, The Versatile Millstone: Workhorse of Many Industries (SPOOM, 199), available directly from SPOOM.
For each model of a millstone pattern, you will need the following: