The Union Mills Homestead gristmill is getting a dressing up for the May 6 opening of the 1797 Shriver family home.
Yesterday morning, Robert Grassi arrived from Purling, N.Y., to "dress," or re-groove, the French Burr millstones that are used in the Homestead's gristmill to grind grains into flour.
"This needs to be done every 40 to 50 tons of grain that passes through the stones," said the bearded, 36-year-old millstone dresser.
Bent over the two 48-inch stones, the top runner stone weighing about 2,500 pounds, Mr. Grassi used a traditional mill pick to chip away at raised sections of the stone.
The runner had been separated from the bed stone, appropriately embedded in the floor, and turned over by a small crane next to the stones. Mr. Grassi's job is to dress, or re-cut, the pattern of grooves so the stones can continue to grind the grain to its proper consistency.
"These are French Burr stones, imported from France, and they're very hard," said Esther Shriver, the Homestead's executive director. "They were brought over on a ship in pieces and put together with plaster of Paris, then a metal band was put around the stone and sweated to fit tight."
French Burr stone is very hard stone, harder than granite. Mr. Grassi said the harder the stone the better for grinding, because the stones don't have to be dressed as often.
Mr. Grassi uses the method that was taught him 10 years ago by a fifth-generation English millstone dresser, Charlie Howell, who did the Homestead's last dressing four years ago.
He likes to do the "stitching" and "cracking" first -- that is, the smaller, more detailed grooves throughout the stone that actually do most of the grinding -- then the larger grooves, called furrows, that run from the outside of the stone to the center.
Mr. Grassi uses a small pick for the stitching and a slightly larger pick for the furrows, which in this case are about 1 1/8 inches wide.
"Then I have to paint the stones with a paint staff to check the surface," he said.
"The paint rubs off on the stone, but it's nontoxic, and that shows up the high spots -- you want everything to be true or level."
As Mr. Grassi picks away at the stone, he said that a key element of his job is patience.
"You have to get a feel for the pick and know how the millstones work, basically," he said.
The way the stones work is this: The grain is fed into a hopper and through a "shoe" over the eye, or open center, of the stone. The top runner stone is positioned within one-eighth inch directly over the bed stone, which is stationary. The runner stone circulates and the friction between the two stones grinds the grain into flour which is caught in a wooden hoop around the stones.
"The distance between the stones, the speed of the top stone and how much grain you're feeding into the stones determines how fine the flour is," said Mr. Grassi, who does dressing at bakeries and historic mills along the East Coast.
"This is a single reduction process," he said "It goes in as whole grain and comes out as finished flour."
Unlike many years ago, when the gristmill was used daily to grind a variety of grains, today only perhaps 5,000 pounds annually of corn, wheat, buckwheat and rye flour is made to sell mainly through the Homestead's gift shop. If used at full capacity, the stones would have to be dressed every two to three weeks, Mr. Grassi said.
Although there are three sets of stones in the gristmill, only the one set is being dressed this week. A second set is used for cornmeal and a third set for educational and public demonstrations, Mrs. Shriver said.
"We use this set for wheat, buckwheat and rye only," she said. "When they had all three sets of millstones running at full capacity they really put out a lot of flour."
Mr. Grassi will be at the gristmill today and tomorrow morning and Mrs. Shriver encourages the public to stop by and watch him work.