In the late 1990s, they began selling baked goods at the Shepherdstown Farmers Market where their brother, Danny, runs Rohrer's Meats.
Janet and Joan Rohrer also sell their baked goods through the Frederick, Md., and Middletown, Md., farmers markets.
Janet is known for her pies and jams, Joan for her peanut brittle and Judy for her cheesecake. They also make cookies, quick breads and specialty items.
Their mother was known for her cakes, especially her white coconut cake, which the sisters also make now.
Kim Lowry of Harpers Ferry, W.Va., has been buying baked goods from the sisters for years.
"Just about everything they make, we've probably tried," Lowry says.
She's particularly fond of the pies.
"Let's just say if I had a birthday party, I'd rather have a birthday pie than a birthday cake," Lowry says.
The sisters learned much about baking from their mother, who at harvest time cooked not only for a family of six, but for 15 farmhands.
Katherine Rohrer is mostly self-taught when it comes to cooking. When she was living at home, she was in charge of the cleaning so she seldom cooked.
After marrying a farmer, the late Arthur Rohrer, Rohrer began cooking more often. She threw out her first pie crust because the dough was too tough to roll.
Where she used lard from hogs on the farm and milk from the family's dairy cows to bake, Rohrer's daughters use Crisco shortening, margarine or butter and fat-free milk.
Lard makes a more tender crust but is not heart-healthy, Williamson says.
Katherine Rohrer has long been known for her white coconut cake, which she sold at church bake sales and the Keedysville Ruritan summer festival auction.
The cake has sold for as much as $100, her daughters say.
Janet Rohrer, who teaches fourth grade at Boonsboro Elementary School, learned to make pies by watching her mother.
"Then I'd do it and she'd criticize," Janet Rohrer jokes. "She still does."
Rohrer plans to enter this year's pie contest at the Ag Expo, which begins July 21.
Her sisters haven't competed in the Ag Expo for a long time because they are considered professionals.
Joan Rohrer, now retired, taught family and consumer sciences at Hancock Middle-Senior High School and Boonsboro High School for 34 years.
As a high school junior and senior, Joan won the high-school pie championship during the Apple Blossom Festival in Winchester, Va.
Joan still uses her mother's almost 60-year-old Sunbeam mixer.
Williamson, now self-employed doing custom sewing, worked with Maryland Cooperative Extension in family and consumer sciences in Baltimore and Howard counties and at the University of Maryland, College Park.
Williamson has been superintendent of the Ag Expo's home arts exhibits for about four years. She's not a judge, but she helps find judges.
The sisters' baking will kick into high gear when the Thanksgiving and Christmas holidays approach.
Last year Janet Rohrer woke up around 3:30 a.m. to bake 45 pies that had been ordered for Thanksgiving. Joan, Judy and their mother helped by preparing the apples and measuring the ingredients. The dough had been made earlier and frozen.
They can't always all get together to bake, but when they do it's a time to enjoy baking and catch up with one another, Joan Rohrer says.