In the fall, Ellen Frank sits behind the wheel of a combine, harvesting soybeans. But the rest of the year, Ellen works behind the counter of her family’s coffee shop in western Iowa, roasting coffee beans sourced from farmers around the world.

“Everybody has their one thing they love to do. All I love to do is roast,” says Ellen, who farms with her husband, Jeff, near Auburn. “It’s fun. You get into the zone.”

Sac County Farm Bureau members Jeff and Ellen Frank say that when they’re inside a tractor cab, they always have a mug of their own fresh-roasted coffee close at hand.

The Franks opened Little Green Truck Coffee Co. in Auburn, population 300, in June 2017 to share their love of high-quality coffee with friends and neighbors.

Since then, the Franks have greeted guests from across the country looking for a java fix on their way north to Okoboji or Highway 20.

“We are in a coffee desert here. There was just no good coffee to be had. But the...