In the back of a small shop in a nondescript industrial park, a metal box the size of a kitchen island is humming. And clanking softly. And, well, slooshing.

Andrew McBath, tall and lanky, bends over the box, listening. “Every batch is different,” he tells me. “Any moment now, you’ll hear it change.”

And he’s right: In a moment, the box stops swishing and starts thudding, like fingers thumping gently on a taut water balloon. McBath cuts the power, raises the lid, and displays what he’s been waiting for: a gleaming, craggy swath of butter, rising out of a froth of buttermilk.

It isn’t much butter—the high-tech churn processes just 25 gallons of cream—but Banner Butter isn’t focused on quantity. This startup in an anonymous Atlanta suburb aims to reframe butter, from suspect