The answer is: Winnowing barley

Ruth 3:2

Boaz, nestled at the threshing floor, was engaged in the task of winnowing barley, which involves separating the grain from the chaff. A simple yet crucial process in ancient agriculture, this meant they were preparing the barley for storage or sale. The winnowing usually took place during the night when the winds stilled and traders often gathered after a long day's work, forming a lively social scene under the stars.

But there's more to it than just agriculture! The setting of Ruth and Boaz at the threshing floor carries profound cultural significance. Threshing floors were more than just farming sites; they stood as symbols of husbandry and inheritance, shaping communities’ fortunes intertwined with survival and prosperity. Think of them as the ancient “marketplaces”—both physical and relational hubs where declarations of loyalty, love, and even future family lines could be laid bare.

Fun fact: The act of winnowing involves tossing the grain into the air. Good grains fall while wind takes away the light chaff. This embodies deeper spiritual truths—here is Ruth declaiming her loyalty and lineage to Boaz, seeking protection and provision, much like how the grain is cared for in the winnowing process.

Furthermore, it's fascinating how Ruth, a Moabite woman, contending with cultural prejudices, stepped onto this threshing floor of potential new beginnings. The theme of unexpected providence echoes powerfully throughout the Book of Ruth, bridging across deeper revelations of faith, loyalty, and communal bonds.