The winepress, which is where grapes are trodden, is an odd place to beat out wheat. The key to successfully threshing wheat is that you toss it into the air and the wind blows away the chaff, and the grain falls to the ground. You do not get wind in a winepress, which is a shallow depression in the rock. But under the circumstances, it is a safer location than the threshing floor, which is more exposed. Gideon was threshing wheat in this way because he was afraid his grain would be stolen by the Midianites.
11 Now the angel of the LORD came and sat under the terebinth at Ophrah, which belonged to Joash the Abiezrite, while his son Gideon was beating out wheat in the winepress to hide it from the Midianites.