Consider that a common way to prepare whole grains for cooking is to soak them for at least a day. Also consider that sprouting is a way to enhance the nutrition of grains.
But then someone would have to have let them sit for a long time in order to ferment, and add yeast to the mix. Maybe it was an offshoot of breadmaking. Someone smelled the alcohol coming from the yeast in the bread and said, "Hmmmm, I wonder if..........."