Using Grain Bin Fans to Minimize Mold

How does one know when and how often to turn on the grain bin fans to prevent or minimize mold? Is it based off experience? Dew point?  Any help would be appreciated.

My best guess is that it's based on temperature and humidity, there are a number of dataloggers out there specific for these metrics that could probably help drive your schedule with some data. Sper scientific has some affordable ones (no affiliation).

The product will make a difference. Corn will absorb water more readily than soy or wheat. But generally once a month or during times of extreme temperature changes where your bin could sweat. You want to keep the inside of the bin at the same temperature as the outside. And try to turn it on during lower humidity days and mid morning to afternoon so the air is dry.