Freezing prevents the natural oils in pecans from going rancid and maintains the flour's freshness.  Place the pecan flour into an airtight container or a heavy-duty freezer bag, removing as much air as possible to prevent freezer burn. Label the bag with the freezing date to keep track of its freshness before placing it in the freezer. Freeze for up to six months. When you're ready to use it, simply remove the pecan flour from the freezer and allow it to come to room temperature before incorporating it into your recipes.