Hey Grannyrosie - yes starch will sour if not kept in the fridge. Except the Sta-Flo kind I buy by the quart at the grocery store. They must put some kind of preservative in it. When I made my own, I always seemed to get lumps so, I just buy Sta-Flo and I don't have to worry about it souring. A quart lasts me a looooong time.