I make my own starch. I mix 2 cups of cold water with one tablespoon of corn starch in a spray bottle. I give it a good shake before I spray onto fabric. If I want more stiffness, I add a little more cornstarch. It keeps in the refrigerator for a couple of weeks with no issues.
I spray this onto fabric and let it soak in so the liquid is not sitting on the surface of the fabric then I usually press it when damp. This way the heat from the iron makes steam (much like when you spritz water on fabric before pressing to make steam.) I always spray on the back side of the fabric. I don't have issues with flaking or spotting.
It works as well as the store bought without any of the chemicals or propellants. If I want a light scent, I can add a few drops of essential oils or even a drop of lemon extract.