I have had spray starch scorch because (1) I did not give it enough time to penetrate fibers, so it was sitting on top of the fabric and/or (2) I used too hot of an iron on it. Usually I did both. In all cases, the scorched starch washed out of the fabric. My dryer method for yardage has never resulted in a scorch, even when using the hottest setting on my iron. With spray starch I have learned to give it a couple of minutes to be absorbed and I also dial down my iron temp a notch.