Originally Posted by trugger
I did prewash the fabric with just a small amount of soap.
No fabric softener.
The only thing I can think of is that you are not allowing the starch enough time to soak in. You mentioned doing what fits on the ironing board; my bet is that a minute seems like a long time (and one minute might not be enough).
I would try spraying the wrong side of the entire fabric piece first, rolling it up to sit for half an hour to an hour, and then ironing. You could also try putting the roll of fabric inside a plastic bag and putting the plastic bag in the frig overnight.
White flakes means the starch is sitting on the surface of the fabric when you iron. If you don't want to use the above method, I'm thinking the suggestion to mist the fabric with water before spraying with starch might be very helpful. I would mist the entire yardage with water first. There is probably some surface tension on the fabric; using slightly damp fabric when you spray the starch on would likely help it be absorbed into the fabric instead of just sitting on top.