ash, it's one of the universe's great mysteries.
sometimes no matter what you do, it still happens. even if you made the same batch the day before exactly the same, one has ash and the other doesn't.
so many things may effect it, the temps, gel or no gel, i think humidity plays a factor in there too, the fragrance oils, how long you keep it in the mold. i think too that if you don't gel and it cools to fast this will cause it also. top surfaces not covered directly. i know some people can spray alcohol on the soap after it sets up slightly and they swear it stops the ash but it has never worked for me.
i have ash 99.9 percent of the time. i do ungelled milk soaps, i've just learned to live it it, doesn't mean i like it though.