No really - two identical recipes made in two different climates can have different results when it comes to ash. Some people will get it in the Spring and Summer months and not in Fall and Winter.
The only soaps that I have had ash with is a lemon scent that I didn't let gel. It's the same recipe as many of my other soaps without ash so I am led to believe it's the FO. I now make certain that soap gels and I don't get the ash. This doesn't work for each situation but give it a try.
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.
Thanks for your replies about this. I sure agree, it's an unpredictable thing. I did a batch that I didn't let gel and no ash. I do another one like it and it does. Patchouli has never ashed before for me. Time of year? I'd believe it since I just don't know what else.
Can't really blame shortening either because I have another recipe with about 1/4 Crisco and it never ashes.