hmm. I have never heard of a sour mustard flavor. I am not even sure what I would equate that too as far as flaws that I do know.
If your thing is to go organic, you should look up 7 bridges cooperative. They are my LHBS, but do a bit of online as well. They are strictly organic. Not my personal cup of tea, but if that is what you want to do they are definitely worth looking up.