could've been just excess tartaric salts.
I venture people don't realize it's a diprotic acid. below the upper pKa, there will be a lot of excess salt
explain to me this "lucid lemonade tek". so I gather it uses sunflower oil (lol), a trigliceride. is there any base involved? if so, there should be no surprise that it would leave a residue (soap).
"Nothing is true, everything is permitted." ~ hassan i sabbah
"Experiments are the only means of attaining knowledge at our disposal. The rest is poetry, imagination." -Max Planck