Ethanol would probably be classified as a natural solvent. The edge cases fall off very quickly, this can definitely be done on case by case basis without introducing onerous bureaucracy.
Where does salt fall here?
Why isn't petroleum natural, when it is plant-based?
What makes petroleum artificial compared to any other substance found on (or in) earth?
It seems you are proposing that "any food that has had a petroleum product added to it at any stage is artificial", which is an oddly narrow focus.
For that matter, does this definition of "artificial" extend to the range of substances that can be synthesized with bio-feedstock?
To expand on our discussion, would this mean that ethanol made other feedstock is natural, but made from petroleum is artificial?