If by refining grain you mean creating alcohol, no, it's not difficult at all. Water, a source of carbs (sugar, corn, etc.), and yeast. Given enough time the stuff ferments creating alcohol. Heck, if you've ever made real sourdough bread from a starter the clear liquid that forms on top over time is actually alcohol (hence the name "hooch"). Distillation can be a bit involved, but it ain't rocket science. And done correctly it can go in to some gas tanks or in to highball glass... Done correctly being the critical point here.
Of course in the US it is illegal to distill alcohol for consumption, even if it is only for personal consumption in small amounts. So any knowledge I have of the topic is based on reading and *purely* hypothetical discussions. Or by making it for cleaning purposes. Or for disinfectant purposes... Yeah, that's it... High proof alcohol is great for cleaning old oil off swords...
LOL! I understand the basic chemistry; it's that "done correctly" bit I have no real understanding of. I can make things rot no problemo. I recently heard of a beer (?) someone made from using the yeasts in his beard. Doesnt sound too appealing, but I can see why it's one of civilization's oldest professions.
As a side note, before I was laid off I worked with an ol' timer who grew up in a "shiner" family in the midwest and he related a couple stories of running from the cops in an old model A (as I remember it, any way)...not that I officially condone illegal activities.