Neutral spirits are produced by the industrial distillation of grain mash to a concentration of 90+% ethanol.
At such a high proof, there remain no qualities by which one may identify the source of the alcohol, be it potatoes, rice, barley, rye, wheat.
Filtering, generally with activated charcoal, is done to remove impurities.
At this point, the alcohol is shipped to commercial distillers under the designation "grain neutral spirits" or "GNS" to be redistilled and then bottled and sold to liquor distributors under names with which you may already be familiar.
If it is destined to become vodka, it is blended with water. If it is to become gin, a distilling column, with shelves on which the various aromatics are placed during the distillation, is used to impart their flavor components to the alcohol.