1. Back in the day, Middle Eastern alchemists were more concerned with medical elixirs than with turning lead into gold. The vapor given off and collected during an alchemical process (as with distillation of alcohol) was called a spirit of the original material.
2. Monks in Europe during the 12 Century believed that the spirit was removed from the “mash” during the distilling process. To this day, some European rye whiskey drinkers still pour out the first shot onto the ground (in order to giving the angels their share).
3. The word al-ghawl is the origin of the English word “ghoul.” “Ghoul” is another word for “spirit.” Get it?
The most believable explanation, however, might just be that imbibing liquor raises ones spirits.
Our vote is for an answer just that simple.