I have traced "John Barleycorn" the Folk song back to the 16th Century when it was sung as the corn was used to make a most potent beer, the like of which may not exist today...Real ale as we Brits call it but much more potent than todays "Health and Safety" conscious beers. John Barleycorn the song describes the process used to make that beer...nothing more ....nothing less....
Best wishes, Mike.