To age (whiskey) in a (charred) barrel; of whiskey: to become aged; hence comb chartering keg a barrel used for this purpose.
1939 FWP Guide Tennessee 426 wTN, Under the leaves in the hollows they stashed (cached) away the fresh corn in ten-gallon kegs and let it charter (char) for months. 1981 Foxfire Summer 146 neGA, To charter moonshine, you just put it in a keg and let it set a few days. . . The older the keg, the longer it takes to charter your liquor. 1987 Greenville News–Piedmont (SC) 26 Nov sec C 12/3, [Advt:] Antique Auction. . . oak chartering keg.