Afraid I'm not too smart on barrels... always seemed too much work for a lazy man to take on . But why ferment something in it? If it's a used barrel it shouldn't be too intense oakwise, and a starter culture won't get you the malolactic flora or other "secondary" critters that you might be looking for. Most cidermakers will either directly incoculate for the malolactic or let it develop naturally. Have you sulfured or otherwise reconditioned the barrel besides reswelling the staves?
Bees, brews and fun
in Lyons, CO