My good buddy and new HBT member, Tangy30, started the following thread a few days ago which I thought would get more attention here: http://www.homebrewtalk.com/f25/oak-cask-question-209032/
He made the mistake of filling an unused barrel with water without adding k-meta and there's now a substantial amount of mold/bacteria growing in it. I haven't seen it but, depending on how much funk we're talking about, it may not be worth risking a batch, especially considering anything that he's going to put in a barrel will go through an extended aging process which would result in an awful lot of time spent if it doesn't turn out right.
I've always used oak chips for aging so I don't have first hand experience with this. I think its a 5 gallon barrel so my recommendation is to pasteurize with 180+ degree water and then using campden to sanitize. That doesn't seem reasonable for a larger volume barrel unless you have a way to heat that much water but for a 5 gallon barrel it seems that it would work. What I am unsure about is whether the mold/bacteria spores would have permeated deep into the barrel. If this is the case, it seems like he would need to find a way to heat the wood core to pasteurization temps and it may not be worth the trouble.
I've searched around and some other ideas are to use barrel cleaning products, however, it sounds like the barrel would need to be reburned afterwords.
Any other ideas? Anyone have first hand experience?