oak barrel leaks

Mold on the _outside_ of a barrel isn't a problem.

Uh oh. That IS a problem.

It may not be that the mold actually went from outside to inside. When you simply emptied the barrel and filled it with water you created ideal conditions for growing spoilage organisms. Barrels should *never* be filled with unsulfited water at pH 7 and left alone for weeks on end. What you have observed is what happens to barrels that aren't properly tended.

My question is how to recover the barrel and put it back in

That barrel may not be recoverable if it's deeply contaminated. If it's a small barrel, you might be able to salvage it by giving it a good rinsing with several changes of *boiling* hot water. Another option is taking the head out of one end and giving it a thorough toasting inside with a propane torch while swabbing it with water to keep it from burning. The idea is to get the wood inside hot enough (at least near the surface) to kill the spoilage organisms. That requires ~190°F and _wet_ heat.

Don't mess around with chemical treatments. They're all a waste of money. Also, _definitely_ don't use bleach in any wood container! Although that would kill any spoilage organisms present, it would also render your barrel forever unfit for wine.

Oh, yeah - be sure to fix that leak. The usual procedure is to locate the leak, drive an icepick into it at that site and then hammer a wooden spile into the hole made by the icepick. You can use a piece broken off the end of a good quality toothpick for the spile. When it gets wet, it'll expand and seal the hole.

Tom S