I am reading a book by English cognac expert Nicholas Faith. He states that wood in Cognac is dried outdoors from 5-6 years. It is intentionally exposed to air and rain. He states that during this time, the rain washes away some of the more bitter tannins. Also, that during this seasoning period, a fungus forms on the wood which helps break down the lignin in the wood and produce a pronounced vanillin taste. So far I haven't seen where he talks about charring/toasting. He does state that new wood (as opposed to well-used barrels) is used to age cognac at the outset but not for too long, so that the wood doesn't flavour the spirit too much. I found the comment about 5-6 years seasoning interesting. He says tests were done comparing cognac aged in outdoors-seasoned wood vs. wood cured in ovens (kilns) artificially. He said the use of naturally-seasoned wood resulted in a softer, superior taste. I wonder if the same would apply to bourbon barrels. Since the wood is blackened to a 1/4 inch or more for bourbon, possibly the effects of the wood are less important, but still I have to wonder whether way back all bourbon wood was seasoned outdoors and whether a similar phenomenon took place here regarding the effect of rain and natural fungus.