I had a chance to visit the cooper M. Gilles Bartholomo in the armagnac region of France. There was no sign out front and we were worried that we would miss it, but luckily a stack of air-drying barrel staves near the road clued us in.
This very small cooperage makes only barrels from local Gascony oak. On the property the staves are stacked up to air dry for between two and three years.
On the day we visited it had been raining, so we wondered if that would slow the drying process. It turns out that rain is a good thing: it washes out some of the tannins. You may be able to see in this picture a smear of dark brown tannins running off the stack of wood.
Wood that had been air drying longer had less of the tannin run-off in front of it. In front of one stack, there was a small puddle filled with tannin water. I convinced one of our hosts that she needed to taste it first lest it be poison, then I gave it a try: it was slightly woody but very tannic and drying on the tongue.
This facility produces a whopping 4 barrels per day, between 400 and 700 annually. The cooper says that contrary to rumor, there is no shortage of wood for barrels at the moment. Barrels cost 750 euros each.
The cooper says that most armagnac barrel buyers request a heavy toast to their barrels. (Remember that for French oak barrels, they are not charred like in bourbon, but toasted.)
All the excess sawdust from the process is sucked up in a ventilation system then deposited out into a shed, where a machine compresses it into fireplace logs.