Yesterday morning I drained the barrel from the first hot water fill, which I had left overnight. There was no apparent leakage from the barrel, confirming that the wood is fresh and the quality of construction is high. Also, the smell of the new wood is really outstanding – in my opinion Tonellerie Vernou has used first-quality wood to make these small barrels.
The water I drained form the barrel was very dark – almost black – suggesting that this first soak effectively removed a lot of easily extractable tannin and "oak" character.
I put about 1.5 pounds of kosher salt in the barrel and refilled it with 150° F water for the second soak. The salt treatment tightens the grain and is very effective at killing any undesirable organisms that may be present (although there is little chance any are, my personal proclivity is to be proactively cautious).
This salt water soak lasted eight hours. I drained the barrel again – this time the water was pale brown, like weak tea – and refilled it with hot water for overnight.
When I drained the barrel this morning the water was a medium-brown. I filled it for a fourth and final soak.