"Ive received a couple emails recently requesting a detailed explanation of the process that we go through when preparing a new barrel. So here is is:
1. Remove the wooden bung
2. Rack beer into the barrel
3. Affix a new bung that allows carbon dioxide to escape
We do not rinse, burn a sulfur wick, or otherwise clean or sanitize the barrel before filling. The most important thing to do is have the beer ready to go into the barrel as quickly as possible after the barrel is emptied. If you obtain a barrel which previously held wine or beer and are not able to fill it within a couple days, then it would be a good idea to rinse the barrel. If you need to hold the barrel for longer than a couple weeks, then you should consider either burning a sulfur wick or filling with a holding solution composed of water, citric acid, and metabisulfite. Your goal is to prevent the growth of microbes like Acetobacter and mold which can cause off-flavors. Spirit barrels are safer for longer (which is good since burning a sulfur wick in one can have explosive consequences), but they too will eventually dry out which can cause them to leak when finally filled."
The Best advice on obtaining a barrel. Cited from the mad fermentationist