Barrel is used to turn grape juice into wine and into vinegar. We can take grapejuice and put it back in barrels. We can take wine and put it back in barrels. We can take vinegar from barrel but we cannot put vinegar inside barrels, an inconsistantcy that is really odd. Simply put, we need to be able to put vinegars in barrels.
Also this. The means of transferring vinegar from barrel to barrel like any other liquid.