As is the case with any manufactured product, there are basic kashrus issues that must be addressed when producing kosher vinegar. In the traditional method of vinegar fermentation, the obvious requirement is that the wine be kosher and mevushel, pasteurized or made by Torah observant workers. Any additional ingredients must be kosher, as well. Furthermore, the casks used to ferment kosher vinegar may not have been previously used to ferment non-kosher vinegar or wines.