A frequently recurring question that appears in relation to whiskey and it’s fitness for kosher consumption is that concerning Scotch whiskey that has been aged in Sherry casks. Since gentile wine is unfit for kosher consumption, would the whiskey that’s aged in such a cask that had previously contained Sherry wine or any other type of wine be problematic for such whiskey?
This entire topic really goes back to a discussion in the Talmud regarding beer stored in gentile and containers that had previously contained gentile wine (since whiskey did not exist in those days). While there were a couple of rabbis who had a problem with such a practice, there were a couple of later rabbis who were okay with it and whose voices we follow in normative Jewish practice, as it is what is described in Rabbi Yosef Karo’s Shulhan Arukh. Based off of the example of beer, it would seem that whiskey would very much follow in the same model.
What goes unstated in both the Talmudic discussion, as well as in the Shulhan Arukh is the reasoning behind this permissibility of storing beer in containers that have previously contained gentile wine. There are several such reasons that rabbinic authorities have articulated over the centuries.
Despite the clear permissibility of whiskey being used in containers that have previously contained gentile wine, there have been various rabbis who are not so okay with Scotch being aged in Sherry casks.
One matter is due to the ratios that they are concerned with their not being enough volume of whiskey against the amount of wine embedded in the barrel.