I freely admit I’ve never been much of a drinker – regardless of Purim and I identify liquors mostly by relation to Monty Python Shticks. Still, one of the more interesting discussions we had in smikha involved what to do with whiskey which is often stored in sherry casks.
I don’t have my Yoreh Deah handy at the moment for citations. The short version is that if the wine isn’t kosher (a likely assumption), and it gets absorbed into the walls of casks, then when the whiskey is stored in said casks the non-kosher wine (or at least the taste) seeps out and would contaminate the whiskey.
R. Moshe dealt with this in Iggros Moshe (can’t check it now), R. Tendler brought this up in class a few times and R. Schachter addressed this issue in a shiur he gave when I was in Gruss. In fact, R. Schachter related a story that he was actually on the phone with someone in a Scottish distillery who explained that the reason why whiskey is stored in these casks is because they want the whiskey to absorb flavor from the wood of the barrel itself. However, since the full flavor would be far too intense and would ruin the whiskey, sherry casks are used such that the sherry mutes the flavor of the wood. Hence, any flavor given over by the remnant sherry is actually a negative taste (notein ta’am lifgam) and thus you don’t have a problem. (Not even dealing with batel b’shishim).
So now Avraham informs me that there is a new debate on the kashrut of whiskey which is I’m sure going to start a massive riot among kiddush clubs worldwide.
I should note however, that if the whiskey was stored in a Cask of Amontillado, you should probably go easy…or at least bring a pick-axe.